EFFECT OF CARBON NANO AND MICROFIBERS ON THE MECHANICAL PROPERTIES AND DURABILITY OF CEMENT PASTES By Chantal K. Ince Thesis Submitted to the Faculty of the Graduate School of Vanderbilt University In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Environmental Engineering December, 2008 Nashville, Tennessee Approved: Dr Florence Sanchez Dr Andrew Garrabrants
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EFFECT OF CARBON NANO AND MICROFIBERS ON THE MECHANICAL
PROPERTIES AND DURABILITY OF CEMENT PASTES
By
Chantal K. Ince
Thesis
Submitted to the Faculty of the
Graduate School of Vanderbilt University
In partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
in
Environmental Engineering
December, 2008
Nashville, Tennessee
Approved:
Dr Florence Sanchez
Dr Andrew Garrabrants
ii
TABLE OF CONTENTS
Page
LIST OF TABLES .......................................................................................................................... iv
LIST OF FIGURES ......................................................................................................................... v
LIST OF ABBREVIATIONS ........................................................................................................ vii
Several factors influence the rate of hydration of cement: age, cement composition, cement
fineness, water to cement (w/c) ratio, temperature and the use of admixtures. The rate of
hydration of the varying cement constituents differs, tricalcium aluminate hydrates fastest
followed by tricalcium silicate and dicalcium silicate (Lea,1935). The hydration rate of cement
6
increases with its fineness. The rate of hydration and the ultimate degree of hydration decrease
with decreasing w/c ratio. The rate of hydration increases with temperature up to 100ºC however
the ultimate degree of hydration is not affected by temperature. Different admixtures can be used
to retard or accelerate the hydration process as necessary, one such admixture is gypsum which
acts as a retarder.
The structure of hardened cement paste is highly heterogeneous consisting mainly of amorphous
C-S-H gel (ca. 70% by mass), CH crystals (ca. 20% by mass), unhydrated cement grains and
voids containing either water or air (Birchall et al., 1978).
Mechanical Properties
The setting and hardening of cement pastes is brought about by the formation of C-S-H gel,
which fills the space between cement grains.
Porosity is one important factor determining the strength of cement paste. Increased porosity
leads to a decrease in the strength of cement paste. Porosity is determined by the w/c ratio and the
degree of hydration. Several experimental methods have been employed in measuring the
porosity of cement pastes, including water saturation method (Kim et al., 2002), water
evaporation (Carde et al., 1999) method, mercury intrusion porosimetry (Care, 2008), and
nitrogen adsorption (Juenger et al., 2001).
Typically the strengths of cement based materials are determined by measuring their
compressive (Shigeyuki et al., 1986), splitting tensile, (Houssam et al.,1994), and flexural
strengths (Houssam et al., 1994).
Durability
The durability of a cement paste can be described as its ability to resist chemical attack. This
chemical attack can result in dissolution and leaching or chemical transformations. Porosity is a
7
major factor influencing the ability of a cement paste to resist chemical attack. The larger the
porosity of the paste the more it allows the chemical attack agent to penetrate and degrade the
paste. The intensity of the attack is also influenced by the specific chemical agent.
Cementitious materials are subjected to several forms of chemical attack in the environment. The
main forms of environmental chemical attack are dissolution and leaching in water, acid attack,
sulfate attack, and sea water attack. In the case of dissolution and leaching in water, CH present in
the cement paste dissolves into the water forming an alkaline solution, this alkaline solution
dissolves calcium hydrates present in the paste (Soroka, 1979). This process continues with time
until all the CH is leached out as long as a continuous supply of fresh water is still available. Acid
attack also dissolves cement paste. The naturally occurring acids which typically attack
cementitious materials are carbonic, humic, and sulfuric acids. During acid attack, the acid reacts
with the calcium hydrates to form salts. During sulfate attack the sulfates react with hydrated
calcium aluminate to form ettringite resulting in an increase in volume and cracking of the
cementitious matrix. In addition some sulfates react with CH to form gypsum (Baghabra Al-
Amoudi, 2002). The intensity of the sulfate attack is affected by the cement type, the sulfate type,
the sulfate concentration, and the quality of the cementitious material. Some of the salts present in
sea water contribute to the chemical attack of cementitious materials. The magnesium chloride
present in sea water reacts with CH to produce Mg(OH)2 and CaCl2. The sulfates present in sea
water also contribute to sulfate attack of cementitious materials (Soroka, 1979).
Most of the environmental chemical attacks on cement result in the leaching of the calcium from
the cement paste.
Leaching studies are therefore a good indicator of the durability of cement paste (Carde et al,
1997) and help to characterize the kinetics involved in the degradation of the material.
8
Pozzolanic Additives and Reinforcements
Pozzolanic Additives and Silica fume
Pozzolans are very common additives to cement pastes because they improve the strength and
durability of cement. The American Concrete Institute (ACI) defines a pozzolan as a siliceous or
siliceous and aluminous material which in itself possesses little or no cementitious value but will,
in finely divided form and in the presence of moisture react with calcium hydroxide to form
compounds possessing cementitious properties (ACI Committe 116R, 1997). Silica fume is a
highly reactive pozzolans used in making high strength concrete; it reacts with calcium hydroxide
to produce a C-S-H gel, thereby increasing the C-S-H content of the cement paste. This increase
in C-S-H gel leads to a decrease in the paste porosity (Feldman et al., 1985). There are several
other popular pozzolans including fly ash, natural Pozzolans, and ground granulated blast furnace
slag (Kulaa et al., 2001). These Pozzolans are used either individually or in combination.
Silica fume also known as microsilica or fumed silica are small spherical produced as a byproduct
of the reduction of high purity quartz and coke in an electric arc furnace to produce silicon metal
or ferrosilicon alloys (Silica Fume Association, 2008). The small size high surface area and high
SiO2 content makes silica fume a pozzolan when combined with Portland cement (Silica Fume
Association, 2008). Table 2.2 lists the composition and some of the physical properties of silica
fume (Jiuzhou Silicon Industries Ltd, 2008).
9
Table 2.2 Composition and Physical Properties of Silica Fume
Component Composition (%)
SiO2 94.7
Al2O3 0.15
Fe2O3 0.096
CaO 0.088
MgO 0.15
K2O 0.91
Na2O 0.16
Total Sulfur 0.50
Total Carbon 1.38
Ignition Loss 2.35
Water 0.75
Surface Area Approx. 20000m2/kg
Density Approx. 200kg/m3 (undensified) Approx. 400-600 kg/m3 (densified)
Carbon Microfibers
Carbon microfibers (CF) are manufactured from pitch fibers or polymer fibers e.g.
polyacrylonitrile (PAN), in either a continuous or short form. CF made from pitch are more
graphitizable than those made from polymers and therefore have higher thermal conductivities
and lower electrical resistivity. CF made from polymers are more widely used because they are
cheaper and have better mechanical properties (Chung, 1994).
The CF are manufactured by the pyrolysis of the pitch or polymer. The PAN fibers are heated
until they are turned into oxidized polyacrylonitrile fibers (OPF). The OPF is carbonized by
heating progressively to higher temperatures in a nitrogen filled chamber. The final carbonization
10
occurs at temperatures greater than 1000ºC in order to establish strength, stiffness, electrical, and
other properties (Toho Tenax America Inc, 2007). In addition, the CF are coated with a polymer
in order to improve their handling characteristics and wettability (Toho Tenax America Inc,
2007).
The properties of CF are determined by their structure which is in turn determined by the
production conditions. The most influencing structural features are the degree of crystallinity, the
interlayer spacing, the crystallite sizes, the preferred orientation of the carbon layers, parallel and
perpendicular to the fiber axis, the transverse and longitudinal radii of curvature of the carbon
layers, the domain structure, and the volume fraction, shape and orientation of microvoids
(Chung, 1994).
Carbon microfibers have been shown to be effective reinforcement in several matrices including
polymers (Patton et al., 2002), metals (Lin et al., 1991), and carbons (Wang, et al., 2009).
Carbon Nanofibers
Carbon nanofibers (CNF) can be broadly defined as tubular structures with the side walls
composed of angled graphitic sheets. These graphitic sheets can be arranged in various
orientations producing nanofibers of various morphologies. These orientations as we will see later
are determined by the conditions under which the carbon nanofibers are grown, the two main
morphologies being the “herringbone (fishbone)” and the “stacked cup” (figure 2.1).
11
Figure 2.1 (a) and (c) Atomic models of stacked cup and herringbone carbon nanofibers, (b) and (d) their respective TEM simulated images for atomic model (Kim, 2005)
Several methods have been employed for the production of CNF. The two main methods used to
produce CNF are (1) the pyrolyzing of fibers spun from an organic precursor and (2) chemical
vapor deposition (CVD). In the earlier, typically fibers are produced by pyrolyzing electrospun
nanofibers from polyacrylonitrile or pitch (Zussman et al., 2005). These CNF typically have
diameters ranging from a few hundred nanometers to several micrometers.
Vapor grown CNF are the most popular CNF used in research because of the ability to produce
them in bulk in a cost effective manner. Vapor grown CNF are produced by decomposing a
hydrocarbon gas in the presence of hydrogen over a metal catalyst. The hydrocarbon gas is fed
into the chamber containing the metal catalyst, which has been activated usually by a sulfur
containing compound, which is maintained at a high temperature (greater than 1100˚C), under
these conditions the nanofibers filaments are grown with a diameter of about 10nm. Growth stops
12
when the catalyst is deactivated. The filaments are then usually thickened by chemical vapor
deposition of carbon.
The growth of the CNF is influenced by many factors including but not limited to the type of
metal catalyst (Chambers et al., 1995; Rodriguez et al., 1995), the hydrogen source gas, the
presence of additives (Kim et al., 1993), reaction temperature and reaction time.
Because of their interesting mechanical, thermal and electrical properties CNF are deemed to
have great potential for composite applications. The tendency of the CNF to form millimeter
sized clumps, however, poses problems in dispersion and therefore difficulties in composite
preparation. One of the key features of CNF, which facilitate their use in composites, is the
presence of many edges that can serve as sites for chemical and physical interactions.
The effects of decalcification were studied on PC and SF specimens with fiber loadings of 0.5
and 2 wt % and their corresponding baselines. After curing for a minimum of 28 days, nine
replicates of each specimen type were decalcified in a 7M NH4NO3 solution. The specimens were
placed on top of a plastic mesh in a container to ensure that the entire surface area of each
specimen was in contact with the solution (Figure 5.3). The solution was added such that there
was a liquid to surface area ratio of 5cm. The specimens were weighed at regular intervals over a
95 day period, and the pH monitored throughout the decalcification process. At the end of the
degradation period 3 replicates of each specimen type were rinsed with DI water and cut to
remove the ends which are more degraded in order to view the thickness of the degraded region
(Figure 5.4). The other replicates were stored in DI water until further use. The NH4NO3 solution
was renewed for one replicate of each of the specimens with fiber loadings of 0.5 wt % after 70
days.
The effects of accelerated decalcification were demonstrated using compressive strength, splitting
tensile strength, and mass loss.
27
Figure 5.3 Set up for decalcification and DI leaching experiments
Liquid level (DI water or NH4NO3 Solution
Specimen
Plastic mesh
28
Figure 5.4 Photograph of specimen decalcified by NH4NO3 for 95 days showing the thickness of the degraded region.
Analytical Method (ICP-MS)
A Perkin-Elmer ELAN DRC III inductively-coupled mass spectrometer (ICP-MS) was used to
perform chemical analysis of the DI leaching leachate samples.
A 7 point calibration with a blank was performed. The calibration concentrations were 10, 25, 50,
100, 250, and 500µg/L. The correlation coefficients of curve was verified to be at least 0.995. An
initial check standard (ICV) of 50µg/L and an initial check blank of 1% nitric acid were then run.
The analysis of the samples was then performed. Continuous check blank (CCB) and continuous
check verification (CCV) were performed at intervals of 12-20 samples during sample analysis.
Degraded Region
Non-degraded Region
29
The CCB was 1% nitric acid and the CCV was about 50µg/L. A spike analysis per 10-20 samples
was performed. The spike concentration was 500µg/L at 10x dilution. All samples were diluted at
10x. Table 5.3 provides the minimum level (ML) and method detection limit (MDL) for the
elements analyzed.
Table 5.3 MDL and ML of Elements Analyzed by ICP-MS
Element MDL (µg/L) ML (µg/L)
Sodium 0.11 0.20
Potassium 0.19 0.50
Aluminum 0.13 0.20
Silicon 0.19 0.50
Iron 0.16 0.50
Calcium 0.20 0.50
30
CHAPTER VI
6. RESULTS AND DISCUSSION
Mechanical Properties
The effects of CNF loading and fiber type (CNF vs. CF) on the compressive strength, splitting
tensile strength and compressive load displacement curves are discussed in the following
sections.
Effect of CNF Loading
Portland cement pastes (PC pastes) and portland cement pastes with silica fume (SF pastes)
prepared with 6 different CNF loadings (0, 0.005, 0.02, 0.05, 0.5, and 2wt %) were tested.
Compressive Strength
Compressive strength at 28 days of the PC and SF pastes with varying CNF loadings are shown
in figures 6.1 and 6.2, respectively.
The following conclusions were made:
• CNF loadings from 0.005 to 0.50 wt % had no significant impact on the compressive
strength of the PC pastes at w/c=0.325.
• A CNF loading of 2 wt % resulted in a decrease of the compressive strength of the PC
pastes at w/c=0.435.
31
• CNF loadings up to 2 wt % had no significant impact on the compressive strength of the
SF pastes.
• The CNF loading had no apparent effect on the variability of the compressive strength
within each specimen type for both pastes.
0
10
20
30
40
50
60
0 0.005 0.02 0.05 0.5 0 2
Com
pres
sive
Stre
ngth
(M
Pa)
CNF Loading (wt %)
minimum
median
maximum
Outliers
P LD1 LD2 LD3 LD4 P2 LD5
w/c =0.325 w/c=0.435
---75th
---25th
---max
---min
PC Pastes PC Pastes
Figure 6.1 Effect of CNF loading on the compressive strength of PC pastes at 28 days
.
32
0
10
20
30
40
50
60
0 0.005 0.02 0.05 0.5 0 2
Com
pres
sive
Str
engt
h (M
Pa)
CNF Loading (wt %)
minimum
median
maximum
Outliers
P LD1 LD2 LD3 LD4 P2 LD5
w/c=0.365 w/c=0.45
---75th
---25th
---max
---min
SF Pastes SF Pastes
Figure 6.2 Effect of CNF loading on the compressive strength of SF pastes at 28 days
Splitting Tensile Strength
Splitting tensile strength at 28 days of the PC and SF pastes with varying CNF loadings are
shown in figure 6.3 and 6.4 respectively:
The following conclusions were made:
• CNF loading of up to 2 wt % had no significant impact on the splitting tensile strength of
the PC and SF pastes.
• CNF loading had no significant effect on the variability of the splitting tensile strength
within each specimen type for both pastes.
33
0
1
2
3
4
5
6
0 0.005 0.02 0.05 0.5 0 2
Split
ting
Tens
ile S
treng
th (M
Pa)
CNF Loading (wt %)
minimum
median
maximum
P LD1 LD2 LD3 LD4 P2 LD5
w/c=0.325 w/c=0.435
---75th
---25th
---max
---min
PC Pastes PC Pastes
Figure 6.3 Effect of CNF loading on the splitting tensile strength of PC pastes at 28 days
34
0
1
2
3
4
5
6
0 0.005 0.02 0.05 0.5 0 2
Split
ting
Tens
ile S
treng
th (M
Pa)
CNF Loading (wt %)
minimum
median
maximum
P LD1 LD2 LD3 LD4 P2 LD5
w/c=0.365 w/c=0.45
--------75th
----25th
---min
---max
SF Pastes SF Pastes
Figure 6.4 Effect of CNF loading on the splitting tensile strength of SF pastes at 28 days
35
Compressive Load Displacement Curves
The load displacement curves for compressive strength tests of PC and SF pastes with various
CNF loadings are shown in figure 6.5. The slopes of the curves prior to failure were studied and
listed in table 6.1.
0102030405060
0 1 2 3 4 5Displacement (mm)
Load
(MPa
)
w/c=0.325
0.05% CNF0.5% CNF
0.02% CNF
0.005% CNF 0% CNF
A)
PC Paste
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MP
a)
w/c=0.435
0% CNF
2% CNF
B)
PC Paste
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MP
a)
w/c=0.365
0% CNF 0.005% CNF
0.02% CNF0.5% CNF0.05% CNF
C)
SF Paste
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
w/c=0.45
2% CNF
0% CNF
D)
SF Paste
Figure 6.5 Effect of CNF loading on the compressive load displacement curves of PC and SF pastes A) PC pastes at w/c=0.325, B) PC pastes at w/c=0.435, C) SF pastes at w/c=0.365, and D) SF pastes at w/c=0.45
36
Table 6.1 Effect of CNF loading on the slope of the compressive load displacement curves of PC and SF pastes prior to failure
Figure 6.9 Effect of CNF loading on the water absorption capacities of: A) PC pastes at w/c=0.325, B) PC pastes at w/c=0.435, C) SF pastes at w/c=0.365, and D) SF pastes at w/c=0.45.
45
The following conclusions were drawn:
• CNF loadings from 0.005 to 0.5 wt % had no significant effect on the water porosity of
PC paste at w/c=0.325.
• A CNF loading of 2 wt % yielded a decrease of about 12% in the water porosity of PC
paste at w/c=0.435.
• CNF loadings from 0.005 to 0.5 wt % had no significant effect on the water porosity of
SF paste at w/c=0.365.
• A CNF loading of 2 wt % yielded a decrease of about 7% in the water porosity of SF
paste at w/c=0.365.
Kinetics of degradation through leaching
The effects of DI leaching on the release flux of calcium from PC and SF pastes reinforced with
0.5 wt % and 2 wt% CNF and 0.5 wt% CF are shown in figure 6.10 and 6.11, respectively. The
following conclusions were drawn:
• A CNF loading of 0.5 wt% and a CF loading of 0.5 wt% had no significant effect on the
flux of calcium from the PC and SF pastes.
• A CNF loading of 2 wt% had no significant effect on the flux of calcium for the PC paste
with w/c=0.435.
• 2 wt% CNF loading slightly decreased the release flux of calcium for the SF paste with
w/c=0.45
46
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
0 1 10 100 1000 10000
Flux
(mg/
m2 s
)
Time (hrs)
Flux of Calcium from PC Pastes
PC-CNF_LD5 PC-P2
A)
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
0 1 10 100 1000 10000
Flux
(mg/
m2 s
)
Time (hrs)
Flux of Calcium from SF Pastes
SF-CNF_LD5 SF-P2
B)
Figure 6.10 Flux of calcium from cement pastes during leaching with DI water: A) PC pastes with w/c=0.435, B) SF pastes with w/c=0.45
0.0001
0.001
0.01
0.1
1
0 10 1000 100000
Flux
(mg/
m2 s
)
Time (hrs)
Calcium Flux from PC Pastes
PC-CF_LD4 PC-P PC-CNF_LD4
A)
0.0001
0.001
0.01
0.1
1
0 10 1000 100000
Flux
(mg/
m2 s
)
Time (hrs)
Calcium Flux from SF Pastes
SF-CF_LD4 SF-P SF-CNF_LD4
B)
Figure 6.11 Flux of calcium from cement pastes leached with DI water: A) PC pastes at w/c=0.325, B) SF pastes at w/c=0.365
47
Accelerated Decalcification using NH4NO3 solution
Mass Loss as a function of time
The percent mass loss with time due to decalcification with NH4NO3 is shown in figure 6.11 for
PC pastes with no fibers, and PC pastes reinforced with 0.5 wt% CNF and PC pastes reinforced
with 0.5 wt% CF (figure 6.11 A) and SF pastes with no fibers, SF pastes reinforced with 0.5 wt%
CNF and SF pastes reinforced with 0.5 wt% CF (figure 6.11 B). The following conclusions were
drawn:
• After 95 days of decalcification there was no significant difference in mass loss between
PC pastes reinforced with 0.5 wt% CNF, CF, and the PC pastes with no fibers.
• After 95 days of decalcification the % mass loss of SF pastes reinforced with 0.5 wt%
CNF was 9% lower than that of the SF pastes with no fibers at w/c=0.365.
48
0123456789
10
0 50 100
Mas
s Lo
ss (%
)
Time (days)
% Mass Loss With Time
PC-P PC-CNF_LD4PC-CF_LD4
A)
w/c=0.325
0123456789
10
0 50 100
Mas
s Lo
ss (%
)
Time (days)
% Mass Loss With Time
SF-P SF-CNF_LD4 SF-CF_LD4
B)
w/c=0.365
Figure 6.12 Percent mass loss of cement pastes as a function of time during decalcification with NH4NO3 solution a) PC pastes at w/c=0.325 b) SF pastes at w/c=0.365
The percent mass loss with time due to decalcification with NH4NO3 for PC pastes with no fibers
and PC pastes reinforced with 2 wt% CNF are shown in figure 6.13 A and SF pastes with no
fibers and SF pastes reinforced with 2 wt% CNF are shown in figure 6.13 B. The following
conclusions were drawn based on these results:
• After 95 days of decalcification the % mass loss of PC pastes reinforced with 2 wt% CNF
was 23% lower than that of the PC pastes with no fibers at w/c=0.435.
• After 95 days of decalcification the % mass loss of SF pastes reinforced with 2 wt% CNF
was 20% lower than that of the PC pastes with no fibers at w/c=0.45.
49
0123456789
10
0 50 100
Loss
of M
ass
(%)
Time (days)
% Mass Loss with Time
PC-P2 PC-CNF_LD5
A)
w/c=0.435
0123456789
10
0 50 100
Loss
of M
ass
(%)
Time (days)
% Mass Loss with Time
SF-P2 SF-CNF_LD5
B)
w/c=0.45
Figure 6.13 Percent mass loss of cement pastes as a function of time during decalcification with NH4NO3 solution a) PC pastes at w/c=0.435 b) SF pastes at w/c=0.45
50
The average % mass loss of the PC and SF pastes cement specimens after NH4NO3 degradation
for 95 days are shown in table 6.5.
Table 6.4 Average % mass loss of the PC and SF cement specimens after NH4NO3 degradation for 95 days
Paste Type Average % Mass Loss Standard Deviation
PC-P 8.7 0.17
PC-CNF_LD4 8.2 0.11
PC-CF_LD4 8.2 0.14
PC-P2 9.3 0.53
PC-CNF_LD5 7.2 0.11
SF-P 6.9 0.20
SF-CNF_LD4 6.3 0.15
SF-CF_LD4 6.8 0.13
SF-P2 6.1 0.13
SF-CNF_LD5 4.9 0.12
Conclusions
There was no significant difference in the % mass loss after 95 days of decalcification of PC and
SF pastes reinforced with 0.5 wt% CNF or CF and PC and SF pastes with no fibers. In contrast,
the mass loss in PC and SF pastes reinforced with 2 wt% CNF there was 23% and 20% less mass
loss respectively than pastes with no fibers.
51
Effect of Decalcification on the Mechanical Properties
Compressive Strength
The results of compressive strength tests on PC Pastes with and without 0.5 wt% CF and CNF
which were degraded using NH4NO3 for ca. 95 days are shown in figure 6.14. The following
conclusions were drawn:
• After decalcification there was no significant difference in the compressive strengths
between the plain PC pastes, PC pastes reinforced with 0.5 wt % CNF and PC pastes
reinforced with 0.5 wt % CF at w/c=0.325.
• After decalcification there was no significant difference in the compressive strengths
between the PC pastes reinforced with 2 wt % CNF and plain PC pastes at w/c=0.435.
0
10
20
30
40
50
60
0%Plain-AN
0.5 wt %CNF-AN
0.5 wt % CF-AN
0%Plain-AN
2.0 wt %CNF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
w/c=0.325 w/c=0.435
---max------75th------25th
---min
PC Pastes PC Pastes
Figure 6.14 Compressive strength of NH4NO3 degraded PC pastes
52
Figure 6.15A shows the results of compressive strength tests on two types of PC pastes at
w/c=0.325: PC paste with no fibers and PC paste with 0.5 wt % CNF. Figure 6.13B shows the
results of compressive strength tests on two types of PC pastes at w/c=0.435: PC paste with no
fibers and PC paste with 2 wt % CNF. The pastes were tested after curing for 28 days and after
accelerated decalcification for ca. 95 days. The following conclusions were drawn:
• Exposure to NH4NO3 for ca. 95 days yielded a 51% decrease in the median compressive
strengths of the PC pastes reinforced with 0.5 wt % CNF and a 42% decrease in the
median compressive strength of PC pastes with no fibers.
• Exposure to NH4NO3 yielded a 62% decrease in the median compressive strength of the
plain PC pastes while a 48% decrease for PC pastes reinforced with 2 wt% CNF.
53
0
10
20
30
40
50
60
0%Plain
0%Plain-AN
2.0 wt %CNF
2.0 wt %CNF-AN
Com
pres
sive
Stre
ngth
(M
Pa)
minimum
median
maximum
w/c=0.435 w/c=0.435
---max
---75th
---25th
---min
PC Pastes PC Pastes
B)
0
10
20
30
40
50
60
0%Plain
0%Plain-AN
0.5 wt %CNF
0.5 wt %CNF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
outlier
w/c=0.325 w/c=0.325
---max---75th
---25th---min
PC Pastes PC Pastes
A)
Figure 6.15 Effect of CNF on the NH4NO3 degradation of PC pastes: A) 0.5 wt% CNF, B) 2 wt% CNF
54
Figure 6.16 shows the results of compressive strength on two types of PC pastes at w/c=0.325;
PC paste with no fibers and PC paste with 0.5 wt % CF. The pastes were tested after curing for
about 28 days and after exposure to NH4NO3 for 95 days. The following conclusions were drawn:
• Decalcification yielded a 53% decrease in the median compressive strength of PC paste
reinforced with 0.5 wt % CF at w/c=0.325.
0
10
20
30
40
50
60
Plain Plain-AN 0.5 wt %CF
0.5 wt %CF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
w/c=0.325 w/c=0.325
---max---75th
---25th
---min
PC Pastes PC Pastes
Figure 6.16 Effect of 0.5 wt % CF reinforcement on the compressive strength of decalcified PC pastes
The results of compressive strength tests on SF cement pastes, which were decalcified using
NH4NO3 for 95 days are shown in figure 6.17. The following conclusions were drawn:
55
• After decalcification there was no significant difference in the compressive strengths of
plain SF pastes, SF pastes reinforced with 0.5 wt % CNF and SF pastes reinforced with
0.5 wt % CF at w/c=0.365.
• After decalcification there was no significant difference in the compressive strengths of
SF pastes reinforced with 2 wt % CNF and plain SF pastes at w/c=0.45.
0
10
20
30
40
50
60
0%Plain-AN
0.5 wt %CNF-AN
0.5 wt % CF-AN
0%Plain-AN
2.0 wt %CNF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
w/c=0.365 w/c=0.45
---max------75th------25th
---min
SF Pastes SF Pastes
Figure 6.17 Compressive strengths of NH4NO3 degraded SF pastes
Figure 6.18(A) shows the results of compressive strength tests on two types of SF pastes at
w/c=0.325: SF paste with no fibers and SF paste with 0.5 wt % CNF. Figure 6.18(B) shows the
results of compressive strength tests on two types of SF pastes at w/c=0.435: SF paste with no
56
fibers and SF paste with 2 wt % CNF. The pastes were tested after curing for a minimum of 28
days and after exposure to NH4NO3 for 95 days. The following conclusions were drawn:
• Decalcification yielded a 18% decrease in the median compressive strengths of the plain
SF pastes with at w/c=0.365.
• Decalcification yielded a 40% decrease in the median compressive strengths of plain SF
pastes at w/c=0.45.
• Decalcification yielded a 48% decrease in the median compressive strengths of SF pastes
reinforced with 2 wt % CNF at w/c=0.45.
57
0
10
20
30
40
50
60
0%Plain
0%Plain-AN
0.5 wt %CNF
0.5 wt %CNF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
w/c=0.365 w/c=0.365
---max
---75th
---25th---min
SF Pastes SF Pastes
A)
0
10
20
30
40
50
60
0%Plain
0%Plain-AN
2.0 wt %CNF
2.0 wt %CNF-AN
Com
pres
sive
Str
engt
h (M
Pa)
minimum
median
maximum
w/c=0.45 w/c=0.45
---max
---75th
---25th
---min
SF Pastes SF Pastes
B)
Figure 6.18 Effect of fiber reinforcement on the compressive strength of NH4NO3 degraded SF pastes 95 day exposure: A) 0.5 wt% CNF, B) 2 wt% CNF
58
Figure 6.19 shows the results of compressive strength on two types of SF pastes at w/c=0.365: SF
paste with no fibers and SF paste with 0.5 wt % CF. The pastes were tested after curing for a
minimum of 28 days and after accelerated decalcification for 95 days. The following conclusions
were drawn:
• There was no change in the compressive strengths of SF pastes reinforced with 0.5 wt %
CF and SF pastes with no fibers at w/c=0.365 after decalcification.
0
10
20
30
40
50
60
Plain Plain-AN 0.5 wt %CF
0.5 wt %CF-AN
Com
pres
sive
Stre
ngth
(M
Pa)
minimum
median
maximum
w/c=0.365
---max
---75th
---25th---min
w/c=0.365
SF Pastes SF Pastes
Figure 6.19 Effects of 0.5 wt % CF reinforcement on the compressive strength of NH4NO3 degraded SF pastes 95 day exposure
59
Compressive Load Displacement Curves
Figure 6.26 shows the effect of NH4NO3 degradation on the compressive load displacement
curves of PC pastes. The slopes prior to failure are summarized in tables 6.9 and 6.10,
respectively. The following conclusions were drawn based on these results:
• After decalcification the median slope of the compressive load displacement curves of PC
pastes reinforced with 2 wt % CNF was 30% lower than that of plain PC pastes at
w/c=0.435.
• Decalcification yielded a 44% decrease in the median slope of the compressive load
displacement curves of PC pastes reinforced with 0.5 wt % CNF at w/c=0.325.
• Decalcification yielded a 50% decrease in the median slope of the compressive load
displacement curves of plain PC pastes w/c=0.435.
• Decalcification yielded a 50% decrease in the median slope of the compressive load
displacement curves of PC pastes reinforced with 2 wt % CNF at w/c=0.435.
60
Figure 6.20 Effects of 95 day exposure to NH4NO3 on the compressive load displacement curves of PC pastes
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
PC-P PC-P-AN
w/c=0.325
P 0% CNF
P-AN 0% CNF
A)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
PC-CNF_LD4PC-CNF_LD4-AN
w/c=0.325
0.5 % CNF
0.5%CNF-AN
B)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
PC-CF_LD4PC-CF_LD4-AN
w/c=0.325
0.5% CF
0.5% CF-AN
C)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
PC-P2 PC-P2-AN
w/c=0.435
P2 0% CNF
P2-AN 0% CNF
D)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
PC-CNF_LD5
PC-CNF_LD5-AN
w/c=0.435
2% CNF
2% CNF-AN
E)
61
Table 6.5 Effect of NH4NO3 degradation on the slope of the compressive load displacement curves of PC pastes prior to failure
Slope (MPa/mm) Paste Type w/c Specimen
Type Fiber (wt%) Mean Standard
Deviation Minimum Median Maximum
PC 0.325 PC-P 0 27.4 9.6 12.2 23.4 40.6
PC-P-AN 0 22.3 1.8 20.9 21.8 24.3
PC-
CNF_LD4 0.50 34.1
4.4 25.8 33.9 39.6
PC-CNF_LD4-AN
0.50 20.7 4.8 17.4 19.0 25.7
PC-CF_LD4
0.50 23.5 6.3 15.0 22.9 35.2
PC-CF_LD4-AN
0.50 19.4 0.4 19.2 19.3 19.8
0.435 PC-P2 0 32.4 10.1 17.0 31.4 47.9
PC-P2-AN 0 13.0 0.5 12.6 12.8 13.5
PC-
CNF_LD5 2 19.0
3.5 13.3 17.8 25.2
PC-CNF_LD5-AN
2 8.1 1.9 5.9 9.0 9.4
Figure 6.27 shows the effect of NH4NO3 degradation on the load displacement curves of SF
pastes which are summarized in tables 6.9 and 6.10 respectively. The following conclusions were
drawn based on these results:
• Decalcification had no significant effect on the slopes of the load displacement curves of
plain SF pastes at w/c=0.365. In contrast, decalcification yielded a decrease in the slopes
of SF pastes reinforced with fibers and plain SF pastes at w/c=0.45.
62
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
SF-P SF-P-AN
P 0%
P-AN 0% CNF
A)
w/c=0.365
0102030405060
0 1 2 3 4 5Displacement (mm)
Load
(MPa
)
SF-CNF_LD4SF-CNF_LD4-AN
w/c=0.365
0.5% CNF
0.5% CNF-AN
B)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MPa
)
SF-CF_LD4 SF-CF_LD4-AN
w/c=0.365
0.5% CF
0.5% CF-AN
C)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MP
a)
SF-P2 SF-P2-AN
w/c=
P2 0%
P2-AN 0%
D)
0
10
20
30
40
50
60
0 1 2 3 4 5
Displacement (mm)
Load
(MP
a)
SF-CNF_LD5 SF-CNF_LD5-AN
w/c=0.45
2% CNF
2% CNF-AN
E)
Figure 6.21 Effect of NH4NO3 degradation on the load displacement curves SF pastes.
63
Table 6.6 Effects of NH4NO3 degradation on the slope of the compressive load displacement curves of SF pastes prior to failure
Slope (MPa/mm)
Paste Type w/c Specimen
Type
CNF (wt %)
MeanStandard Deviation Minimum Median Maximum
SF 0.365 SF-P 0 19.2 7.1 7.7 17.6 31.0
SF-P-AN 0 19.4 4.9 13.9 21.8 22.7
SF-
CNF_LD4 0.50 29.0
6.6 17.0 32.9 35.1
SF-CNF_LD4-AN
0.50 19.6 0.8 18.8 19.7 20.3
SF-
CF_LD4 0.50 24.6
7.9 16.6 20.1 37.3
SF-CF_LD4-AN
0.50 21.3 1.7 19.3 22.3 22.3
0.45 SF-P2 0 28.0 3.7 21.7 28.5 33.4
SF-P2-AN 0 17.9 3.7 15.4 16.2 22.2
SF-
CNF_LD5 2 29.0
4.3 21.0 31.3 32.8
SF-CNF_LD5-AN
2 13.5 3.1 10.8 12.8 16.9
64
CHAPTER VII
7. CONCLUSIONS
CNF loadings up to 2 wt % had no significant effect on the mechanical properties of PC and SF
pastes, except in the case of PC pastes reinforced with 2 wt% CNF where there was a decrease in
the compressive strength. Addition of 0.5 wt% CF impacted the mechanical properties of PC and
SF pastes by increasing their compressive and splitting tensile strengths.
A CNF loading of 0.5 wt% and a CF loading of 0.5 wt% had no significant effect on the mass
loss of the PC paste due to decalcification. The higher CNF loading of 2 wt% seemed to increase
the durability of the PC pastes. This increase in the durability was characterized by a lower water
porosity, a lower mass loss and a lower loss of compressive strength due to exposure to
ammonium nitrate solution.
Due to the heterogeneous nature of cement pastes there is a high level of variability in mechanical
test results. It is therefore necessary to have a large number of replicates (greater than 5) for each
test in order to draw accurate conclusions from the results obtained.
65
CHAPTER VIII
8. FURTHER WORK
A CNF loading of 2 wt% showed the most potential for improving the durability of PC pastes.
This CNF loading was also found to decrease the compressive strength of PC pastes. This lower
compressive strength could possibly be attributed to the presence of large clumps of fibers visible
in the paste. This hypothesis should be investigation by studying the level of fiber dispersion
within the paste and effective means of improving that dispersion.
Additional investigations are also necessary to conclusively determine the effect of CNF loading
on the durability of PC and SF pastes. This investigation should include study of the pastes
microstructure using scanning electron microscopy, and a more detailed look at the porosity and
pore size distribution using mercury intrusion porosimetry and BET porosimetry.
66
Appendix
Compressive Strength Data
Baseline
PC-P; w/c=0.325
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 15090
3.7 2.0 14660
3.7 2.0 17440
3.8 2.0 12880
3.8 2.0 14010
3.8 2.0 19030
3.8 2.0 16680
3.9 2.0 17610
3.8 2.0 17590
3.8 2.0 13160
3.7 2.0 17000
3.8 2.0 17270
3.8 2.0 15380
3.7 2.0 16320
3.8 2.0 15110
67
PC-P2; w/c=0.435
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.6 2.0 16080
3.5 2.0 8670
3.4 2.0 18100
3.5 2.0 18450
3.4 2.0 14330
3.7 2.0 14000
3.8 2.0 15160
3.8 2.0 10780
3.7 2.0 13680
3.8 2.0 9270
PC-CNF; w/c=0.325; 0.005 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 18120
3.8 2.0 14330
3.8 2.0 17810
3.8 2.0 16610
3.9 2.0 19460
68
PC-CNF; w/c=0.325; 0.02 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 12900
3.9 2.0 20800
3.8 2.0 19240
3.8 2.0 18400
3.8 2.0 15690
PC-CNF; w/c=0.325; 0.05 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 12900
3.9 2.0 20800
3.8 2.0 19240
3.8 2.0 18400
3.8 2.0 15690
69
PC-CNF; w/c=0.325; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 18090
3.7 2.0 17690
3.8 2.0 17360
3.8 2.0 17750
4.0 2.0 13550
3.8 2.0 17840
3.9 2.0 5350
3.9 2.0 17740
PC-CNF; w/c=0.435; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 9300
3.7 2.0 6780
3.8 2.0 11460
3.8 2.0 9660
3.7 2.0 11830
3.8 2.0 9740
4.0 2.0 8840
3.7 2.0 11600
3.9 2.0 11590
3.9 2.0 8170
70
PC-CF; w/c=0.325; 0.5 wt% CF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 22400
3.7 2.0 22800
3.7 2.0 19540
3.9 2.0 21000
3.9 2.0 17760
3.8 2.0 20400
3.8 2.0 16980
3.8 2.0 21500
SF-P; w/c=0.365
Average Height (in)
Average Diameter(in)
Ultimate Strength(lb)
3.7 2.0 18430
3.6 2.0 19140
3.7 2.0 14020
3.8 2.0 16990
4.0 2.0 14550
3.9 2.0 11540
4.0 2.0 14010
3.8 2.0 12760
3.9 2.0 13310
71
SF-P2; w/c=0.45
Average Height (in)
Average Diameter(in)
Ultimate Strength(lb)
3.7 2.0 21400
3.8 2.0 10430
3.8 2.0 16720
3.8 2.0 14510
3.7 2.0 17670
3.8 2.0 14390
3.8 2.0 13410
3.8 2.0 12360
3.8 2.0 15540
3.8 2.0 12330
SF-CNF; w/c=0.365; 0.005 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 13760
3.9 2.0 13100
3.9 2.0 15520
3.9 2.0 13490
3.9 2.0 10660
72
SF-CNF; w/c=0.365; 0.02 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 16670
3.9 2.0 11660
3.9 2.0 15350
3.9 2.0 17110
3.9 2.0 10090
SF-CNF; w/c=0.365; 0.05 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 15850
3.8 2.0 14380
3.9 2.0 13880
3.9 2.0 14670
3.9 2.0 15050
73
SF-CNF; w/c=0.365; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 12180
3.7 2.0 15950
3.6 2.0 15890
3.8 2.0 16660
3.8 2.0 16170
3.8 2.0 14500
3.9 2.0 11100
3.9 2.0 13670
SF-CNF; w/c=0.45; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 13780
3.8 2.0 16610
3.8 2.0 10750
3.8 2.0 12940
3.7 2.0 11830
3.8 2.0 13670
3.8 2.0 15700
3.9 2.0 14170
3.7 2.0 16210
3.9 2.0 8170
74
SF-CF; w/c=0.365; 0.5 wt% CF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 19550
3.7 2.0 16440
3.7 2.0 23700
3.7 2.0 18350
3.9 2.0 13360
3.9 2.0 15910
3.9 2.0 17790
3.8 2.0 13490
3.8 2.0 10660
Ammonium Nitrate Solution Degraded Specimens (95 days exposure)
PC-P; w/c=0.325
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 8280
3.8 2.0 9510
3.8 2.0 10310
PC-P2; w/c=0.435
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.6 2.0 5330
3.7 2.0 5440
3.7 2.0 5450
75
PC-CNF; w/c=0.325; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 8570
3.8 2.0 8780
3.9 2.0 8360
PC-CNF; w/c=0.435; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 5200
3.7 2.0 3860
3.8 2.0 5080
PC-CF; w/c=0.325; 0.5 wt% CF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 9510
3.7 2.0 9750
3.7 2.0 10030
SF-P; w/c=0.365
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 8790
3.8 2.0 12240
3.7 2.0 11580
76
SF-P2; w/c=0.45
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 8670
3.8 2.0 7970
3.7 2.0 9530
SF-CNF; w/c=0.365; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 10800
3.9 2.0 10260
3.8 2.0 10280
SF-CNF; w/c=0.45; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 6830
3.9 2.0 7060
4.0 2.0 10240
SF-CF; w/c=0.365; 0.5 wt% CF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 13260
3.8 2.0 12350
3.8 2.0 13620
77
Splitting Tensile Strength Data
Baseline
PC-P; w/c=0.325
Average Height (in)
Average Diameter(in)
Ultimate Strength(lb)
4.0 2.0 7200
4.0 2.0 5980
4.0 2.0 6790
4.0 2.0 5230
4.0 2.0 7710
3.8 2.0 3070
3.8 2.0 2930
3.7 2.0 2660
PC-P2; w/c=0.435
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 3040
3.5 2.0 3720
3.6 2.0 3090
78
PC-CNF; w/c=0.325; 0.005 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
4.0 2.0 7790
3.8 2.0 2510
3.9 2.0 3730
PC-CNF; w/c=0.325; 0.02 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 2560
3.8 2.0 2320
3.8 2.0 2890
PC-CNF; w/c=0.325; 0.05 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 2730
3.9 2.0 4710
3.9 2.0 2890
PC-CNF; w/c=0.325; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 6470
3.7 2.0 4990
3.7 2.0 5690
79
PC-CNF; w/c=0.435; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 3540
3.8 2.0 3930
3.8 2.0 2660
PC-CF; w/c=0.325; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.7 2.0 9300
3.8 2.0 8040
3.7 2.0 7470
SF-P; w/c=0.365
Average Height (in)
Average Diameter(in)
Ultimate Strength(lb)
3.7 2.0 5240
3.7 2.0 5360
3.6 2.0 3750
3.6 2.0 5110
3.9 2.0 3720
3.9 2.0 4680
3.9 2.0 2770
80
SF-P2; w/c=0.45
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 2160
3.8 2.0 3830
3.7 2.0 2170
SF-CNF; w/c=0.365; 0.005 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 3380
3.9 2.0 3840
3.9 2.0 4100
SF-CNF; w/c=0.365; 0.02 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 5080
3.9 2.0 5060
3.9 2.0 3090
SF-CNF; w/c=0.365; 0.05 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 3650
3.8 2.0 3650
3.9 2.0 3460
81
SF-CNF; w/c=0.365; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.8 2.0 3250
3.8 2.0 3570
3.7 2.0 5850
3.7 2.0 7050
SF-CNF; w/c=0.45; 2 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.9 2.0 3750
3.9 2.0 3480
3.9 2.0 3510
SF-CF; w/c=0.365; 0.5 wt% CNF
Average Height (in)
Average Diameter(in)
Ultimate Strength (lb)
3.6 2.0 5640
3.8 2.0 7360
3.6 2.0 5430
3.8 2.0 7240
82
Ammonium Nitrate Solution Degraded Specimens (95 days exposure)
Concentration (mg/L)pH Sodium Potassium Aluminum Silicon Iron Calcium
95
REFERENCES
ACI Committe 116R. (1997). Cement and concrete terminology (ACI 116R). Manual of concrete practice, Part I. Detroit: American Concrete Institute.
Ali, M., Majumdar, A., & Rayment, D. (1972). Carbon Fiber Reinforcement of Cement. Cement and Concrete Research , 2 (2), 201-212.
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