-
leor an unproven issue?
b
c
d
a
AR raw materials, transportation or orientation and
polycondensation of the reaction products. Publications
ated binders, state that this new material is likely to have
high potential to
This paper presents a review of the literature about the
durability of alkali-activated binders. The subjectsof this paper
are resistance to acid attack, alkalisilica reaction, corrosion of
steel reinforcement, resis-
. . . . . .
. . . . . .
The production of one tonne of OPC generates 0.55 tonnes of
chem-ical CO2 and requires an additional 0.39 tonnes of CO2 in fuel
emis-sions for baking and grinding, accounting for a total of 0.94
tonnes ofCO2 [2]. Other authors [3] reported that the cement
industry emit-ted in 2000, on average, 0.87 kg of CO2 for every kg
of cement
carbon dioxide emissions and the fact that OPC structures
whichhave been build a few decades ago are still facing
disintegrationproblems points out the handicaps of OPC. Portland
cement basedconcrete presents a higher permeability that
allowswater and otheraggressive media to enter leading to
carbonation and corrosionproblems. The early deterioration of
reinforced concrete structuresbased on Ordinary Portland cement
(OPC) is a current phenomenonwith signicant consequences both in
terms of the cost for the reha-bilitation of these structures, or
even in terms of environmental
Corresponding author. Tel.: +351 253 510200; fax: +351 253
510213.
Construction and Building Materials 30 (2012) 400405
Contents lists available at
B
evE-mail address: [email protected] (F. Pacheco-Torgal).3.
Alkalisilica reaction (ASR) . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 4024. Corrosion of steel reinforcement . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 4025. Resistance to high temperatures and
to fire. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 4036. Resistance to freezethaw . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 4037.
Efflorescences . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 4038. Conclusions. . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 404
References . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 404
1. Introduction
With an annual production of almost 3 Gt Ordinary Portland
ce-ment (OPC) is the dominant binder of the construction industry
[1].
produced. As a result the cement industry contributes about 7%
ofthe totalworldwide CO2 emissions [4]. The projections for the
globaldemand of Portland cement show that in the next 40 years it
willhave a twofold increase reaching 6 Gt/year [5]. The urge to
reduceKeywords:Alkali-activated bindersOrdinary Portland
cementEco-efciencyDurabilityEforescences
Contents
1. Introduction . . . . . . . . . . . . . . . . .2. Resistance
to acid attack . . . . . . .0950-0618/$ - see front matter 2011
Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.017tance to high
temperatures and to re, resistance to freezethaw. Special attention
is given to the caseof eforescences, an aspect that was received
very little concern although it is a very important one.
2011 Elsevier Ltd. All rights reserved.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 400
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 401Accepted 4 December 2011 become
an alternative to Portland cement. While some authors state that
the durability of these materialsconstitutes the most important
advantage over Portland cement others argue that its an unproven
issue.Received in revised form 28 November 2011 on the eld of
alkali-activUniversity of Minho, C-TAC Research Unit, Guimares,
PortugalUniversity of Minho, Department of Civil Engineering,
Guimares, PortugalDepartment of Polymer, Building and Housing
Research Center (BHRC), Amirkabir University of Technology, Tehran
Polytechnic, IranState Key Laboratory of Coastal and Offshore
Engineering, Dalian University of Technology, Dalian, China
r t i c l e i n f o
rticle history:eceived 6 September 2011
a b s t r a c t
The alkali activation of alumino-silicate materials is a complex
chemical process evolving dissolution ofF. Pacheco-Torgal , Z.
Abdollahnejad , A.F. Camesaa, a b, M. Jamshidi c, Y. Ding
dReview
Durability of alkali-activated binders: A c
Construction and
journal homepage: www.elsll rights reserved.ar advantage over
Portland cement
SciVerse ScienceDirect
uilding Materials
ier .com/locate /conbui ldmat
-
nd Bimpacts associated with these operations. Research works
[68]carried out so far in the development of alkali-activated
cementsshowed that much has already been investigated and also that
anenvironmental friendly alternative to Portland cement is
rising.Davidovits et al. [9] was the rst author to address the
carbon diox-ide emissions of these binders stating that they
generate just 0.184tons of CO2 per ton of binder. Duxson et al.
[10] do not conrm thesenumbers; they stated that although the CO2
emissions generatedduring the production of Na2O are very high,
still the productionof alkali-activated binders is associated to a
level of carbon dioxideemissions lower than the emissions generated
in the production ofOPC. According to those authors the reductions
can go from 50% to100%. Duxson andVanDeventer [11]mention an
independent studymade by Zeobond Pty. Ltd. in which a low emissions
Portland ce-ment (0.67 ton/ton) and alkali-activated binders were
compared,reporting that the latter had 80% lower CO2 emissions.
Weil et al.[12] mentioned that the sodium hydroxide and the sodium
silicateare responsible for the majority of CO2 emissions in
alkali-activatedbinders. These authors compared Portland cement
concrete and al-kali-activated concrete with similar durability
reporting that latterhave 70% lower CO2 emissions which conrmed the
aforemen-tioned reductions. McLellan et al. [13] reported a 44% to
64% reduc-tion in greenhouse gas emissions of alkali-activated
binders whencompared to OPC. Habert et al. [14] carry out a
detailed environ-mental evaluation of alkali activated binders
using the Life CycleAssessmentmethodology conrming that they have a
lower impacton globalwarming thanOPCbut on the other side they have
a higherenvironmental impact regarding other impact categories. The
highcost of alkali-activated binders is one of themajor
factorswhich stillremain a severe disadvantage over Portland cement
[14]. Therefore,investigations about the replacement of waterglass
by sodic wastesare needed [15]. Currently alkali-activated binders
only becomeseconomic competitive for high performance structural
purposes,because the cost of alkali-activated concretes is
locatedmidway be-tween OPC concretes and high performance
concretes. Since theaverage ERMCO concrete class production lies
between C25/30and C30/37 and only 11% of the concrete ready-mixed
productionis above the strength class C35/45 [16], this means that
alkali-acti-vated binders are targeting a small market share.
Therefore, in theshort term the above cited disadvantage means that
the study of al-kali-activated applications should focus on high
cost materials suchas, commercial concrete repair mortars.
Pacheco-Torgal [1720]showed that alkali-activated mortars can be as
much as 7 timescheaper than current commercial repair mortars thus
pointing aviable alternative for alkali-activated binders. These
materials arestill at the beginning stages of development and hence
need furtherresearchwork in order to become technically and
economically via-ble constructionmaterials. Besides the durability
of alkali-activatedbinder is a subject of some controversy, while
Duxson et al. [10]state this is the most important issue on
determining the successof these newmaterials and other authors [21]
mention that the factthat samples from the former Soviet Union that
have been exposedto service conditions for in excess of 30 years
showing little degra-dation means that geopolymers do therefore
appear to stand thetest of time. But since those materials were of
the (Si + Ca) type thatconclusion cannot be extended to geopolymers
dened as alkalialuminosilicate gel, with aluminium and silicon
linked in a tetrahedralgel framework [11]. On the other side
Juenger et al. [1] argue thatThe key unsolved question in the
development and application of alkaliactivation technology is the
issue of durability andmore recently VanDeventer et al. [22]
recognized that whether geopolymer concretesare durable remains the
major obstacle to recognition in standardsfor structural concrete.
In this work relevant knowledge about the
F. Pacheco-Torgal et al. / Construction adurability
alkali-activated cements will be reviewed. The subjectsof this
paper are as follows:2. Resistance to acid attack
Several authors reported that chemical resistance is one of
themajor advantages of alkali-activated binders over Portland
cement.Glukhovsky [23], used alkali-activated slag mortars noticing
thatthey showed increase tensile strength even after being
immersedin lactic and hydrochloric acid solutions (pH = 3). Other
authors[24] studied the exposure of alkali-activated slag mortars
duringsix months in 5% acid solution concentration, reporting that
for cit-ric acid changes were low, for nitric and hydrochloric acid
changeswere moderate although severe changes was noticed when
sul-phuric acid was used. Davidovits et al. [9] reported mass
lossesof 6% and 7% for alkali-activated binders immersed in 5%
concen-tration hydrochloric and sulphuric acids during 4 weeks. For
thesame conditions he also reported that Portland cement based
con-cretes suffered mass losses between 78% and 95%. Palomo et
al.[25] studied metakaolin mixtures activated with NaOH and
water-glass when submitted to, sulphuric acid (pH = 3), sea
water(pH = 7) and sodium sulphate (pH = 6), during 90 days. They
re-ported a minor exural strength decrease from 7 to 28
daysimmersion, between 28 and 56 days exural strength
rises,decreasing again from 56 to 90 days and rising from that day
for-ward. They reported that behaviour was similar to the several
acidsolutions. According to these authors, unreacted sodium
particlesare not in the structure of the hardened material,
remaining in asoluble condition thus when in contact with a
solution they areleached increasing the binder porosity and
lowering mechanicalstrength. On the other hand, strength increase
after 3 months indi-cates that the reaction process is still
evolving, with the formationof zeolitic precipitates (faujasite)
thus lowering porosity andincreasing strength. Shi and Stegmann
[26] compared the acidresistance of several binders;
alkali-activated slags (AASs), OPCbinders, y ash/lime binders (FAL)
and high alumina cement(AC), when immersed in nitric (pH = 3) and
acetic (pH = 3 e 5) acidsolutions. They reported that OPC binders
presented higher masslosses than AAS and FAL binders while AC
pastes were completelydissolved. According to these authors, OPC
pastes are more porousthan AAS but less porous than FAL pastes, so
chemical attack ismore inuenced by the nature of hydration products
than fromporosity. They also reported that low pH acids are
responsible forthe highest chemical attack. Bakharev et al. [27]
also comparedOPC and alkali-activated slag concrete resistance to
sulphat attack,reporting that the former showed a lower strength
reduction, thatcould be explained due to the binder structure
chemical differ-ences. Bakharev et al. [28] studied OPC and slag
concretes activatedwith NaOH and waterglass, immersed in an acetic
acid solution(pH = 4) during one year. They reported a 33% strength
loss forthe former and 47% for OPC concretes. They claim that the
strengthloss is inuenced by Ca content, 64% for OPC concretes and
just 39%for alkali-activated slag concretes. Besides slag compounds
havelower Ca/Si molar ratio and are more stable in acid medium.
Asfor OPC concrete calcium compounds, they possess high Ca/Si
mo-lar ratios and react with acetic acid forming acetic calcium
com-pounds which is very soluble. They concluded that concreteswith
less free calcium have a higher performance in acid medium.The work
of Song et al. [29] also conrm that alkali-activated yash concretes
possess high chemical resistance, when immersedin a 10%
concentration sulphuric acid solution during 8 weeks,
theyshowedmass and strength losses respectively of 3% and 35%.
Gour-ley and Johnson [30] mentioned that a Portland cement
concretewith a service life of 50 years lose 25% of its mass after
80 immer-sions cycles in a sulphuric acid solution (pH = 1) while
an alkali-activated concrete required 1400 immersions cycles to
lose the
uilding Materials 30 (2012) 400405 401same mass, thus meaning a
service life of 900 years. Pacheco-Torgal et al. [31] mentioned an
average mass loss of just 2.6% after
-
being submitted to the attack of (sulphuric, hydrochloric and
ni-tric) acids during 28 days, while the mass loss for Portland
cementconcretes is more than twice that value. Those authors
mentionthat weight loss results for mine waste binders are not very
depen-dent from the type of acid, however, other authors [3234]
reportdifferent results for geopolymers based on y ash and blast
furnaceslag.
3. Alkalisilica reaction (ASR)
The chance of ASR may take place in alkali-activated binders
isan unknown subject. For OPC binders, however, the knowledge ofASR
has been intensively studied; therefore some explanationscould be
also applied to understand the possibility of ASR when
al-kali-activated binders are used. ASR was reported by the rst
timeby Stanton [35] and needs the simultaneous action of three
ele-ments in order to occur: (a) enough amorphous silica, (b)
alkalineions and (c) water [36]. The ASR begins when the reactive
silicafrom the aggregates is attacked by the alkaline ions from
cementforming an alkalisilica gel, which attracts water and starts
to ex-pand. The gel expansion leads to internal cracking, what have
beenconrmed by others [37] reporting 4 MPa pressures. Those
internaltensions are higher than OPC concrete tensile strength,
thus lead-ing to cracking. However some authors believe that ASR is
not justa reaction between alkaline ions and amorphous silica but
also re-quires the presence of Ca2+ ions [38]. Davidovits [39]
compared al-kali-activated binders and OPC binders when submitted
to theASTM C227 mortar-bar test, reporting a shrinkage behaviour
inthe rst case and a serious expansion for the OPC binder.
Other
authors [40] reported some expansion behaviour for
alkali-acti-vated binders although smaller than for OPC binders.
However,Puertas [41] believe ASR could occur for alkali-activated
slag bind-ers containing reactive opala aggregates. Bakharev et al.
[42] com-pared the expansion of OPC and alkali-activated binders
reportingthat the rst ones had higher expansion. This is clear from
themicrostructure analysis (Fig. 1). Garca-Lodeiro et al. [43]
showedthat alkali-activated y ash is less susceptible to generate
expan-sion by alkalisilica reaction than OPC. They also showed
thatthe calcium plays an essential role in the expansive nature of
thegels. Recent investigations [44] show that siliceous
aggregatesare more prone to ASR than calcareous aggregates in
alkali-acti-
resistance similar to the one OPC binders. Miranda et al. [47]
even
402 F. Pacheco-Torgal et al. / Construction and Building
Materials 30 (2012) 400405Fig. 1. Alkali-activated concrete after
10 months curing. (A) Reactive aggregate. (G)Alkalisilica gel
[42].Fig. 2. Transverse sections of carbonated alkali-activated
slag concretes after 1000 h ofphenolphthalein indicator. Samples
are 76.2 mm in diameter [50].demonstrated that alkali-activated y
ash binders have superiorpH conditions than OPC binders. They
reported that pH decreasedwith hydration reaction development,
however an alkaline condi-vated mixtures. Therefore the study of
ASR, in alkali-activatedbinders is not a closed subject, at least
for the mixtures containingcalcium.
4. Corrosion of steel reinforcement
The corrosion of steel reinforcement is one the causes that
inu-ences the structural capability of concrete elements. As
concreteattack depends on its high volume and therefore is not of
greatconcern, an attack to the steel reinforced bars is a serious
threateased by the fact that steel bars are very near of concrete
surfaceand are very corrosion sensitive. In OPC binders, steel bars
are pro-tected by a passivity layer, due to the high alkalinity of
calciumhydroxide. The steel bars corrosion may happen if pH
decreasesthus destroying the passivity layer, due to carbonation
phenome-non or chloride ingress. The steel corrosion occurs due to
an elec-trochemical action, when metals of different nature are
inelectrical contact in the presence of water and oxygen. The
processconsists in the anodic dissolution of iron when the
positivelycharged iron ions pass into the solution and the excess
of nega-tively charged electrons goes to steel through the cathode,
wherethey are absorbed by the electrolyte constituents to form
hydroxylions. These in turn combine with the iron ions to form
ferrichydroxide, which then converts to rust. The volume increase
asso-ciated with the formation of the corrosion products will lead
tocracking and spalling of the concrete cover. For
alkali-activatedbinders the literature is small about its
capability to prevent rein-forced steel corrosion. Some studies
about chloride diffusionclearly show that alkali-activated binders
are able to prevent theingress of harmful elements that could start
steel corrosion. Royet al. [45] compared chloride diffusion for OPC
and alkali-activatedbinders reporting that the former presented
almost half of the dif-fusion values of the OPC binders. Saraswathy
et al. [46] studied al-kali-activated y ash mixtures reporting a
steel corrosionexposure to a 1% CO2 environment, with the extent of
carbonation revealed by a
-
search about reinforced steel corrosion is therefore needed,
con-
spalling behaviour. The internal pore structure of the latter
allows
7. Eforescences
The subject of eforescences in alkali-activated binders is
rela-tively new, since very few authors have addressed this
problem.According to Skvara et al. [65,66] the bond between the
sodiumions (Na+) and the aluminosilicate structure is weak and that
ex-plains the leaching behaviour. According to those authors in
thecrystalline zeolites the leaching of sodium is negligible
contraryto what happens in the aluminosilicate polymers. It is the
presenceof water that weakens the bond of sodium in the
aluminosilicatepolymers, a behaviour that is conrmed by the
alkali-activatedbinder structure model. Pacheco-Torgal and Jalali
[67] also foundthat sodium eforecences are higher in
alkali-activated bindersbased on aluminosilicate prime materials
calcined at a tempera-ture range below the dehydroxylation
temperature with the addi-tion of sodium carbonate as a source of
sodium cations (Fig. 3).Temuujin et al. [68] refer that although
ambient cured y ash alka-li-activated binders exhibited
eforescences that phenomena doesnot occur when the same
alkali-activated binders are cured at ele-vated temperature which
means the leachate sodium could be asign of insufcient
geopolymerisation. Recently Van Deventeret al. [69] recognized that
current two part geopolymers sufferfrom severe eforescence which is
originated by the fact thatalkaline and/or soluble silicates that
are added during processingcannot be totally consumed during
geopolymerisation. Only re-cently Kani et al. [70] showed that
eforescences can be reducedeither by the addition of alumina-rich
admixtures or by hydrother-mal curing at temperatures of 65 C or
higher. These authors foundthat the use of 8% of calcium aluminate
cement greatly reduces themobility of alkalis leading to minimum
eforescences (this cementhas 28% of CaO) (Fig. 4). These results
are very important because
nd Building Materials 30 (2012) 400405 403a quick escape of the
water vapour resulting in lower internal porepressure.
6. Resistance to freezethaw
According to Yunsheng and Wei [59] alkali-activated y ash
canwithstand 2.2 times more freezethaw cycles as compared to
con-crete made from OPC with the same compressive strength.
Dolezalet al. [60] reported the loss of only 30% of the resistance
in alkali-activated y ash binders after being subjected to 150
freezethawcycles. Other authors [61] analyzed the resistance of
alkali-acti-vated slag-waste shales based binders reporting a high
compres-sive strength even after freezethaw 100 cycles. Slavik et
al. [62]obtained high freezethaw resistance in alkali-activated
bindersbased on uidized bed combustion bottom ash. The
investigationsof Brooks et al. [63] conrm the high resistance to
freezethaw ofcerning alkalinity stability with curing time, as well
as aboutchloride diffusion and carbonation resistance.
5. Resistance to high temperatures and to re
Concretes based on Portland cement show a weak performancewhen
subjected to a thermal treatment and when the temperaturerises
above 300 C they begin to disintegrate. As to the alkali-acti-vated
binders they show a high stability when submitted to
hightemperatures even around 1000 C [52]. Other authors [53]
studiedthe activation of metakaolin and shale wastes reporting a
highmechanical performance after a thermal phase. The specimensshow
some slight strength loss between 600 C and 1000 C, how-ever in
some cases they show a strength increase at 1200 C. Konget al. [54]
studied alkali-activated metakaolin binders observingthat the
residual strength after a thermal phase up to 800 C isinuenced by
the Si/Al ratio. The higher residual strength was ob-tained by the
mixtures with a Si/Al ratio between 1.5 and 1.7. Kri-venko and
Guziy [55] found that alkali-activated binders show ahigh
performance in the resistance to re, thus suggesting that
thismaterial is suitable for use in works with a high re risk like
tun-nels and tall buildings. Pern et al. [56] conrmed that
alkali-acti-vated binders can be used as a 120 min anti-re material
inaccordance with related standards of the Czech Republic.
Theanti-re material must show a temperature lower than 120 C inthe
opposite side of the re action. Temuujin et al. [57] used
alka-li-activated binders as steel coatings stating that they
maintainedhigh structural integrity even after being submitted to a
heat treat-ment by a gas torch. Zhao and Sanjayan [58] compared the
perfor-mance of OPC concrete and alkali activated concrete under
thestandard curve re test mentioning that only the former
exhibittion remained even after 5 years, since carbonation
phenomenonad not take place. Aperador et al. [48] mention that
alkali-activatedslag concrete is associated to poor carbonation
resistance a majorcause for corrosion of steel reinforcement.
Bernal et al. [49] showsthat the activation of granulated blast
furnace slag (GBFS)metaka-olin (MK) blends have low carbonation
resistance. The sameauthors [50] found that alkali-activated slag
concretes presentsome susceptibility to carbonation which depends
on the bindercontent (Fig. 2). Lloyd et al. [51] show that
geopolymer cement isprone to alkali leaching leading to a reduction
in the pH which isessential to prevent steel corrosion. They also
mention that thepresence of calcium is crucial for having durable
steel-reinforcedconcrete which is a setback for SiAl geopolymers.
Further re-
F. Pacheco-Torgal et al. / Construction athe alkali-activated
binders. More recently Fu et al. [64] studied al-kali-activated
slag concrete reporting an excellent freezethawresistance.Fig. 3.
Alkali-activated mine mortars specimens after water immersion:
Above
mortars based on plain mine waste mud calcined at 950 C for 2 h;
Below mortarsbased on mine waste mud calcined at different
temperatures with sodiumcarbonate [67].
-
nd Bthey constitute a step back in the development of
alkali-activatedbinders. For one the use of hydrothermal curing has
serious limita-tions for on-site concrete placement operations. On
the other handthe use of calcium based mixtures reduces the acid
resistance andraises the chances for the occurrence of ASR. Besides
the use ofsuch calcium content reduces the global warming
emissionsadvantage over Portland cement.
8. Conclusions
The literature review about the durability of
alkali-activatedbinders shows that:
(a) New investigations are needed on the use of sodic wastes
toreplace sodium silicate in order to reduce the cost of
thesematerials.
(b) The new binders present higher chemical resistance, how-
Fig. 4. Effect of admixtures on alkali leaching (as a proxy for
eforescence extent)[70].
404 F. Pacheco-Torgal et al. / Construction aever it seems that
depends more on the low content of sol-uble calcium compounds than
it is from their lowpermeability.
(c) Although these binders contain a high level of alkali
ele-ments, they do not appear to be associated with the occur-rence
of ASR, which may be due to the fact that themajority of alkali
elements are associated with other reac-tion products. However that
explanation forgets the crucialrole played by calcium in the ASR
development meaningthat although its rather natural the absence of
ASR in freecalcium alkali-activated binders, that problem must
betaken under consideration when calcium based binders
wereused.
(d) As to the capability to keep an alkaline environment
troughtime, which is crucial to maintain reinforced steel safe
fromcorrosion, the current studies are not enough to prove it, as
amatter of fact their resistance to carbonation is lower thanOPC
binders and recent investigation show that it is difcultto
synthesize a low-Ca geopolymer capable of preserving thesteel
reinforcement passivation lm.
(e) The use of calcium in alkali-activated binders is
indispens-able to keep a high pH but at the same time could be
theresponsible for triggering ASR.
(f) Contrary to standard OPC binders alkali-activated
bindersshow a high stability when submitted to high
temperatureswhich dependent on the Si/Al ratio. The investigations
onthe re behaviour of alkali-activated binders show thatthese
materials are specially recommended for works witha high re risk
like tunnels and tall buildings.
(g) Alkali-activated binders show a high resistance to
freezethaw cycles.
(h) Alkali-activated binders are prone to the formation of
efo-rescences however this disadvantage can be greatly reducewhen
using hydrothermal curing treatments or calcium alu-minate
admixtures. Nevertheless, hydrothermal curing haslimited
applications for on situ concrete placement opera-tions and the use
of a calcium based admixture raises issuesabout its acid
resistance. Furthermore, alkali-activated bind-ers containing
calcium based admixture have a higher globalwarming impact than
alkali-activated SiAl mixtures.
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Durability of alkali-activated binders: A clear advantage over
Portland cement or an unproven issue?1 Introduction2 Resistance to
acid attack3 Alkalisilica reaction (ASR)4 Corrosion of steel
reinforcement5 Resistance to high temperatures and to fire6
Resistance to freezethaw7 Efflorescences8 ConclusionsReferences