Hindawi Publishing CorporationISRN Polymer ScienceVolume 2013, Article ID 509185, 8 pageshttp://dx.doi.org/10.1155/2013/509185
Review ArticleGeopolymer Binders: A Need for Future Concrete Construction
K. Srinivasan and A. Sivakumar
Structural Engineering Division, VIT University, Vellore 632014, Tamilnadu, India
Correspondence should be addressed to A. Sivakumar; [email protected]
Received 30 April 2013; Accepted 6 June 2013
Academic Editors: C. Bernal and G. Gentile
Copyright © 2013 K. Srinivasan and A. Sivakumar. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.
Applications of polymer based binder material can be an ideal choice in civil infrastructural applications since the conventionalcement production is highly energy intensive. Moreover, it also consumes significant amount of natural resources for the large-scale production in order to meet the global infrastructure developments. On the other hand the usage of cement concrete is onthe increase and necessitates looking for an alternative binder to make concrete. Geopolymer based cementitious binder was oneof the recent research findings in the emerging technologies. The present study is aimed at providing a comprehensive review onthe various production processes involved in the development of a geopolymer binder. More studies in the recent past showed amajor thrust for wider applications of geopolymer binder towards a cost economic construction practice. This also envisages thereduction of global warming due to carbon dioxide emissions from cement plants.
1. Introduction
Research studies in the past had shown that fly ash-basedgeopolymer has emerged as a promising new cement alter-native in the field of construction materials. The termgeopolymer was first coined and invented by Davidovits[1] which was obtained from fly ash as a result of geo-polymerization reaction. This was produced by the chemicalreaction of aluminosilicate oxides (Si
2O5, Al2O2) with alkali
polysilicates yielding polymeric Si–O–Al bonds. Hardjitoand Rangan [2] demonstrated in their extensive studiesthat geopolymer based concrete showed good mechanicalproperties as compared to conventional cement concrete.A comprehensive analysis on the various works done ingeopolymer concrete is listed in Table 1.
Geopolymer can be producedwith the basic rawmaterialscontaining silica and alumina rich mineral composition.Several studies have reported the use of the beneficial uti-lization of these materials in concrete. Most of the studiesinvestigated the use of alkali activators containing sodiumhydroxide and sodium silicate or a potassium hydroxide andpotassium silicate. Cheng and Chiu [3] reported the pro-duction of geopolymer concrete using slag and metakaolinwith potassium hydroxide and sodium silicate as alkaline
medium. Palomo et al. [4] produced geopolymers using flyashwith sodiumhydroxide and sodium silicate as well as withpotassium hydroxide with potassium silicate combinations.The results from the studies exhibited an excellent formationof geopolymer with rapid setting properties. It can be notedthat the presence of calcium content in fly ash played asignificant role in compressive strength development [5].Thepresence of calcium ions provides a faster reactivity and thusyields good hardening of geopolymer in shorter curing time.
2. Background of Geopolymerization Process
Polymerization reaction is best observed in the presence ofalkaline medium such as sodium hydroxide, or potassiumhydroxide and the addition of silicates can be additionalionic composition with good bonding effects. The reactantsin the chain reaction can be accelerated due to highermolar concentration of alkali ions; however, the increase inthe concentration leads to rapid loss in consistency duringmixing attributed to faster polymer reaction. The inclusionof sodium silicate in sodium hydroxide solution provideshigher silicate content and due to which the gel formation islikely to provide faster polymerization. A similar reaction isobserved in the case of potassium silicate added to potassium
2 ISRN Polymer ScienceTa
ble1:Summaryof
vario
usworks
done
ongeop
olym
erconcrete.
Sl.no.
Authors/ref.
Year
Testcond
ucted
Typeso
fbindera
ndalkaliactiv
ator
used
Curin
gregime
Observatio
ns
(1)
Gorettaetal.[6]
2004
Com
pressiv
estre
ngth.
ClassC
flyashand
granulated
blast-furnace
slag,
sodium
silicate.
Hot
airo
vencurin
gat
80∘Cto
120∘Cand
ambienttem
perature.
Ther
espo
nsew
asattributed
tomateriallossb
yprop
agation
ofbo
thlateralandradialcracks
andpresence
ofmicrocracks
andaggregates
inthem
atrix
.
(2)
Bakh
arev
[7]
2005
Com
pressiv
estre
ngth.
FTIR,X
RD,and
SEM.
ClassF
flyash.
Sodium
silicatea
ndsodium
hydroxide.
Potassium
hydroxide
Hot
airo
venat75∘Cto
150∘C.
Anincrease
oftemperature
ofheattre
atmentcauseda
decrease
ofSi/A
lratiosinalum
inosilicategel,andlong
curin
gatroom
temperature
narrow
edther
ange
ofdistrib
utionof
theS
i/Alratios.
(3)
Bakh
arev
[7]
2005
Com
pressiv
estre
ngth.
ClassF
flyash.
Sodium
silicatea
ndsodium
hydroxide.
Hot
airo
vencurin
gat
75∘Cand95∘C.
Flyashactiv
ated
bysodium
silicate,6h
heatcurin
gismore
beneficialthan24
hheat.
Flyashactiv
ated
bysodium
hydroxideh
admores
table
streng
thprop
ertie
s.
(4)
Fernandez-Jim
enez
etal.[8]
2005
Com
pressiv
estre
ngth.
ClassF
flyashand
sodium
hydroxide
solutio
n.
Hot
airo
vencurin
gat
80∘C.
Thep
articlesiz
edistrib
utionandthem
ineralcompo
sitionof
thes
tartingfly
ash,thetypea
ndconcentrationof
the
activ
ator,and
soforth.
(5)
Dux
sonetal.[9]
2005
Com
pressiv
estre
ngth.
Metakaolin
.So
dium
silicatea
ndsodium
hydroxide
solutio
n.
Hot
airo
vencurin
gat
80∘C.
Thisdemon
stratesthatthe
characteris
ticso
fgeopo
lymersc
anbe
tailo
redfora
pplications
with
requ
irementsforspecific
microstructural,chemical,m
echanical,andthermal
prop
ertie
s.
(6)
Bakh
arev
[10]
2006
Com
pressiv
estre
ngth,
shrin
kage
measurements,
XRD,
andSE
M.
Flyash.
Sodium
silicatea
ndsodium
hydroxide.
Potassium
hydroxide
Hot
airo
venat100∘C.
Geopo
lymer
materialsprepared
usingcla
ssFfly
ashand
sodium
andpo
tassium
silicates
howhigh
shrin
kage
aswell
aslargec
hanges
incompressiv
estre
ngth
with
increasin
gfired
temperature
inther
ange
800–
1200∘C.
(7)
Skvara
etal.[11]
2006
Com
pressiv
estre
ngth.
Flyashandgrou
ndblast-furnace
granulated
slag.
Sodium
hydroxide.
Hot
airo
vencurin
gat
100∘C–
120∘C.
Theh
ardn
esso
fgeopo
lymer
isapproxim
ately
twiceh
igher
than
forO
PCthatcouldindicatelessdeform
abilityand
high
erbrittleness.
(8)
Chindaprasirt
etal.
[12]
2007
Com
pressiv
estre
ngth.
Lign
itefly
ash(FA)
Sodium
silicatea
ndsodium
hydroxide
solutio
nas
alkali
activ
ators.
Hot
airo
vencurin
gat
120∘C.
Thes
amples
with
ahighstr
engthwereo
btainedusingthe
delay
timea
fterm
olding
andbefore
subjectin
gthes
ampleto
heatof
1hwith
heatcurin
gin
theo
venat75∘Cof
notless
than
twodays.
(9)
Kong
etal.[13]
2007
Com
pressiv
estre
ngth.
Metakaolin
and
low-calcium
flyash.
Grade
Dsodium
silicate
solutio
nandpo
tassium
hydroxide.
Hot
airo
vencurin
gat
100∘C.
Flyashpo
resc
ontain
high
erprop
ortio
nof
microspores
than
metakaolin
geop
olym
er.Flyash-basedgeop
olym
ergives
bette
rstre
ngth
than
metakaolin
.
(10)
Temuu
jinetal.[14]
2009
Com
pressiv
estre
ngth.
Flyash.
Sodium
silicatea
ndsodium
hydroxide
solutio
n.
Hot
airo
vencurin
gat
75∘Cand100∘C.
Additio
nof
thec
alcium
compo
unds
CaO
andCa(OH) 2
improves
mechanicalpropertiesa
ndcuredatam
bient
temperature.
Calcium
compo
undadditio
nredu
cesm
echanicalproperties
curedatele
vatedtemperatures.
ISRN Polymer Science 3Ta
ble1:Con
tinued.
Sl.no.
Authors/ref.
Year
Testcond
ucted
Typeso
fbindera
ndalkaliactiv
ator
used
Curin
gregime
Observatio
ns
(11)
Kong
andSanjayan
[15]
2008
Com
pressiv
estre
ngth.
Low-calcium
(classF)
flyash.So
dium
silicate
solutio
nandpo
tassium
hydroxide.
Hot
airo
vencurin
gat
80∘C.
Thes
treng
thdeclinedwith
inclu
sionof
geop
olym
er/aggregatecompo
sites.
Whileaggregates
undergoexpansionatele
vated
temperatures,theg
eopo
lymer
matrix
experie
nced
contraction.
(12)
Diaze
tal.[16]
2010
Com
pressiv
estre
ngth.
ClassF
flyash.
Sodium
silicatea
ndsodium
hydroxide
solutio
n.
Hot
airo
vencurin
gat
80∘C.
Highera
mou
ntof
finep
articlesw
illresultin
high
ersurfa
cearea,higherreactivity
resulting
inhigh
ercompressiv
estr
ength.
(13)
Kong
andSanjayan
[17]
2010
Com
pressiv
estre
ngth.
ClassF
flyash.
Sodium
silicatea
ndsodium
hydroxide.
Hot
airo
vencurin
gat
100∘C.
Ther
ateo
fexpansio
nof
thea
ggregatewith
temperature
isan
influ
entia
lfactorinthep
erform
ance
ofgeop
olym
erconcrete
undere
levatedtemperatures.
(14)
Kumar
etal.[18]
2010
Com
pressiv
estre
ngth.
FTIR,X
RD,and
SEM.
FlyAs
h.So
dium
hydroxide.
Hot
airo
venat100∘Cto
250∘C.
Com
binedeffecto
fparticlesiz
eand
change
inreactiv
itydu
eto
mechanicalactivationalteredtheg
eopo
lymerisa
tion
reactio
n.Th
eimprovem
entinph
ysicalprop
ertie
sisrelated
tothe
intrinsic
structure
developeddu
etoenhanced
geop
olym
erisa
tion.
(15)
Won
gpae
tal.[19
]2010
Com
pressiv
estre
ngth.
Flyashandric
ehusk
bark
ash.
Sodium
silicatea
ndsodium
hydroxide
solutio
n.
Hot
airo
vencurin
gat
75∘Cto
125∘C.
Paste
contentand
thea
ggregatecontentP
/Aggregateof
0.34
andSi/A
lof0
.63show
edtheh
ighestcompressiv
estre
ngth.
(16)
Jamsto
rpetal.[20]
2010
Com
pressiv
estre
ngth.
Kaolin
(Al 2S
i 2O5(OH) 4),
fumed
silica.
Metakaolin
andsodium
hydroxide(NaO
H).
Fentanylbase
and
Zolpidem
tartrate.
Hot
airo
vencurin
gat
100∘Cto
150∘C.
Samples
with
pore
sizes
ofabou
t40n
m,exh
ibitedas
atisfying
initialreleaseo
f60–
80%of
theA
PIcontentw
ithin
10hand
nearlyallw
ithin
24h,as
well
asfairlyhigh
compressio
nstreng
thso
f50–
60MPa.
(17)
Elim
bietal.[21]
2011
Setting
time,lin
ear
shrin
kage,com
pressiv
estr
ength,XR
D,and
SEM.
Metakaolin
,kaolin
ite,
andsodium
hydroxide
andsodium
silicate.
Calcined
at450∘Cand
ambienttem
perature.
Above7
00∘C,
thereisa
nincrease
ofsetting
time.
Thec
ompressiv
estre
ngth
increasesw
henthec
alcinatio
ntemperature
ofkaolinite
clays
isbetween500and700∘Cbu
tdrop
sabo
ve700∘C.
(18)
Natalietal.[22]
2011
Flexuralstreng
thand
fracture
toug
hness.
Metakaolin
,ladlesla
g,andsodium
hydroxide
andsodium
silicate.
Calcined
at700∘Cfor5
hours.
Geopo
lymer
matrix
isableto
determ
inea
flexu
ralstre
ngth
increm
ent,rang
ingfro
m30%up
to70%depend
ingon
the
fiber
type,com
paredto
theu
nreinforcedmaterial.
(19)
Nazarietal.[23]
2011
Com
pressiv
estre
ngth.
Seeded
flyashandric
ehu
skbark
ash.
Sodium
silicatea
ndsodium
hydroxide.
Hot
airo
venat80∘C.
Theh
igheststreng
thwas
achieved
usinga1
2MNaO
Hsolutio
n.Ovencurin
gof
thes
pecimensa
t80∘Cwas
foun
dto
betheo
ptim
umtemperature.
4 ISRN Polymer Science
Table1:Con
tinued.
Sl.no.
Authors/ref.
Year
Testcond
ucted
Typeso
fbindera
ndalkaliactiv
ator
used
Curin
gregime
Observatio
ns
(20)
McLellanetal.[24]
2011
Com
pressiv
estre
ngth.
Com
parativ
estudy
ofOPC
andfly
ash.So
dium
silicatea
ndsodium
hydroxides
olution.
Hot
airo
venat100∘C.
Thereisa
nestim
ated
44–6
4%im
provem
entingreenh
ouse
gase
miss
ions
over
OPC
.Emiss
ions
from
geop
olym
erconcretecanbe
97%lower
upto
14%high
er.
(21)
Somna
etal.[25]
2011
Com
pressiv
estre
ngth.
Flyash.So
dium
silicate
andsodium
hydroxide
solutio
n.Hot
airo
venat100∘C.
Sodium
hydroxide-activ
ated
grou
ndfly
ashcuredatroom
temperature
canbe
prod
uced
with
reason
ablestreng
th.
Groun
dfin
eflyashcanbe
used
asas
ourcem
aterialfor
makinggeop
olym
ercuredatam
bienttem
perature.
ISRN Polymer Science 5
KOH, NaOH
O O
(Si2O5, Al2O2)n + nH2O n(OH)3-Si-O-Al(OH)3
n(OH)3-Si-O-Al-(OH)3KOH, NaOH
(Na, K) (-Si-O-Al-O)n + 3nH2O
(Orthosialate) (Na, K)-poly(sialate)KOH, NaOH
KOH, NaOH
O O O
Oligo(sialate-siloxo) (Na, K)-poly(sialate-siloxo)
(Si2O5, Al2O2)n + nSiO2 + nH2O
-Si-O-Al-O-Si-(OH)3 (Na, K) (-Si-O-Al-O-Si-O-)n + nH2O
(OH)2
n(OH)3
n(OH)3
-Si-O-Al-O-Si-(OH)3
Polymerization reactions O O
O O
O-Si-O-Al-OPoly(sialate) {Si : Al = 1 (-Si-O-Al-O-)}
Poly(sialate-siloxo)
O O O
O O O
O-Si-O-Al-O-Si-O
{ Si : Al= 2(-Si-O-Al-O-Si-O-)}O O O O
O O O O
O-Si-O-Al-O-Si-O-Si-O
{Si : Al = 3 (-Si-O-Al-O-Si-O-Si-O)}
Poly(sialate-disiloxo)
K-oligo(sialate-siloxo)
Polycondensation
OH-Si-O-Al-O-Si-OH
OH OH OH
OH OHOH(−) (K+)
Si
O-Si-O-Al-O-Si-O
O
O O
O O
Si K-poly(sialate-siloxo)(K+)
O(−)
Figure 1: Polymerization reaction [1].
hydroxide solution. It is known that the conventional organicpolymerization involves the formation of monomers in agiven solution in which the reaction can be made faster topolymerize and form a solid polymer.The geopolymerizationprocess involves three separate processes and during initialmixing, the alkaline solution dissolves silicon and aluminiumions in the raw material (fly ash, slag, silica fume, bentonite,etc.). It is also understood that the silicon or aluminium
hydroxide molecules undergo a condensation reaction whereadjacent hydroxyl ions from these near neighbors condenseto form an oxygen bond linking the water molecule, andit is seen that each oxygen bond is formed as a result of acondensation reaction and thereby bonds the neighboring Sior Al tetrahedra. A clear representation of the chain reactioninvolved during the polymerization is explained in Figure 1with a fundamental understanding from the literature.
6 ISRN Polymer Science
Polymers are sensitive towards heat and can form astronger chain due to polycondensation. It is noted fromthe basic chemical reaction when subjected to heat causessilicon and aluminium hydroxide molecules to polycondenseor polymerize, to form rigid chains or nets of oxygen bondedtetrahedra. Also, at higher elevated temperatures it producesstronger geopolymers. Aluminium ions require a metallicNa+ ions for charge balance. Davidovits and Davidovics [26]reported that geopolymers can harden rapidly at room tem-perature and can gain the compressive strength up to 20MPain 1 day. Comrie et al. [27] conducted tests on geopolymermortars and reported that most of the 28-day strength wasgained during the first 2 days of curing. Geopolymer cementis found out to be acid resistant, because, unlike the Portlandcement, geopolymer cements do not depend on lime andare not dissolved by acidic solutions. Most of the studiesconcluded that the concentration of NaOH solution playsthe most important role on the strength of the fly ash-based geopolymers.The addition of calcium oxide along withsodium hydroxide accelerates the geopolymerisation in flyash. Guo et al. [28] conducted experimental studies in classC fly ash-based geopolymers using a mixed alkali activatorof sodium hydroxide and sodium silicate solution. It wasreported that a high compressive strength can be obtainedwhen the molar ratio of silicate to sodium is 1.5, and themass proportion of Na
2O to class F fly ash was 10%. The
compressive strength of these samples was around 63MPawhen it was cured at 75∘C for 8 h followed by curing at 23∘Cfor 28 d.
Low-calcium fly ash is preferred than high calcium(ASTM class C) fly ash for the formation of geopolymers,since the presence of calcium in high amount may affect thepolymerization process [29]. The suitability of different typesof fly ash can be a potential source for studying the type andefficiency of geopolymerization reaction. It was also reportedthat geopolymerisation reaction can be effective in low-calcium fly ash depending on if it contains unburnt carbonless than 5% and 10% CaO content, reactive silica about 40–50%, and particles finer than 45microns [30]. However, it wasreported by Van Jaarsveld et al. [5] that fly ash with higheramount of CaO produced higher compressive strength, dueto the formation of calcium-aluminate hydrate and othercalcium compounds, especially in the early ages. The mostpreferred alkaline solution used in geopolymerisation is acombination of sodium hydroxide (NaOH) or potassiumhydroxide (KOH) and sodium silicate or potassium silicate[4, 31–35].
Palomo et al. [4] reported that reactions occur at a highrate when the alkaline liquid contains soluble silicate, eithersodium or potassium silicate, compared to the use of onlyalkaline hydroxides. Xu and van Deventer [33] confirmedthat the addition of sodium silicate solution to the sodiumhydroxide solution as the alkaline liquid enhanced the reac-tion with fly ash. Furthermore, geopolymerisation with theNaOH solution resulted in higher dissolution of mineralsthan KOH solution. A combination of sodium hydroxide andsodium silicate solution, after curing the specimens for 24hours at 65∘C, provided higher strength [33]. It was reportedthat the proportion of alkaline solution to aluminosilicate
powder by mass should be approximately 0.33 to allow thegeopolymeric reactions to occur. Alkaline solutions formed athick gel instantaneously upon mixing with the aluminosili-cate powder.The previous studies also reported that mixtureswith high water content, that is, H
2O/Na2O = 25, developed
very low compressive strengths. Palomo et al. [4] reportedthat curing temperature is an important indicator for strengthgain in fly ash-based geopolymers and improves themechani-cal strength. Higher curing temperature and optimum curingtimewere found to influence the compressive strength gain ingeopolymer concrete. Alkaline liquid that contained solublesilicates was proved to increase the rate of reaction comparedto alkaline solutions that contained only hydroxide.
3. Long Term Durability Properties ofGeopolymer Concrete
Durability aspects of geopolymer products have good sus-tainability to weathering effects; however, they are not resis-tant towards high temperature beyond 400∘C. Several exper-imental studies showed that geopolymer concrete specimensimmersed in sulfuric acid and chloric acid were foundto be resistant to acid attack. While the Portland basedcement showed deletrieous reaction and results in surfacedeterioration followed by weight loss (Davidovits, 1994).Extensive studies also demonstrated that heat-cured fly ash-based geopolymer concrete has an excellent resistance tosulfate attack due the formation of stronger polymer chaindue to polycondensation reaction. The effects of acid attackalso cause reduction in compressive strength of heat-curedgeopolymer concrete; the extent of degradation dependson the concentration of the acid solution and the periodof exposure. However, the sulfuric acid resistance of heat-cured geopolymer concrete is significantly better than that ofPortland cement concrete as reported in earlier studies.
Several studies have shown that fiber addition is aneffectivemethod to improve themechanical characteristics ofbrittle material such as concrete by providing crack arrestingmechanism [36]. Limited studies have been carried outto analyze the effect of fibre reinforcement in geopolymerconcrete. Future studies are needed to study the effect of steeland glass fibres in geopolymer concrete to be investigatedsystematically. Also, it is well known that increase in fracturetoughness is provided essentially by fiber bridging near thecrack opening prior to crack propagation. The linear elasticbehavior of the matrix could not be affected significantlyfor low volumetric fiber fractions. However, postcrackingbehavior can be substantially modified, with increases ofstrength, toughness, and durability of thematerial.The futurestudy has to be focussed on the effect of fibre addition on thepostcrack performance of geopolymer concrete.
4. Summary
It is understood from the earlier studies that good scientificinformation is available on the evaluation of chemical andphysical properties of geopolymer concrete. Also, very fewworks has been reported on the effect of fibre reinforcement
ISRN Polymer Science 7
in geopolymer concrete. Further studies are needed to inves-tigate the fracture resistance of this brittle composite. Theaddition of glass fibres can exhibit a reasonable improvementon the strength properties of geopolymer concrete due tostrain hardening properties at failure. The concentration andtype of alkali need to be investigated extensively to choosethe combination and dosage of alkali for fly ash. The effectof alkali activators on the rate of hardening of geopolymersat different curing regimes needs to be well documented.Curing regime on the hardening properties of geopolymericconcrete needs special attention to improve the strengthproperties. The rate of strength gain in different curingregimes needs to be explored using ultrasonic pulse velocitymeasurements.Themechanical characteristics of geopolymerconcrete specimens at elevated temperature (600–800∘C)need to be assessed for checking its potential applications asheat resisting construction material.
References
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[3] T. W. Cheng and J. P. Chiu, “Fire-resistant geopolymer produceby granulated blast furnace slag,”Minerals Engineering, vol. 16,no. 3, pp. 205–210, 2003.
[4] A. Palomo, M.W. Grutzeck, andM. T. Blanco, “Alkali-activatedfly ashes: a cement for the future,” Cement and ConcreteResearch, vol. 29, no. 8, pp. 1323–1329, 1999.
[5] J. G. S. Van Jaarsveld, J. S. J. Van Deventer, and G. C. Lukey,“The characterisation of source materials in fly ash-basedgeopolymers,” Materials Letters, vol. 57, no. 7, pp. 1272–1280,2003.
[6] K. C. Goretta, N. Chen, F. Gutierrez-Mora, J. L. Routbort, G.C. Lukey, and J. S. J. van Deventer, “Solid-particle erosion ofa geopolymer containing fly ash and blast-furnace slag,” Wear,vol. 256, no. 7-8, pp. 714–719, 2004.
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[8] A. Fernandez-Jimenez, A. Palomo, andM.Criado, “Microstruc-ture development of alkali-activated fly ash cement: a descrip-tive model,” Cement and Concrete Research, vol. 35, no. 6, pp.1204–1209, 2005.
[9] P. Duxson, J. L. Provis, G. C. Lukey, S. W. Mallicoat, W.M. Kriven, and J. S. J. Van Deventer, “Understanding therelationship between geopolymer composition, microstructureand mechanical properties,” Colloids and Surfaces A, vol. 269,no. 1–3, pp. 47–58, 2005.
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