Accepted Manuscript
Fly Ash-based Geopolymer: Clean Production, Properties and Applications
Xiao Yu Zhuang, Liang Chen, Sridhar Komarneni, Chun Hui Zhou, Dong Shen Tong,Hui Min Yang, Wei Hua Yu, Hao Wang
PII: S0959-6526(16)30079-8
DOI: 10.1016/j.jclepro.2016.03.019
Reference: JCLP 6868
To appear in: Journal of Cleaner Production
Received Date: 23 October 2015
Revised Date: 2 March 2016
Accepted Date: 2 March 2016
Please cite this article as: Zhuang XY, Chen L, Komarneni S, Zhou CH, Tong DS, Yang HM, Yu WH,Wang H, Fly Ash-based Geopolymer: Clean Production, Properties and Applications, Journal of CleanerProduction (2016), doi: 10.1016/j.jclepro.2016.03.019.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service toour customers we are providing this early version of the manuscript. The manuscript will undergocopyediting, typesetting, and review of the resulting proof before it is published in its final form. Pleasenote that during the production process errors may be discovered which could affect the content, and alllegal disclaimers that apply to the journal pertain.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
Graphic abstract
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
1
Fly Ash-based Geopolymer: Clean Production, Properties and Applications
Xiao Yu Zhuang,a Liang Chen,a,b Sridhar Komarneni,d Chun Hui Zhou,a,b,c* Dong
Shen Tong,a,b Hui Min Yang,e Wei Hua Yu,a Hao Wangc
a Research Group for Advanced Materials & Sustainable Catalysis (AMSC), State Key Laboratory Breeding Base
of Green Chemistry-Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology,
Hangzhou 310014, China
b Engineering Research Center of Non-metallic Minerals of Zhejiang Province. Key Laboratory of Clay Minerals
of Ministry of Land and Resources of The People's Republic of China, Zhejiang Institute of Geology and Mineral
Resource, Hangzhou 310007, China
c Centre of Excellence in Engineered Fibre Composites, University of Southern Queensland, Toowoomba,
Queensland 4350, Australia
d Materials Research Laboratory, Department of Ecosystem Science and Management and Materials Research
Institute, The Pennsylvania State University, University Park, PA 16802, USA
e Key Laboratory of High Efficient Processing of Bamboo of Zhejiang Province, China National Bamboo Center,
Hangzhou, Zhejiang, 310012
* C.H.ZHOU E-mail: [email protected] [email protected]
ABSTRACT
Fly ash is the fine solid particulate residue driven out of the boiler with the flue gases in coal-fired
power plants. Now it can be used for making geopolymer which acts as a cement-like product. The
geopolymer technology provides an alternative good solution to the utilization of fly ash with little
negative impact on environment. This review summarizes and examines the scientific advances in the
preparation, properties and applications of fly ash-based geopolymer. The production of fly ash-based
geopolymer is mainly based on alkali activated geopolymerization which can occur under mild
conditions and is considered as a cleaner process due to much lower CO2 emission than that from the
production of cement. The geopolymerization can trap and fix the trace toxic metal elements from fly
ash or external sources. The Si/Al ratios, the type and the amount of the alkali solution, the temperature,
the curing conditions, and the additives are critical factors in a geopolymerization process. The
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
2
mechanical performances of the fly ash-based geopolymer, including compressive strength, flexural
and splitting tensile strength, and durability such as the resistance to chloride, sulfuric, acid, thermal,
freeze-thaw and efflorescence, are the primary concerns. These properties of fly ash-based geopolymer
are inherently dependent upon the chemical composition and chemical bonding and the porosity. The
mechanical properties and durability can be improved by fine tuning Si/Al ratios, alkali solutions,
curing conditions, and adding slag, fiber, rice husk-bark ash and red mud. Fly ash-based geopolymer is
expected to be used as a kind of novel green cement. Fly ash-based geopolymer can be used as a class
of materials to adsorb and immobilize toxic or radioactive metals. The factors affecting the
performances of fly ash-based geopolymer concrete, in particular aggregate, are discussed. For future
studies on fly ash-based geopolymer, further enhancing mechanical performance, scaling up production
and exploring new applications are suggested.
Key words: Fly ash; Alkali activation; Geopolymer; Waste utilization; Cement, Concrete
1. Introduction
Fly ash is one of the solid residues composed of the fine particles that are driven out of
the boiler with flue gases in coal-fired power plants. It is generally captured from flue gases
by electrostatic precipitators or other particle filtration equipment before the flue gases reach the
chimneys (Ahmaruzzaman, 2010; Gorai et al., 2006). Depending upon the source of the coal being
burned, the components of fly ash vary considerably. In general, the components of fly ash typically
include SiO2, Al2O3, CaO and Fe2O3, which exists in the form of amorphous and crystalline oxides or
various minerals. According to the American Society for Testing and Materials standard C 618 (ASTM
C618-12a; 2012), fly ash can be classified as Class C and Class F types based on their calcium oxide
contents. Class C fly ash has a high calcium content, and is mainly generated from the burning of
lignite coal sources. Class C fly ash has a total SiO2, Al2O3 and Fe2O3 content between 50 wt.% and 70
wt. % and CaO content more than 20 wt.%. Class F fly ash has a low calcium content, and is generated
from burning anthracite or bituminous coal. Class F fly ash has a total SiO2, Al2O3 and Fe2O3 content
over 70 wt% and CaO content less than 10% (Bankowski et al., 2004, Antiohos and Tsimas, 2007). In
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
3
addition to Si, Al, Fe, and Ca, usually fly ash also contains many other trace metal elements, such as Ti,
V, Cr, Mn, Co, As, Sr, Mo, Pb and Hg. The concentrations of the toxic trace elements in fly ash could
be 4-10 times higher than those in coal (Neupane and Donahoe, 2013; Nyale et al., 2014; Yao et al.,
2015). It may also include small concentrations of dioxins and polycyclic aromatic
hydrocarbon compounds (Shibayama et al., 2005; Nomura et al., 2010). Thus, fly ash is considered as a
hazardous material, and the improper disposal of fly ash will not only increase the occupation of land
but also deteriorate the environment and ecology. In last few decades, increasing efforts have been
made towards the utilization of fly ash, especially in an efficient and green fashion.
Fig.1 a The generation of fly ash from 2008-2013 in the USA. b The utilization fields of fly ash in
2013 in the USA (Data from American Coal Ash Association).
Due to the cost and availability of oil and natural gas, coal-fired power plants will be still run for a
long period, especially in the coal-rich countries, for example, China, the USA, India and Australia
(Lior, 2010). Under such a circumstance, the generation of fly ash remain significant and thus its
economic and green utilization technology of fly ash are desired (Fig.1a). Fly ash can be used for soil
amendment (Ukwattage et al., 2013) and nutrients (Kováčik et al., 2011). It can also be used to make a
low-cost adsorbent for waste removal (Rubel et al., 2005; Yildiz, 2004). Besides, it can act as silica and
alumina sources for zeolite production (Chang and Shih, 2000; Izidoro et al., 2012) (Fig.1b). More
recently, fly ash has been used as an alternative source to make geopolymer, a new binder or cement
roughly comparable to hydrated cement in appearance, reactivity and properties. In principle,
geopolymer is a product of alkali activation of any aluminosilicate materials. It has a three-dimensional
0
1,00,00,000
2,00,00,000
3,00,00,000
4,00,00,000
5,00,00,000
6,00,00,000
7,00,00,000
8,00,00,000
2008 2009 2010 2011 2012 2013
Fly
ash
gen
era
tion
(s
hot
ton
)
Year
Unreutilized Reutilizeda
52.99%9.80%
0.18%
12.89%
0.58%
1.15%
0.01%
7.90%
8.72%
0.07%
0.02%
1.34%4.34%
The usage of fly ash in 2013 Concrete/Concreteproducts/GroutBlended cement/Feed forclinkerFlowable fills
Structural fills/embankments
Road base/sub-base
Soil modification/stabilization
Blastig crit/roofing granules
Mining application
Wastestabilization/solidificationAgriculture
Aggregate
Oil field services
Miscellaneous/other
b
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
4
aluminosilicate network structure with an empirical formula of Mn [-(SiO2) z-AlO2] n·w H2O, where z is
the Si/Al molar ratio, M is an alkali cation, such as Na+ or K+, n is the polymerization degree, and w is
the water content (Palomo et al., 1999a). Importantly, such a geopolymer has the similar bind
performances to those of ordinary Portland cement (OPC). The alkali activation is conducted by adding
NaOH, KOH, Na2SiO3 or K2SiO3 into fly ash together or individually. The so-called geopolymerization
can occur at room temperature or slightly elevated temperatures (usually<100°C), and much
importantly, with little CO2 emission (Davidovits, 1991; Verdolotti et al., 2008; Zhang et al., 2016).
The geopolymer technology provides a new good and green solution to the utilization of fly ash,
avoiding its negative impact on environment and ecology. The alumina and silica in fly ash can be
activated with alkali to form geopolymer. Moreover, the toxic trace metal elements can be trapped and
fixed in the geopolymer structure (Li et al., 2013a). Remarkably, the process of the production of fly
ash-based geopolymer has lower CO2 emission compared with that of OPC during which much
limestone (CaCO3) is calcined and decomposed at high temperatures (Davidovits, 1994; McLellan et
al., 2011). Approximately 0.8 ton of CO2 is produced when one ton of OPC is produced (Rashad and
Zeedan, 2011; Yang, 2009). Fly ash-based geopolymer usually show mechanical strength and durability
nearly comparable to hydrated Portland cement and can used as a class of green cement with natural
resource efficiency (Nasvi and Gamage, 2012).
In particular, recent years have witnessed many scientific advances in the preparation technology,
and the insights into the performances of the fly ash-based geopolymer. The fast-growing knowledge in
turn results in many modification methods to significantly improve the production and the
performances of the fly ash-based geopolymer. Meanwhile, there are increasing pilot and commercial
process. The large-scale use of fly ash-based geopolymer in construction industry seems to come true.
In this review article, the state-of-the-art preparation of fly ash-based geopolymer is examined.
Attention will therein be paid to understanding how the Si/Al ratios, the type and the amount of the
alkali solution, the temperature, the curing conditions, and the additives are controllably used to
reinforce properties of fly ash–based geopolymer. Discussed are the critical properties, including
compressive, flexural and splitting tensile strength, and the durability such as chloride, sulfate, acid,
thermal, freeze-thaw and efflorescence resistance. Then, the applications of fly ash–based geopolymer
are surveyed. They involve cement-based construction, adsorption and immobilization of toxic metals
materials. The existing challenges and future work are finally analyzed and proposed.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
5
2. Preparation and formation
The basic and simplified principle of the formation of fly ash-based geopolymer is the
alkali-facilitated decomposition of aluminoslicate in the fly ash and then polycondensation. The
reactions can proceed under mild temperatures so the production is considered to be energy and source
efficient, namely much cleaner. However, the real reactions occurred in the process are very
complicated and remain elusive. Apparently, there are reactions between fly ash and alkali and
condensation between the resultant Si4+ and Al3+ species, followed by other complicated nucleation,
oligomerization, and polymerization, which finally lead to a new aluminoslicate-based polymer with
new amorphous three-dimensional network structure. In tests or uses, the as-prepared fly ash-based
geopolymer paste is further cast into a mould and placed into an oven at a required temperature or left
at room temperature to be cured for a specific time to form construction (Fig. 2.).
Fig.2. The schematic drawings showing the process from fly ash to fly ash-based geopolymer
cement/concrete.
The critical role in the formation geopolymerization are thought be played by alkali activation on
fly ash: in an alkaline solution (Na2SiO3, NaOH, KOH or K2SiO3), the silica, the alumina, or the
aluminosilicates in fly ash hydrolyze, -Si-O-Si- or -Si-O-Al- bonds of aluminosilicate break and release
active Al3+ and Si4+ species. The active Al3+ and Si4+ species react to form nuclei and aluminosilicate
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
6
oligomers consists of SiO4 and AlO4 tetrahedra. The chains in aluminosilicate oligomers can be in the
form of polysialate -Al-O-Si- chain, polysialate siloxo -Al-O-Si-Si- chain, and polysialate disiloxo
-Al-O-Si-Si-Si- chain, depending upon the Si/Al ratio (Fig. 3). In aluminosilicate monomers, Si4+ is
partially substituted by Al3+, and the resultant negative charge in the aluminosilicate chains is balanced
by alkali cations such as Na+ or K+ (Davidovits, 2002; Dimas et al., 2009) (Fig. 2). In the context, the
Si/Al ratio significantly determines the final structure of the resulted geopolymer materials (He et al.,
2012). For example, it have been found that the Si/Al ratio in the fly ash reactant has a remarkable
effect on the porosity (size and amount) of amorphous geopolymer which is one of important
parameters to govern the mechanical strength of geopolymer products (Kriven et al., 2003; Duxson et
al., 2005b).
Fig.3. Dependent upon the different Si/Al molar ratio, different aluminosilicate chains is formed in the
aluminosilicate oligomers which then further to form geopolymer (Davidovits, 2002) (Reprinted and
adapted by courtesy of Geopolymer Institute).
In addition to the Si/Al ratio, the microstructure of the formed fly ash-based geopolymer is
strongly affected by the alkaline solution. When fly ash contacts with alkaline (e.g. NaOH, KOH), Si4+,
Al 3+ and other ions start to be released and to transfer. For instance, the amount of released Si4+ and
Al 3+ is influenced by the concentration of NaOH solution. NaOH solution of high concentration (10
mol/L) is beneficial for decomposing aluminosilicate in the fly ash and then release Si4+ and Al3+
(Table 1). For example, the solubility of Al3+ and Si4+ in NaOH solution is higher than that in KOH
solution with the same concentration (Xu and Van Deventer, 1999). Moreover, the transfer of Al3+ and
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
7
Si4+ species and the polycondensation of aluminosilicate oligomers can also be accelerated by an
alkaline solution of high concentration (Lizcano et al., 2011). Furthermore, different alkaline cations
have different sizes and charge density, and they hydrate differently. These will then have a certain
effect on the nucleation of aluminosilicate chain, the growth of the chain, the charge density on the
chain, the rate, and the extent of polymerization (Duxson et al., 2005a). For instance, the K+ cation
(1.33 Å) is larger than the Na+ cation (0.97 Å) and the K+ cation lead to a lower surface charge density
and a higher degree of polymerization of geopolymer matrix (van Jaarsveld and van Deventer, 1999).
In addition, alkaline cations can even serve as a structure-directing agent in the geopolymerization. In
brief, the leaching rate of Si4+ and Al3+ decide the real available Si/Al ratio in a series of reactions to
form geopolymer and subsequently play a pivotal role in the structure of fly ash-based geopolymer.
Interestingly, a recent study revealed that the addition of Na2SiO3 to alkali solution can increase such a
Si/Al ratio, resulting in a lower porosity and a finer pore system of geopolymer matrix (Ma et al.,
2013).
The setting time of fly ash-based geopolymer is usually considered for the workability of final fly
ash-based geopolymer products. In general, the final setting can be achieved within 1–2 h at room
temperature while Class C fly ash with high CaO content and calcium-content additives, such as CaCl2,
were found to shorten the setting time of fly ash-based geopolymer paste (Rattanasak et al., 2011). In
geopolymerization, Si4+ or Al3+ species react with Ca2+, either in the fly ash or from an external
calcium-content additives, to form calcium silicate hydrate gel (C-S-H), calcium aluminate hydrate gel
(C-A-H) or calcium aluminum silicate gel (C-A-S-H) (C = CaO, S = SiO2, A = Al2O3, H = H2O) in the
presence of water (Diaz et al., 2010; Chindaprasirt et al., 2011). Ca2+ is beneficial for accelerating the
nuclei formation and agglomeration of C-A-S-H gel and C-S-H gel (Geetha and Ramamurthy, 2013).
The rapid formation of amorphous C-A-S-H gel and C-S-H gel leads to a shorter setting time of the
final products and decreases the porosity, while the rapid setting time has a negative on the formation
of more geopolymer gel (N-A-S-H). The high NaOH concentration can prolong the setting time by
limiting the leaching of calcium and allows normal geopolymerization process to control the setting of
geopolymer paste (Hanjitsuwan et al., 2014).
At room temperature, however, the dissolution of fly ash is not completed (Chen et al., 2011; Xu
et al., 2010). In addition, the low reactivity of fly ash increases the setting time of fly ash-based
geopolymer. As a result, curing is a necessary step, namely, geopolymer paste needs to be kept within a
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
8
reasonable range of temperature and moisture and the extended curing time promotes the formation of
a more cross-linked binding and denser microstructure. It is found that when the curing temperature
increases from 30 to 50°C, the reactivity of fly ash becomes higher and the geopolymerization is almost
more complete when the curing temperature lies between 60 and 90°C (Hardjito et al., 2004).
To improve the reactivity of fly ash and the performances of geopolymer, slag, chitosan, fiber, rice
husk-bark ash (RHBA) and red mud have been added into fly ash to synthesize geopolymer (Table 1).
Interestingly, the addition of slag, which is the waste from iron extraction process from raw ore, can
enhance the reactivity of fly ash during geopolymerization (Li and Liu, 2007). Blast furnace slag (BFS)
is the by-product of iron production industry and it contains more than 70% of SiO2 and CaO (Manz,
1999). Idawati et al. (2014) investigated the fly ash/ground blast furnace slag (GBFS)-based
geopolymer with different fly ash/slag ratios and they found the geopolymerization of slag-based
geopolymer was dominated by C–A–S–H type gel, while fly ash-based geopolymer was dominated by
sodium aluminosilicate (N–A–S–H) gel. Kumar et al. (2010) substituted fly ash by 5 - 50% GBFS to
synthesize geopolymer at 27°C and found that the reaction was dominated by dissolution and
precipitation of C-S-H gel. Moreover, Yang et al. (2012) found that the initial setting time of fly
ash/GBFS-based geopolymer increased and the degree of polymerization of the geopolymer decreased
due to the high content of calcium in GBFS. RHBA is a solid waste generated from rice husk and
eucalyptus bark by biomass power plants. RHBA contains about 75% SiO2 and the addition of RHBA
enriched the silica content of the geopolymer matrix and increased the amount of -Si-O-Si- bonds in the
geopolymer gel (N-A-S-H gel). Red mud is the major residue of Bayer process with highly alkaline of
alumina refining from bauxite ores (Zhang et al., 2010a). The annual generation of red mud is
estimated to be about 70 million tons in the world (Klauber et al., 2011). Due to the use of a highly
concentrated NaOH solution in the bauxite processing, red mud is a highly alkaline material. Red mud
essentially consists of oxides and hydroxides of Fe, Al and Si, as well as minor quantities of CaO and
TiO2. Addition of red mud can adjust the Si/Al ratio and reduce the consumption of alkali activator
(Piga and Stoppa, 1993). The addition of chitosan and fiber can increase the hydrogen bonds, bridge the
micro cracks and delay the development of micro cracks (Li et al., 2013b).
Table 1. Preparation and compressive strength of fly ash-based geopolymer with additives
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
9
Material/Alkaline activators
Feedstock
Mix
T
(°C)
Curing time
/Temperature (°C)
Compressive
strength (MPa)
Refs
Fly ash
Na2SiO3 +NaOH (10 mol)
CaCl2, CaSO4, Na2SO4,
sucrose
48 h/
65
26.9-32.2 Rattanasak et al.,
2011
Fly ash
NaOH (4.5, 7.0, 9.5, 12.0, 14.0,
16.5 mol/L)
-
/25-28
<25.5 Somna et al., 2011
Fly ash+ RHBA/
Na2SiO3 +NaOH
(4,8,12 mol/L)
2/5
25 36 h-28 days/
25-90
14.8-55.6 Bohlooli et al.,
2012
Fly ash+RHBA/
Na2SiO3 or
water glass+NaOH
(5-12 mol/L)
2/5
25 2-7day/
25-90
12.6-35.1 Riahi et al.,
2012
Fly ash+
wastepaper sludge/
Na2SiO3+NaOH
1/5
91 days
23-60
31.2-60.6 Yan et al.,
2012
Pulverized coal combustion Fly
ash+
PCC Bottom ash+
flue gas desulfurization gypsum/
Na2SiO3+NaOH
n.a. 48 h
40
25.5-55.5 Boonserm et al.,
2012
Fly ash+
Crushed granite rock+
natural river sand/
Na2SiO3+NaOH
AT 6-72 h
60-120
42.0-58.0 Joseph and
Mathew, 2012
FFA+ N-carboxymethyl chitosan
NaOH (10 mol/L)
AT 6 days
60
<30.0 Li et al., 2013b
Fly ash + RHBA/
water glass+NaOH
7,28days/ RT
36h/
40–90
<58.9 Nazari et al.,
2013
FFA+crushed granite stone+
Superplasticizer/
Na2SiO3+NaOH
5/2
48 h;
1,3,7 days/
70
40.85-53.08 Demie et al., 2013
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
10
FFA+BFS
K2SiO3/Al (85 g/L) + NaOH
(30g/L)
7 days
RT
Ogundiran et al.,
2013
FFA/NaOH
3/5
25 7 day /
28 day/
60
1.38-9.93 Jun and Oh
2014
Fly ash+Palm oil fuel ash/
Na2SiO3+NaOH
24h
65
<38 Ranjbar et al.,
2014
GGBF+Palm oil fuel ash+
Fly ash+
Manufactured-sand/
Na2SiO3+NaOH
24h
65
9-66 Islam et al.,
2014
FFA+Red mud
NaOH (50wt.%) + sodium
trisilicate (2 mol/L)
28 days
AT
11.3-21.3 Zhang et al.,
2014a
*T: temperature, RT: room temperature, AT: ambient temperature, BFS: Blast furnace slag, FFA: Class F fly ash,
RHBA: Rice husk-bark ash, GGBF: Ground granulated blast furnace slag
Using waste materials, fly ash and additives like slag, RHBA, red mud and fibers, to produce a
construction material geopolymer can help reduce the consumption of mineral reserves such as
limestone and the emission of greenhouse gases. Without proper utilization, fly ash is a solid waste.
Improper disposal of fly ash brings the danger of the release of toxic elements. By contrast, fly
ash-based geopolymer can solidify and immobilize the trace of heavy metal elements. Furthermore, the
simple alkaline activation of fly ash to produce geopolymer completely bypasses the high-temperature
calcination process in OPC production. All these would justify the thought that the production of fly
ash-based polymer is a cleaner process with improved natural resource efficiency.
3. Properties
3.1 Compressive strength
The improvement of mechanical properties of fly ash-based geopolymer is major concerns
because its main uses are in construction materials as cement and concrete. The compressive strength
of fly ash-based geopolymer is dependent on alkali solutions, Si/Al ratios, calcium content, curing
conditions (temperature and time) and the various additives.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
11
The type and the concentration of the alkaline solution influence the release of Si4+ and Al3+ from
fly ash during geopolymerization. Alkaline solution of a high concentration is generally beneficial for
obtaining high compressive strength but there is an optimal range (de Vargas et al., 2011). Görhan and
Kürklü (2014) prepared fly ash-based geopolymer with different NaOH concentrations (3 mol/L, 6
mol/L and 9 mol/L). A highest compressive strength of 22 MPa was achieved when the fly ash-based
geopolymer paste was activated in 6 mol/L NaOH and cured at 85°C for 24 h.
Na2SiO3 solution is usually used with NaOH to increase compressive strength (Criado et al., 2005).
This is because of Na2SiO3 with high viscosity can help the formation of geopolymer gels and a
compact final fly ash-based geopolymer microstructure is achieved. Moreover, the activation procedure
also influences the compressive strength of fly ash-based geopolymer. For example, Rattanasak and
Chindaprasirt (2009) first added NaOH solution to fly ash to leach the Si4+ and Al3+ species for 10 min,
followed by using Na2SiO3 to help form a uniform geopolymer paste for another 1 min. Such separate
activation gave a higher strength for the fly ash-based geopolymer. When fly ash was separately mixed
and activated with NaOH (10 mol/L) and Na2SiO3 with the NaOH/Na2SiO3 molar ratio of 1.0 and cured
at 65°C for 48 h, the compressive strength of fly ash-based geopolymer was 60-70.0 MPa.
As discussed in previous section, the Si/Al ratios are determined by the source materials and alkali
solution (Na2SiO3 is used). High Si/Al ratios increase the amount of -Si-O-Si- bonds to get a higher
compressive strength of fully condensed structural matrix of geopolymer, since the -Si-O-Si- bonds are
stronger than -Si-O-Al- and -Al-O-Al- bonds. The addition of slag, RHBA, and red mud can alter the
Si/Al ratios (Table 1). For example, Yang et al. (2014a) prepared geopolymer fly ash and high
magnesium nickel slag (HMNS) activated by Na2SiO3 solution. It was discovered that the major phase
in fly ash/HMNS geopolymer was a type of sodium magnesium aluminosilicate gel. The addition of
HMNS increased the silica content. In addition, HMNS particles worked as micoaggregates and
decreased the total volume of pores in the geopolymer pastes. As a result, the geopolymer possessed a
high compressive strength of above 60 MPa when 20% HMNS was used for the preparation. Though
the higher content of slag increased the compressive strength of fly ash/HMNS-based geopolymer, it
caused rapid setting and crack due to autogenous shrinkage of slag (slag/binder>70%) (Jang et al.,
2014). Wang et al. (2015) prepared fly ash/slag-based geopolymer with different fly ash/slag ratios (0
wt.%, 20 wt.%, 40 wt.%, and 60 wt.%) and various NaOH solutions (0.5%, 1% and 1.5%), and then
cured for 1, 3, 7 and 28 days. The increasing portion of slag increased the compressive strength of
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
12
geopolymer and the optimal compressive strength was 93.06 MPa. Deb et al. (2014) activated Class F
fly ash/GBFS-based geopolymer (GBFS/Class F fly ash ratio=0%, 10% and 20%) in NaOH and
Na2SiO3 solution, respectively. High compressive strength increased with the increase of the
GBFS/Class F fly ash ratio. When the geopolymer concrete synthesized by 20% slag and 80% fly ash
with 40% NaOH and Na2SiO3 solution and cured at 20°C, it had the highest compressive strength of 51
MPa. Xu et al. (2014) used GBFS of grade 80, 100 and 120 and fly ash to synthesize geopolymer with
an activating solution prepared from concentrated Hanford secondary waste (HSW) stimulant (5 mol/L
NaOH mixed with solid binders). The highest compressive strength was 52.5 MPa when the fly
ash/GBFS mass ratio was 5/3.
The addition of RHBA enriched the silica content of the geopolymer matrix, increased the amount
of -Si-O-Si- bonds in the geopolymer gel (N-A-S-H gel) and the compressive strength (Sata et al.,
2007; Tangchirapat et al., 2008). Nazari et al. (2011) added RHBA into fly ash to synthesize
geopolymer paste and cured it in oven at 80°C for 28 days. They found the geopolymer had the
compressive strength of about 60 MPa. Songpiriyakij et al. (2010) prepared fly ash-based geopolymer
using the reactants of fly ash, RHBA and NaOH and curing at 27°C first for 24h and then curing at
60°C for 24h. It was found that the optimal SiO2/Al 2O3 ratio to obtain the highest compressive strength
(73 MPa) was 15.9. Red mud of highly alkalinity is the major residue of Bayer process of alumina
refining from bauxite ores. Zhang et al. (2014a) prepared geopolymer using fly ash and red mud at
23°C. They found compressive strengths ranging from 11.3 to 21.3 MPa and the highest compressive
strength was obtained when the Si/Al molar ratio was 2.
Calcium is proved to interfere with the gelation of silica and alumina in geopolymerization
process and alter the microstructures of fly ash-based geopolymer and thus alter the compressive
strength (Schmucker and Mackenzie, 2005). The coexistence of C-S-H gel and the N-A-S-H gel
usually improves the compressive strength of final products. One of reasons is that the amorphous
C-S-H gel decreases the porosity (Temuujin and van Riessen, 2009).
Curing time and temperature also affect the compressive strength of fly ash-based geopolymer.
Longer curing time, in the range of 6 hours to 28 days, produced fly ash-based geopolymer with a
higher compressive strength (Table 1). Curing at high temperatures increases the compressive strength
by removing the water from the fresh geopolymer, causing the collapse of the capillary pores with a
denser structure (Leung and Pheerapha, 1995). Fly ash-based geopolymer can be cured at room
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
13
temperature, but the compressive strength develops slowly and always needs prolonged curing time
(Somna et al., 2011). Nasvi et al. (2012; 2014) found that the crack closure and crack initiation
thresholds of fly ash-based geopolymer cured at elevated temperatures (60-80°C) was higher (30-60%
peak stress) compared to those (15-30% of peak stress) cured at ambient temperature (23°C and 40°C).
However, prolonged curing at higher temperatures breaks down the granular structure of geopolymer,
resulting in the dehydration and the excessive shrinkage, and finally decreasing the compressive
strength (Palomo et al., 1999b).
Steam curing is the conventional heating technique, relying on the conduction of heat from the
exterior to the interior of fly ash-based geopolymer paste by steam. The heating is non-uniform and
required a long heating period to attain the required temperature. Microwave heating is based on
internal energy dissipation associated with the excitation of molecular dipoles in electromagnetic fields,
and it delivers faster and more uniform heating (Kim et al., 2015). Chindaprasirt et al., (2013b)
prepared fly ash-based geopolymer pastes with 10 mol/L NaOH and Na2SiO3 solution and cured them
under the 90-W microwave radiation for 5 min followed by additional heating at 65°C for 6 h. The
compressive strength was comparable to that of the fly ash-based geopolymer cured at 65°C for 24 h.
The microwave radiation quickened the dissolution of fly ash in the alkaline solution and formed a
denser microstructure. Accordingly, the microwave radiation shortened the required curing time and
enhanced the geopolymerization.
To put together, increasing the Si/Al ratios usually enhance the compressive strength of fly
ash-based geopolymer. Though the increase of the Si/Al ratios can be realized by adding the external
slag, RHBA and red mud, the inherent reasons are complicated. Advances in the preparation indicated
that one of major reasons can be ascribed to the increased amount of -Si-O-Si- bonds rather than
-Si-O-Al- and -Al-O-Al- bonds. To this end, the use of Na2SiO3 or K2SiO3 with NaOH for the
activation of fly ash can increase the Si/Al ratios, thereby leading to a more compact structure with
higher compressive strength (Fig. 3.). In addition, the presence of calcium in fly ash or used as additive
is beneficial for forming the amorphous C-S-H gel and C-A-S-H gel and decreases the porosity and
obtain geopolymer with a higher compressive strength. Curing had a significant effect on the
compressive strength of fly ash-based geopolymer by changing the porosity and density of the product.
3.2 Flexural and splitting tensile strength
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
14
Fly ash-based geopolymer would suffer from brittle failure with low tensile strength and fracture
toughness. A typical method is to incorporate chitosan or fibers into the fly ash-based geopolymer
matrix because this hybridization can improve the bond strength and reinforcing bending behaviors in
strain hardening and multiple cracking procedure. In this way, the flexural and splitting tensile strength
can be enhanced. The fibers for reinforcing fly ash-based geopolymer composites include steel (ST)
fiber (Shaikh, 2013), polyvinyl alcohol (PVA) fiber (Nematollahi, 2015; Zhang et al., 2006; Zhang et
al., 2008b; Sun and Wu, 2008), sweet sorghum fiber (Chen et al., 2014), and cotton (Alomayri et al.,
2014a; 2014b).
In order to obtain higher flexural strength, Shaikh (2013) added 2 v/v% steel fiber, 2 v/v% PVA
fiber and a hybrid combination of 1 v/v% ST + 1 v/v% PVA fiber and investigated the deflection
hardening behavior of hybrid fiber reinforced fly ash-based geopolymer. They found a higher bond
strength and flexural strength between the PVA fiber and geopolymer matrix than with cement matrix.
The alkalinity of geopolymer matrix did not affect the degradation of PVA and steel fiber as seen in
SEM (Fig.4.). Alomayri et al. (2014a) added cotton fabric layers in fly ash-based geopolymer structure
to improve flexural strength. The flexural strength of the fly ash-based geopolymer increased from 8.2
MPa to 31.7 MPa when the cotton fiber content was increased from 0 to 8.3 wt%. Moreover, the
orientation of cotton fabric layers had effects on the flexural strength of fly ash-based geopolymer. The
higher flexural strength of the fly ash-based geopolymer reinforced with horizontally laid cotton fabric
could be attributed to the better uniformity in load distribution among the consecutive layers of cotton
fabric, while the geopolymer with vertical fabric orientation suffered from detachments and
delamination between the cotton fabric and geopolymer matrix, and had a lower flexural strength
(Alomayri et al., 2014b).
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
15
Fig. 4. SEM image of steel fiber in fly ash-based geopolymer matrix (left). SEM image of PVA fiber
in fly ash-based geopolymer matrix (right) (Reprinted from Shaikh (2013), Copyright (2013), with
permission from Elsevier).
Splitting tensile strength can be increased by using N-carboxymethyl chitosan, and the fibers, such
as PVA fiber and sweet sorghum fiber as additives in fly ash-based geopolymer (Table 1). Nematollahi
et al., (2015) prepared geopolymer with short PVA fibers (2% v/v), Class F fly ash activated in 8.0
mol/L NaOH (28.6% w/w) and Na2SiO3 (71.4% w/w) solution. The bond strength of the geopolymer
increased more than the cracking strength, resulting in a high fiber-bridging strength. The splitting
tensile strength of PVA reinforced Class F fly ash-based geopolymer was 4.7 MPa.
Chitosan with stable crystalline structure from strong hydrogen bonds suffers poor solubility at
higher pH required for geopolymer. N-carboxymethyl chitosan, a chitosan derivative, can avoid this
problem and realize the better coordination with geopolymer gel (Mourya et al., 2010; Pillai et al.,
2009). Li et al., (2013b) mixed NaOH solution (10 mol/L), N-carboxymethyl chitosan uniform solution
with fly ash under stirring under ambient conditions for 20 min. Then, the specimens were aged at
room temperature for 24 h and placed in an oven for curing at 60°C for 6 days. N-carboxymethyl
chitosan biopolymer coated on fly ash particles and N-carboxymethyl chitosan were well incorporated
into geopolymer matrix. In particular, there were additional hydrogen bonds formed between
N-carboxymethyl chitosan macromolecules and fly ash-based geopolymer, in addition to the hydrogen
bonds within the N-carboxymethyl chitosan macromolecules (Fig. 5). All these interactions led to a
more condensed network structure in geopolymer. Thus the fly ash-based geopolymer reinforced by
N-carboxymethyl chitosan exhibit enhanced the mechanical behavior of the fly ash-based geopolymer.
The N-carboxymethyl chitosan reinforced fly ash-based geopolymer had a substantial increase of the
tensile strength from 7 MPa to 8 MPa when the N-carboxymethyl chitosan content increased to 0.1
wt.%.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
16
Fig. 5. Fly ash-based geopolymer with N-carboxymethyl chitosan; the dashed lines: the hydrogen
bonds formed between N-carboxymethyl chitosan macromolecules and fly ash-based geopolymer as
well as within the N-carboxymethyl chitosan macromolecules (Reprinted and adapted from Li et al.
(2013b), with permission of Springer).
Chen et al., (2014) used alkali-pretreated sweet sorghum fiber with fly ash to prepare
geopolymer. The sweet sorghum fiber was obtained from the bagasse waste after juice being extracted
from sweet sorghum stalks for ethanol production. When 2 % sweet sorghum fibers were used, an
increase about 36 % of the splitting tensile strength of the geopolymer was obtained. But further
increase of the fiber content decreased tensile strength. The flexural strength of the fiber-reinforced
geopolymer showed a similar trend. The addition of 2 % fiber effectively carried higher tensile load
and thus delayed the growth of microcracks and increased the flexural strength. However, further
increase of the fiber content induced fiber agglomeration, resulting in an increase of air bubbles
entrapped in the composite and nonuniform fiber dispersion. As consequence, flexural strength
decreased. The addition of cotton to fly ash-based geopolymer showed the similar trend in flexural
strength.
According the studies mentioned above, the increase of splitting tensile strength and flexural
strength in chitosan-reinforced and fiber-reinforced fly ash-based geopolymer was primarily because
the micro- and macro-fibers can increase the hydrogen bonds, bridge the micro cracks, transfer the load,
and delay the development of micro cracks (Dias and Thaumaturgo, 2005).
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
17
3.3 Durability
The durability of fly ash-based geopolymer and geopolymer concrete includes resistance to
chloride, sulfate, acid, freeze-thaw cycles, heat, fire and efflorescence. Durability is closely related to
the microstructure and the migration behavior of ions from fly ash-based geopolymer. These in turn can
be adjusted by the alkali solution, curing and addition of calcium and silica fume composite during the
preparation of fly ash-based geopolymer.
3.3.1 Chloride resistance
Resistance to chloride is one of the main areas in durability of cement and concrete. Chloride
penetration promotes the corrosion of the embedded steel bars when steel bars are used as
reinforcements for geopolymer concrete. Chloride penetrates into fly ash-based geopolymer through
capillary absorption, hydrostatic pressure and diffusion of ions.
The relatively high concentration of NaOH enabled the leaching of more Si and Al from fly ash
and produced a better degree of polycondensation and resulted in a decrease the porosity of fly
ash-based geopolymer. The porosity of the material affects the chloride penetration. For example,
Chindaprasirt and Chalee (2014) prepared fly ash-based geopolymer using a Na2SiO3/NaOH mixture
solution as the activator. The concentrations of NaOH were 8, 10, 12, 14, 16 and 18 mol/L with a
constant SiO2/Al 2O3 molar ratio. The chloride penetration decreased with the increase of NaOH
concentration used in geopolymerization process owing to the refinement of the pore structures as a
result of polycondensation reaction.
Ismail et al. (2013) examined the permeability of chlorides in Class F fly ash/slag-based
geopolymer, slag-based geopolymer, and OPC by the chloride accelerated method (NordTest NT Build
492) and the ponding method (ASTM C1543). AgNO3 was used to reveal chloride penetration depths.
The result showed that a little formation of silver chloride for the slag-based geopolymer (Fig. 6A), and
fly ash/slag-based geopolymer (Fig. 6B, Fig. 6C), while OPC-based concrete (Fig. 6D) had the deepest
chloride penetration depth. They found the slag promote the formation of denser C–A–S–H gel
contributing to a higher mechanical strength, and durability under chloride exposure and fly ash
promote the formation of more porous N–A–S–H gels, reducing the resistance to chloride transport.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
18
Although a higher porosity was observed in the geopolymer compared to the OPC specimens,
geopolymer still showed a higher chloride resistance.
Fig. 6. Boundary of chloride penetration in 28-day cured concretes at the end of the Nord Test
procedure, as a function of slag/fly ash ratio: (A) 100 wt.% slag, (B) 75 wt.% slag/25 wt.% fly ash, (C)
50 wt.% slag/50 wt.% fly ash, (D) OPC (Reprinted from Ismail et al. (2013), Copyright (2013), with
permission from Elsevier).
Yang et al., (2014b) prepared fly ash/slag-based geopolymer (Slag/Fly ash ratio= 0, 0.25 and 0.50)
and exposed the materials to a 3% NaCl solution for 72 h. The C-A-S-H gel formed in the fly
ash/slag-based geopolymer resulted in lower chloride diffusion compared with the N–A–S–H gel. In
addition, the incorporation of slag in fly ash-based geopolymers led to the refinement of the pore
structure.
3.3.2 Sulfate resistance
The migration of Na+ from fly ash-based geopolymer into the sulfate solution results in vertical
cracks and causes the deterioration of strength. In addition, the sulfate solution usually caused the
breaking of -Si-O-Si- bonds in geopolymer gel and the leaching of silicon (Baščarević et al., 2015).
Bakharev (2005a) prepared fly ash-based geopolymer using NaOH, KOH, or Na2SiO3 as activator and
investigated the durability after exposed them to sulfate environments (5% MgSO4 solution, 5%
Na2SO4 solution and a solution of 5% MgSO4 +5% Na2SO4) for 5 months. After immersion, the fly
ash-based geopolymer samples changed little. The geopolymer activated by NaOH had the best sulfate
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
19
resistance owing to a more stable cross-linked structure.
Sukmak et al., (2015) used a mixture of silty clay and fly ash as the source materials to prepare
geopolymer and examined the resistance of the geopolymer in 5 wt% Na2SO4 and 5 wt% MgSO4
solutions. The decrease in the compressive strength of the clay/fly ash-based geopolymer after 240
days of exposure was 10.8% in Na2SO4 solution and 21.6% in MgSO4 solution. Ettringite, gypsum and
brucite, were detected after the exposure to sulfate environment. The C-S-H phase disappeared due to
its reaction with sulfates and forming ettringite phase.
3.3.3 Acid resistance
The lifetime of cement and concrete can be severely shortened in the acidic environment. For fly
ash-based geopolymer, the acid attack is associated with the depolymerization of aluminosilicate
network structure and the liberation of silicic acid (Si(OH)4). When immersed in a strong acid solution,
Na+ and K+ from fly ash-based geopolymer could be substituted by H+ or H3O+, breaking -Si-O-Al-
bond and -Si-O-Si- bond, and releasing silicic acid (Breck, 1974).
Different alkali solutions (NaOH, KOH and Na2SiO3) have been used by Bakharev (2005b) to
prepare fly ash-based geopolymer followed by immersing the geopolymers in 5% CH3COOH and
H2SO4 solutions for 5 months. The fly ash-based geopolymer activated by 8% NaOH had more stable
structure and showed high resistance to both acid solutions, while the fly ash-based geopolymer
activated by KOH showed an increase in the average pore diameter and the number of active sites in
the geopolymer gels on the surface, leading to a lower durability.
The effect of calcium and silica fume on the acid resistance of fly ash-based geopolymer is also
noteworthy. Lloyd et al. (2012) investigated the corrosion rates of Class C fly ash-based and slag-based
geopolymer in HNO3 and H2SO4 acids (pH=1.0-3.0). It was found that the calcium content introduced
from the Class C fly ash or slag reduced the mass transport rates by forming fine and tortuous pore
networks in geopolymer. In addition, as the increase of alkali content (Na2O), the nature of the
corroded layer became harder, more brittle and more prone to the development of cracks (Fig. 7.). The
high content of alkali is beneficial for releasing more calcium and aluminium and for forming
geopolymer gels while when removed upon exposure to acid, the geopolymer structure was more
vulnerable under acidic conditions. Chindaprasirt et al. (2014) added silica fume (1.5%, 3.75% and
5.0%) to fly ash to prepare geopolymer composite mortars. The acid resistance of composite mortars
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
20
was tested in 3 vol% H2SO4 acid. The optimum silica fume addition of 3.75% increased the strength of
fly ash-based geopolymer and showed the best acid durability owing to the increase of C-S-H gels and
a more dense structure.
Fig.7. The appearance of the corroded layers on the fly ash-based geopolymer samples, containing 7%
Na2O (left) and 15% Na2O (right) after 28 days exposure to pH 1.0 sulphuric acid (Reprint from Lloyd
et al. (2012), with permission from Springer).
Curing at a high temperature is beneficial to the resistance of geopolymer to acid. Nguyen et al.
(2013) cured the fly ash-based geopolymer at 80°C for 10 h, and then immersed the geopolymer in HCl
solution (1 mol/L, 2 mol/L and 4 mol/L). It was found that the fly ash-based geopolymer still
maintained a compressive strength of about 20 MPa which was much higher than OPC in HCl solution
(1 mol/L, 2 mol/L and 4 mol/L). In addition, Chindaprasirt et al. (2013a) cured fly ash-based
geopolymer with 90 W microwaves for 5 min. They found the microwave radiation accelerated the
geopolymerization and gave enhanced densification comparable to the conventional curing. The
microwave cured fly ash-based geopolymer was immersed in 3 vol% of H2SO4 and found that it only
had a small loss of strength under the acid attack.
3.3.4 Thermal resistance
When fly ash-based geopolymer is exposed to elevated temperatures, shrinkage of geopolymer
occurs in proportion to the amount of water being vaporized from the structure (Rickard et al., 2011).
Some of the fly ash-based geopolymers exhibit a strength increase after exposure to high temperature,
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
21
and have been used as concrete, thermal barriers, refractories and fire resistant structures. Heat
travelled faster in geopolymer concrete than in OPC concrete when exposed to fire, resulted in less
temperature gradient inside geopolymer concrete (Sarker et al., 2014). OPC concrete showed an
average residual strength of 90%, 52% and 11-16% respectively after exposed to fire at 400°C, 650°C
and 800-1,000°C, whereas the average residual strengths of geopolymer concretes were 93%, 82%, and
21-29% after the same treatments. Moreover, the OPC concrete suffered severe spalling and extensive
surface cracking after exposure at 800-1,000°C, while there was no spalling and only minor surface
crackings in the geopolymer concrete. Guerrieri and Sanjayan (2010) exposed fly ash/slag-based
geopolymer (fly ash/slag ratio=100, 65/35, 50/50, 35/65) to 800°C. They found the geopolymer
specimens with very low initial strengths (< 7.6MPa) experienced an increase in residual strength up to
90% gain after exposure to 800°C while specimens with initial strengths of 28 MPa and specimens with
initial strengths of 83 MPa had residual strength losses of approximately 70% and 90% after exposure
to 800°C, respectively. The different residual strengths of fly ash/slag-based geopolymer after exposure
to 800°C were caused by the further hydration and sintering of the unreacted fly ash or slag.
Geopolymer with higher initial strengths have a smaller capacity to allow for thermal incompatibilities
between the inner and outer parts of the specimen due to uneven temperatures arising during heating.
Rickard et al. (2010) investigated the thermal characteristics of Class F fly ash-based geopolymer at the
temperature>500°C. The maximum shrinkage was approximately 3% when the geopolymer was heated
to 900°C. The iron oxides (15 wt.%) in fly ash directly affected the thermal properties of the
geopolymer by influencing the thermal expansion, altering the phase composition and changing the
morphology after heating.
The pore structure and density of fly ash-based geopolymer facilitates the escape of moisture and
help avoid damaging during heating. Kong et al., (2007) prepared fly ash-based geopolymer and
exposed it to 800°C. They found a small amount of moisture escaped from fly ash matrix and the pore
spaces provided escape routes for moisture in the matrix thereby decreasing the likelihood of the
damage to the matrix at elevated temperatures. Bakharev (2006) compared the effects of heating at
800-1200°C on the geopolymer made form Class F fly ash activated by NaOH and KOH, respectively.
The geopolymer activated by NaOH had a rapid strength deterioration and a high shrinkage at 800°C
due to a dramatic increase of average pore size, while the other activated by KOH showed a significant
increase of compressive strength upon heating and the strength deterioration only started at 1000°C.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
22
The addition of foaming agent of a low concentration led to a low density with cellular structure.
Rickard and van Riessen (2014) prepared foamed Class F fly ash-based geopolymer with a Si/Al ratio
of 2.5 (ρ 0.9 g/cm3, k 0.3 W/m·K). Under a simulated fire for 60 to 90 min, the foamed
geopolymer lost its strength significantly. Foaming significantly reduced the strength of Class F fly
ash-based geopolymer, while the thermal insulating property improved as their thermal conductivities
were reduced by approximately half.
Using Ca(OH)2 as additive to synthesize fly ash-based geopolymer formed the C–S–H gel and
helped the different mineral formation and transformation processes at elevated temperatures.
Dombrowski et al. (2007) prepared fly ash-based geopolymer and investigated the influence of the
calcium content on thermal resistance. When the geopolymer exposed to temperatures higher than
600°C, sodalite and amorphous aluminosilicates were formed and then they were transformed into
nepheline, resulted in a denser structure. As the temperature was further increased, the nepheline was
converted into albite. The fly ash-based geopolymer with 8% Ca(OH)2 addition for the preparation had
the highest strength and the lowest shrinkage with the highest amount of nepheline at 800°C and of
feldspar at 1,000°C.
Geopolymer exposed to fire has the tendency to shrinkage and cracking as well. According to the
International Standards Organization standard (ISO 834), Sarker et al. (2014) test the fire resistance of
the fly ash-based geopolymer and OPC by exposing the samples to fire heating at 400°C, 650°C, 800°C
and 1000°C. When exposed to fire at 1,000°C, fly ash-based geopolymer had only minor surface
cracking and the average mass loss of only 4.8%, while OPC had the average mass loss of 90%.
3.3.5 Freeze-thaw resistance
Freeze-thaw attack usually causes cement and concrete expansion, internal cracking, and scaling
mass loss (Hobbs, 2001). It is a major attack to cement and concrete second to chloride attack. Fly ash
based-geopolymer has been reported to show no sign of damage even after 150 freezing cycles.
Temuujin et al. (2014) prepared geopolymer from Class F fly ash activated by a NaOH/Na2SiO3
solution and cured it at 70°C for 22 h. The freeze-thaw cycles of geopolymer were higher than 40.
The addition of Na2SiO3 solution did not improve the freeze-thaw durability of fly ash-based
geopolymer. The presence of crystalline, anhydrite and amorphous calcium compounds (such as lime)
in fly ash negatively influenced the freeze-thaw resistance. Na2SiO3 reacted with calcium compounds
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
23
(CaO, CaSO4 and amorphous calcium aluminosilicate) in the fly ash source and formed C–A–S–H gel
or Ca(OH)2. The formation of Ca(OH)2 weakened internal structure and increased water permeability
and had a negative effect on the freeze-thaw resistance.
Air entrainment has been proved as an effective method to increase freeze-thaw resistance of OPC
(Mindess and Young, 1981). Sun and Wu (2013) compared fly ash-based geopolymer and OPC with or
without air entrainment for 300 freeze–thaw cycles according to ASTM C666. OPC without air
entrainment deteriorated most seriously, showing a strength loss of about 20% after 300 cycles, while
OPC with air entrainment lost only 5%. Fly ash-based geopolymer without air entrainment had a final
loss of 8.4% after 300 cycle. With the air entainment, fly ash-based geopolymer showed a strength loss
of 6.8%. Clearly, the air entrainment had no much positive influence on fly ash-based geopolymer.
Brooks et al. (2010) studies the effects of air entrainment on the scaling rate of fly ash-based
geopolymer. Air-entrained fly ash-based geopolymer showed slight scaling after 40 freeze-thaw cycles
while non-air entrained fly ash-based geopolymer showed no scaling. Air entrainment significantly
reduced the compressive strength of fly ash-based geopolymer 10-30% than the non-air entrained fly
ash-based geopolymer and the uniform and stable pore structure believed to increase freeze-thaw
durability was not formed in non-air entrained fly ash-based geopolymer.
3.3.6 Efflorescence resistance
Geopolymer, especially with a high alkali content and a low calcium content, tends to have a
porous and open microstructure. The aqueous solution remains entrapped in the pores or bonded to the
network when the three-dimensional geopolymer structure has finally formed (Davidovits, 2008).
Within the pore network, the excess sodium oxide is mobile, and is prone to form white crystal (i.e.
efflorescence) when in contact with atmospheric CO2 and results in the degradation of geopolymer
(Najafi and Allahverdi, 2009; Pacheco-Torgal and Jalali, 2010).
The efflorescence behavior of fly ash-based geopolymers is strongly dependent on the alkali
activator solution type, curing temperature and calcium content. Using KOH instead of NaOH as
activator reduces the efflorescence of geopolymer (Duxson et al., 2006). The high alkali concentration
in the pore solution and the weak binding of Na+ in the geopolymer structure are the reasons for more
mobile Na+ in pore solution and cause the severe efflorescence of geopolymer (Bortnovsky et al., 2008).
K+ is more strongly bound to the aluminosilicate gel framework, and also potassium carbonate crystals
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
24
are usually less visually evident than their sodium counterparts (Szklorzová and Bílek, 2008; Škvára et
al., 2008). Zhang et al., (2014b) activated fly ash by NaOH to synthesize geopolymer and cured (23°C,
80°C). They found geopolymer at high temperature exhibiting much lower efflorescence than those
synthesized at low temperature. The curing was beneficial for reorganization and crystallization of
N-A-S-H gels and decreasing the efflorescence rate.
The presence of calcium helps formed C–S–H in fly ash-based geopolymer and a smaller pore size
with low-permeability, which prevents alkali diffusion (Lloyd et al., 2010). Conversely, for foamed fly
ash-based geopolymer, the foaming caused large pore size and high porosity of geopolymer and it led
to fast alkali leaching and caused faste efflorescence consequently (Zhang et al., 2014b).
4. Fly ash-based geopolymer for adsorption and immobilization of toxic metals
Geopolymerization offers an alternative technique to immobilize soluble heavy metals from fly
ash, slag or other industrial and residential wastes (Malviya and Chaudhary, 2006; Ojovan and Lee,
2005; Li and Wang, 2005). The hazardous elements, such as Ba, Cd, Co, Cr, Cu, Nb, Ni, Pb, Sn, and U
can be tightly fixed in the three-dimension structure of fly ash-based geopolymer matrix. The main
mechanisms of metal immobilization in fly ash-based geopolymer are physical encapsulation and
chemical stabilization. The high pH values enhance the oxyanionic mobility, such as As, B, Mo, Se, V
and W (Izquierdo et al., 2009). Temuujin et al. (2014) prepare geopolymer from high-calcium
Mongolian fly ash (CaO =14–30 wt.%) with a high radioactivity (314–343 Bq/kg) and used NaOH
solution or mixtures of NaOH and Na2SiO3 as activator and cured it at 70°C for 22 h. The radioactivity
of the radioactive high-calcium Mongolian fly ash-based geopolymer product was then became 130–
152 Bq/kg, within the standard safe limits for construction of dwellings.
Fly ash-based geopolymer showed higher immobilization of metal ions than OPC and fly ash itself.
Li et al., (2013a) compared the immobilization of 133Cs+ in fly ash-based geopolymer and OPC.
Leaching tests was carried out in deionized water, sulfuric acid and magnesium sulfate solutions,
respectively. It was revealed that neither the microstructure nor the geopolymeric phases of fly
ash-based geopolymer were significantly affected by the incorporation of 133Cs+. The cumulative
fraction leaching concentration (CFLC) of fly ash-based geopolymer in deionized water was only 5.4 %
of that of OPC for 25°C, and 6.1 % for 70°C. The leaching of 133Cs+ from the geopolymer in 5% (w/w)
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
25
magnesium sulfate solution was only 9.1 % that from OPC. The difference of leaching of 133Cs+
between the geopolymer and OPC in sulfate acid solution was small. Al-Zboon et al., (2011) used fly
ash-based geopolymer as an adsorbent for lead Pb(II) removal from wastewater. They found the lead
removal efficiency of fly ash-based geopolymer was 90.6%, which was much higher than that of raw
fly ash (39.87%) (pH = 5; C0 = 100 ppm; contact time = 120 min). The removal efficiency was 95%
when the dose of fly ash-based geopolymer was 0.07 g at 40°C, pH=5, and 120 min contact time in
1,000 ppm standard lead (Pb) solution.
The fly ash-based geopolymer showed different metal immobilization behaviors in acid and
sulfate solutions. Zhang et al., (2008a) prepared geopolymer with fly ash, sand and some heavy metal
additives, such as Cr(VI), Cd(II) and Pb(II), to investigate the immobilization effect of heavy metal
ions and the leaching behavior in H2SO4 and Na2SO4 solutions. The low level of heavy metal salts had
little effect on the compressive strength of the geopolymer. The immobilization of these species was
based on the chemical binding into the geopolymer gel or into aluminosilicate phases in geopolymer.
They found Pb was immobilized effectively by a chemical binding mechanism in geopolymer, Cr(VI)
was ineffectively immobilized, and Cd immobilization was depended on the solubility of a hydroxide
phase with effectively at high pH but poor at low pH.
5. Fly ash-based geopolymer for concrete
The growing environmental awareness and the demand for high efficiency of natural resource
encourage the construction industry to look for alternative materials (McKelvey et al., 2002; Schneider
et al., 2011). Fly ash has already been used as supplementary cementitious material in concrete industry
for over 50 years in the world (Uysal and Akyuncu, 2012). In the hydration of traditional cement, fly
ash with a high content of Al2O3 and SiO2 can be activated by Ca(OH)2 and thus produce more C-S-H
gel, C-A-H gel and C-A-S-H gel to fill the capillary of concrete effectively, thereby increasing concrete
strength (Sahmaran and Li, 2009). Fly ash can reduce the hydration heat and thermal cracking of
concrete at early stage, and improve the mechanical and durability properties.
Fly ash-based geopolymer concrete completely moves away from OPC and the high CO2 emission
associated with OPC production (Cakir and Akoz, 2008; Aldea et al., 2000; Habert et al., 2011). Fly
ash-based geopolymer itself is a good binder that can be used as cement to mix with aggregates to
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
26
produce the geopolymer concrete. Fly ash-based geopolymer cement has shown a better performance
than OPC in some areas aspects or conditions. For example, fly ash-based geopolymer concrete has a
denser microstructure with lower chloride diffusion and lower porosity compared with OPC concrete.
Reddy et al. (2013) used Class F fly ash as source material and NaOH and Na2SiO3 solution as
activator to synthesize geopolymer cement. They found that the geopolymer concrete had excellent
resistance to chloride attack and less corrosion cracking when exposed to simulated seawater and
induced current.
Alkali silica reaction (ASR) is a common chemical reaction between the OH- in the pores within
the concrete matrix and the reactive aggregate compounds in concrete (Swamy and Al-Asali, 1988;
Diamond, 1975). ASR causes the strength loss, cracking, and expansion of the concrete structure. Fly
ash-based geopolymer concrete is significantly less vulnerable to ASR than OPC concrete.
Kupwade-Patil and Allouche (2013) prepared steel reinforced fly ash-based geopolymer concrete with
quartz, sandstone and siliceous limestone as aggregates, and compared the chloride diffusion in a cyclic
wet-dry chloride environment over a period of 12 months with OPC concrete. It was found that fly
ash-based geopolymer concrete specimens did not exceed the ASTM threshold for expansion while
OPC concrete exceeded the permissible threshold. In addition, the leaching and visual cracks were
observed in the OPC concrete but not in the fly ash-based geopolymer concrete.
In concrete, aggregate takes up as high as 85% of the material. Interactions among aluminosilicate
framework, alkali cations, additives and aggregate in fly ash-based geopolymer concrete are important
factors that influence the overall mechanical performance. The strong interfacial interactions between
the aggregate and the fly ash-based geopolymer matrix in a large zone contributes to the high splitting
tensile strengths between geopolymer and steel reinforcements (Topark-Ngarm et al., 2015).
The size of the aggregates affects the fly ash-based geopolymer concrete performance. Kong and
Sanjayan (2010) studied the effect of aggregate size on the compressive strength at high temperatures
of the fly ash-based geopolymer concrete containing crushed old basalt aggregates, river sand and slag
aggregates. It was found the thermal incompatibility between the geopolymer matrix and the aggregates
caused the strength loss of geopolymer concrete specimens at elevated temperatures. Large aggregates (>
10 mm) resulted in good strength performances at both ambient and elevated temperatures while
smaller sized aggregates (< 10 mm) promoted spalling and extensive cracking at elevated temperature.
Recycled coarse aggregate has been used with fly ash geopolymer to synthesize concrete with
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
27
acceptable properties. Sata et al., (2013) used crushed structural concrete beams and crushed clay
bricks as recycled coarse aggregates for making fly ash-based geopolymer concrete. The geopolymer
concrete with recycled aggregate showed lower compressive strengths (2.9–10.3 MPa) than those
containing natural aggregate, however, it was within the typical strength distribution reported
(American Concrete Institute (ACI) committee 522, 2010). In addition, the total void ratio of the
geopolymer concrete with recycled aggregate (21.7-26.9%) was similar to those with natural aggregate
(24.2-27.4%), and the water permeability was 0.71-1.47 cm/s versus 1.18-1.71 cm/s. Nuaklong et al.,
(2016) used recycled aggregates from old concrete with compressive strength of 30-40 MPa and high
calcium fly ash to make fly ash-based geopolymer. They found fly ash-based geopolymer with recycled
aggregate showed compressive strengths of 30.6-38.4 MPa, which were slightly lower than those of fly
ash-based geopolymer concretes with crushed limestone.
Different superplasticizers (naphthalene (N) and polycarboxylates (PC)) as the water reduction
admixture have been used to improve the workability of the geopolymer concrete by Nematollahi and
Sanjayan (2014). PC superplasticizer with a dosage of 3.3 wt.% caused significant reduction (54%) in
strength with reference to concrete without superplasticizer. By contrast, N superplasticizer with a
dosage of 1.19% caused a 22% reduction in strength. The use of superplasticizers was not beneficial to
geopolymer concrete used at elevated temperatures.
Injecting and storing CO2 into underground has been proposed as one of the long-term strategies
for handling greenhouse gases (Laudet et al., 2011; Bachu and Bennion, 2009). OPC-based sealant has
been used in injection wells and it has been found experiencing cement degradation under CO2-rich
down-hole conditions. The low permeability of fly ash-based geopolymer can effectively prevent CO2
leakage. Nasvi et al. (2013) found that the apparent CO2 permeability of fly ash-based geopolymer
cement is in the range of 2×10-21 - 6×10-20 m2, which is lower than the typical oil well cements (10-20 -
10-11 m2). Moreover, Nasvi et al. (2014) prepared fly ash-based geopolymer cement from fly ash
activated by a mixed Na2SiO3/NaOH solution and tested the CO2 permeability under three conditions:
(1) temperatures of 23–70°C; (2) CO2 injection pressures of 6–17 MPa; and (3) confining pressures of
12–20 MPa. The results showed that the apparent CO2 permeability of geopolymer increased with
curing temperature and the increasing rates were as high as 200–1,000 %. The maximum permeability
(0.04 lD) value obtained was approximately 5,000 times lower than the permeability value (200 lD)
recommended by the American petroleum industry (API) for a typical well sealant. The findings
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
28
indicated that there is a great potential in using fly ash-based geopolymer cement for carbon storage.
6. Conclusions and future work
Geopolymer technology offers a facile approach for fly ash utilization. In principle, the
geopolymerization includes the dissolution of alumina, silica, aluminosilicate in the fly ash feedstock
by alkali, the recombination of Al3+ and Si4+ species and the generation of three-dimensional
amorphous aluminosilicate polymers. The preparation and formation, and properties of the fly
ash-based geopolymer products depend heavily upon the chemical and physical characteristics of fly
ash, alkali activators, curing conditions and the addition of slag, fiber and red mud.
NaOH and Na2SiO3 are used as alkali activators; CaCl2 is used as chemical additives to form
C-A-S-H gel, C-A-H gel and C-S-H gel and change the setting time; and slag, fiber, RHBA and red
mud are used as additives to change the Si/Al ratios and introduce the hydrogen bonds between
geopolymer gel (N-A-S-H gel) and the additive molecules.
For the practical applications of fly ash-based geopolymer, mechanical properties (such as
compressive strength, splitting tensile strength and flexural strength) and durability (chloride, sulfate,
acid, thermal, freeze-thaw cycles and efflorescence resistances) should be comprehensively considered.
The Si/Al ratios of reactants, alkali solutions, curing conditions, and the addition of slag, fibers, RHBA,
red mud and calcium can be fine tuned to improve those properties. The changes of Si/Al ratios, alkali
solutions, and adding slag, RHBA, red mud and calcium can lead to the different gels, including
N-A-S-H gel, C-A-S-H gel, C-A-H gel and C-S-H gel. The gels influence the final structure of
geopolymer and control the ionic transport. Alkali solutions influence the hydrolyzation of fly ash and
the porosity of geopolymer structure. The porosity influences the migration of alkali from fly ash-based
geopolymer into the ion solutions, the moisture and then has an effect on the mechanical strength and
durability. Fly ash-based geopolymer with compact and denser structure shows high mechanical
strength and good resistance to chloride, sulfate and acid solutions and good efflorescence.
Fly ash-based geopolymer can be used as cement to mix with aggregates to form concrete. In this
context, considering the low cost, low CO2 emission and low energy usage in the production of fly
ash-based geopolymer, fly ash-based geopolymer cement and concrete are regarded as possible
alternative green materials to OPC. Fly ash-based geopolymer has also been used to adsorb and
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
29
immobilize toxic metals and it shows better adsorption and immobilization performance than those of
OPC. Besides, fly ash-based geopolymer cement has been used as a well sealant to store CO2 in the
underground. However, the CO2 permeability value of fly ash-based geopolymer is still lower than the
permeability value for a typical well sealant recommended by the API.
Though last decades or so have witness remarkable advance in the science and technology of fly
ash-based geopolymer as discussed above, there exists several issues and some issues are proposed
below for future work.
(1) Inherently, to control the production and to improve the performances of fly ash-based
geopolymer, the reaction mechanisms in each step should be uncovered in details. To this end, involved
are many aspects such as thermodynamics, kinetics, identifications of intermediates and insights into
their structures, and the degrees to which the -Si-O-Al- are oligomerized and polymerized. All these
will become more sophisticated once the additional elements or additives are included. But further
studies must be made in order to ensure that the correlation of production-structure-performances is
clear-out.
(2) Most of fly ash-based geopolymer concretes are brittle and sensitive to cracking. Such
behavior not only imposes constraints in applications, but also affects the long-term durability of
geopolymer concretes (Zhao et al., 2007; Zhang et al., 2010b; Pernica et al., 2010). Therefore,
innovation in the preparation to create improved fly ash-based geopolymer composites is still needed.
(3) At present, in most cases, fly ash-based geopolymer are merely produced at laboratory scale
with empirical formulations. It could be exciting to see a report by Wagners (Wagners Earth Friendly
Concrete product) that the production of fly ash-based geopolymer concrete is being realized on a
large-scale. To put producing and using fly ash-based geopolymer on a large-scale are encouraging and
need further input and endeavor,
(4) As for the uses of fly ash-based geopolymer for toxic metals adsorption and immobilization
and sealing CO2, the performances are still unsatisfactory. Changing of the recipes for preparation is
worth for further investigation.
(5) Instead of using fly ash-based geopolymer as alternative cement, it is also possible to endow
fly ash-based geopolymer with more functionalities or unique properties. Consequently, new
applications of fly ash-based geopolymer are worth exploring and can be found. For instance, fly
ash-based geopolymer with biomass can be developed as a class of novel lightweight fireproof
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
30
materials.
Abbreviations
ACI: American Concrete Institute
API: American Petroleum Industry
ASR: Alkali silica reaction
ASTM: American Society for Testing and Materials
BFS: Blast furnace slag
C-A-H gel: Calcium aluminate hydrate gel
C-A-S-H gel: Calcium aluminum silicate gel
CCS: Carbon capture and storage
C-S-H gel: Calcium silicate hydrate gel
CFA: Class C fly ash
CFLC: Cumulative fraction leaching concentration
FFA: Class F fly ash
GGBF: Ground granulated blast furnace slag
HHW: Harford secondary waste
HMNS: High magnesium nickel slag
ISO: International Standards Organization
N-A-S-H gel: Sodium aluminosilicate gel
OPC: ordinary Portland cement
PC: Polycarboxylates
PVA: Polyvinyl alcohol
RHBA: Rice husk-bark ash
Acknowledgement
The authors wish to acknowledge the financial support from the National Natural Scientific Foundation of China (21373185; 21506188),
the Distinguished Young Scholar Grants from the Natural Scientific Foundation of Zhejiang Province (ZJNSF, R4100436), ZJNSF
(LQ12B03004), Zhejiang “151 Talents Project’’, the projects (2010C14013 and 2009R50020-12) from Science and Technology
Department of Zhejiang Provincial Government and the financial support by the open fund from Key Laboratory of Clay Minerals of
Ministry of Land and Resources of The People's Republic of China(2014-K02), and Engineering Research Center of Non-metallic
Minerals of Zhejiang Province (ZD2015k07), Zhejiang Institute of Geology and Mineral Resource, China, and the State Key Laboratory
Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology (GCTKF2014006). The authors also feel
grateful to four anonymous reviewers for their comments and suggestions, which are much helpful for us to improve the manuscript.
References
ACI committee 522, 2010.Pervious concrete, Report no. 522R-10, American Concrete Institute, Detroit, USA, pp.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
31
38
Ahmaruzzaman, M., 2010. A review on the utilizat ion of fly ash. Prog. Energ. Combus. 36 327–363
Aldea, C.M., Young, F., Wang, K., Shah, S.P. 2000. Effects of curing conditions on properties of concrete using
slag replacement. Cement Concrete Res. 30(3):465–472.
Alomayri, T., Shaikh, F.U.A., Low, I.M., 2014a. Synthesis and mechanical properties of cotton fabric reinforced
geopolymer composites. Composites B 60 36-42
Alomayri, T., Shaikh, F.U.A., Low, I.M., 2014b. Effect of fabric orientation on mechanical properties of cotton
fabric reinforced geopolymer composites. Mater. Des. 57 360-365
Al-Zboon, K., Al-Harahsheh M.S., Hani, F.B., 2011. Fly ash-based geopolymer for Pb removal from aqueous
solution. J Hazard. Mater. 188 414–421
American Coal Ash Association. 2015. https://www.acaa-usa.org/Publications/Production-Use-Reports
Antiohos, S.K., Tsimas, S., 2007. A novel way to upgrade the coarse part of ahigh calcium fly ash for reuse into
Cement Systems. Waste Manage. 27: 675-683
Bachu, S., Bennion, D., 2009. Experimental assessment of brine and/or CO2 leakage through well cements at
reservoir conditions. Int. J. Greenhouse Gas Contr. 3:494-501.
Bakharev, T., 2005a. Durability of geopolymer materials in sodium and magnesium sulphate solutions. Cement
Concrete Res. 35:1233-1246.
Bakharev, T., 2005b. Resistance of geopolymer materials to acid attack. Cement Concrete Res. 35(4):658-670.
Bakharev, T., 2006. Thermal behaviour of geopolymers prepared using class F fly ash and elevated temperature
curing. Cement Concrete Res. 36 (6) 1134-1147.
Bankowski, P., Zou, L., Hodges, R., 2004. Reduction of metal leaching in brown coal fly ash using geopolymers. J.
Hazard. Mater. B114:59-67
Baščarević, Z., Komljenović, M., Miladinović, Z., Nikolić, V., Marjanović, N., Petrović, R., 2015. Impact of
sodium sulfate solution on mechanical properties and structure of fly ash based geopolymers. Mater. Struct. 48
683–697
Bohlooli, H., Nazari, A., Khalaj, G., Kaykha, M.M., Riahi, S., 2012. Experimental investigations and fuzzy logic
modeling of compressive strengthof geopolymers with seeded fly ash and rice husk bark ash. Compos. Part B-Eng.
43 1293-1301
Boonserm, K., Sata, V., Pimraksa, K., Chindaprasirt, P., 2012. Improved geopolymerization of bottom ash by
incorporating fly ash and using waste gypsum as additive. Cement Concrete Comp. 34 819-824
Bortnovsky, O., Dĕdeček, J., Tvarůžková, Z., Sobalík, Z., Šubrt J. 2008. Metal ions as probes for characterization
of geopolymer materials. J Am. Ceram. Soc.1:3052–7.
Breck, D.W., 1974. Zeolite Molecular Sieves: Structure, Chemistry and Use, Wiley-Interscience, New York, pp
415-418.
Brooks, R., Bahadory, M., Tovia, F., Rostami, H., 2010. Properties of alkali-activated fly ash: high performance to
lightweight. Int. J Sustain. Eng. 3 3 211–218
Cakir, O., Akoz, F. 2008. Effect of curing conditions on the mortars with and without GGBFS. Construct. Build.
Mater. 22(3):308–14.
Chang, H., Shih, W.H. 2000. Synthesis of Zeolites A and X from Fly Ashes and Their Ion-Exchange Behavior with
Cobalt Ions. Ind. Eng. Chem. Res. 39, 4185-4191
Chen, C., Gong, W., Lutze, W., Pegg, I. L., Zhai, J., 2011. Kinetics of fly ash leaching in strongly alkaline solutions.
J. Mater. Sci. 46:590-597.
Chen, R., Ahmari, S., Zhang, L.Y., 2014. Utilization of sweet sorghum fiber to reinforce fly ash-based geopolymer.
J. Mater. Sci. 49 2548–2558
Chindaprasirt, P., Chalee, W., 2014. Effect of sodium hydroxide concentration on chloride penetration and steel
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
32
corrosion of fly ash-based geopolymer concrete under marine site. Constr. Build. Mater. 63 303–310
Chindaprasirt, P., Jaturapitakkul, C., Chalee, W., Rattanasak, U., 2009. Comparative study on the characteristics of
fly ash and bottom ash geopolymers. Waste Manage. 29(2):539-543
Chindaprasirt, P., Paisitsrisawat, P., Rattanasak, U., 2014. Strength and resistance to sulfate and sulfuric acid of
ground fluidizedbed combustion fly ash-silica fume alkali-activated composite. Adv. Powder Technol. 25
1087-1093
Chindaprasirt, P., Rattanasak, U., Jaturapitakkul, C., 2011. Utilization of fly ash blends from pulverized coal and
fluidized bed combustion in geopolymeric materials. Cement Concrete Comp. 33:55-60.
Chindaprasirt, P., Rattanasak, U., Taebuanhuad, S., 2013a. Resistance to acid and sulfate solutions of
microwave-assisted high calcium fly ash geopolymer. Mater. Struct. 46:375–381
Chindaprasirt, P., Rattanasak, U., Taebuanhuad, S., 2013b. Role of microwave radiation in curing the fly ash
geopolymer. Adv. Powder Technol. 24 703–707
Criado, M., Palomo, A., Fernández-Jiménez , A., 2005. Alkali activation of fly ashes. Part 1: Effect of curing
conditions on the carbonation of the reaction products. Fuel 84:2048–2054.
Davidovits, J., 1991. Geopolymers Inorganic polymeric new materials. J. Therm. Anal. Calorim. 37 1633-1656
Davidovits, J., 1994. Global warming impact on cement and aggregates industries. World Resource Review. 6
263-278,
Davidovits, J., 2002. 30 years of successes and failures in geopolymer applications, Market trends and potential
breakthroughs. In: Geopolymer 2002 Conference. Saint-Quentin (France), Melbourne (Australia): Geopolymer
Institute
Davidovits, J., 2008. Geopolymer Chemistry and Applications, 2nd edition, Geopolymer Institute, Saint-Quentin,
France, pp. 145–92,.
de Vargas, A.S., Dal Molin, D.C.C., Vilela, A.C.F., da Silva, F.J., Pavã, B., Veit, H., 2011. The effects of Na2O/SiO2
molar ratio, curing temperature and age on compressive strength, morphology and microstructure of
alkali-activated fly ash-based geopolymers. Cement Concrete Comp. 33:653-660.
Deb, P.S., Nath, P., Sarker, P.K., 2014. The effects of ground granulated blast-furnace slag blending with fly ash
and activator content on the workability and strength properties of geopolymer concrete cured at ambient
temperature. Mater. Des. 62 32-39
Demie, S., Nuruddin, M., Shafiq, N., 2013. Effects of micro-structure characteristics of interfacial transition zone
on the compressive strength of self-compacting geopolymer concrete. Constr. Build. Mater. 41 91-98
Diamond, S., 1975. A review of alkali-silica reaction and expansion mechanisms 1. Alkalies in cement and in
concrete pore solutions. Cement Concrete Res., 5(4), 329–346.
Dias, D.P., Thaumaturgo, C., 2005. Fracture toughness of geo-polymeric concretes reinforced with basalt fibres.
Cement Concrete Compos. 27:49
Diaz, E.I., Allouche, E.N., Eklund, S., 2010. Factors affecting the suitability of fly ash as source material for
geopolymers. Fuel 89 992-996.
Dimas, D., Giannopoulou, I., Panias, D., 2009. Polymerization in sodium silicate solutions: a fundamental process
in geopolymerization technology. J. Mater. Sci. 44:3719–3730.
Dombrowski, K., Buchwald, A., Weil, M., 2007. The influence of calcium content on the structure and thermal
performance of fly ash based geopolymers. J. Mater. Sci. 42 3033-3043.
Duxson, P., Lukey, G. C., Separovic, F., van Deventer, J. S. J., 2005a. Effect of alkali cations on aluminum
incorporation in geopolymeric gels. Ind. Eng. Chem. Res. 44, 832-839
Duxson, P., Provis, J.L., Lukey, G.C., Mallicoat, S.W., Kriven, W.M., van Deventer, J.S.J., 2005b. Understanding
the relationship between geopolymer composition, microstructure and mechanical properties, Colloid Surf.
A.-Physicochem. Eng. Asp 269(1–3):47–58.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
33
Duxson, P., Provis, J.L., Lukey, G.C., van Deventer, J.S.J. 2006. 39K NMR of free potassium in geopolymers. Ind.
Eng. Chem. Res. 45(26):9208–9210.
Geetha, S., Ramamurthy, K., 2013. Properties of geopolymerised low-calcium bottom ash aggregate cured at
ambient temperature. Cement Concrete Comp. 43 20-30
Geopolymer industry. 2015.
http://www.geopolymer.org/news/world-first-production-run-2500-tonnes-of-geopolymer/
Görhan, G., Kürklü, G., 2014. The influence of the NaOH solution on the properties of the fly ash-based
geopolymer mortar cured at different temperatures. Composite Part B 58:371-377.
Gorai, B., Jana, R.K., Premchand, 2006. Characteristics and utilization of copper slag-a review. Resour. Conserv.
Recycl. 39 299-313.
Guerrieri, M., Sanjayan, J.G., 2010. Behavior of combined fly ash/slag-based geopolymers when exposed to high
temperatures. Fire Mater. 34(4):163-175.
Habert, G., d’Espinose de Lacaillerie, J.B., Roussel, N., 2011. An environmental evaluation of geopolymer based
concrete production: reviewing current research trends. J. Clean. Prod. 19 1229-1238
Hanjitsuwan S., Hunpratub S., Thongbai P., Maensiri S., Sata V., Chindaprasirt P. 2014. Effects of NaOH
concentrations on physical and electrical properties of high calcium fly ash geopolymer paste. Cement Concrete
Comp. 45 9–14
Hardjito, D., Wallah, S., Sumajouw, D., Rangan, B., 2004. On the development of fly ash-based geopolymer
concrete. ACI Mater. J. 101:467-472.
Heah C.Y., Kamarudin H., Bakri M.A.A.M., Bnhussain M., Luqman M., Nizar I. K., Ruzaidi C.M., Liew Y.M.,
2012. Study on solids-to-liquid and alkaline activator ratios on kaolin-based geopolymers. Constr. Build. Mater. 35
912–922
He, J., Zhang, J., Yu, Y., Zhang, G., 2012. The strength and microstructure of two geopolymers derived from
metakaolin and red mud–fly ash admixture: a comparative study. Constr. Build. Mater. 30:80–91.
Hobbs, D. W. 2001. Concrete deterioration: causes, diagnosis, and minimising risk. Int. Mater. Rev. 46 3 117-144
Idawati, I., Bernal, S.A., Provis, J.L., Nicolas, S.R., Hamdan, S., van Deventer, J.S.J., 2014. Modification of phase
evolution in alkali-activated blast furnace slag by the incorporation of fly ash. Cement Concrete Comp. 45 125-135
Islam, A., Alengaram, U.J., Jumaat, M.Z., Bashar, I.I., 2014. The development of compressive strength of ground
granulated blastfurnace slag-palm oil fuel ash-fly ash-based geopolymer mortar. Mater. Des. 56 833-841
Ismail, I., Bernal, S.A., Provis, J.L., Nicolas, R.S., Brice, D.G., Kilcullen, A.R., Hamdan, S., van Deventer, J.S.J.,
2013. Influence of fly ash on the water and chloride permeability of alkali-activated slag mortars and concretes.
Constr. Build. Mater. 48 1187-1201
Izidoro, J. C., Fungaro, D.A., dos Santos, F.S., Wang, S. 2012. Characteristics of Brazilian coal fly ashes and their
synthesized zeolites, Fuel Process. Technol. 97 38–44
Izquierdo, M., Querol, X., Davidovits, J., Antenucci, D., Nugteren, H., Fernández-Pereira, C. 2009. Coal fly
ash-slag-based geopolymers: microstructure and metal leaching. J Hazard. Mater., 166(1), 561-566.
Jang, J.G., Lee, N.K., Lee H.K., 2014. Fresh and hardened properties of alkali-activated fly ash/slag pastes with
superplasticizers. Constr. Build. Mater. 50 169–176
Joseph, B., Mathew, G., 2012. Influence of aggregate content on the behavior of fly ash-based geopolymer
concrete. Sci. Iran. A 19 (5), 1188-1194
Jun, Y., Oh, J., 2014. Mechanical and microstructural dissimilarities in alkali-activation for six Class F Korean fly
ashes. Constr. Build. Mater. 52 396-403
Kim, B.J., Yi, C., Kang, K.I., 2015. Microwave curing of alkali-activated binder using hwangtoh without
calcination, Constr. Build. Mater. 98 465–475
Klauber, C., Grafe, M., Power, G., 2011. Bauxite residue issues: II. Options for residue utilization.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
34
Hydrometallurgy 108:11-32.
Kong, D.L., Sanjayan, J.G., 2010. Effect of elevated temperatures on geopolymer paste, mortar and concrete.
Cement Concrete Res. 40(2):334-9.
Kong, D.L.Y., Sanjayan, J.G., Sagoe-Crentsil, K., 2007. Comparative performance of geopolymers made with
metakaolin and fly ash after exposure to elevated temperatures. Cement Concrete Res. 37 1583–1589
Kováčik, P., Macák, M., Ducsay, L., Halčínová, M., Jančich, M., 2011. Effect of ash-fly ash mixture application on
soil fertility. J. Elem. 16 215–225
Kriven, W.M., Bell, J.L., Gordon, M., 2003. Microstructure and microchemistry of fully reacted geopolymers and
geopolymer matrix composites. Ceram. Trans. 153:227-250.
Kumar, S., Kumar, R., Mehrotra, S.P., 2010. Influence of granulated blast furnace slag on the reaction, structure
and properties of fly ash-based geopolymer. J. Mater. Sci. 45(3):607-615.
Kupwade-Patil, K., Allouche, E. N., 2013. Impact of alkali silica reaction on fly ash-based geopolymer concrete. J.
Mater. Civ. Eng. 25(1): 131-139
Laudet, J.B., Garnier, A., N. Neuville, Y. Le guen, D. Fourmaintraux, Rafai, N., Burlion, N., Shao, J.F., 2011. The
behavior of oil well cement at downhole CO2 storage conditions: static and dynamic laboratory experiments.
Energy Procedia 4:5251-5259.
Leung, C.K.Y., Pheerapha, T., 1995. Very high early strength of microwave cured concrete. Cement Concrete Res.
25(1):136-146
Li, Q., Sun, Z.Q., Tao, D.J., Xu, Y., Li, P.M., Cui, H., Zhai, J.P., 2013a. Immobilization of simulated radionuclide
133Cs+ by fly ash-based geopolymer. J Hazard. Mater. 262 325–331
Li, Z., Chen, R., Zhang, L.Y., 2013b. Utilization of chitosan biopolymer to enhance fly ash-based geopolymer. J.
Mater. Sci. 48:7986-7993
Li, Z., Liu, S., 2007. Influence of slag as additive on compressive strength of fly ash-based geopolymer. J. Mater.
Civ. Eng. 19(6):470-474.
Lior, N., 2010. Sustainable energy development: the present (2009) situation and possible paths to the future.
Energy 35, 3976–3994.
Lizcano, M., Hyunsoo, K., Basu, S., Radovic, M., 2011. Mechanical properties of sodium and potassium activated
metakaolin-based geopolymers. J. Mater. Sci. 47:2607–2616.
Lloyd, R.R., Provis, J.L., van Deventer, J.S.J., 2010. Pore solution composition and alkali diffusion in inorganic
polymer cement, Cement Concrete Res. 40 1386–1392
Lloyd, R.R., Provis, J.L., van Deventer, J.S.J., 2012. Acid resistance of inorganic polymer binders. 1. Corrosion
rate. Mater. Struct. 45:1–14
Ma, Y., Hu, J., Ya, G., 2013. The pore structure and permeability of alkali activated fly ash. Fuel 104 771-780.
Malviya, R., Chaudhary, R., 2006. Factors affecting hazardous waste solidification/stabilization: a review. J.
Hazard. Mater. 137(1): 267-276
Manz, O.E., 1999. Coal fly ash: a retrospective and future look. Fuel 78 133-136.
McKelvey, D., Sivakumar, V., Bell, A., McLaverty, G., 2002. Shear strength of recycled construction materials
intended for use in vibro ground improvement. Ground Improve. 6(2):59-68.
McLellan, B. C., Williams, R. P., Lay, J., van Riessen, A., Corder,G.D., 2011. Costs and carbon emissions for
geopolymer pastes in comparison to ordinary Portland cement. J. Clean. Prod. 19 1080-1090
Mindess, S., Young, J.F, Darwin, D., 1981. Concrete, Prentice Hall, Englewood Cliffs, NJ, 481.
Mourya, V.K, Inamdar, N.N., Tiwari, A., 2010. Carboxymethyl chitosan and its applications. Adv. Mat. Lett. 1(1),
11-33
Najafi, K.E., Allahverdi, A., 2009. Effects of chemical composition on basic engineering properties of inorganic
polymeric binders based on natural pozzolan. Ceram. Silik 53(3):195–204.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
35
Nasvi, M. M.C., Gamage, R. P., 2012. Geopolymer as well cement and the variation of its mechanical behavior
with curing temperature. Greenhouse Gas Sci. Technol. 2:46–58
Nasvi, M.C.M., Ranjith, P.G., Sanjayan, J., 2013. The permeability of geopolymer at down-hole stress conditions:
Applicationfor carbon dioxide sequestration wells. Appl. Energ. 102 1391-1398
Nasvi, M.C.M., Ranjith, P.G., Sanjayan, J., Bui, H., 2014. Effect of temperature on permeability of geopolymer: A
primary wellsealant for carbon capture and storage wells. Fuel 117 354-363
Nazari, A., Bagheri, A., Riahi, S., 2011. Properties of geopolymer with seeded fly ash and rice husk bark ash.
Mater. Sci. Eng. A 528 7395–7401.
Nazari, A., Khalaj, G., Riahi, S., 2013. ANFIS-based prediction of the compressive strength of geopolymers with
seeded fly ash and rice husk–bark ash. Neural. Comput. Appl. 22: 689–701
Nematollahi, B., Sanjayan, J., 2014. Effect of different superplasticizers and activator combinations on workability
and strength of fly ash based geopolymer. Mater. Des. 57 667–672
Nematollahi, B., Sanjayan, J., Shaikh, F.U.A., 2015. Tensile Strain Hardening Behavior of PVA Fiber-Reinforced
Engineered Geopolymer Composite. J. Mater. Civ. Eng., 27(10): 04015001
Neupane, G., Donahoe, R.J., 2013. Leachability of elements in alkaline and acidic coal fly ash samples during
batch and column leaching tests. Fuel 104, 758–770.
Nguyen, K.T., Lee, Y.H., Lee J, Ahn N, 2013. Acid resistance and curing properties for green fly ash-geopolymer
concrete. J. Asian Archit. Build. 12 317-322
Nomura, Y., Fujiwara, K., Terada, A., Nakai, S., Hosomi, M., 2010. Prevention of lead leaching from fly ashes by
mechanochemical treatment. Waste Manage. 30 1290–1295
Nuaklong P., Sata V., Chindaprasirt P., 2016. Influence of recycled aggregate on fly ash geopolymer concrete
properties. J. Clean. Prod. 112 2300-2307
Nyale, S.M., Eze, C.P., Akinyeye, R.O., Gitari, W.M., Akinyemi, S.A., Fatoba, O.O., Petrik, L.F., 2014. The
leaching behaviour and geochemical fractionation of trace elements in hydraulically disposed weathered coal fly
ash. J. Environ. Sci. Health A 49, 233–242.
Ogundiran, M.B., Nugteren, H.W., Witkamp, G.J., 2013. Immobilisation of lead smelting slag within spent
aluminate-fly ash-based geopolymers. J. Hazard. Mater. 248-249 29-36
Ojovan, M.I., Hand, R.J., Ojovan, N.V., Lee, W.E., 2005. Corrosion of alkali–borosilicate waste glass K-26 in
non-saturated conditions. J. Nucl. Mater. 340(1): 12-24.
Pacheco-Torgal, F., Jalali, S., 2010. Influence of sodium carbonate addition on the thermal reactivity of tungsten
mine waste mud based binders. Construct. Build. Mater. 24(1):56–60.
Palomo, A., Blanco-Varela, M.T., Granizo, M.L., Puertas, F., Vazquez, T., Grutzeck, M.W., 1999a. Chemical
stability of cementitious materials based on metakaolin. Cement Concrete Res. 29(7):997–1004.
Palomo, A., Grutzeck, M., Blanco, M., 1999b. Alkali-activated fly ashes: a cement for the future. Cement Concrete
Res. 29:1323-1332
Pernica, D., Reis, P.N.B., Ferreira, J.A.M., Louda, P., 2010. Effect of test conditions on the bending strength of a
geopolymer-reinforced composite. J. Mater. Sci. 45:1189–1192
Piga, F.P., Stoppa, L., 1993. Recovering metals from red mud generated during alumina production. JOM.
45(11):55-59.
Pillai, C.K.S., Paul, W., Sharma, C.P., 2009. Chitin and chitosan polymers: Chemistry, solubility and fiber
formation. Prog. Polym. Sci. 34 641–678
Ranjbar, N., Mehrali, M., Alengaram, U.J., Metselaar, H.S.C., Jumaat, M.Z., 2014. Compressive strength and
microstructural analysis of fly ash/palm oil fuel ash based geopolymer mortar under elevated temperatures. Constr.
Build. Mater. 65 114-121
Rashad, A.M., Zeedan, S.R., 2011. The effect of activator concentration on the residual strength of alkali-activated
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
36
fly ash pastes subjected to thermal load. Constr. Build. Mater. 25:3098-3107.
Rattanasak, U., Chindaprasirt, P., 2009. Influence of NaOH solution on the synthesis of fly ash geopolymer. Miner.
Eng. 22 1073–1078
Rattanasak, U., Pankhet, K., Chindaprasirt, P., 2011. Effect of chemical admixtures on properties of high-calcium
fly ash geopolymer. Int. J. Miner. Metall. Mater. 18(3):364-369
Reddy, D.V., Edouard, J.B., Sobhan, K., 2013. Durability of fly ash–based geopolymer structural concrete in the
marine environment. J. Mater. Civ. Eng. 25:781-787.
Riahi, S., Nazari, A., 2012. The effects of nanoparticles on early age compressive strength of ash-based
geopolymers. Ceram. Int. 38 4467-4476
Rickard, W.D.A., van Riessen, A., 2014. Performance of solid and cellular structured fly ash geopolymers exposed
to a simulated fire. Cement Concrete Compos. 48 75-82
Rickard, W.D.A., van Riessen, A., Walls, P., 2010. Thermal character of geopolymers synthesized from Class F fly
ash containing high concentrations of iron and alpha quartz. Int. J. Appl. Ceram. Technol. 7 81-88.
Rickard, W.D.A., Williams, R.P., Temuujin, J., van Riessen, A., 2011. Assessing the suitability of three Australian
fly ashes as an aluminosilicate source for geopolymers in high temperature applications. Mater. Sci. Eng. A 528
3390-3397.
Rubel, A., Andrews, R., Gonzalez, R., Groppo, J., Robl, T., 2005. Adsorption of Hg and NOx on coal by-products.
Fuel 84:911–6.
Sahmaran, M., Li, V.C., 2009. Durability properties of micro-cracked ECC containing high volumes fly ash. Cem
Concr Res 39:1033–1043.
Sarker, P.K., Kelly, S., Yao, Z., 2014. Effect of fire exposure on cracking, spalling and residual strength of fly ash
geopolymer concrete. Mater. Des. 63 584-592
Sata, V., Jaturapitakkul, C., Kiattikomol, K., 2007. Influence of pozzolan from various byproduct materials on
mechanical properties of high-strength concrete. Constr. Build. Mater. 21 (7) 1589–1598.
Sata, V., Wongsa, A., Chindaprasirt, P., 2013.Properties of pervious geopolymer concrete using recycled aggregates.
Constr. Build. Mater. 42 33–39
Schmucker, M., Mackenzie, J.D.M., 2005. Microstructure of sodium polysialatesiloxo geopolymer. Ceram. Int.
31:433-440.
Schneider, M., Romer, M., Tschudin, M., Bolio, H., 2011. Sustainable cement production present and future.
Cement Concrete Res. 41:642-650.
Shaikh, F.U.A., 2013. Deflection hardening behaviour of short fibre reinforced fly ash-based geopolymer
composites. Mater. Des. 50(0):674-682.
Shibayama, A., Kim, Y., Harjanto, S., Sugai, Y., Okada, K., Fujita, T., 2005. Remediation of Contaminated Soil by
Fly Ash Containing Dioxins from Incineration by using Flotation. Mater. Trans. 46 5 990-995
Škvára, F., Pavlasová, S., Kopecky, L., Myšková, L., Alberovská, L. 2008. High temperature properties of fly
ash-based geopolymers. In: Bílek V, Keršner Z, editors. 3rd International symposium on non-traditional cement
and concrete. Czech Republic: Brno, pp 741–50.
Somna, K., Jaturapitakkul, C., Kajitvichyanukul, P., Chindaprasirt, P., 2011. NaOH-activated ground fly ash
geopolymer cured at ambient temperature. Fuel 90 2118-2124
Songpiriyakij, S., Kubprasit, T., Jaturapitakkul, C., Chindaprasirt, P., 2010. Compressive strength and degree of
reaction of biomas- and fly ash-based geopolymer. Constr. Build. Mater. 24:236-240.
Standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete (ASTM C618-12a);
2012. http://blocksjordan.net/Portals/0/C%20618%20-%2000%20%20_QZYXOC0WMA__.pdf
Sukmak, P., De Silva, P., Horpibulsuk, S., Chindaprasirt, P., 2015. Sulfate resistance of clay-portland cement and
clay high-Calcium fly ash geopolymer. J. Mater. Civ. Eng. 27(5): 04014158
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
37
Sun, P.J., Wu, H.C., 2008. Transition from brittle to ductile behavior of fly ash using PVA fibers. Cem. Concr.
Compos. 30 29–36
Sun, P.J., Wu, H.C., 2013. Chemical and freeze–thaw resistance of fly ash-based inorganic mortars. Fuel 111 740–
745
Swamy, N., and Al-Asali, M. 1988. Effect of alkali-silica reaction on the structural behavior of reinforced concrete
beams. ACI Mater. J. 86(4), 33–40.
Szklorzová, H., Bílek, V., 2008. Influence of alkali ions in the activator on the performance of alkali-activated
mortars. In: Bílek V, Keršner Z, editors. 3rd International symposium on non-traditional cement and concrete.
Czech Republic: Brno, p. 777–784.
Tangchirapat, W., Buranasing, R., Jaturapitakkul, C., Chindaprasirt, P., 2008. Influence of rice husk–bark ash on
mechanical properties of concrete containing high amount of recycled aggregates. Constr. Build. Mater. 22(8)
1812–1819.
Temuujin, J., Minjigmaa, A., Davaabal, B., Bayarzul, U., Ankhtuya, A., Jadambaa, T., MacKenzie, K.J.D., 2014.
Utilization of radioactive high-calcium Mongolian fly ash for the preparation of alkali-activated geopolymers for
safe use as construction materials. Ceram. Int. 40 16475–16483
Temuujin, J., van Riessen, A., 2009. Effect of fly ash preliminary calcination on the properties of geopolymer, J
Hazard. Mater. 164 634–639.
Topark-Ngarm, P., Chindaprasirt, P., Sata, V., 2015. Setting time, strength, and bond of high-calcium fly ash
geopolymer concrete, J. Mater. Civ. Eng., 27(7): 04014198
Ukwattage, N.L., Ranjith, P.G., Bouazza, M., 2013. The use of coal combustion fly ash as a soil amendment in
agricultural lands (with comments on its potential to improve food security and sequester carbon). Fuel 109 400–
408
Uysal, M., Akyuncu, V., 2012. Durability performance of concrete incorporating Class F and Class C fly ashes.
Constr. Build. Mater. 34 170–178
van Jaarsveld, J.G.S, van Deventer, J.S.J., 1999. Effect of the alkali metal activator on the properties of fly
ash-based geopolymer. Ind. Eng. Chem. Res. 38:3932–3941.
Verdolotti, L., Iannace, S., Lavorgna, M., Lamanna, R., 2008. Geopolymerization reaction to consolidate
incoherent pozzolanic soil. J. Mater. Sci. 43(3):865-873
Wagners Earth Friendly Concrete. 2015. http://www.wagner.com.au/capabilities/efc/
Wang, W.C., Wang, H.Y., Lo, M.H., 2015. The fresh and engineering properties of alkali activated slag as a
function of fly ash replacement and alkali concentration. Constr. Build. Mater. 84 224–229
Xu, H., Li, Q., Shen, L., Zhang, M., Zhai, J., 2010. Low-reactive circulating fluidized bed combustion (CFBC) fly
ashes as source material for geopolymer synthesis. Waste Manage. 30:57-62.
Yang, T., Yao, X., Zhang, Z., Wang, H., 2012. Mechanical property and structure of alkali activated fly ash and slag
blends. J. Sust. Cem. Based Mater. 1(4):167-178.
Yang, T., Yao, X., Zhang, Z.H., 2014a. Geopolymer prepared with high-magnesium nickel slag: Characterization
of properties and microstructure. Constr. Build.Mater. 59 188-194
Yang, T., Yao, X., Zhang, Z.H., 2014b. Quantification of chloride diffusion in fly ash–slag-based geopolymers by
X-ray fluorescence (XRF). Constr. Build. Mater. 69 109–115
Yang, Z.X., Ha, N.R., Jang, M.S., Hwang, K.H., 2009. Geopolymer concrete fabricated by waste concrete sludge
with silica fume. Mater. Sci. Forum 620-622:791-795
Yao, Z.T., Ji, X.S., Sarker, P.K., Tang, J.H., Ge, L.Q., Xia, M.S., Xi, Y.Q., 2015. A comprehensive review on the
applications of coal fly ash. Earth-Sc. Rev. 141 105–121
Yildiz, E. 2004. Phosphate removal from water by fly ash using cross flow microfiltration. Sep. Purif. Technol.
35:241–52.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
38
Zhang, G., He, J.A., Gambrell, R.P., 2010a. Synthesis, characterization, and mechanical properties of red
mud-based geopolymers. Trans. Res. Record 2167:1-9.
Zhang, J.G., Provis, J.L., Feng, D.W., van Deventer, J,S.J., 2008a. Geopolymers for immobilization of Cr6+, Cd2+,
and Pb2+. J Hazard. Mater. 157 587–598
Zhang, M., El-Korchi, T., Zhang, G.P., Liang, J.Y., Tao, M.J., 2014a. Synthesis factors affecting mechanical
properties, microstructure, and chemical composition of red mud-fly ash-based geopolymers. Fuel 134 315-325
Zhang, Y., Li, S., Xu, D., Wang, B., Xu, G., Yang, D., Wang, N., Liu, H., Wang, Y., 2010b. A novel method for
preparation of organic resins reinforced geopolymer composites. J. Mater. Sci. 45(5) 1189-1192.
Zhang, Y., Sun, W., Li, Z., Zhou, X., Chau, C., 2008b. Impact properties of geopolymer based extrudates
incorporated with fly ash and PVA short fiber. Constr. Build. Mater. 22: 370–383.
Zhang, Y., Sun, W., Li, Z.J., 2006. Impact behavior and microstructural characteristics of PVA fiber reinforced fly
ash geopolymer boards prepared by extrusion technique. J. Mater. Sci. 41 2787-2794
Zhang Z.H., Provis J.L., Reid A., Wang H., 2014b. Fly ash-based geopolymers: The relationship between
composition, pore structure and efflorescence. Cement Concrete Res. 64 30–41
Zhang, Z.H., Zhu, H.J., Zhou, C.H., Wang, H., 2016. Geopolymer from kaolin in China: An overview. Appl. Clay
Sci. 119 31–41
Zhao, Q., Nair, B., Rahimian, T., Balaguru, P., 2007. Novel geopolymer based composites with enhanced ductility.
J. Mater. Sci. 42:3131-3137.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
Highlights
� Fly ash is activated by alkali to form geopolymer and such a process is cleaner.
� Slag, rice husk-bark ash, fiber and red mud are added to improve the performance of fly ash-based
geopolymer.
� Mechanical properties and durability of fly ash-based geopolymer are main concerns.
� Fly ash-based geopolymer is used as cement and as fixation materials for toxic metals.
� Improving performance, scaling-up production and finding new applications are proposed for
future.
Top Related