Research Article The Effect of Water Repellent Surface Impregnation on Durability of Cement-Based Materials Peng Zhang, 1,2 Huaishuai Shang, 1 Dongshuai Hou, 1 Siyao Guo, 1 and Tiejun Zhao 1 1 Center for Durability & Sustainability Studies, Qingdao University of Technology, Qingdao 266033, China 2 Institute of Concrete Structures and Building Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany Correspondence should be addressed to Peng Zhang; [email protected] and Huaishuai Shang; [email protected] Received 14 April 2017; Accepted 22 June 2017; Published 25 July 2017 Academic Editor: Jun Liu Copyright © 2017 Peng Zhang et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In many cases, service life of reinforced concrete structures is severely limited by chloride penetration until the steel reinforcement or by carbonation of the covercrete. Water repellent treatment on the surfaces of cement-based materials has oſten been considered to protect concrete from these deteriorations. In this paper, three types of water repellent agents have been applied on the surface of concrete specimens. Penetration profiles of silicon resin in treated concrete have been determined by FT-IR spectroscopy. Water capillary suction, chloride penetration, carbonation, and reinforcement corrosion in both surface impregnated and untreated specimens have been measured. Results indicate that surface impregnation reduced the coefficient of capillary suction of concrete substantially. An efficient chloride barrier can be established by deep impregnation. Water repellent surface impregnation by silanes also can make the process of carbonation action slow. In addition, it also has been concluded that surface impregnation can provide effective corrosion protection to reinforcing steel in concrete with migrating chloride. e improvement of durability and extension of service life for reinforced concrete structures, therefore, can be expected through the applications of appropriate water repellent surface impregnation. 1. Introduction e development of cement and concrete dates to the mid- 1800s, and it proved to be a revolutionary innovation in building materials. Today, reinforced concrete is the single most widely used building material in the world for both entire buildings and key structural elements that need to be able to withstand various substantial loads. Reinforced concrete is used in such large amounts because it shares the characteristics of relatively good durability, low maintenance cost, and convenience. However, it is nowadays generally accepted that service life of many reinforced concrete struc- tures is frequently not sufficient. e cost for early repair measures is oſten significantly higher than the cost for new construction. e major origin of these problems of maintenance and repair costs and poor serviceability is a lack of durability for reinforced concrete structures [1–3]. Moisture transport in cement-based materials is a crucial physical process for their durability since many effects that influence the durability of the building structure are induced by water itself as well as harmful substances transported by it. If cement-based materials, such as mortar and concrete, are exposed to water, a series of deteriorating processes can take place. One dominant process or a combination of different processes may eventually limit the expected service life of reinforced concrete structures. e corrosive attack of water with respect to concrete can be subdivided at least into three different types. First, pure water in permanent contact with cement-based materials acts as a solvent. e binding matrix consisting of Ca(OH) 2 and C-S-H gel is gradually dissolved by hydrolysis. Second, gases of the environment may be dissolved in the aqueous pore solution of concrete. In this way, acids are formed, for instance, by dissolution of CO 2 and SO 2 , which could react rapidly with the hydration products of cement. In the third type of corrosive attack water acts essentially as a vehicle and transports dissolved compounds, such as chloride ions, into the porous system of cementitious matrix. Besides the corrosive attacks, water also plays an Hindawi Advances in Materials Science and Engineering Volume 2017, Article ID 8260103, 9 pages https://doi.org/10.1155/2017/8260103
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Research ArticleThe Effect of Water Repellent Surface Impregnation onDurability of Cement-Based Materials
Peng Zhang12 Huaishuai Shang1 Dongshuai Hou1 Siyao Guo1 and Tiejun Zhao1
1Center for Durability amp Sustainability Studies Qingdao University of Technology Qingdao 266033 China2Institute of Concrete Structures and Building Materials Karlsruhe Institute of Technology 76131 Karlsruhe Germany
Correspondence should be addressed to Peng Zhang zhp0221163com and Huaishuai Shang shanghuaishuaialiyuncom
Received 14 April 2017 Accepted 22 June 2017 Published 25 July 2017
Academic Editor Jun Liu
Copyright copy 2017 Peng Zhang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
In many cases service life of reinforced concrete structures is severely limited by chloride penetration until the steel reinforcementor by carbonation of the covercrete Water repellent treatment on the surfaces of cement-based materials has often been consideredto protect concrete from these deteriorations In this paper three types of water repellent agents have been applied on the surfaceof concrete specimens Penetration profiles of silicon resin in treated concrete have been determined by FT-IR spectroscopy Watercapillary suction chloride penetration carbonation and reinforcement corrosion in both surface impregnated and untreatedspecimens have been measured Results indicate that surface impregnation reduced the coefficient of capillary suction of concretesubstantially An efficient chloride barrier can be established by deep impregnationWater repellent surface impregnation by silanesalso canmake the process of carbonation action slow In addition it also has been concluded that surface impregnation can provideeffective corrosion protection to reinforcing steel in concrete withmigrating chlorideThe improvement of durability and extensionof service life for reinforced concrete structures therefore can be expected through the applications of appropriate water repellentsurface impregnation
1 Introduction
The development of cement and concrete dates to the mid-1800s and it proved to be a revolutionary innovation inbuilding materials Today reinforced concrete is the singlemost widely used building material in the world for bothentire buildings and key structural elements that need tobe able to withstand various substantial loads Reinforcedconcrete is used in such large amounts because it shares thecharacteristics of relatively good durability low maintenancecost and convenience However it is nowadays generallyaccepted that service life of many reinforced concrete struc-tures is frequently not sufficient The cost for early repairmeasures is often significantly higher than the cost fornew construction The major origin of these problems ofmaintenance and repair costs and poor serviceability is a lackof durability for reinforced concrete structures [1ndash3]
Moisture transport in cement-based materials is a crucialphysical process for their durability since many effects that
influence the durability of the building structure are inducedby water itself as well as harmful substances transported by itIf cement-based materials such as mortar and concrete areexposed to water a series of deteriorating processes can takeplace One dominant process or a combination of differentprocesses may eventually limit the expected service life ofreinforced concrete structures The corrosive attack of waterwith respect to concrete can be subdivided at least into threedifferent types First pure water in permanent contact withcement-based materials acts as a solvent The binding matrixconsisting of Ca(OH)
2and C-S-H gel is gradually dissolved
by hydrolysis Second gases of the environment may bedissolved in the aqueous pore solution of concrete In thisway acids are formed for instance by dissolution of CO
2and
SO2 which could react rapidly with the hydration products
of cement In the third type of corrosive attack water actsessentially as a vehicle and transports dissolved compoundssuch as chloride ions into the porous system of cementitiousmatrix Besides the corrosive attacks water also plays an
HindawiAdvances in Materials Science and EngineeringVolume 2017 Article ID 8260103 9 pageshttpsdoiorg10115520178260103
2 Advances in Materials Science and Engineering
(a) (b) (c)
Figure 1 Types of surface treatments (a) impregnation (b) coatingand (c) cementitious coating surface
important role in some other physical and chemical damagefor concrete such as freeze-thaw action alkali-aggregate re-action steel corrosion and drying shrinkage
It is obvious that all these three types of aggressive attacksjust mentioned act from the surface of concrete Throughouthistory a range of protective materials have been appliedto the exposed surfaces of structural concrete elements toprevent the ingress of water including oils waxes or paintsNowadays big progress has been achieved in the productionof water repellent agents and development of water repellenttreatment It has been proved that surface impregnationby water repellent agents should be an effective preventivemethod for concrete structures [4ndash9] For broader informa-tion about the studies on water repellent treatment the pro-ceedings ofHYDROPHOBE conference series (HydrophobesIndashVIII) can be known from [10ndash17]
In this contribution the basic mechanism of water repel-lent treatment on cement-based materials has been brieflydescribed Three types of water repellent agents which are informs of liquid cream and gel have been applied on the sur-face of two types of cement-based materials The consequenteffects of surface impregnation on reducing water capillarysuction chloride penetration carbonation and reinforce-ment corrosion in concrete will be measured and discussed
2 Basic Mechanism of WaterRepellent Treatment
In general water repellent surface treatments aremainly clas-sified in three groups according to the mechanism by whichthe protection is achieved In Figure 1 types of surface treat-ments are illustrated according to this classification [18] Sur-face treatment by silanes belongs to ldquoimpregnationrdquo whosebasic mechanisms are given in the next two paragraphs
The most important silicon-based water repellent agentsare those made of silanes and siloxanes which are polymerscontaining three alkoxy groups denoted OR1015840 linked to asilicon atom with each silicon atom carrying an organic alkylgroup denoted R The silicon functional alkoxy group reactswith water and yields a reactive silanol group (hydrolysisstage) Further condensation by crosslinking to the hydroxylgroups forms polysiloxane (silicon resin) as the active waterrepellent product which is linked to the inorganic substrateby way of covalent siloxane bonds as shown in Figure 2
R R R
OH OH
Alkylalkoxysilane Silanol
R R R R R R
-Si-O-Si-O-Si-
OH OHOH O O OHO HOHO
Cementitious materials Hydrophobic
Hydrolysis
Reaction
Polysiloxane
Condensation
+（2OO２
OH-Si-O（ + H-Si-OH２O-Si-O２
OH-Si-OH OH-Si-OHHO-Si-OH
Figure 2 Mechanisms for hydrolysis and polymerization of silanein cement-based materials
The organofunctional alkyl groups will reduce the criticalsurface tension of the material surface and thus provide hy-drophobicity while the silicon functional groups provide re-activity with the substrate and control the penetration depth
The effect of water repellents is essentially based on theirlow surface tension The behaviour of water when contact-ing the surface of amaterial is governed by the surface tensionwhich can be measured by the contact angle as shown phe-nomenologically in Figure 3The intensity of the water repel-lent property is associated with the contact angle betweenwater and the treated surface Contact angles of a waterdroplet of more than 90∘ represent hydrophobic propertywith less than 90∘ hydrophilic property The higher the con-tact angle is the more water repellent the surface becomesThe hydrophobicity of water repellents is in fact realized intwo steps Firstly the beading effect causes the water dropletto quickly run off and leave the surface Secondly when watertends to spread and form a water film over the surface waterabsorption is reduced by excluding via treated capillaries
3 Materials and Methods
31 Materials and Preparation of Specimens Two types ofmortar and concrete specimens were prepared for the testseries Ordinary Portland cement type 425 crushed aggre-gates with a maximum diameter of 20mm and density of2620 kgm3 and river sand with a maximum grain sizeof 5mm and density of 2610 kg m3 were used The exactcompositions of the concrete used in this project are givenin Table 1 The mix with WC = 05 was named concrete CMortar with a higher water-cement ratio (WC = 06) wasalso prepared and calledmortarM Some specimens preparedwith both concrete C and mortar M were later surfaceimpregnated with different amount of water repellent agentsThe concrete specimens were used for water absorption testchloride penetration test carbonation test and steel corrosiontest The mortar specimens were prepared only for neutronradiography test in order to avoid the influence of courseaggregate during the image analysis
Advances in Materials Science and Engineering 3
(a)
(b)
Figure 3 The principle of water repellency (a) untreated concrete contact angle 120579 less than 90∘ (b) water repellent treated contact angle 120579greater than 90∘
Table 1 Composition of the two types of mixtures used in thisproject kgm3
Type WC Cement Sand Aggregate WaterConcrete C 05 320 653 1267 160Mortar M 06 300 1650 mdash 180
From all mixes given in Table 1 cubes with side length of100mmwere produced Another type of prismatic specimenswith dimensions of 280 times 150 times 115mm with two steel barswas also prepared for steel corrosion test All specimenswere compacted in steel forms and cured for one day beforedemolding After that the specimens were moved into acuring room (119879 = 20 plusmn 2∘C RH gt 95) At an age of 28 daysthey were taken out of the curing room for water repellentsurface treatment
32 Water Repellent Surface Impregnation After 28 days ofmoist curing the specimenswere further stored at RHof 60for 7 days for drying Then one of the molded surfaces ofcubic specimens and the top surface (280 times 115mm) of therectangular parallelepiped specimens have been impregnatedwith three different types of water repellent agents Theagentsrsquo type usage amount and the corresponding samplescodes are listed in Table 2 After that the specimens werestored again at RH of 60 for another 7 days in order toallow sufficient polymerization of silane Then the surfaceimpregnated specimens were ready for further tests
One series have been impregnated with liquid silane Inthis case concrete surface was put in contact with liquidsilane for one hour During this period liquid silane couldbe absorbed into specimen due to capillary suction In secondseries one of themolded surfaceswas covered by silane creamThe amount of usage on the surface was 400 gm2 For thethird to fifth series 100 400 and 600 gm2 of silane gelwere applied Both silane cream and gel were covered on theconcrete surfaces with a small brush
From the specimens treated by water repellent agentslayers from the treated surface with a thickness of 1mmeach have been milled consecutively by means of a speciallybuilt milling cutter The powder obtained from this processwas collected The silicon content of these powders was thendetermined by means of FT-IR spectroscopy This methodhas been developed and further refined for this specificapplication by Gerdes and Wittmann [19]
33 Water Absorption and Chloride Penetration Water ab-sorption of surface treated and untreated specimens has beenmeasured by a standard method [20] Before the test the
Pure water or 3 NaClsolution
Wax Wax
Cut surface
3ndash5 mm
Figure 4 Schematic illustration for water absorption and chloridepenetration test of concrete
cubic specimens were cut into two halves and dried in aventilated oven at a temperature of 50∘C for 7 days until massequilibrium was reached When the specimens cooled downto the room temperature the treated and untreated specimenswere put in contact with water for selected periods of time asshown in Figure 4 Then the amounts of absorbed water bycapillary suction were measured by weighing the specimensafter 1 2 4 8 24 48 and 72 hours
In a similar way as described in the last paragraph chlo-ride penetration test (3 NaCl solution) for water repellenttreated and untreated specimens were carried out for 28 daysAfter the test powder wasmilled consecutively starting at thespecimensrsquo surface which had been exposed to salt solutionThe chloride content of the powderwas then determinedwiththe ion selective electrode method In this way the chlorideprofiles in water repellent surface impregnated and untreatedspecimens have been determined
34 Neutron Radiography Water repellent mortar speci-mens and untreated companion specimens were also testedby neutron radiography at Paul-Scherrer-Institute (PSI) inSwitzerland Neutron radiography has been identified as anideal and unique nondestructive technique to study watermovement andmoisture distributions in cement-basedmate-rials because of their strong attenuation by hydrogen andtheir insensitivity to the dominant ingredients such as silicaand calcium in cement-based materials More details aboutthis technique can be found in [21ndash26]
First neutron images were taken on samples which werein hygral equilibrium with the room atmosphere (RH asymp60 T asymp 20∘C) Then neutron images were taken againon water repellent treated and untreated mortar specimensafter contact with water for 05 and 2 hours In this way thewatermovement in samples was visualized In addition somesurface impregnated and untreated samples were placed inwater for three days This period was sufficient to saturatethe samples completely Then neutron images were taken onthese water saturated specimens Both untreated and surfaceimpregnated mortar specimens in the water saturated state
4 Advances in Materials Science and Engineering
Table 2 Three types of water repellent agents used in this project and their uses
Type Amount of use NoteRef mdash mdash No treatment reference sampleL1 Liquid silane 470 gm2 Surface absorptionC400 Silane cream 400 gm2 Surface brushingG100 Silane gel 100 gm2 Surface brushingG400 Silane gel 400 gm2 Surface brushingG600 Silane gel 600 gm2 Surface brushing
were investigated From the neutron images the moisturedistribution can be analyzed quantitatively
35 Accelerated Carbonation After drying in lab for 7 daysboth surface treated and untreated specimens were submittedto accelerated carbonation for 7 and 28 days According tothe Chinese standard [27] the concentration of CO
2gas was
maintained constant at 20 plusmn 2 relative humidity in carbon-ation box was about 70 the temperature was 20plusmn3∘C Foursurfaces except for the treated surface and its opposite surfacehad been sealed with wax before being placed in carbonationsituation In this way carbonation normal to two oppositesurfaces into concrete was imposed After 7 and 28 dayscarbonation depth in the surface impregnated and untreatedsamples weremeasured by spraying phenolphthalein solutionwith 1 in ethanol
36 Reinforcement Corrosion This test followed ASTM G109-07 [28] specimens were 280 times 150 times 115mm with areservoir of NaCl solution on the test surface The reservoirwith size of 150 times 75 times 75mm was located at the center of topsurface Upper reinforced steel was positioned 20mm fromponded surface and bottom steels were 25mm from bottomsurface The ends of steel were protected with electroplaterrsquostape and a 200-mm portion in the middle is bare During thetest the half-cell potential and the corrosion current densityof the steel rebar in surface impregnated and untreatedconcrete specimens were measured continuously every week
4 Results and Discussion
41 Effect of Water Repellent Surface Impregnation on WaterAbsorption Water absorption of both untreated and surfacetreated concrete specimens has been measured for 72-hourcontact with water Results obtained at different time areshown in Figure 5 Points indicated in Figure 5 are averagevalues of three independent measurements The variationof the individual measurements is also shown It can belearned from the results that all the surface impregnatedconcrete absorbedmuch lesswater compared to the untreatedconcrete In this case it is not liquid water but water vaporis trapped by capillary condensation once it has crossed thesilane impregnated layer In addition capillary condensationcan take place in nanopores of concrete as silane moleculescannot enter these narrow spaces because of geometricalreasons Therefore a small amount of capillary condensedwater still can migrate into the pores by diffusion Butcompared to the untreated concrete the amount of absorbed
C-RefC-L1
C-C400C-G400
2 4 6 80Square root of contact time (Ｂ05)
0
400
800
1200
1600
2000
Am
ount
of a
bsor
bed
wat
er (g
Ｇ2)
Figure 5 The amount of absorbed water in surface impregnatedand untreated concrete at different time of water absorption and thelinear fitting lines
water is reduced significantly by surface impregnation witheach type of silane
For a homogeneous porous material a simple expressioncan be deduced from theory of capillarity to describe capillarysuction as function of time see (1) [29 30] This equation isonly a first approximation because the skin effect of concretewill always be the origin of a deviation of measured resultsfrom the theoretical prediction
Δ119882 = 119860radic119905 (1)
where Δ119882 stands for the amount of absorbed water bycapillary suction per unit area and t for the duration of con-tact A is the coefficient of capillary suction The coefficientof capillary suction deduced from Figure 5 for treated anduntreated concrete can be calculated The results indicatethat the coefficient of capillary suction for untreated sampleis 2487 g(m2h05) while for sample L1 (impregnated byliquid silane) it is 409 g(m2h05) approximately one-sixthof untreated sample for samples C400 (silane cream) andG400 (silane gel) the coefficients are 345 and 245 g(m2h05)respectively They are less than one-seventh and one-tenth ofthat of untreated sampleThis obviously indicates that surfaceimpregnation with water repellent silanes can significantlyreduce water penetration into concrete
Advances in Materials Science and Engineering 5
20 mm M-Ref M-G400
(a) Neutron image after 05 hours
M-Ref M-G400
(b) Image after 2 hours
Figure 6 Observations of water penetration into mortar specimens after 05 and 2 hours by means of neutron radiography
Poly
silox
ane c
once
ntra
tion
()
C-L1C-C400C-G400
00
02
04
06
08
2 4 6 8 10 120Depth (mm)
Figure 7 Polysiloxane profiles in water repellent treated concretewith silane liquid silane cream and silane gel
Figure 6 shows the visual observation of water pene-tration into untreated and water repellent surface treatedmortar specimens after 05 and 2 hours by means of neutronradiography It can be clearly seen that after half an hourof contact with water a penetration front becomes visiblein untreated concrete This irregular front gradually movesinto the porous material with increasing of time But forthe surface impregnated sample water uptake could not beobserved with the naked eyes even after two hours becauseof the polysiloxane film formed from silane which made thenear-surface region hydrophobic
After being applied on the surfaces of concrete silanepenetrated and formed polysiloxane (silicon resin) in thenear-surface zone The polysiloxane concentration in surfaceimpregnated samples has been measured by FT-IR spec-troscopyThe results are shown in Figure 7 It can be seen thatin each case a penetration depth of about nine millimetershas been reached This treatment can be called deep impreg-nation in contrast to simple surface impregnation In somecases a simple surface impregnation is sufficient However tobuild up a reliable and durable chloride barrier a minimumpenetration depth of 7mm is often required [5] This has tobe confirmed in the context of quality assurance after surfacetreatment in practice If the penetration depth is too small
the ingress of aggressive ions with water is slowed down butnot prevented for long time
In addition neutron images of three types of impregnatedand water saturated mortar specimens are shown in Figure 8The upper impregnated surface is of interest exclusively inthis context It can be clearly seen with the naked eye thatthe neutron transmission is significantly higher in the outerimpregnated layer The thickness of the impregnated layercan be estimated from the results shown in Figure 8 Theaverage values determined by visual inspection are 20 41and 63mm for samples G100 G400 and G600 respectively
The moisture distribution was further measured in thenear-surface zone as indicated with the rectangular frameshown in Figure 8 (M-G600) from the neutron imagesobtained from water saturated specimens Results are shownin Figure 9 As expected the moisture content in theuntreated specimen is essentially homogeneously distributedall over the volume The observed slight decrease of watercontent close to the surfacemay be attributed to a small waterloss during handling before taking the first neutron image
However on the surface impregnated specimens theinfluence of the water repellent near-surface zone can beobserved clearly As expected the water content in the waterrepellent zone is significantly reducedThe width of the waterrepellent zone can also be observed clearly In samples M-G100 awater repellent layer with a thickness of approximately2mm has been established In samples M-G400 and M-G600 the thickness of the water repellent zone can beestimated to be approximately 4 and 6mm respectivelyWhatis most important however is the fact that in sample M-G100 the water content in the water repellent zone is certainlysubstantially reduced but still a certain amount of water canbe observed in this region In contrast in sample M-G600 aminimum amount of water can be detected only From theseresults it can again be concluded that deep impregnation isnecessary for an efficient chloride barrier
42 Effect ofWater Repellent Surface Impregnation onChloridePenetration The surfaces of treated and untreated concretespecimens have been brought in contact with an aqueousNaCl solution with concentration of 3 for 28 days Thechloride profiles were determined The results are shown inFigure 10 It can be seen that a lot of chloride ions penetratedinto untreated concrete even up to depth of 30mm It alreadyhas been shown that capillary suction is a most powerfulmechanism for the transport of chlorides into concrete If
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
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BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
2 Advances in Materials Science and Engineering
(a) (b) (c)
Figure 1 Types of surface treatments (a) impregnation (b) coatingand (c) cementitious coating surface
important role in some other physical and chemical damagefor concrete such as freeze-thaw action alkali-aggregate re-action steel corrosion and drying shrinkage
It is obvious that all these three types of aggressive attacksjust mentioned act from the surface of concrete Throughouthistory a range of protective materials have been appliedto the exposed surfaces of structural concrete elements toprevent the ingress of water including oils waxes or paintsNowadays big progress has been achieved in the productionof water repellent agents and development of water repellenttreatment It has been proved that surface impregnationby water repellent agents should be an effective preventivemethod for concrete structures [4ndash9] For broader informa-tion about the studies on water repellent treatment the pro-ceedings ofHYDROPHOBE conference series (HydrophobesIndashVIII) can be known from [10ndash17]
In this contribution the basic mechanism of water repel-lent treatment on cement-based materials has been brieflydescribed Three types of water repellent agents which are informs of liquid cream and gel have been applied on the sur-face of two types of cement-based materials The consequenteffects of surface impregnation on reducing water capillarysuction chloride penetration carbonation and reinforce-ment corrosion in concrete will be measured and discussed
2 Basic Mechanism of WaterRepellent Treatment
In general water repellent surface treatments aremainly clas-sified in three groups according to the mechanism by whichthe protection is achieved In Figure 1 types of surface treat-ments are illustrated according to this classification [18] Sur-face treatment by silanes belongs to ldquoimpregnationrdquo whosebasic mechanisms are given in the next two paragraphs
The most important silicon-based water repellent agentsare those made of silanes and siloxanes which are polymerscontaining three alkoxy groups denoted OR1015840 linked to asilicon atom with each silicon atom carrying an organic alkylgroup denoted R The silicon functional alkoxy group reactswith water and yields a reactive silanol group (hydrolysisstage) Further condensation by crosslinking to the hydroxylgroups forms polysiloxane (silicon resin) as the active waterrepellent product which is linked to the inorganic substrateby way of covalent siloxane bonds as shown in Figure 2
R R R
OH OH
Alkylalkoxysilane Silanol
R R R R R R
-Si-O-Si-O-Si-
OH OHOH O O OHO HOHO
Cementitious materials Hydrophobic
Hydrolysis
Reaction
Polysiloxane
Condensation
+（2OO２
OH-Si-O（ + H-Si-OH２O-Si-O２
OH-Si-OH OH-Si-OHHO-Si-OH
Figure 2 Mechanisms for hydrolysis and polymerization of silanein cement-based materials
The organofunctional alkyl groups will reduce the criticalsurface tension of the material surface and thus provide hy-drophobicity while the silicon functional groups provide re-activity with the substrate and control the penetration depth
The effect of water repellents is essentially based on theirlow surface tension The behaviour of water when contact-ing the surface of amaterial is governed by the surface tensionwhich can be measured by the contact angle as shown phe-nomenologically in Figure 3The intensity of the water repel-lent property is associated with the contact angle betweenwater and the treated surface Contact angles of a waterdroplet of more than 90∘ represent hydrophobic propertywith less than 90∘ hydrophilic property The higher the con-tact angle is the more water repellent the surface becomesThe hydrophobicity of water repellents is in fact realized intwo steps Firstly the beading effect causes the water dropletto quickly run off and leave the surface Secondly when watertends to spread and form a water film over the surface waterabsorption is reduced by excluding via treated capillaries
3 Materials and Methods
31 Materials and Preparation of Specimens Two types ofmortar and concrete specimens were prepared for the testseries Ordinary Portland cement type 425 crushed aggre-gates with a maximum diameter of 20mm and density of2620 kgm3 and river sand with a maximum grain sizeof 5mm and density of 2610 kg m3 were used The exactcompositions of the concrete used in this project are givenin Table 1 The mix with WC = 05 was named concrete CMortar with a higher water-cement ratio (WC = 06) wasalso prepared and calledmortarM Some specimens preparedwith both concrete C and mortar M were later surfaceimpregnated with different amount of water repellent agentsThe concrete specimens were used for water absorption testchloride penetration test carbonation test and steel corrosiontest The mortar specimens were prepared only for neutronradiography test in order to avoid the influence of courseaggregate during the image analysis
Advances in Materials Science and Engineering 3
(a)
(b)
Figure 3 The principle of water repellency (a) untreated concrete contact angle 120579 less than 90∘ (b) water repellent treated contact angle 120579greater than 90∘
Table 1 Composition of the two types of mixtures used in thisproject kgm3
Type WC Cement Sand Aggregate WaterConcrete C 05 320 653 1267 160Mortar M 06 300 1650 mdash 180
From all mixes given in Table 1 cubes with side length of100mmwere produced Another type of prismatic specimenswith dimensions of 280 times 150 times 115mm with two steel barswas also prepared for steel corrosion test All specimenswere compacted in steel forms and cured for one day beforedemolding After that the specimens were moved into acuring room (119879 = 20 plusmn 2∘C RH gt 95) At an age of 28 daysthey were taken out of the curing room for water repellentsurface treatment
32 Water Repellent Surface Impregnation After 28 days ofmoist curing the specimenswere further stored at RHof 60for 7 days for drying Then one of the molded surfaces ofcubic specimens and the top surface (280 times 115mm) of therectangular parallelepiped specimens have been impregnatedwith three different types of water repellent agents Theagentsrsquo type usage amount and the corresponding samplescodes are listed in Table 2 After that the specimens werestored again at RH of 60 for another 7 days in order toallow sufficient polymerization of silane Then the surfaceimpregnated specimens were ready for further tests
One series have been impregnated with liquid silane Inthis case concrete surface was put in contact with liquidsilane for one hour During this period liquid silane couldbe absorbed into specimen due to capillary suction In secondseries one of themolded surfaceswas covered by silane creamThe amount of usage on the surface was 400 gm2 For thethird to fifth series 100 400 and 600 gm2 of silane gelwere applied Both silane cream and gel were covered on theconcrete surfaces with a small brush
From the specimens treated by water repellent agentslayers from the treated surface with a thickness of 1mmeach have been milled consecutively by means of a speciallybuilt milling cutter The powder obtained from this processwas collected The silicon content of these powders was thendetermined by means of FT-IR spectroscopy This methodhas been developed and further refined for this specificapplication by Gerdes and Wittmann [19]
33 Water Absorption and Chloride Penetration Water ab-sorption of surface treated and untreated specimens has beenmeasured by a standard method [20] Before the test the
Pure water or 3 NaClsolution
Wax Wax
Cut surface
3ndash5 mm
Figure 4 Schematic illustration for water absorption and chloridepenetration test of concrete
cubic specimens were cut into two halves and dried in aventilated oven at a temperature of 50∘C for 7 days until massequilibrium was reached When the specimens cooled downto the room temperature the treated and untreated specimenswere put in contact with water for selected periods of time asshown in Figure 4 Then the amounts of absorbed water bycapillary suction were measured by weighing the specimensafter 1 2 4 8 24 48 and 72 hours
In a similar way as described in the last paragraph chlo-ride penetration test (3 NaCl solution) for water repellenttreated and untreated specimens were carried out for 28 daysAfter the test powder wasmilled consecutively starting at thespecimensrsquo surface which had been exposed to salt solutionThe chloride content of the powderwas then determinedwiththe ion selective electrode method In this way the chlorideprofiles in water repellent surface impregnated and untreatedspecimens have been determined
34 Neutron Radiography Water repellent mortar speci-mens and untreated companion specimens were also testedby neutron radiography at Paul-Scherrer-Institute (PSI) inSwitzerland Neutron radiography has been identified as anideal and unique nondestructive technique to study watermovement andmoisture distributions in cement-basedmate-rials because of their strong attenuation by hydrogen andtheir insensitivity to the dominant ingredients such as silicaand calcium in cement-based materials More details aboutthis technique can be found in [21ndash26]
First neutron images were taken on samples which werein hygral equilibrium with the room atmosphere (RH asymp60 T asymp 20∘C) Then neutron images were taken againon water repellent treated and untreated mortar specimensafter contact with water for 05 and 2 hours In this way thewatermovement in samples was visualized In addition somesurface impregnated and untreated samples were placed inwater for three days This period was sufficient to saturatethe samples completely Then neutron images were taken onthese water saturated specimens Both untreated and surfaceimpregnated mortar specimens in the water saturated state
4 Advances in Materials Science and Engineering
Table 2 Three types of water repellent agents used in this project and their uses
Type Amount of use NoteRef mdash mdash No treatment reference sampleL1 Liquid silane 470 gm2 Surface absorptionC400 Silane cream 400 gm2 Surface brushingG100 Silane gel 100 gm2 Surface brushingG400 Silane gel 400 gm2 Surface brushingG600 Silane gel 600 gm2 Surface brushing
were investigated From the neutron images the moisturedistribution can be analyzed quantitatively
35 Accelerated Carbonation After drying in lab for 7 daysboth surface treated and untreated specimens were submittedto accelerated carbonation for 7 and 28 days According tothe Chinese standard [27] the concentration of CO
2gas was
maintained constant at 20 plusmn 2 relative humidity in carbon-ation box was about 70 the temperature was 20plusmn3∘C Foursurfaces except for the treated surface and its opposite surfacehad been sealed with wax before being placed in carbonationsituation In this way carbonation normal to two oppositesurfaces into concrete was imposed After 7 and 28 dayscarbonation depth in the surface impregnated and untreatedsamples weremeasured by spraying phenolphthalein solutionwith 1 in ethanol
36 Reinforcement Corrosion This test followed ASTM G109-07 [28] specimens were 280 times 150 times 115mm with areservoir of NaCl solution on the test surface The reservoirwith size of 150 times 75 times 75mm was located at the center of topsurface Upper reinforced steel was positioned 20mm fromponded surface and bottom steels were 25mm from bottomsurface The ends of steel were protected with electroplaterrsquostape and a 200-mm portion in the middle is bare During thetest the half-cell potential and the corrosion current densityof the steel rebar in surface impregnated and untreatedconcrete specimens were measured continuously every week
4 Results and Discussion
41 Effect of Water Repellent Surface Impregnation on WaterAbsorption Water absorption of both untreated and surfacetreated concrete specimens has been measured for 72-hourcontact with water Results obtained at different time areshown in Figure 5 Points indicated in Figure 5 are averagevalues of three independent measurements The variationof the individual measurements is also shown It can belearned from the results that all the surface impregnatedconcrete absorbedmuch lesswater compared to the untreatedconcrete In this case it is not liquid water but water vaporis trapped by capillary condensation once it has crossed thesilane impregnated layer In addition capillary condensationcan take place in nanopores of concrete as silane moleculescannot enter these narrow spaces because of geometricalreasons Therefore a small amount of capillary condensedwater still can migrate into the pores by diffusion Butcompared to the untreated concrete the amount of absorbed
C-RefC-L1
C-C400C-G400
2 4 6 80Square root of contact time (Ｂ05)
0
400
800
1200
1600
2000
Am
ount
of a
bsor
bed
wat
er (g
Ｇ2)
Figure 5 The amount of absorbed water in surface impregnatedand untreated concrete at different time of water absorption and thelinear fitting lines
water is reduced significantly by surface impregnation witheach type of silane
For a homogeneous porous material a simple expressioncan be deduced from theory of capillarity to describe capillarysuction as function of time see (1) [29 30] This equation isonly a first approximation because the skin effect of concretewill always be the origin of a deviation of measured resultsfrom the theoretical prediction
Δ119882 = 119860radic119905 (1)
where Δ119882 stands for the amount of absorbed water bycapillary suction per unit area and t for the duration of con-tact A is the coefficient of capillary suction The coefficientof capillary suction deduced from Figure 5 for treated anduntreated concrete can be calculated The results indicatethat the coefficient of capillary suction for untreated sampleis 2487 g(m2h05) while for sample L1 (impregnated byliquid silane) it is 409 g(m2h05) approximately one-sixthof untreated sample for samples C400 (silane cream) andG400 (silane gel) the coefficients are 345 and 245 g(m2h05)respectively They are less than one-seventh and one-tenth ofthat of untreated sampleThis obviously indicates that surfaceimpregnation with water repellent silanes can significantlyreduce water penetration into concrete
Advances in Materials Science and Engineering 5
20 mm M-Ref M-G400
(a) Neutron image after 05 hours
M-Ref M-G400
(b) Image after 2 hours
Figure 6 Observations of water penetration into mortar specimens after 05 and 2 hours by means of neutron radiography
Poly
silox
ane c
once
ntra
tion
()
C-L1C-C400C-G400
00
02
04
06
08
2 4 6 8 10 120Depth (mm)
Figure 7 Polysiloxane profiles in water repellent treated concretewith silane liquid silane cream and silane gel
Figure 6 shows the visual observation of water pene-tration into untreated and water repellent surface treatedmortar specimens after 05 and 2 hours by means of neutronradiography It can be clearly seen that after half an hourof contact with water a penetration front becomes visiblein untreated concrete This irregular front gradually movesinto the porous material with increasing of time But forthe surface impregnated sample water uptake could not beobserved with the naked eyes even after two hours becauseof the polysiloxane film formed from silane which made thenear-surface region hydrophobic
After being applied on the surfaces of concrete silanepenetrated and formed polysiloxane (silicon resin) in thenear-surface zone The polysiloxane concentration in surfaceimpregnated samples has been measured by FT-IR spec-troscopyThe results are shown in Figure 7 It can be seen thatin each case a penetration depth of about nine millimetershas been reached This treatment can be called deep impreg-nation in contrast to simple surface impregnation In somecases a simple surface impregnation is sufficient However tobuild up a reliable and durable chloride barrier a minimumpenetration depth of 7mm is often required [5] This has tobe confirmed in the context of quality assurance after surfacetreatment in practice If the penetration depth is too small
the ingress of aggressive ions with water is slowed down butnot prevented for long time
In addition neutron images of three types of impregnatedand water saturated mortar specimens are shown in Figure 8The upper impregnated surface is of interest exclusively inthis context It can be clearly seen with the naked eye thatthe neutron transmission is significantly higher in the outerimpregnated layer The thickness of the impregnated layercan be estimated from the results shown in Figure 8 Theaverage values determined by visual inspection are 20 41and 63mm for samples G100 G400 and G600 respectively
The moisture distribution was further measured in thenear-surface zone as indicated with the rectangular frameshown in Figure 8 (M-G600) from the neutron imagesobtained from water saturated specimens Results are shownin Figure 9 As expected the moisture content in theuntreated specimen is essentially homogeneously distributedall over the volume The observed slight decrease of watercontent close to the surfacemay be attributed to a small waterloss during handling before taking the first neutron image
However on the surface impregnated specimens theinfluence of the water repellent near-surface zone can beobserved clearly As expected the water content in the waterrepellent zone is significantly reducedThe width of the waterrepellent zone can also be observed clearly In samples M-G100 awater repellent layer with a thickness of approximately2mm has been established In samples M-G400 and M-G600 the thickness of the water repellent zone can beestimated to be approximately 4 and 6mm respectivelyWhatis most important however is the fact that in sample M-G100 the water content in the water repellent zone is certainlysubstantially reduced but still a certain amount of water canbe observed in this region In contrast in sample M-G600 aminimum amount of water can be detected only From theseresults it can again be concluded that deep impregnation isnecessary for an efficient chloride barrier
42 Effect ofWater Repellent Surface Impregnation onChloridePenetration The surfaces of treated and untreated concretespecimens have been brought in contact with an aqueousNaCl solution with concentration of 3 for 28 days Thechloride profiles were determined The results are shown inFigure 10 It can be seen that a lot of chloride ions penetratedinto untreated concrete even up to depth of 30mm It alreadyhas been shown that capillary suction is a most powerfulmechanism for the transport of chlorides into concrete If
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Materials Science and Engineering 3
(a)
(b)
Figure 3 The principle of water repellency (a) untreated concrete contact angle 120579 less than 90∘ (b) water repellent treated contact angle 120579greater than 90∘
Table 1 Composition of the two types of mixtures used in thisproject kgm3
Type WC Cement Sand Aggregate WaterConcrete C 05 320 653 1267 160Mortar M 06 300 1650 mdash 180
From all mixes given in Table 1 cubes with side length of100mmwere produced Another type of prismatic specimenswith dimensions of 280 times 150 times 115mm with two steel barswas also prepared for steel corrosion test All specimenswere compacted in steel forms and cured for one day beforedemolding After that the specimens were moved into acuring room (119879 = 20 plusmn 2∘C RH gt 95) At an age of 28 daysthey were taken out of the curing room for water repellentsurface treatment
32 Water Repellent Surface Impregnation After 28 days ofmoist curing the specimenswere further stored at RHof 60for 7 days for drying Then one of the molded surfaces ofcubic specimens and the top surface (280 times 115mm) of therectangular parallelepiped specimens have been impregnatedwith three different types of water repellent agents Theagentsrsquo type usage amount and the corresponding samplescodes are listed in Table 2 After that the specimens werestored again at RH of 60 for another 7 days in order toallow sufficient polymerization of silane Then the surfaceimpregnated specimens were ready for further tests
One series have been impregnated with liquid silane Inthis case concrete surface was put in contact with liquidsilane for one hour During this period liquid silane couldbe absorbed into specimen due to capillary suction In secondseries one of themolded surfaceswas covered by silane creamThe amount of usage on the surface was 400 gm2 For thethird to fifth series 100 400 and 600 gm2 of silane gelwere applied Both silane cream and gel were covered on theconcrete surfaces with a small brush
From the specimens treated by water repellent agentslayers from the treated surface with a thickness of 1mmeach have been milled consecutively by means of a speciallybuilt milling cutter The powder obtained from this processwas collected The silicon content of these powders was thendetermined by means of FT-IR spectroscopy This methodhas been developed and further refined for this specificapplication by Gerdes and Wittmann [19]
33 Water Absorption and Chloride Penetration Water ab-sorption of surface treated and untreated specimens has beenmeasured by a standard method [20] Before the test the
Pure water or 3 NaClsolution
Wax Wax
Cut surface
3ndash5 mm
Figure 4 Schematic illustration for water absorption and chloridepenetration test of concrete
cubic specimens were cut into two halves and dried in aventilated oven at a temperature of 50∘C for 7 days until massequilibrium was reached When the specimens cooled downto the room temperature the treated and untreated specimenswere put in contact with water for selected periods of time asshown in Figure 4 Then the amounts of absorbed water bycapillary suction were measured by weighing the specimensafter 1 2 4 8 24 48 and 72 hours
In a similar way as described in the last paragraph chlo-ride penetration test (3 NaCl solution) for water repellenttreated and untreated specimens were carried out for 28 daysAfter the test powder wasmilled consecutively starting at thespecimensrsquo surface which had been exposed to salt solutionThe chloride content of the powderwas then determinedwiththe ion selective electrode method In this way the chlorideprofiles in water repellent surface impregnated and untreatedspecimens have been determined
34 Neutron Radiography Water repellent mortar speci-mens and untreated companion specimens were also testedby neutron radiography at Paul-Scherrer-Institute (PSI) inSwitzerland Neutron radiography has been identified as anideal and unique nondestructive technique to study watermovement andmoisture distributions in cement-basedmate-rials because of their strong attenuation by hydrogen andtheir insensitivity to the dominant ingredients such as silicaand calcium in cement-based materials More details aboutthis technique can be found in [21ndash26]
First neutron images were taken on samples which werein hygral equilibrium with the room atmosphere (RH asymp60 T asymp 20∘C) Then neutron images were taken againon water repellent treated and untreated mortar specimensafter contact with water for 05 and 2 hours In this way thewatermovement in samples was visualized In addition somesurface impregnated and untreated samples were placed inwater for three days This period was sufficient to saturatethe samples completely Then neutron images were taken onthese water saturated specimens Both untreated and surfaceimpregnated mortar specimens in the water saturated state
4 Advances in Materials Science and Engineering
Table 2 Three types of water repellent agents used in this project and their uses
Type Amount of use NoteRef mdash mdash No treatment reference sampleL1 Liquid silane 470 gm2 Surface absorptionC400 Silane cream 400 gm2 Surface brushingG100 Silane gel 100 gm2 Surface brushingG400 Silane gel 400 gm2 Surface brushingG600 Silane gel 600 gm2 Surface brushing
were investigated From the neutron images the moisturedistribution can be analyzed quantitatively
35 Accelerated Carbonation After drying in lab for 7 daysboth surface treated and untreated specimens were submittedto accelerated carbonation for 7 and 28 days According tothe Chinese standard [27] the concentration of CO
2gas was
maintained constant at 20 plusmn 2 relative humidity in carbon-ation box was about 70 the temperature was 20plusmn3∘C Foursurfaces except for the treated surface and its opposite surfacehad been sealed with wax before being placed in carbonationsituation In this way carbonation normal to two oppositesurfaces into concrete was imposed After 7 and 28 dayscarbonation depth in the surface impregnated and untreatedsamples weremeasured by spraying phenolphthalein solutionwith 1 in ethanol
36 Reinforcement Corrosion This test followed ASTM G109-07 [28] specimens were 280 times 150 times 115mm with areservoir of NaCl solution on the test surface The reservoirwith size of 150 times 75 times 75mm was located at the center of topsurface Upper reinforced steel was positioned 20mm fromponded surface and bottom steels were 25mm from bottomsurface The ends of steel were protected with electroplaterrsquostape and a 200-mm portion in the middle is bare During thetest the half-cell potential and the corrosion current densityof the steel rebar in surface impregnated and untreatedconcrete specimens were measured continuously every week
4 Results and Discussion
41 Effect of Water Repellent Surface Impregnation on WaterAbsorption Water absorption of both untreated and surfacetreated concrete specimens has been measured for 72-hourcontact with water Results obtained at different time areshown in Figure 5 Points indicated in Figure 5 are averagevalues of three independent measurements The variationof the individual measurements is also shown It can belearned from the results that all the surface impregnatedconcrete absorbedmuch lesswater compared to the untreatedconcrete In this case it is not liquid water but water vaporis trapped by capillary condensation once it has crossed thesilane impregnated layer In addition capillary condensationcan take place in nanopores of concrete as silane moleculescannot enter these narrow spaces because of geometricalreasons Therefore a small amount of capillary condensedwater still can migrate into the pores by diffusion Butcompared to the untreated concrete the amount of absorbed
C-RefC-L1
C-C400C-G400
2 4 6 80Square root of contact time (Ｂ05)
0
400
800
1200
1600
2000
Am
ount
of a
bsor
bed
wat
er (g
Ｇ2)
Figure 5 The amount of absorbed water in surface impregnatedand untreated concrete at different time of water absorption and thelinear fitting lines
water is reduced significantly by surface impregnation witheach type of silane
For a homogeneous porous material a simple expressioncan be deduced from theory of capillarity to describe capillarysuction as function of time see (1) [29 30] This equation isonly a first approximation because the skin effect of concretewill always be the origin of a deviation of measured resultsfrom the theoretical prediction
Δ119882 = 119860radic119905 (1)
where Δ119882 stands for the amount of absorbed water bycapillary suction per unit area and t for the duration of con-tact A is the coefficient of capillary suction The coefficientof capillary suction deduced from Figure 5 for treated anduntreated concrete can be calculated The results indicatethat the coefficient of capillary suction for untreated sampleis 2487 g(m2h05) while for sample L1 (impregnated byliquid silane) it is 409 g(m2h05) approximately one-sixthof untreated sample for samples C400 (silane cream) andG400 (silane gel) the coefficients are 345 and 245 g(m2h05)respectively They are less than one-seventh and one-tenth ofthat of untreated sampleThis obviously indicates that surfaceimpregnation with water repellent silanes can significantlyreduce water penetration into concrete
Advances in Materials Science and Engineering 5
20 mm M-Ref M-G400
(a) Neutron image after 05 hours
M-Ref M-G400
(b) Image after 2 hours
Figure 6 Observations of water penetration into mortar specimens after 05 and 2 hours by means of neutron radiography
Poly
silox
ane c
once
ntra
tion
()
C-L1C-C400C-G400
00
02
04
06
08
2 4 6 8 10 120Depth (mm)
Figure 7 Polysiloxane profiles in water repellent treated concretewith silane liquid silane cream and silane gel
Figure 6 shows the visual observation of water pene-tration into untreated and water repellent surface treatedmortar specimens after 05 and 2 hours by means of neutronradiography It can be clearly seen that after half an hourof contact with water a penetration front becomes visiblein untreated concrete This irregular front gradually movesinto the porous material with increasing of time But forthe surface impregnated sample water uptake could not beobserved with the naked eyes even after two hours becauseof the polysiloxane film formed from silane which made thenear-surface region hydrophobic
After being applied on the surfaces of concrete silanepenetrated and formed polysiloxane (silicon resin) in thenear-surface zone The polysiloxane concentration in surfaceimpregnated samples has been measured by FT-IR spec-troscopyThe results are shown in Figure 7 It can be seen thatin each case a penetration depth of about nine millimetershas been reached This treatment can be called deep impreg-nation in contrast to simple surface impregnation In somecases a simple surface impregnation is sufficient However tobuild up a reliable and durable chloride barrier a minimumpenetration depth of 7mm is often required [5] This has tobe confirmed in the context of quality assurance after surfacetreatment in practice If the penetration depth is too small
the ingress of aggressive ions with water is slowed down butnot prevented for long time
In addition neutron images of three types of impregnatedand water saturated mortar specimens are shown in Figure 8The upper impregnated surface is of interest exclusively inthis context It can be clearly seen with the naked eye thatthe neutron transmission is significantly higher in the outerimpregnated layer The thickness of the impregnated layercan be estimated from the results shown in Figure 8 Theaverage values determined by visual inspection are 20 41and 63mm for samples G100 G400 and G600 respectively
The moisture distribution was further measured in thenear-surface zone as indicated with the rectangular frameshown in Figure 8 (M-G600) from the neutron imagesobtained from water saturated specimens Results are shownin Figure 9 As expected the moisture content in theuntreated specimen is essentially homogeneously distributedall over the volume The observed slight decrease of watercontent close to the surfacemay be attributed to a small waterloss during handling before taking the first neutron image
However on the surface impregnated specimens theinfluence of the water repellent near-surface zone can beobserved clearly As expected the water content in the waterrepellent zone is significantly reducedThe width of the waterrepellent zone can also be observed clearly In samples M-G100 awater repellent layer with a thickness of approximately2mm has been established In samples M-G400 and M-G600 the thickness of the water repellent zone can beestimated to be approximately 4 and 6mm respectivelyWhatis most important however is the fact that in sample M-G100 the water content in the water repellent zone is certainlysubstantially reduced but still a certain amount of water canbe observed in this region In contrast in sample M-G600 aminimum amount of water can be detected only From theseresults it can again be concluded that deep impregnation isnecessary for an efficient chloride barrier
42 Effect ofWater Repellent Surface Impregnation onChloridePenetration The surfaces of treated and untreated concretespecimens have been brought in contact with an aqueousNaCl solution with concentration of 3 for 28 days Thechloride profiles were determined The results are shown inFigure 10 It can be seen that a lot of chloride ions penetratedinto untreated concrete even up to depth of 30mm It alreadyhas been shown that capillary suction is a most powerfulmechanism for the transport of chlorides into concrete If
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
4 Advances in Materials Science and Engineering
Table 2 Three types of water repellent agents used in this project and their uses
Type Amount of use NoteRef mdash mdash No treatment reference sampleL1 Liquid silane 470 gm2 Surface absorptionC400 Silane cream 400 gm2 Surface brushingG100 Silane gel 100 gm2 Surface brushingG400 Silane gel 400 gm2 Surface brushingG600 Silane gel 600 gm2 Surface brushing
were investigated From the neutron images the moisturedistribution can be analyzed quantitatively
35 Accelerated Carbonation After drying in lab for 7 daysboth surface treated and untreated specimens were submittedto accelerated carbonation for 7 and 28 days According tothe Chinese standard [27] the concentration of CO
2gas was
maintained constant at 20 plusmn 2 relative humidity in carbon-ation box was about 70 the temperature was 20plusmn3∘C Foursurfaces except for the treated surface and its opposite surfacehad been sealed with wax before being placed in carbonationsituation In this way carbonation normal to two oppositesurfaces into concrete was imposed After 7 and 28 dayscarbonation depth in the surface impregnated and untreatedsamples weremeasured by spraying phenolphthalein solutionwith 1 in ethanol
36 Reinforcement Corrosion This test followed ASTM G109-07 [28] specimens were 280 times 150 times 115mm with areservoir of NaCl solution on the test surface The reservoirwith size of 150 times 75 times 75mm was located at the center of topsurface Upper reinforced steel was positioned 20mm fromponded surface and bottom steels were 25mm from bottomsurface The ends of steel were protected with electroplaterrsquostape and a 200-mm portion in the middle is bare During thetest the half-cell potential and the corrosion current densityof the steel rebar in surface impregnated and untreatedconcrete specimens were measured continuously every week
4 Results and Discussion
41 Effect of Water Repellent Surface Impregnation on WaterAbsorption Water absorption of both untreated and surfacetreated concrete specimens has been measured for 72-hourcontact with water Results obtained at different time areshown in Figure 5 Points indicated in Figure 5 are averagevalues of three independent measurements The variationof the individual measurements is also shown It can belearned from the results that all the surface impregnatedconcrete absorbedmuch lesswater compared to the untreatedconcrete In this case it is not liquid water but water vaporis trapped by capillary condensation once it has crossed thesilane impregnated layer In addition capillary condensationcan take place in nanopores of concrete as silane moleculescannot enter these narrow spaces because of geometricalreasons Therefore a small amount of capillary condensedwater still can migrate into the pores by diffusion Butcompared to the untreated concrete the amount of absorbed
C-RefC-L1
C-C400C-G400
2 4 6 80Square root of contact time (Ｂ05)
0
400
800
1200
1600
2000
Am
ount
of a
bsor
bed
wat
er (g
Ｇ2)
Figure 5 The amount of absorbed water in surface impregnatedand untreated concrete at different time of water absorption and thelinear fitting lines
water is reduced significantly by surface impregnation witheach type of silane
For a homogeneous porous material a simple expressioncan be deduced from theory of capillarity to describe capillarysuction as function of time see (1) [29 30] This equation isonly a first approximation because the skin effect of concretewill always be the origin of a deviation of measured resultsfrom the theoretical prediction
Δ119882 = 119860radic119905 (1)
where Δ119882 stands for the amount of absorbed water bycapillary suction per unit area and t for the duration of con-tact A is the coefficient of capillary suction The coefficientof capillary suction deduced from Figure 5 for treated anduntreated concrete can be calculated The results indicatethat the coefficient of capillary suction for untreated sampleis 2487 g(m2h05) while for sample L1 (impregnated byliquid silane) it is 409 g(m2h05) approximately one-sixthof untreated sample for samples C400 (silane cream) andG400 (silane gel) the coefficients are 345 and 245 g(m2h05)respectively They are less than one-seventh and one-tenth ofthat of untreated sampleThis obviously indicates that surfaceimpregnation with water repellent silanes can significantlyreduce water penetration into concrete
Advances in Materials Science and Engineering 5
20 mm M-Ref M-G400
(a) Neutron image after 05 hours
M-Ref M-G400
(b) Image after 2 hours
Figure 6 Observations of water penetration into mortar specimens after 05 and 2 hours by means of neutron radiography
Poly
silox
ane c
once
ntra
tion
()
C-L1C-C400C-G400
00
02
04
06
08
2 4 6 8 10 120Depth (mm)
Figure 7 Polysiloxane profiles in water repellent treated concretewith silane liquid silane cream and silane gel
Figure 6 shows the visual observation of water pene-tration into untreated and water repellent surface treatedmortar specimens after 05 and 2 hours by means of neutronradiography It can be clearly seen that after half an hourof contact with water a penetration front becomes visiblein untreated concrete This irregular front gradually movesinto the porous material with increasing of time But forthe surface impregnated sample water uptake could not beobserved with the naked eyes even after two hours becauseof the polysiloxane film formed from silane which made thenear-surface region hydrophobic
After being applied on the surfaces of concrete silanepenetrated and formed polysiloxane (silicon resin) in thenear-surface zone The polysiloxane concentration in surfaceimpregnated samples has been measured by FT-IR spec-troscopyThe results are shown in Figure 7 It can be seen thatin each case a penetration depth of about nine millimetershas been reached This treatment can be called deep impreg-nation in contrast to simple surface impregnation In somecases a simple surface impregnation is sufficient However tobuild up a reliable and durable chloride barrier a minimumpenetration depth of 7mm is often required [5] This has tobe confirmed in the context of quality assurance after surfacetreatment in practice If the penetration depth is too small
the ingress of aggressive ions with water is slowed down butnot prevented for long time
In addition neutron images of three types of impregnatedand water saturated mortar specimens are shown in Figure 8The upper impregnated surface is of interest exclusively inthis context It can be clearly seen with the naked eye thatthe neutron transmission is significantly higher in the outerimpregnated layer The thickness of the impregnated layercan be estimated from the results shown in Figure 8 Theaverage values determined by visual inspection are 20 41and 63mm for samples G100 G400 and G600 respectively
The moisture distribution was further measured in thenear-surface zone as indicated with the rectangular frameshown in Figure 8 (M-G600) from the neutron imagesobtained from water saturated specimens Results are shownin Figure 9 As expected the moisture content in theuntreated specimen is essentially homogeneously distributedall over the volume The observed slight decrease of watercontent close to the surfacemay be attributed to a small waterloss during handling before taking the first neutron image
However on the surface impregnated specimens theinfluence of the water repellent near-surface zone can beobserved clearly As expected the water content in the waterrepellent zone is significantly reducedThe width of the waterrepellent zone can also be observed clearly In samples M-G100 awater repellent layer with a thickness of approximately2mm has been established In samples M-G400 and M-G600 the thickness of the water repellent zone can beestimated to be approximately 4 and 6mm respectivelyWhatis most important however is the fact that in sample M-G100 the water content in the water repellent zone is certainlysubstantially reduced but still a certain amount of water canbe observed in this region In contrast in sample M-G600 aminimum amount of water can be detected only From theseresults it can again be concluded that deep impregnation isnecessary for an efficient chloride barrier
42 Effect ofWater Repellent Surface Impregnation onChloridePenetration The surfaces of treated and untreated concretespecimens have been brought in contact with an aqueousNaCl solution with concentration of 3 for 28 days Thechloride profiles were determined The results are shown inFigure 10 It can be seen that a lot of chloride ions penetratedinto untreated concrete even up to depth of 30mm It alreadyhas been shown that capillary suction is a most powerfulmechanism for the transport of chlorides into concrete If
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Materials Science and Engineering 5
20 mm M-Ref M-G400
(a) Neutron image after 05 hours
M-Ref M-G400
(b) Image after 2 hours
Figure 6 Observations of water penetration into mortar specimens after 05 and 2 hours by means of neutron radiography
Poly
silox
ane c
once
ntra
tion
()
C-L1C-C400C-G400
00
02
04
06
08
2 4 6 8 10 120Depth (mm)
Figure 7 Polysiloxane profiles in water repellent treated concretewith silane liquid silane cream and silane gel
Figure 6 shows the visual observation of water pene-tration into untreated and water repellent surface treatedmortar specimens after 05 and 2 hours by means of neutronradiography It can be clearly seen that after half an hourof contact with water a penetration front becomes visiblein untreated concrete This irregular front gradually movesinto the porous material with increasing of time But forthe surface impregnated sample water uptake could not beobserved with the naked eyes even after two hours becauseof the polysiloxane film formed from silane which made thenear-surface region hydrophobic
After being applied on the surfaces of concrete silanepenetrated and formed polysiloxane (silicon resin) in thenear-surface zone The polysiloxane concentration in surfaceimpregnated samples has been measured by FT-IR spec-troscopyThe results are shown in Figure 7 It can be seen thatin each case a penetration depth of about nine millimetershas been reached This treatment can be called deep impreg-nation in contrast to simple surface impregnation In somecases a simple surface impregnation is sufficient However tobuild up a reliable and durable chloride barrier a minimumpenetration depth of 7mm is often required [5] This has tobe confirmed in the context of quality assurance after surfacetreatment in practice If the penetration depth is too small
the ingress of aggressive ions with water is slowed down butnot prevented for long time
In addition neutron images of three types of impregnatedand water saturated mortar specimens are shown in Figure 8The upper impregnated surface is of interest exclusively inthis context It can be clearly seen with the naked eye thatthe neutron transmission is significantly higher in the outerimpregnated layer The thickness of the impregnated layercan be estimated from the results shown in Figure 8 Theaverage values determined by visual inspection are 20 41and 63mm for samples G100 G400 and G600 respectively
The moisture distribution was further measured in thenear-surface zone as indicated with the rectangular frameshown in Figure 8 (M-G600) from the neutron imagesobtained from water saturated specimens Results are shownin Figure 9 As expected the moisture content in theuntreated specimen is essentially homogeneously distributedall over the volume The observed slight decrease of watercontent close to the surfacemay be attributed to a small waterloss during handling before taking the first neutron image
However on the surface impregnated specimens theinfluence of the water repellent near-surface zone can beobserved clearly As expected the water content in the waterrepellent zone is significantly reducedThe width of the waterrepellent zone can also be observed clearly In samples M-G100 awater repellent layer with a thickness of approximately2mm has been established In samples M-G400 and M-G600 the thickness of the water repellent zone can beestimated to be approximately 4 and 6mm respectivelyWhatis most important however is the fact that in sample M-G100 the water content in the water repellent zone is certainlysubstantially reduced but still a certain amount of water canbe observed in this region In contrast in sample M-G600 aminimum amount of water can be detected only From theseresults it can again be concluded that deep impregnation isnecessary for an efficient chloride barrier
42 Effect ofWater Repellent Surface Impregnation onChloridePenetration The surfaces of treated and untreated concretespecimens have been brought in contact with an aqueousNaCl solution with concentration of 3 for 28 days Thechloride profiles were determined The results are shown inFigure 10 It can be seen that a lot of chloride ions penetratedinto untreated concrete even up to depth of 30mm It alreadyhas been shown that capillary suction is a most powerfulmechanism for the transport of chlorides into concrete If
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
6 Advances in Materials Science and Engineering
20 mm
(a) M-G100 (b) M-G400 (c) M-G600
Figure 8 Neutron images as obtained on the tree types of water repellent surface impregnated and water saturated mortar specimens Theupper half of the neutron images taken on square slabs is shown only
M-G600M-G400
M-G100Ref untreated
4 8 12 160Depth (mm)
000
004
008
012
016
Wat
er co
nten
t in
wet
impr
egna
ted
mor
tar (
gcＧ
3)
Figure 9Water content in surface impregnated andwater saturatedmortar specimens G100 G400 and G600 For comparison thewater distribution in untreated mortar is also shown
there is no capillary action salt solution cannot be taken upby the porous material and if the micropores are not waterfilled chloride cannot diffuse into the porous structure eitherTherefore by means of surface impregnation with silanes itrestrained water from penetrating into concrete and conse-quently prevented chloride migration During the exposureperiod for treated concrete no chloride has penetrated intodeep part of the material The small amount of chloride ionswhich can be detected in the first 3mm is due to surfaceroughness and open big pores in the near-surface zoneTherefore surface impregnation with silane is an efficientchloride barrier for porous cement-based materials
43 Effect ofWater Repellent Surface Impregnation on Carbon-ation After 7 and 28 days of carbonation the carbonationdepth of water repellent treated and untreated concrete hasbeen measured The results are shown in Figure 11 It canbe obviously found that surface impregnated specimens havelower carbonation depth than untreated concrete Amongthe surface treatments application of 400 gm2 silane creamand silane gel reduces approximately one half of carbonationdepth compared to the reference concrete whose efficiency ismuch better than 100 gm2 covering usage
RefC-L1
C-C400C-G400
00
02
04
06
08
Chlo
ride c
onte
nt re
lated
to th
ew
eigh
t of c
emen
t (
)
10 20 300Depth (mm)
Figure 10 Chloride profiles of surface impregnated and untreatedconcrete after continuous contact with NaCl solution for 28 days
By surface impregnation with silanes the hydrophobicfilm protects concrete from water penetration which usu-ally makes the hydrophobic layer almost dry Very littlecarbonation action takes place in this area because theneutralization between CO
2gas and calcium hydrate or C-
S-H gel needs water while this layer also makes the moisturediffusion of concrete very low and consequently makes thearea behind the hydrophobic layer moist under which con-dition carbonation cannot happen either However it mustbe noticed that the conclusion that surface impregnationreduces carbonation depth by about one half was obtainedunder RH of 70 in the carbonation box If the environmentis very dry the untreated concrete would lose water verysoon but in the treated concrete the drying rate is sloweddown and consequently liquid water in the pores wouldmakecarbonation process quicker [31]
44 Effect of Water Repellent Surface Impregnation on Rein-forcement Corrosion Thehalf-cell potential (Cu-CuSO
4) and
corrosion current density of the steel rebar in reinforcedconcrete have been measured The results are shown in Fig-ure 12 It indicates clearly that the concrete specimenswithoutsurface impregnation exhibits high level of negative corrosionpotentials and corrosion current densities especially afterapproximately 33 weeks of exposure period At this stage
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Materials Science and Engineering 7
RefC-C400
C-G100C-G400
287(d carb)
00
50
100
150
Carb
onat
ion
dept
h (m
m)
Figure 11 Carbonation depth of untreated and surface impregnated concrete after 7 and 28 days of accelerated carbonation
Uncertain
C-RefC-G400
gt90 risk of steel corrosion
lt10
8 16 24 32 40 48 560Time (weeks)
minus500
minus400
minus300
minus200
minus100
0
CuC
uS
4ha
lf-ce
ll po
tent
ial (
mV
)
(a) Cu-CuSO4 half-cell potential
Moderate-to-high corrosion
Low-to-moderate corrosion
C-RefC-G400
Negligible
8 16 24 32 40 48 560Time (weeks)
00
01
02
03
04
05
06
07
08
Cor
rosio
n cu
rren
t den
sityI ＝
ＩＬＬ
(A
cＧ
2)
(b) Corrosion current density
Figure 12 Cu-CuSO4half-cell potential (a) and corrosion current density (b) of reinforced steel in reference untreated and surface
impregnated concrete by silane
the corrosion potential was about minus460mV According to theASTM standard this means the risk of corrosion was greaterthan 90 [32] The corrosion current density was about 04sim05 120583Acm2 which means the steel reinforcement started tocorrode while for water repellent surface treated concreteboth the electric potential and corrosion current densitywere kept much lower throughout the period measured Therisk of corrosion was maintained lower than 10 from theresults of corrosion potential From the results of corrosioncurrent density corrosion can be neglected This showsthat corrosion did not happen in water repellent treated
specimens Therefore corrosion activities can be reducedconsiderably by surface impregnation
5 Conclusions
Based on the results presented herein the following conclu-sions can be drawn
(1)When the surface of water repellent treated concrete isin contact with water there is no aqueous water penetrationbut small amount of water vapor is still absorbed andcondenses in the untreated pores of the material Therefore
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
8 Advances in Materials Science and Engineering
the hydrophobic layer with several millimeters of thicknesscan reduce significantly water absorption into concrete
(2) Water vapor however does not contribute to iontransport If the pores of concrete are not water filled ionsdiffusion is slowed down effectively Hence surface impreg-nation with silane provides an effective chloride barrier As aconsequence the service life of a concrete structure exposedto sea water or deicing salt can be extended
(3) Carbonation depth of surface impregnated concretecan be reduced one half under the environmental RH of 70compared to the untreated concrete
(4) Surface impregnation with silanes also provides effec-tive corrosion protection to reinforcing steel in concretecontacted with chloride solution In order to prolong theservice life of reinforced concrete structures water repellenttreatment can be taken into consideration to reduce the riskof steel corrosion provided surface treatment is adequatelymaintained which can be achieved by appropriate applicationand deep impregnation (gt6mm) [33] In addition the dura-bility of silane impregnation itself and its long-term residualprotection has to be studied In this sense the efficiency of theprotective measure should be controlled in regular intervalsOnce the initial requirements are not fulfilled anymore thetreatment should be repeated
Conflicts of Interest
The authors declare no conflicts of interest
Acknowledgments
Financial support of ongoing projects by National NaturalScience Foundation of China (51420105015 51278260) BasicResearch Program of China (2015CB655100) and 111 Projectis gratefully acknowledged
References
[1] H S Muller M Haist and M Vogel ldquoAssessment of the sus-tainability potential of concrete and concrete structures consid-ering their environmental impact performance and lifetimerdquoConstruction and Building Materials vol 67 pp 321ndash337 2014
[2] U M Angst R D Hooton J Marchand et al ldquoPresent andfuture durability challenges for reinforced concrete structuresrdquoMaterials and Corrosion vol 63 no 12 pp 1047ndash1051 2012
[3] H Huang G Ye C Qian and E Schlangen ldquoSelf-healing incementitious materials materials methods and service condi-tionsrdquoMaterials amp Design vol 92 pp 499ndash511 2016
[4] J Vries R B Polder and H Borsje ldquoDurability of hydrophobictreatment of concreterdquo in Proceedings of the 2nd InternationalConference on Water Repellent Treatment of Building Materialspp 77ndash90 Aedificatio Publishers 1998
[5] P Zhang Y Cong M Vogel et al ldquoSteel reinforcement corro-sion in concrete under combined actions The role of freeze-thaw cycles chloride ingress and surface impregnationrdquo Con-struction and Building Materials vol 148 pp 113ndash121 2017
[6] P Hou X Cheng J Qian and S P Shah ldquoEffects and mecha-nisms of surface treatment of hardened cement-basedmaterialswith colloidal nanoSiO2 and its precursorrdquo Construction andBuilding Materials vol 53 pp 66ndash73 2014
[7] Y Cai P Hou C Duan et al ldquoThe use of tetraethyl orthosilicatesilane (TEOS) for surface-treatment of hardened cement-basedmaterials A comparison study with normal treatment agentsrdquoConstruction and Building Materials vol 117 pp 144ndash151 2016
[8] C Schrofl VMechtcherine A Kaestner P Vontobel J Hovindand E Lehmann ldquoTransport of water through Strain-hardeningCement-based Composite (SHCC) applied on top of crackedreinforced concrete slabs with and without hydrophobizationof cracks - Investigation by neutron radiographyrdquo Constructionand Building Materials vol 76 pp 70ndash86 2015
[9] J-G Dai Y Akira F H Wittmann H Yokota and P ZhangldquoWater repellent surface impregnation for extension of servicelife of reinforced concrete structures in marine environmentsThe role of cracksrdquo Cement and Concrete Composites vol 32no 2 pp 101ndash109 2010
[10] F H Wittmann T A J M Siemes and L G W VerhoefHydrophobe I TU Delft Delft The Netherlands 1995
[11] F H Wittmann and A Gerdes Hydrophobe II ETH ZurichSwitzerland 1998
[12] K Littmann and A E Charola Hydrophobe III University ofHannover Hanover Germany 2001
[13] J Silfwerbrand ldquoHydrophobe IVrdquo Stockholm Sweden 2005[14] H De Clercq and A E Charola ldquoHydrophobe V KIK-IRPArdquo
Brussels Belgium 2008[15] E Borrelli and V Fassina ldquoHydrophobe VIrdquo Rome Italy 2011[16] J-M Mimoso ldquoHydrophobe VIIrdquo Lisbon Portugal 2014[17] J G Dai H Yokota and T J Zhao ldquoHydrophobe VIIIrdquo Hong
Kong 2017[18] H Kus Long term performance of water repellents on rendered
autoclaved aerated concrete [PhD Thesis] Royal Institute ofTechnology Stockholm Sweden 2002
[19] A Gerdes and F H Wittmann ldquoQuantitation of hydrophobicmass by FT-IR spectroscopyrdquo Restor Build Monum vol 5 pp201ndash210 1999
[20] TC 14-CPV Test Method CPC 112 Absorption of Water byConcrete by Capillarity RILEM Publications 1982
[21] E H Lehmann A Kaestner C Grunzweig D Mannes PVontobel and S Peetermans ldquoMaterials research and non-destructive testing using neutron tomography methodsrdquo Inter-national Journal of Materials Research vol 105 no 7 pp 664ndash670 2014
[22] G Frei E H Lehmann D Mannes and P Boillat ldquoTheneutronmicro-tomography setup at PSI and its use for researchpurposes and engineering applicationsrdquo Nuclear Instrumentsand Methods in Physics Research Section A Accelerators Spec-trometers Detectors and Associated Equipment vol 605 no 1-2pp 111ndash114 2009
[23] P Zhang F H Wittmann T-J Zhao E H Lehmann and PVontobel ldquoNeutron radiography a powerful method to deter-mine time-dependentmoisture distributions in concreterdquoNucle-ar Engineering and Design vol 241 no 12 pp 4758ndash4766 2011
[24] P Zhang F H Wittmann M Vogel H S Muller and TZhao ldquoInfluence of freeze-thaw cycles on capillary absorptionand chloride penetration into concreterdquo Cement and ConcreteResearch vol 100 pp 60ndash67 2017
[25] P Zhang Z Liu S Han et al ldquoVisualization of rapid penetra-tion of water into cracked cement mortar using neutron radi-ographyrdquoMaterials Letters vol 195 pp 1ndash4 2017
[26] P Zhang P Wang D Hou Z Liu M Haist and T ZhaoldquoApplication of neutron radiography in observing and quantify-ing the time-dependentmoisture distributions inmulti-cracked
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Materials Science and Engineering 9
cement-based compositesrdquo Cement and Concrete Compositesvol 78 pp 13ndash20 2017
[27] GBT 50082-2009 Standard for Test Methods of Long-termPerformance and Durability of Ordinary Concrete Ministry ofConstruction Beijing China 2009
[28] ASTM G 109-07 Standard Test Method for Determining the Ef-fects of Chemical Admixtures on the Corrosion of Embedded SteelReinforcement in Concrete Exposed to Chloride EnvironmentsAmerican Society for Testing and Materials Philadelphia PaUSA 2013
[29] C Hall ldquoBarrier performance of concrete a review of fluidtransport theoryrdquo Materials and Structures vol 27 no 5 pp291ndash306 1994
[30] D A Quenard K Xu H M Kunzel D P Bentz and N SMartys ldquoMicrostructure and transport properties of porousbuilding materialsrdquo Materials and Structures vol 31 no 5 pp317ndash324 1998
[31] JHeinrichs S Schmeiser andAGerdes ldquoNumerical simulationof the influence of water repellent treatment on carbonationof concreterdquo in Proceedings of the 4th International Conferenceon Water Repellent Treatment of Building Materials pp 27ndash44Aedificatio Publishers Stockholm Sweden 2005
[32] ASTM C 876-15 Standard Test Method for Corrosion Potentialsof Uncoated Reinforcing Steel in Concrete American Society forTesting and Materials Philadelphia Pa USA 2015
[33] S Meier and F Wittmann ldquoRecommendations for water repel-lent surface impregnation of concreterdquo Restoration of Buildingsand Monuments vol 17 no 6 pp 347ndash358 2011
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Submit your manuscripts athttpswwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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