Journal of Cleaner Production 147 (2017) 546e559

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Journal of Cleaner Production

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Review

A review on fly ash characteristics e Towards promoting high volume

utilization in developing sustainable concrete
T. Hemalatha a, *, 1, Ananth Ramaswamy b, 2
a
CSIR-Structural Engineering Research Centre, Chennai, India
b
Indian Institute of Science, Bangalore, India

a r t i c l e i n f o a b s t r a c t

Article history: The use of fly ash in concrete dates back to the late 20th century and its advantages and disadvantages
Received 27 August 2016 had been widely researched. Despite the broad based research carried out across the globe in utilizing fly
Received in revised form ash as a cement replacement material in concrete, the level of replacement is still limited to a maximum
20 January 2017
of 35% of cement by mass. In view of increasing the level of fly ash replacement in cement to minimize
Accepted 20 January 2017
Available online 25 January 2017
the carbon footprint, this work summarizes the following: firstly, the current state of fly ash applications
in concrete by considering about 200 papers published since 1980 to till date. Secondly, the analysis of
form-structure-property of fly ash reported in various literature and its correlation with strength and
Keywords:
Fly ash
durability characteristics. Thirdly, the contradictions reported in literature regarding the performance of
Class F fly ash, particularly, in the context of shrinkage, high temperature curing, water demand etc. Overall, this
Class C review brings to light that, apart from chemical composition, the influence of other factors such as
Pozzolanic morphology, crystallinity, size etc. have major influence in altering the hydration mechanism which in
Alkali activation turn bring changes in mechanical and durability properties of fly ash concrete. The critical examination of
Geopolymer properties of fly ash provides insight for wider utilization of fly ash, facilitating a higher replacement of
cement possibly upto 60% in a scientific way rather than by trial and error basis. Further, this review
recommends for the classification of fly ash apart from the existing ASTM classification of fly ash as Class
F and Class C. Furthermore, amendments in existing codes are recommended for high volume utilization
of fly ash.
© 2017 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
2. Content analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
3. Factors affecting the properties of FA blended cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
3.1. Type of fly ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
3.1.1. Mitigation of sulphate attack and alkali silicate reaction (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
3.2. Crystalline or amorphous nature of fly ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
3.3. Size of fly ash particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
3.4. Dosage of fly ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
3.4.1. HVFA as a structural concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
3.5. Water to binder ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
3.6. Curing temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
4. Cementing efficiency and pozzolanic reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
5. Influence on the fresh properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
6. Influence on shrinkage properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553

* Corresponding author. CSIR-Structural Engineering Research Centre, Chennai,

India.
E-mail address: hemalatha@serc.res.in (T. Hemalatha).
1
Senior Scientist.
2
Professor.

http://dx.doi.org/10.1016/j.jclepro.2017.01.114
0959-6526/© 2017 Elsevier Ltd. All rights reserved.
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 547

7. Methods to improve the strength of FA concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

7.1. Alkali activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
7.2. Nano modified fly ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
8. Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
9. Future research and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556

1. Introduction only limited literature on review of FA that provides in depth

knowledge as a cement replacement material. Among the recent
Fly ash (FA) is the major solid waste generated from coal-firing review papers published on fly ash research, Yao et al. (2015).
power stations. The most important areas of fly ash application describes the generation, physico-chemical properties, hazards
reported are: concrete production (Malhotra, 1990), road basement and applications of coal fly ash in various fields such as soil
material (Sobolev et al., 2014), waste stabilization/solidification amelioration, construction industry, ceramic industry, catalysis,
(Pereira et al., 2009), cement clinkers (Teixeira et al., 2016) and depth separation, zeolite synthesis, etc. Bukhari et al. (2015) made
more recently geopolymer concrete (Embong et al., 2016). From the a review in the progress of conversion of coal fly ash to zeolite.
perspective of power generation, FA is a waste material and thermal Wang et al. (2014) centre their review on production of high
electricity stations are looking for ways to exploit fly ash disposal in performance glass-ceramics using coal fly ash as a raw material.
an economically advantageous way. However, from the perspective Shaheen et al. (2014) reviewed the applications and challenges of
of construction industry, FA is looked upon as a supplementary using coal fly ash in soil improvements. Lothenbach et al. (2011)
cementitious material (SCM) which is used in mass, conventional reviewed the effects of various SCMs on microstructure and hy-
and high performance concrete as a cement replacement material. dration mechanism. As many SCMs are reviewed in this paper,
Besides the environmental benefits of waste disposal and CO2 only limited insights into the behavior of fly ash in cement is
sequestration (Dananjayan et al., 2016; Ukwattage et al., 2015), FA provided. Recently, Paris et al. (2016) reviewed the utilization of
improves workability, reduces heat of hydration and thermal various industrial waste products as supplements to Portland
cracking in concrete at early ages and improves mechanical as well cement. In their paper, only a brief review on fly ash is given. From
as durability characteristics of concrete especially at later ages the previous review papers, it is realized that the information
(Sahmaran and Li, 2009). Despite the benefits offered by FA, 100% of provided on fly ash characteristics is generalized for various ap-
fly ash utilization is not achieved due to various limitations re- plications and those reviews are discrete and brief in nature with
ported (Vargas and Halog, 2015). Unravelling the chemical regard to FA. According to environmental protection agency (EPA,
composition of fly ash identified its potential to use as a raw ma- 2008), the use of fly ash in concrete reduces the greenhouse
terial in cement industry. Further, increase in production of fly ash emissions equivalent to emissions from 2.5 million cars on road
across the globe compels one to utilize more and more fly ash in the every year. Hence, significant reduction in greenhouse emissions
construction industry. Towards achieving this goal, numerous can be achieved by increasing the utilization of FA in concrete. For
research works are being carried out across the world and many these reasons, this review paper aims to provide a single docu-
dimensions such as degree of hydration of high volume fly ash ment using exhaustive research findings related to FA utilization in
(HVFA) cement systems (Lam et al., 1998), durability characteristics cement concrete that can serve as a ready reference and guide for
of HVFA engineered cement composites (Sahmaran and Li, 2009), the researcher working with fly ash as a cement replacement
mechanical and fracture properties of FA concrete (Lam et al., material. The literature collected for this review are grouped based
2000), influence of type of FA on freeze thaw resistance (Uysal on the i) Influence of intrinsic properties of fly ash such as crys-
and Akyuncu, 2012) etc. are reported extensively. tallinity, size, chemical composition etc. on hydration kinetics ii)
The objective of this work is to consolidate the findings from the Influence of external factors such as water to cement ratio, level of
reported researches to gain more understanding in to the physico- replacement, curing temperature etc. on hydration mechanism iii)
chemical and mechanical characterization of fly ash in its natural as Form-structure-property of fly ash and its correlation with
well as modified forms. According to Indian standard (IS - 1489, strength and durability characteristics iv) Contradictions discussed
2000), the maximum percentage of fly ash used is limited to 35% related to shrinkage properties, curing temperature, water de-
in the manufacturing of Portland Pozzolana cement. From the mand etc.
available literature, it is understood that FA is not able to enhance
the strength characteristics in its natural form when used beyond
35% of replacement. In such cases, FA-cement requires modification 3. Factors affecting the properties of FA blended cement
in the mix in order to form more hydration products to enhance the
strength. This work exhaustively investigates the characteristics of The physical properties of FA, especially the shape and the size
different types of fly ashes and explores various methods to engi- have considerable effect on the properties of FA-cement system.
neer the concrete mixes with admixtures. It is found that with Further, the chemical composition has traditionally been the basis
proper engineering procedure, it is possible to achieve more than for assessing the suitability of FA for its use as a cement replace-
50% replacement of FA. This increase in replacement level of FA ment material (Blissett and Rowson, 2012). Therefore, the hydra-
from 35% to more than 50% in cement would facilitate towards tion mechanism of FA-cement system is influenced greatly by the
achieving near 100% utilization of FA produced in the country. inherent properties of FA such as crystalline structure, physical and
chemical characteristics (Durdzinski et al., 2015a) and external
2. Content analysis factors such as water to binder ratio, level of replacement, curing
temperature etc. A review of various factors affecting the hydration
Though the literature available on fly ash characteristics is vast, mechanisms are discussed in this study.
548 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

3.1. Type of fly ash

American Society for Testing and Materials (ASTMs) (ASTM -

C618-8a, 2009) classifies FA into two classes: “C” and “F”. “Class
F” FA is mainly produced by burning anthracite or bituminous coal
in which combination of SiO2, Al2O3, and Fe2O3 content is exceeding
70%. Whereas “Class C” FA is produced by burning lignite or sub-
bituminous coal that contains combination of aforementioned
chemicals between 50% and 70%. Class F is categorized as a normal
pozzolan, a material consisting of silicate glass, modified with
aluminium and iron (RILEM 73-SBC Committee, 1988). CaO content
is less than 10% in “Class F” FA, hence, in order to form calcium
silicate hydrate (CSH) through pozzolanic reaction, it requires
Portlandite (CH) formed from cement hydration. Therefore, the
chemical composition mainly determines the performance of fly
ash in concrete (Medhat and Michail, 2000). The range of values of
element oxides present in “Class F” and “Class C” FA as reported in
various literature discussed in this study are consolidated in Table 1.
It is evident from the table that there is a wide variation in the
element oxides within a type of fly ash which may be attributed to
the variation in sources, processing condition etc.
Low-calcium fly ashes react slowly, especially during the early
stages of hydration due to the presence of more crystalline phases,
which are considered chemically inert in concrete (Hemmings and
Berry, 1988). Due to the advancement in characterization tech-
niques, it is possible to analyze the hydration products formed at
various stages. In order to identify the morphology and chemical
composition of formed hydrated products, scanning electron mi-
croscopy images (SEM) are often employed. SEM images of FA
concrete along with energy dispersive spectrum (EDS) (Fig. 1)
shows the composition of various hydration products in the same
image at different spots. Figure (Fig. 1) shows that in a low calcium
fly ash incorporated concrete, even at 28 days, unreacted fly ash and
unhydrated spots are present (Hemalatha, 2011). High calcium fly
ashes are less sensitive to inadequate curing (Poon et al., 1997) and
react faster to provide better early age strength. However, high- Fig. 1. Scanning electron microscope images showing the chemical composition of two
calcium fly ashes are generally less efficient in suppressing different spots a) fly ash and b) unhydrated spot.
expansion due to alkali silica reaction (ASR) (Smith, 1988) and
sulphate attack (Dunstan, 1980) when compared to low-calcium
ashes. It is believed that calcium substitution in the glass phase results in higher reactivity owing to the reduced degree of SiO4
generally increases the reactivity of high-calcium fly ashes (Mehta, polymerization (Ivan Odler, 2009; Mehta, 1985).
1985, 1998) and therefore enables the formation of calcium-silicate Several studies reported the effectiveness of fly ash in
and calcium aluminate phases in the absence of an external source decreasing the expansion of concrete by reducing the amount of
of lime. Moreover, it is noticed that Class C fly ashes not only differ alkali ions available in the pore solution that react with potentially
from Class F fly ashes with the content of lime, but also with the reactive aggregates (Bleszynski and Thomas, 1998; Medhat and
lime depolymerized glass phase (Ghosh and Sarkar, 1993). It is said Michail, 2000). The detrimental effect of reduced pH in acceler-
that the CaO content in the glass phase of high calcium fly ashes ating the corrosion of reinforcement in concrete is also often re-
ported. However, Diamond (1981) reported that the alkalinity of
pore solution is not only due to the presence of calcium hydroxide
Table 1 (CH) formed from cement hydration but also due to the presence of
Range of element oxides present in “Class C” and “Class F” fly ash as reported in the sodium and potassium ions in cement and fly ash. Hence, though
literature.
there is a reduction in pH due to decrease in CH owing to high FA
Element oxides Class C Class F content, the presence of Naþ and Kþ balances the pH value
Percentage (Wesche, 1991). ACI manual of concrete practice (ACI, 1979) also
confirms the prevalence of same alkaline environment in both FA
CaO 15.1e54.8 0.50e14.0
SiO2 11.8e46.4 37.0e62.1
and conventional concrete that offers comparable corrosion pro-
Al2O3 2.6e20.5 16.6e35.6 tection despite the reduced pH of concrete owing to pozzolanic
Fe2O3 1.4e15.6 2.6e21.2 action of fly ash. Further, literature (Joshi and Lohtia, 1997) shows
MgO 0.1e6.7 0.3e5.2 that the inclusion of fly ash even improves the corrosion resistance
K2O 0.3e9.3 0.1e4.1
by densification of concrete when properly proportioned and
Na2O 0.2e2.8 0.1e3.6
SO3 1.4e12.9 0.02e4.7 adequately cured.
P2O5 0.2e0.4 0.1e1.7 The mechanism through which the composition/type of fly ash
TiO2 0.6e1.0 0.5e2.6 controls the durability problems such as carbonation, chloride and
MnO 0.03e0.2 0.03e0.1 sulfate attack, etc. are similar. Hence, typically, the influence of type
Loss on Ignition (LOI) (%) 0.3e11.7 0.3e32.8
of FA on resistance to sulphate attack and alkali silica reaction are
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 549

reviewed in the following sub section. similar approach, Malvar and Lenke (2006) derived a chemical in-
dex based on the constituents of fly ash (or cement), through
which, for a given- aggregate reactivity, cement and fly ash, it is
3.1.1. Mitigation of sulphate attack and alkali silicate reaction (ASR)
possible to arrive at the minimum replacement of cement with fly
Sulfate attack and alkali silicate reaction (ASR) are two major
ash needed to ensure a 90% reliability, that a 14-day expansion
durability problems that can be controlled by the use of fly ash. The
would remain below 0.08%, so as to conform to ASTM C1260. With
influence of low and high calcium fly ashes on chemical attack vary
regard to ASR, more than the total alkali content of the cement-FA
as high calcium fly ash contains appreciable amounts of soluble
system, the presence of soluble alkali affects the expansion. It is
calcium, aluminium and sulfur bearing minerals. High calcium FA
reported that even with higher Na2Oeq content in fly ash, the
also contains significant amounts of calcium aluminate glass which
alkalinity of pore solution is reduced in FA-cement system
is more soluble than the glass in low calcium fly ash and may slowly
(Diamond, 1981; Hobbs, 1982).
release calcium and aluminium into solution (Diamond, 1983).
Understanding the chemistry governing ASR facilitates the use
When such types of FA come into contact with water, it increases
of even susceptible aggregate in the concrete safely. Mitigation of
the pH of the solution and makes the FA, a potential source for
ASR with FA replacement takes place due to (i) reduced perme-
ettringite formation (McCarthy and Solem-Tismack, 1994). Ettrin-
ability of the concrete limiting its capacity to imbibe water (ii)
gite formation is responsible for expansion of cement that leads to
dilution of free alkali metal ions available in the concrete owing to
cracking (Tixier and Mobasher, 2003). Three of the aluminate
reduced cement. FA with pozzolanic property reacts with calcium
compounds react with ingressing sulphates depending upon the
hydroxide produced during the cement hydration thus helping in
availability of calcium hydroxide to form various forms of calcium
lowering the alkalinity of the concrete below that of the pH needed
alumino sulphate hydrate (Tixier and Mobasher, 2003) as shown by
to support the formation of the alkali-silicate gels (Shehata and
Equations (1)e(3).
Thomas, 2002).
Inference: It is difficult to generalize the suitability of type of fly
C4 AH13 þ 3CSH2 þ 14H/C6 AS3 H32 þ CH (1)
ash for resistance to sulphate attack or ASR owing to the wide
variation in the composition within a similar type of fly ash as
C4 ASH12 þ 2CSH2 þ 16H/C6 AS3 H32 (2) evident from Table 1. However, in pursuit of mitigating sulfate-
resistant or ASR in concrete, studies have demonstrated that
C3 A þ 3CSH2 þ 26H/C6 AS3 H32 (3) either the use of Class F or Class C FA is suitable, but in proper
dosage. Further, either Class F or Class C which is most effective in
where C ¼ Calcium; CH ¼ Portlandite; H¼H2O; A ¼ Al2O3; S ¼ SO3 reducing the alkalinity of the pore solution of paste samples is
Class F fly ash increases the sulfate resistance by consuming the found to be the best for mitigating sulfate-resistant or ASR in
available CH formed during cement hydration, making CH unavai- concrete.
lable to react with sulfates thus hampering the formation of alu-
mino silicate hydrate compounds. Whereas, Class C fly ash that is 3.2. Crystalline or amorphous nature of fly ash
rich in lime can hydrate independently producing its own calcium
hydroxide thereby increasing the exposure to sulfate attack. Dun- As mentioned earlier, fly ash is derived as a coal-combustion by-
stan (Dunstan, 1976, 1984) reported that the main contributors to product having inherent heterogeneous property. Fly ash is
the sulphate resistance in FA are CaO and Fe2O3. He reported the generally considered to contain three different types of constitu-
reduced sulphate resistance with increased calcium oxide above ents: crystalline minerals, unburnt carbon particles and non crys-
the lower limit of 5% or with decreased ferric oxide. Due to this talline aluminosilicate glass (Ward and French, 2005) each with
reason concretes containing low-calcium fly ash are more resistant unique reactivity when used in concrete as a cement replacement
to sulfate attack than those containing high-calcium fly ash or no fly material. Presence of unburnt carbon is undesirable in FA. Study
ash. Further, it is reported that Class F fly ash reduces the perme- shows that the process of removing this unburnt carbon through
ability of concrete thereby preventing ionic ingress, migration and calcination process (Temuujin and Van Riessen, 2009), transforms
concentration (Sumer, 2012) thus increasing the sulphate amorphous phases present in FA into crystalline phases partially.
resistance. With the help of the advanced techniques available, it is iden-
Similar to sulphate attack, another problem encountered in tified that FA constitutes the distinct crystalline phases such as
concrete durability is alkali silica reaction (ASR). Some research quartz, mullite, hematite, ferrite spinels, anhydrite, melilite, mer-
works have shown that high-calcium fly ash is less effective than winite, periclase, tri calcium aluminate and lime (Chancey, 2008;
low-calcium fly ash in mitigating ASR (Ali Akbar Ramezanianpour, McCarthy et al., 1989). Most of the fly ashes are made of glassy
2014). The lower efficacy of high calcium fly ash is attributed pri- material having poorly ordered atomic structure (amorphous na-
marily to its reduced ability to bind alkalis to its hydration products ture) and due to this nature, the constituent materials mainly
(Shehata and Thomas, 2000a). In case of high calcium fly ash, it is involve in the chemical reaction (Durdzinski et al., 2015b). Thus fly
proved that FA replacement of up to 60% is required in order to ash with higher amorphous content is more effective in enhancing
control ASR. However, the disadvantage of high calcium fly ash in the pozzolanic reaction.
controlling ASR and sulphate resistance may be eliminated by Sakai et al. (2005) reported the effect of amorphous content on
incorporating silica fume as ternary blend in fly ash cement system the pozzolanic reaction of the fly ashes at later ages. A greater de-
(Thomas et al., 1999). Further, Shehata and Thomas (Shehata et al., gree of pozzolanic reaction is expected with higher amorphous
1999; Shehata and Thomas, 2000b) investigated the effect of content of the fly ash. Further, it is reported that in an alkaline
composition of FA on ASR for a wide range of commercially avail- environment, low calcium fly ash is non reactive due to the inert
able fly ashes to establish the relationships between composition of nature of most crystalline phases present in it. Whereas, high cal-
the ash and minimum dosage of FA necessary to control the dele- cium fly ashes are reactive due to the presence of some reactive
terious reaction. They found that bulk chemical composition of the crystalline phases in it (Chancey, 2008). Tkaczewska (2014) added
fly ash provides a reasonable indication of its performance in the advantage of using finer fly ash in increasing the degree of
physical expansion tests. However, the minimum dosage of FA depolymerization of SiO4 that increases the pozzolanic reactivity.
required to suppress expansion could not be generalized. In a Inference: Conventionally, reactivity of fly ash is expressed by
550 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

bulk element oxides (composition) as determined by x-ray fluo- purely to particle size reduction alone enhancing the reactivity. The
rescence spectroscopy. However, the composition alone is not vibratory-milled fly ash is not the finest of those studied, but a
sufficient since the presence of crystalline or amorphous phases mechanochemical activation process (changes in reactivity induced
also determine the reactivity of fly ash. Though the amorphous by straining or fracture of chemical bonds during milling) was
phases are reactive in both low and high calcium fly ash, the postulated to be taking place (Kumar et al., 2007).
quantity of reactive crystalline phases determines the reactivity of Inference: Finer fly ash is more preferable in strength devel-
fly ash. Hence, it is equally important to know the amount of opment as it provides more nucleation sites for the hydration of
reactive crystalline and amorphous phases to understand the cement. However, coarser fly ash cannot be eliminated as it has
reactivity of fly ash. certain positive role to play when used in cement/concrete. Hence,
fine and coarser fly ash in proper proportion would yield better
3.3. Size of fly ash particles results in terms of strength and durability.

Fineness of fly ash is one of the major factors (Slanicka, 1991) 3.4. Dosage of fly ash
that determines the suitability of using FA in the production of
concrete since the size of FA used in cement significantly affects the For many years, the incorporation of fly ash as partial replace-
properties of fly ash cement/concrete (Erdogdu and Turker, 1998). ment of cement in concrete has been a common practice. The
The packing and nucleation effect in cement hydration greatly quantity of fly ash to replace the cement for typical application is
depends on the size of the fly ash used in cement (Chindaprasirt limited to 15e20% by mass of the total cementitious material
et al., 2007b). Chindaprasirt et al (Chindaprasirt et al., 2007a, (Bendapudi, 2011). According to the British standard (British
2004, 2007b). conducted an exhaustive study to investigate the Standards Institution, 1997a,b) as well as Indian standard (IS -
influence of fineness on chloride penetration (Chindaprasirt et al., 1489, 2000), a maximum of 35% by mass of FA as a cement
2007a), strength, drying shrinkage, sulphate resistance component can be used. However, the use of high volume fly ash
(Chindaprasirt et al., 2004) etc. They reported the advantage of (HVFA) as partial replacement of cement in concrete has also been
using finer fly ash in increased compressive strength, reduced studied extensively (Alasali and Malhotra, 1991; Malhotra, 1986;
shrinkage, reduced expansion etc. Coarse fly ash is found to be less Malhotra, 1990). Malhotra established that fly ash can be used as
reactive and requires more water resulting in more porous mortar high replacement (more than 50%) in concrete ensuring acceptable
with a larger degree of susceptibility to the sulfate attack. Although material responses such as strength, durability, permeability,
the negative effects of coarser fly ash are often reported as the shrinkage etc (Malhotra, 1986; Malhotra, 1990). Langley et al.
reason for reduced strength, increased drying shrinkage, sulphate (1989) investigated the mechanical and elastic properties of con-
attack etc., coarser fly ashes are found to perform better against crete replacing 56% of fly ash for cement by weight and found that
sulfuric acid attack (Chindaprasirt et al., 2004). Better bonding HVFA concrete performs satisfactorily in freezing and thawing
between coarser fly ash and cement matrix, increased volume of fly tests. Though the small percentage of FA is beneficial in optimizing
ash (because of the reduced specific gravity of 1.88 of coarser fly the workability and low cost, it may not improve durability to a
ash) and reduced volume of OPC are reportedly the reasons for considerable extent (Aggarwal et al., 2010).
increased sulphuric acid resistance. Itskos et al. (2010) reported the In a low volume fly ash concrete, the FA acts as a pozzolanic
use of FA grain fraction between 7 and 150 mm that results in better material. Whereas, in high volume fly ash concrete, only part of the
pozzolanic properties with the presence of more intense glass and FA participates in the pozzolanic reaction while the other part re-
the weak crystalline phase. They suggested further grinding of FA mains unreacted even after a long period of curing (Berry et al.,
particles (under the subsequent release of the pozzolanic and sili- 1990, 1994; Feldman et al., 1990). Berry et al (Berry et al., 1990,
con ingredients) crumble the superficial glass to increase their 1994). characterized the high volume fly ash pastes upto 365 days
specific surface area significantly. On the other hand, reduction in and found that cement in HVFA pastes is not fully hydrated even at
the particle size of fly ash increases the amorphous SiO2 content 365 days. They reported the participation of ash in both early
and tends to decrease the amount of SO3 which can prevent the (sulpho-pozzolanic) and late (alumino-silicate) hydration re-
hydration reaction of harmful ions in concrete or mortar (Jones actions. Further, research studies indicated that HVFA cement paste
et al., 2006). The positive effect of fineness of fly ash on the me- may be considered as a new composite material in which FA par-
chanical properties of the concrete on increasing the compressive ticles act as reactive micro-aggregates embedded in hydration
strength is often reported (Yazici and Arel, 2012). While finer FA products, and generate crack which propagates around these fly
fractions are enriched with glass, minerals such as mullite, lime, ash particles (Zhang, 1995). Consequently, the compressive stress-
and Portlandite are the characteristics of coarser fractions. Hence, strain curve of HVFA paste is less linear than that of plain cement
the preferable utilization of finer fraction (less than 63 mm) in paste (Zhang, 1995). Thus, it is evident that high volume of fly ash
concrete and cement could enhance their pozzolanic activity. modifies the microstructure of the cement paste which in turn af-
However, the elimination of coarser fraction could suppress some fects the macromechanical behavior of the concrete. Previous
cementitious properties (Vassilev and Vassileva, 2007). studies (Alasali and Malhotra, 1991; Langley et al., 1989; Malhotra,
Size of fly ash can be reduced through milling processes for 1990) revealed that HVFA concretes generally have higher modulus
obtaining ashes of different particle size distributions and are of elasticity, lower shrinkage and creep when compared to the
widely reported in literature (Bouzoubaa et al., 1997; Bouzoubaa Portland cement (PC) concretes having equivalent compressive
et al., 1999; Kumar et al., 2007). During milling process, change in strength. This is because the unreacted fly ash particles have higher
particle shape may occur, as the glassy spherical ash particles are modulus of elasticity than the cement hydration products (Zhang,
shattered into fragments which brings added complication in the 1995). However, other important properties, such as compressive
analysis. Kumar et al. (2007) studied a particular ash which had stress-strain relation and fracture behavior, have not been thor-
shown reduction in particle size by classification, vibratory milling oughly quantified for a high volume fly ash concrete.
and attrition milling. They found that the strength of concrete made
with fly ash subjected to vibratory milling is higher than a concrete 3.4.1. HVFA as a structural concrete
containing fly ash that has been produced through attrition milling. Building code requirements for structural concrete (American
However, they reported that such effects could not be attributed Concrete Institute ACI Committee, 2011) limits the use of fly ash
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 551

as a cement replacement material to 35% in structural concrete. 70%). Fig. 2 shows the increased compressive strength with reduced
However, number of works have been carried out since 1980's to w/b ratio. However, the rate of increase is not the same for various
gain the acceptance for HVFA in mass concreting (Alasali and replacement levels of fly ash which shows the different levels of
Malhotra, 1991; Bilodeau and Malhotra, 2000; Giaccio and water requirement for different replacement levels which is in
Malhotra, 1988). High-volume fly ash concrete (HVFAC) is a con- agreement with the reported literature (Lam et al., 2000). Lam et al.
crete generally defined with at least 50% of the Portland cement (2000) showed that the complete reaction of 1 ml of 25% replace-
replaced by fly ash. The investigations have shown that HVFAC has ment of fly ash produces 2.52 ml of net volumes of hydration
superior structural performance (Arezoumandi and Volz, 2013; products, however, 50% replacement produces only 3.25 ml of hy-
Arezoumandi et al., 2015) with lower shrinkage, creep and water dration products by volume of binder which is also reflected in the
permeability (Bilodeau and Malhotra, 2000) when compared to experimental results. Further, it is reported that inspite of the low
conventional concrete. Cross et al. (2005) replaced the cement with water demand required for FA reaction than cement, water con-
100% Class C fly ash in pull out specimens and reported lower bond sumption is more in HVFA concrete owing to the pozzolanic reac-
strength for the HVFAC when compared to the conventional con- tion. This large consumption of water could consequently hamper
crete. However, studies conducted by Gopalakrishnan (2005) the cement hydration (Narmluk and Nawa, 2011).
showed the identical bond strength between HVFAC and conven- Inference: Although the advantage of reduced water to binder
tional concrete specimens. He conducted pullout tests on speci- ratio in increasing the strength is reported widely, reduced w/b
mens having 20 bars embedded into a 150 mm concrete cube to ratio results in the early age cracking of mixes. Hence, when low
determine the effects of using 50% fly ash replacement of cement. water to binder ratio is used, care should be taken to avoid this early
Arezoumandi et al. (2013) used 70% Class C fly ash as cement age cracking.
replacement in a relatively high total cementitious content (450 kg/
m3) mix and reported higher bond strength in the HVFAC compared
3.6. Curing temperature
to the conventional concrete for both pull out specimens and splice
beams.
Besides all the other factors considered in achieving potential
Inference: Studies showed the superior performance of HVFA in
strength and durability of concrete, curing conditions also play a
structural concrete. At long terms, FA concrete showed better re-
significant role (ACI Committee 308, 2001; Almusallam, 2001; Xue
sults even with higher replacement levels than that of control
et al., 2015). When supplementary cementitious materials are
concrete without fly ash. Hence, for applications that allow long
incorporated in cement, curing becomes even more important as
term strength, HVFA concretes can be recommended. Further, the
most of the SCMs are pozzolanic in nature (Al-Gahtani, 2010;
type of fly ash and replacement levels are closely related and
Bentur and Goldman, 2011; Khan and Ayers, 1995). In such type
combinedly affect the structural property, hence, the level of
of concretes, the rate and degree of hydration depend on the type of
replacement needs to be fixed based on the type of fly ash used.
curing process and period that follows placing and consolidation of
the concrete at fresh state.
3.5. Water to binder ratio
For a concrete with mineral admixtures, the minimum length of
curing should be optimized in terms of properties such as strength,
Achieving high strength concrete by using large quantities of fly
permeability and durability. The study carried out by Khan and
ash is difficult. However, the possibility of achieving high strength
Ayers (1995) shows that the minimum duration of curing for the
in fly ash concrete is reported with low water/binder (w/b) ratios
silica fume, OPC and fly ash cement concrete are 3, 3.75 and 6.5
(Bijen and Selst, 1993; Dunstan, 1986; Lam et al., 1998). Advance-
days respectively. In another study by Narmluk and Nawa (2011), it
ment in the concrete technology enables one to develop high
is reported that at temperature less than 35 C, presence of fly ash at
strength concrete with lower w/b ratios even with large volumes of
all replacement levels accelerate the cement hydration due to the
fly ash. The reactivity of fly ash is significantly altered by changing
cement dilution effect. However, at higher curing temperatures
the w/b, the substitution rate of fly ash for cement, curing tem-
(50 C), with high level of fly ash replacement, hydration is
perature (Kobayakawa et al., 1998) etc. Lam et al. (1998) demon-
impeded, because the pozzolanic reaction competes with the
strated, at w/b ratio of 0.5, 45% of fly ash replacement resulted in
cement hydration in consuming water to produce large amounts of
about 30% reduction in 28-day compressive strength, whereas at a
reaction product from early ages that counteract the dilution effect.
w/b ratio of 0.3, reduction in strength is only 17%. Further, it is re-
Escalante-Garcia and Sharp (1998) reported that in the paste with
ported that with 45% replacement of fly ash in cement, it is possible
to attain 28 day compressive strength of 80 MPa with lower water
to binder ratio of 0.24 (Poon et al., 2000). The low water to binder 80
ratio in fly ash cement also results in lower- heat of hydration and 0.4
chloride ingress when compared to the equivalent plain cement
70
0.28
concrete. At low water to binder ratio of 0.19 and 0.24 for plain 60
Compressive strength (MPa)

cement and fly ash cement pastes, about 40% of the cement and 80%
of the fly ash remain unreacted at the age of 90 days respectively. 50

These unreacted cement and fly ash particles serve as micro- 40

aggregates, which also contribute to the strength of the cementi-
tious material. Furthermore, the problem of delayed setting and 30

low early age strength in high volume fly ash concretes can also be
20
overcome by reducing water to binder ratio (Bentz et al., 2010).
In the study conducted by the first author at various replace- 10
ment levels of fly ash at different ages of curing, a significant
0
improvement of strength is observed with decrease in water to CEM 20FA 30FA 35FA 40FA 50FA 60FA 70FA
Mixes
binder ratio from 0.4 to 0.28. The study carried out shows that, at 7
days, there is an increase in compressive strength of fly ash cement Fig. 2. Compressive strength of FA-cement pastes with water to binder ratio of 0.4 and
pastes in the range of 3%e37% at various replacement levels (20%e 0.28 at 7 days.
552 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

w/b ratios of 0.50 and cured in water, fly ash slightly enhanced the as chemical properties like composition, glass content etc. (Babu
cement hydration at low temperatures but showed a retarding ef- and Rao, 1996). Further, Gopalan and Haque (1985), in their work
fect at elevated curing temperatures. Thus, it is reported that high suggested that the “k” factor depends on the other factors such as
temperature curing may not always result in a higher strength curing period, strength of concrete and class of fly ash. Further-
development. This is because at higher temperature (above 70  C) more, Bijen and Selst (1993) found that the “k” value also depends
the formation of mono sulfoaluminate (AFm) is more than that of upon the external factors like water to cement ratio. They reported
ettringite (AFt). According to thermodynamic calculation, AFt is the that “k” is a function of the water/cement ratio for conventional fly
stable phase below 70 C whereas AFm is stable even above 70 C ash and noted that the cementing efficiency of fly ash tends to
(Caijun Shi et al., 2006). Hence, at temperature above 70 C, the AFt decrease with increase in the water/cement ratio (Bijen and Selst,
is converted to AFm. When directly formed, AFm increases the solid 1993). On the contrary, Smith suggested that it does not vary
volume by about 79%, however, when converted from AFt to AFm, it with water to cement ratio.
decreases the solid volume by 7% thus reducing the strength. Besides cementing efficiency, pozzolanicity is considered as an
While there are reports about the reduced strength of FA- another important term in regard to fly ash concrete. Among all the
cement with high temperature curing, few reports are also stat- beneficial effects (lubrication, pozzolanic and filler effect) (Dhir
ing the beneficial role of fly ash mixtures in improving the long et al., 2012; Siddique, 2004; Sua-iam and Makul, 2015) of fly-ash
term strength (Maltais and Marchand, 1997) at increased curing reported in cement/concrete, pozzolanic action is considered as
temperature. Yazici et al. (2005) studied the effect of steam curing most important. Pozzolanic reaction mainly depends upon the
on Class C high-volume fly ash concrete mixtures and concluded content of Al2O3 and SiO2 present in FA and is activated by Por-
that steam curing improved the early strength (1 day) of mixes tlandite formed during the cement hydration to produce more
from about 10 to 20 MPa, but, the long term strength has not hydrated gel. This gel fills the capillary pores in concrete that in turn
improved. The main problem of decreased early age strength with improves the strength (Cao et al., 2000). Hence, the reactivity of fly
high volume fly ash replacement in cement is addressed by many ash depends highly upon its chemical composition. However, in
methods including lower water to cement ratio as discussed in general, all the pozzolanic materials are composed of aluminosili-
section 3.5. Varga et al (Varga et al., 2012, 2014). conducted a study cate glass that reacts with calcium hydroxide produced during
by using a lower water to cement (w/c) ratio to minimize the po- cement hydration to form hydration products as shown by Equa-
tential reductions in early strength development that can occur tions (4)e(7) (Papadakis, 1999; Zeng et al., 2012).
with the high volume replacement of fly ash. However, they found
that while improving the mechanical and transport properties by 3CH þ 2S/C3 S2 H3 (4)
lowering w/c, the mixtures are more susceptible to early-age
cracking (Varga et al., 2012, 2014). Hence, they recommended in- A þ F þ 8CH þ 18H/C8 AFH26 (5)
ternal curing method to reduce self-desiccation which would
reduce autogenous shrinkage and cracking potential while
enabling more of the fly ash to react. Internal curing may enable the
A þ CSH2 þ 3CH þ 7H/C3 ACSH12 (6)
mixture to react for a longer time since water can be supplied to the
concrete over a longer period. The results indicate that HVFA A þ 4CH þ 9H/C4 AH13 (7)
mixtures with internal curing provide benefits in terms of reduced
transport coefficients when compared to the OPC mixtures (Varga where CH ¼ Portlandite; S ¼ SiO2; H ¼ H2O; A ¼ Al2O3; F ¼ Fe2O3;
et al., 2014). S ¼ SO3
Inference: Though few studies report the improved strength of These reactions take place at different stages of curing to form
FA concrete cured at elevated temperature, few works state the various hydration products. Hence, strength and durability of FA
reduced strength under high temperature curing. In order to incorporated cement/concrete varies depending upon the age and
resolve this reported discrepancy, further studies are needed to replacement levels. It is well known that the pozzolanic reaction
understand the reaction kinetics in FA concrete with the change in can take place only when a sufficient amount of calcium hydroxide,
temperature. a by-product of the hydraulic reaction of cement is available. The
pozzolanic reaction can thus only happen after the hydraulic re-
4. Cementing efficiency and pozzolanic reaction action. The scanning electron microscope image (Fig. 3) shows the
unreacted fly ash in FA-concrete where Class F fly ash is used. This
The concept of cementing factor (k) is introduced by Smith figure indicates that the pozzolanic reaction has not yet started
(1967) to develop a rational method for incorporation of fly ash even at 28 days (Hemalatha et al., 2015). The hydration rate of
in cement/concrete. The overall quality, durability and performance pozzolanic materials depends on the amount of calcium hydroxide
of concrete can be assessed by cementing efficiency. In general, fly
ash exhibits a very little cementing efficiency at the early ages and
acts rather like fine aggregate (filler), but at later ages, the pozzo-
lanic property becomes effective leading to a considerable strength
improvement. This obviously means that the cementing efficiency
of fly ash improves with age due to the pozzolanic reaction. Ac-
cording to Smith “the mass of fly ash can be equivalent to the mass
of cement in relation to the development of compressive strength”.
In other words, “k” is a factor that explains the difference between
the contribution of the Portland cement and the contribution of
mineral admixtures in the development of a specific property. This
cementing efficiency is generally determined through compressive
strength tests due to its simplicity and reliability. The “k” value of
fly ash depends on many of its inherent characteristics such as
physical properties like particle shape, size and distribution as well Fig. 3. SEM showing unreacted fly ash at 28 days.
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 553

in hydrating cement-FA blends and the reaction degree of mineral water (Fung and Kwan, 2010; Nochaiya et al., 2010; Wong and
admixtures (Belie et al., 2011; Pane and Hansen, 2005). For a hy- Kwan, 2008). These dual effects encountered with fine fillers can
draulic reaction to take place, the presence of CaO plays a signifi- increase the packing density but the amount of excess water per
cant role, however, the existence of amorphous or glassy silica and surface area may or may not increase. Hence, to balance the
aluminum oxide also have an important role in the pozzolanic re- desirable increase in packing density and undesirable increase in
action. Thus, the amount of CaO can be associated with strength at surface area, it is required to have a filler that is finer than cement
earlier age while that of SiO2 and Al2O3 are associated with the but coarser than nano silica/silica fume. Based on these criteria,
strength at later age. The compressive strength of the FA-cement Kwan and Chen (2013) used fly ash microsphere (FAM), a good filler
systems therefore have to be compared against the ratio of Ca/Si for improving the packing density without excessively increasing
and Ca/Al, where CaO, SiO2 and Al2O3 represent the total weight the surface area. It has a spherical particle size of micrometer scale,
percentage of these components in the entire binder. finer than cement and ordinary fly ash but coarser than nanosilica/
Inference: Pozzolanic reaction is affected mainly by the pres- silica fume. Further, it is reported that if fly ash with different
ence of amorphous or glassy silica and alumina content in FA. particle size is added to cement, the particle size distribution of the
Hence, calcium to silica as well as calcium to alumina ratio de- FA-cement system changes, affecting the packing density of the
termines the pozzolanic activity of the FA in cement. Further, the pastes so that the water retention of the pastes will vary. Thus, the
pozzolanic reaction in FA-cement system depends mainly on the fluidity of the pastes is expected to change (Nagataki et al., 1984;
cementing efficiency of the fly ash used. Therefore, the knowledge Hosino et al., 1995, 1996), which indicates that fly ash fineness
on cementing efficiency of fly ash is required for the optimized use determines the properties of the end material.
of FA. Inference: While few studies report the lesser requirement of
water due to pore refinement and spherical morphology of fly ash
5. Influence on the fresh properties for workability of concrete, few studies report the high water de-
mand owing to its larger surface area. This well known contradic-
All mineral admixtures, particularly, fly ash can provide plasti- tion related to water demand with fly ash utilization needs to be
cising effects enhancing the paste and concrete workability (Kim resolved.
et al., 2012). Lee et al. (2003) summarized the following factors as
reasons for the plasticising effect of fly ash. Firstly, increase in paste 6. Influence on shrinkage properties
volume owing to lower density of FA compared to that of cement.
Secondly, due to dilution effect, FA reduces the flocculation of the One of the main reasons for cracking in concrete is the strains
cement particles. Thirdly, due to the slower reaction of the fly ash induced by shrinkage. Though the integrity of structure is not
owing to the reduced growth of hydration products at early age. affected by the stresses caused due to restrained shrinkage, it in-
Apart from all these reasons, the spherical shape of fly ash particles creases the durability related problems (Al-Saleh and Al-Zaid,
facilitate the movement of neighboring particles particularly at 2006; Holt and Leivo, 2004). While drying shrinkage is caused
high replacement levels by ball bearing effect. Hence, FA can be due to the loss of water from the concrete, autogeneous shrinkage
highly cost-effective that offers lower environmental impact than is caused due to the change in macroscopic volume, when no
chemical superplasticisers (Kashani et al., 2014) in enhancing the moisture is transferred to the surrounding environment. Hence,
flowability. The studies conducted by Bentz et al. (2012). also shrinkage of concrete should always be addressed as a total
confirmed the beneficial role of fly ash in enhancing the fluidity of amount, combining both drying and autogenous deformations. It is
the mix. The replacement of cement by fly ash will decrease the reported that the problem of volume change due to shrinkage can
yield stress, due to decrease in density of cement particle as re- be often overcome by the use of filler materials such as fly ash or
ported earlier (Lee et al., 2003) and therefore reduces the number of sand (Rao, 2001). Mokarema et al. (2005) stated that mixtures with
flocculated cement particle to cement particle connections. How- supplementary cementitious material exhibited greater drying
ever, the type of fly ash used has a significant role in affecting the shrinkage than the Portland cement concrete mixtures. Especially,
fresh properties. According to Ponikiewski and Golaszewski (2014), mixtures containing fly ash exhibit greater drying shrinkage than
high calcium fly ash negatively affects the workability which in turn those containing microsilica and slag cement. A concrete mixture
affects the strength and durability properties too. The performance using supplemental cementitious materials such as fly ash, micro-
of a concrete at fresh state is highly dependent on the flowability of silica and slag cement have a more refined pore structure than
the cement paste which in turn is governed by many factors such as ordinary Portland cement concrete mixtures. Due to this reason,
water/binder (w/b), type, dosage of SCM (ACI Committee 234, more smaller capillary voids are present in these mixtures and
2006; ACI Committee 363, 1992) etc. Besides these factors, previ- hence the removal of water from these voids may result in more
ous studies (Kwan and Wong, 2008; Lee et al., 2003; drying shrinkage. Guneyisi et al. (2010) also added that concrete
Nanthagopalan et al., 2008) have shown that the packing density with higher amount of cementitious materials has finer pore
of the cementitious materials is also an important factor governing structure that may proportionally increase the free shrinkage.
the flowability of the cement paste, especially at low w/b ratio. Particularly, the damage due to autogeneous shrinkage can be
Basically, higher packing density means lesser water demand and reduced significantly with the use of fly ash in cements/concrete
hence more water is released (after filling the voids) to coat the (Akkaya et al., 2007; Chan et al., 1998). Both Class F and Class C fly
solid particles and lubricate the cement paste. In general, any solid ash are considered to be good in reducing the drying shrinkage
material finer than cement, whether cementitious or inert can be (Maslehuddin et al., 1987; Zhao et al., 2015). According to the
used to fill the voids in cement to increase the packing density literature (Maslehuddin et al., 1989; Sahmaran et al., 2007),
(Kwan and Chen, 2013). Among the various fillers reported, very shrinkage is reduced by the presence of FA that densifies the mix to
fine fillers such as nano silica and silica fume are considered as the prevent the evaporation of internal moisture. Another reason re-
best for increasing the packing density. One way, the small particle ported in the literature for the restrained shrinkage (Bisaillon et al.,
size enables these fillers to fill into the voids in cement without 1994; Maslehuddin et al., 1987; Zhang, 1995) is the presence of
loosening the packing of cement grains to effectively increase the unhydrated FA particles in the mix that serve as fine aggregates.
packing density. However, on the other hand, large specific surface However, few studies have contradicted these findings and re-
area dramatically increases the solid surface area to be coated with ported that fly ash with smaller size than cement increases the
554 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

autogeneous shrinkage (Tangtermsirikul, 1998; Wang et al., 2001). hydrolyses first and the solution reaches a high pH value very
These studies report that small sized fly ash reduces the distance quickly (Eq. (8)) (Qian et al., 2001):
between the particles which in turn decreases the pore size in the
paste and as a consequence, capillary pressure in the paste in- CaðOHÞ2 /Ca2þ þ 2OH (8)
creases when water is consumed during hydration of cement
In that high pH solution, very quick dissolution of network
(Tangtermsirikul, 1998). This phenomenon is also explained by the
modifiers such as Ca2þ, Kþ, Naþ, etc., in fly ash takes place. Silicate
removal of adsorbed water when concrete continues to dry. In
or aluminosilicate network formers in fly ashes are also depoly-
general, adsorbed water is held by hydrostatic tension in the small
merized and dissolved into the solution. Subsequently, the forma-
capillaries. When this water is removed, it produces tensile
tion of calcium silicate hydrate and calcium aluminate hydrate
stresses, which cause the concrete to shrink. The shrinkage caused
C4AH13 take place when Ca2þ ions in solution contact these dis-
due to the removal of adsorbed water is significantly larger than
solved monosilicate and aluminate species. Hence, the pozzolanic
that associated with the loss of free water.
reaction rate is determined by the dissolution of aluminosilicate
Inference: While some studies report the reduced shrinkage
glass as this is the slowest process during the initial pozzolanic
with FA incorporation, few other studies report to the contrary, an
reaction. When reaction progresses, after a certain period, the
increase in shrinkage properties. Hence, the effect of various levels
surface of fly ash particles is coated by hydration products precip-
of different types of fly ash on shrinkage properties of concrete
itate and later on the reaction is controlled by the diffusion of OH
needs to be studied in order to understand the mechanism to
and Ca2þ through the precipitated products and into the inner side
reduce shrinkage in FA concrete.
of precipitated products. When alkali like Na2SO4 is added, Na2SO4
reacts with Ca(OH)2 first as expressed by Eq. (9) (Qian et al., 2001):
7. Methods to improve the strength of FA concrete
Na2 SO4 þ CaðOHÞ2 þ 2H2 O/CaSO4 :2H2 O þ 2NaOH (9)
7.1. Alkali activation
Addition of Na2SO4 increases the pH of the solution, accelerates
Fly ash utilization has been increasing in concrete industry due the dissolution of fly ashes and speeds up the pozzolanic reaction
to its benefits such as lesser heat of hydration and improved between Ca(OH)2 and the fly ashes. Meanwhile, the introduction of
durability. However, its contribution to strength occurs only at later Na2SO4 increases the concentration of SO2 4 resulting in the for-
ages due to the slow pozzolanic reaction. Efforts have been made to mation of more ettringite (AFt). The generation of AFt increases the
overcome this well known deficiency of fly ash by adopting various solid volume compared to C-S-H and therefore densifies the
methods. Chemical activation is one such methods that can be structure and as a result increases the early strength of hardened
carried out either through alkali or sulfate activation. The glass cement pastes significantly (EPRI, 1991). Thus, Na2SO4 as an acti-
phases of fly ash have been broken down in alkali activation to vator performs the dual function in improving the early strength by
accelerate the reaction at early ages (Frany et al., 1989; Xu and accelerating the early pozzolanic reaction and through the forma-
Sarkar, 1991) whereas sulfate reacts with aluminium oxide in the tion of more AFt.
glass phase of fly ash to produce ettringite (AFt) in sulfate activa-
tion. In both these cases, strength is increased at early ages (Shi, 7.2. Nano modified fly ash
1996, 1998; Xu and Sarkar, 1991). The alkali activation of fly ash is
a physico-chemical process that transforms a powdery ash into a As mentioned in earlier section 7.1, slow development in early-
material with good cementitious properties (Fernandez-Jimenez age strength of fly ash cement-systems is often considered to be a
and Palomo, 2003; Jaarsveld and Deventer, 1999; Palomo et al., major drawback (Hassett and Eylands, 1997; Lam et al., 2000; Sakai
2004, 1999) resulting in high mechanical strength, excellent et al., 2005). In order to overcome this shortcoming, many methods
bonding to reinforcement steel (Fernandez-Jimenez et al., 2006) including alkali activation have been explored to accelerate the
and so on. Poon et al. (2001) studied the activation of fly ash cement early-age hydration of fly ash-cement systems. The use of nano
systems using anhydrite and found that with accelerated curing, particles in cement-FA system is one among them and more pop-
large amount of ettringite is formed during early ages of hydration ular due to its advantages. The nano particles act as a nuclei for
resulting in high early age strength. The effectiveness of Na2SO4 and cement to accelerate the cement hydration and densify the
CaCl2 is also investigated (Shi, 1996, 1998) and found that the microstructure and interfacial transition zone (ITZ), thereby
former increased the early age strength while the latter increased reducing the permeability (Sanchez and Sobolev, 2010). Further, the
the later age strength. Kovtun et al. (2016) attempted direct electric combination of fly ash and nano materials can tightly bond the
curing in alkali activated fly ash concrete using sodium hydroxide hydration product which is regarded as an important factor for
and sodium silicate and succeeded in achieving improved early age accelerating the pozzolanic reaction as it compensates for the low
strength. However, for the successful alkali activation process, it is early strength development (Shaikh et al., 2014; Supit et al., 2013;
very important to know the percentage of reactive silica in the fly Supit and Shaikh, 2015).
ash, as it is reacting with the alumina and the alkalis (Fernandez- Among the nano materials used in enhancing the early-age
Jimenez and Palomo, 2003). Besides the reactive silica content, properties of FA-cement systems (Nazari and Riahi, 2011; Sato
the vitreous phase content and the particle size distribution are and Diallo, 2010), nano silica (NS) has often been the first choice
also playing the key role in their potential reactivity. According to (Li, 2004; Said and Zeidan, 2009; Ye et al., 2007). The reason for its
Fernandez-Jimenez and Palomo (2003), the main characteristics of popularity is three fold: firstly, the accelerating effect on cement
a fly ash to be a material with optimal binding properties for alkali hydration, secondly, its pozzolanic reaction and finally, the
activation are 1) the percentage of unburnt material lower than 5% improved particle packing of the matrix. Overcoming the drawback
2) Fe2O3 content not greater than 10% 3) presence of low content of of pozzolan replaced cement-based materials system, these char-
CaO and reactive silica between 40% and 50% 4) particles with size acteristics of NS greatly enhance the physical and mechanical
lesser than 45 mm between 80% and 90% 5) presence of high content properties of fly ash/slag systems (Zhang and Islam, 2012; Zhang
of vitreous phase. et al., 2012). As low as 1% incorporation of NS in high volume fly
In the absence of an activator, when a lime-fly ash blended ash cement pastes reduced the length of dormant period and
cement is mixed with water, Ca(OH)2 in the blended cement accelerated the hydration (Zhang and Islam, 2012). Further, it is
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 555

Fig. 4. Schematic diagram showing the state of the art, drawbacks, solutions and future directions to increase the FA utilization in concrete.

reported that NS of smaller mean size (12 nm) is more effective in setting caused by HVFA. When used as an addition/replacement
than larger size (150 nm) in increasing the early age strength of in cement, limestone/NC besides providing additional nucleation
HVFA concrete. surfaces for the cement hydration, also acts as an additional source
When NS is used in addition to FA in cement systems, they both of calcium ions to the pore solution (Bentz, 2006). Further, the
adsorb, react with, or consume Portlandite (CH) generated from presence of CaCO3 nanoparticles increases the rate of reaction of
cement hydration to get a considerable improvement in strength. tricalcium aluminate (C3A) to form carboaluminate complex
The dosage of NS is also a factor and in general, it should not be less thereby increasing the total hydration products yielding improved
than 5% by mass of binder (Jo et al., 2007). Jo et al. (2007) examined strength (Hemalatha et al., 2016; Weerdt et al., 2010). In addition,
the characteristics of NS in cement mortar and concluded that NS CaCO3 also reacts with tricalcium silicate (C3S) and accelerates
not only acts as a filler in improving the microstructure but also setting and early strength development (Pera et al., 1999). As a
promotes pozzolanic reaction. With the incorporation of NS, Nazari consequence of the formation of large volume of hydrates, the
and Riahi (2010) reported the improved strength and water dilution effect of the binding material is compensated by the
permeability in high strength self compacting concrete (HSSCC), increased degree of hydration resulting in higher initial strengths
especially during early age of hydration. Addition of 4% of NS by (Georgescu and Saca, 2009).
weight of cement accelerates the C-S-H gel formation in HSSCC. Inference: The strength of cement-FA system can be improved
Roychand et al. reported that with 5% and 7.5% of NS in HVFA by various means including the methods discussed so far. For an
blended mix, increase the compressive strength from 76 to 94% effective strength improvement either through alkali activation or
respectively at 7 days. While assuming NS has been fully hydrated, nano additions, knowledge on characteristics of FA is needed. In
addition of 5 g of NS can adsorb almost 50% of the CH produced order to form calcium silicate gel in case of nano addition or alu-
from 100 g of cement. A total of 20 g of CH can be generated, mino silicate gel in case of alkali activation, Ca/Si and Ca/Al ratio are
yielding a gel with Ca/Si ratio of 1.7. Since NS and FA compete in considered to be important factor respectively. By adopting either
adsorbing CH, where NS is far more reactive than FA, it can be of these methods, it is possible to achieve 60% replacement of
deduced that there may be a shortage of CH in a NS added FA cement by FA without compromising the strength and durability.
cementitious material system, thus preventing FA hydration at the Ternary blend of cement, FA and NS/NC can be recommended for a
later age, especially when the FA content is high. HVFA concrete.
Similar to NS, nano-CaCO3 (NC) is another nano material that
has been introduced recently in concrete to accelerate the hydra- 8. Discussion and conclusions
tion process (Shaikh and Supit, 2014). Although the use of calcium
carbonate was first considered as a filler to partially replace cement According to American coal ash association (ACAA), coal usage is
or gypsum, some studies have shown the advantages of using expected to increase 3.4% over the next two decades despite the
CaCO3 nanoparticles in terms of strength, accelerating effect and retirement of many coal plants. Similarly, in Indian scenario, the ash
economic benefits as compared to cement and other supplemen- generation figures are expected to be greater than 2100 million
tary cementitious materials (Celik et al., 2014; Kawashima et al., tonnes in 2031-32 as per an estimate by Technology, information,
2013). At early ages, in the presence of CaCO3, calcium aluminate forecasting and assessment council (TIFAC). In order to reduce the
monocarbonate is formed instead of monosulfate. Further, CaCO3 impact on the environment due to growing fly ash production and
delays the transformation of stable ettringite to unstable mono- to improve sustainability in construction sector, there is a global
sulfate (Kakali et al., 2000) thus increasing the total volume of solid need to understand the benefits of utilizing fly ash in concrete.
phases. Study by Kawashima et al. (2013) showed that 5% of NC In view of this, the progress made all over the world in the
addition in 50% replacement of cement with fly ash offset the delay utilization of fly ash in cement/concrete is critically reviewed and
556 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

discussed in this study. It is proved that most of the properties increasing the strength of high volume FA concrete by reduced
(strength/durability) of FA concrete depend upon the alkali content water to binder ratio, early/later age strength may be increased,
of pore solution which is controlled by the consumption of CH but the mix ends up with early age cracking. Hence, it is
formed during cement hydration, presence of soluble alkalis, essential to address the combined influence of various factors to
amorphous phases etc. Hence, comprehensive knowledge on derive the maximum benefit of fly ash with cement in an opti-
characteristics of different types of fly ash and its hydration mally designed mix.
mechanism would improve the basic understanding of using FA in 3. Most of the structural engineering applications need compres-
cement/concrete in a more scientific manner rather than using by sive strength of about 30 MPa that is possible with the high
trial and error basis. volume replacement of FA. Further, the long term strength of FA
While current techniques and procedures are well-established concrete is higher than that of cement concrete, hence, FA
to engineer the concrete with large volumes of fly ash to produce concrete can be recommended in applications where early age
good results, utilization of high volumes of FA remains unaccom- strength is not significantly necessary.
plished due to problems such as high carbonation, slow develop- 4. Currently, there is an emerging trend in the development of
ment of strength, increased shrinkage etc. Nevertheless, along with geopolymer wherein 100% of FA is utilized. However, in order to
the limitations in the use of high volumes of fly ash in concrete, make this new concrete more robust and acceptable, the re-
suitable methods (high temperature curing, mechanical grinding, ported disadvantages shown in schematic diagram (Fig. 4) need
chemical activation) and materials (by adding nano silica/nano to be resolved. In this context, the engineered FA concrete which
carbonate) to address these limitations have been explored and can replace cement upto 60% is reported to be a better alter-
found to be successful. With the progress in the current research native in terms of both strength and durability.
along with the findings reported so far, the next couple of years 5. From the detailed review of fly ash as cement substitute mate-
would see the replacement of FA to a maximum of 60% by mass, rial, it is recommended to have further classifications of fly ash
which may pave the way for amendments in various codes for high apart from the existing ASTM classifications.
volume utilization of fly ash. The application of codes may come
into force on a large scale acceptance in a span of further few years Nomenclature
improving the present utilization of the FA produced. For instance,
the current utilization of FA produced in a country like India is 55%. FA Fly ash
This can grow to a near 100 percent with the modification of its NS Nano silica
code for 60% FA replacement. A schematic diagram (Fig. 4) showing NC Nano calcium carbonate
the state of the art in cementitious materials, limitations of CH CaOH2/Portlandite
different materials in use, drawbacks in using FA and a road map to S SiO2
maximize FA utilization is proposed. H H2O
In the literature, properties of FA concrete is discussed with a A Al2O3
focus on two types of fly ash as “Class F” and “Class C”. According to F Fe2O3
ASTM standard, FA is classified based on the content of SiO2, Al2O3 S SO3
and Fe2O3. Whereas, the chemical composition of two major types C Calcium
of fly ash shown in Table 1 reveals that there is a wide variation in CSH Calcium silicate hydrate
the element oxides for a same type of FA. This study reveals that
C6 AS3 H32 Ettringite
apart from SiO2, Al2O3 and Fe2O3, other oxides are also responsible
for the reactivity of fly ash, hence, properties cannot be generalized
only with Class F (low calcium) or Class C (high calcium) fly ash. References
Nevertheless, with the advancements in the characterization tools
ACAA. American Coal Ash Association. https://www.acaa-usa.org/About-Coal-Ash/
such as X-ray diffractometer, thermo gravimetric analyzer, scan- A-Sustainable-Future. (Accessed: 1 June 2017).
ning electron microscopy, Fourier transform infra red analyzer etc. ACI, 1979. ACI Manual of Concrete Practice, 1979. American Concrete Institute. URL:
https://books.google.co.in/booksid¼HTGHnQEACAAJ.
that are employed for cementitious applications, it is possible to
ACI Committee 234, 2006. Guide for the Use of Silica Fume in Concrete. American
analyze the FA for chemical and physical characteristics to utilize it Concrete Institute, Detroit, USA.
more effectively. Further, understanding the hydration mechanism ACI Committee 308, 2001. Guide to Curing Concrete (ACI 308R-01). American
of FA in cement and its correlation with property development Concrete Institute, Farmington Hills.
ACI Committee 363, 1992. State-of-the-Art Report on High-strength Concrete.
through these advanced techniques facilitate the intervention of American Concrete Institute, Detroit, USA.
the hydration mechanism either through physical measures Aggarwal, V., Gupta, S., Sachdeva, S., 2010. Concrete durability through high volume
(majorly through size reduction) or chemically (incorporating nano fly ash concrete (HVFC) - a literature review. Int. J. Eng. Sci. Technol. 2,
4473e4477.
materials) to increase the efficiency of fly ash in concrete. Akkaya, Y., Ouyang, C., Shah, S.P., 2007. Effect of supplementary cementitious ma-
terials on shrinkage and crack development in concrete. Cem. Concr. Compos.
9. Future research and recommendations 29, 117e123.
Al-Gahtani, A., 2010. Effect of curing methods on the properties of plain and
blended cement concretes. Constr. Build. Mater. 24, 308e314.
1. With all the reported procedure to use FA in high volumes, 100% Al-Saleh, S.A., Al-Zaid, R.Z., 2006. Effects of drying conditions, admixtures and
utilization of produced FA is still not achieved because of the specimen size on shrinkage strains. Cem. Concr. Res. 36, 1985e1991.
Alasali, M., Malhotra, V., 1991. Role of concrete incorporating high volumes of fly ash
existence of certain grey areas discussed in this study which in controlling expansion due to alkali aggregate reaction. ACI Mater. J. 88,
needs to be given attention in future to improve the utilization 159e163.
of FA as a cement/sand substitute material. The future research Ali Akbar Ramezanianpour, 2014. Cement Replacement Materials Properties,
Durability, Sustainability, first ed. Springer, Newyork, p. 336.
needs to be geared up in the direction to solve the reported
Almusallam, A., 2001. Effect of environmental conditions on the properties of fresh
discrepancies related to shrinkage, water demand, accelerated and hardened concrete. Cem. Concr. Compos. 23, 353e361.
curing etc. as highlighted in inference of various sections. American Concrete Institute ACI Committee, 2011. Building Code Requirements for
2. As fly ash reactivity is dependent on more than one factor, while Structural Concrete ACI 318-08 and Commentary 318R-11. ACI 318-08/318R-11.
American Concrete Institute, Farmington Hills, MI, USA.
attempting to achieve one property through modification of one Arezoumandi, M., Volz, J.S., 2013. Effect of fly ash replacement level on the shear
factor, other properties may disturbed. For instance, while strength of high-volume fly ash concrete beams. J. Clean. Prod. 59, 120e130.
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 557

Arezoumandi, M., Looney, T.J., Volz, J.S., 2015. Effect of fly ash replacement level on Report No. REC-ERC-76. U.S. Bureau of Reclamation, Denver, CO, USA, p. 23.
the bond strength of reinforcing steel in concrete beams. J. Clean. Prod. 87, Dunstan, E., 1980. A possible method for identifying fly ashes that will improve the
745e751. sulfate resistance of concretes. Cem. Concr. Aggreg. 2, 20e30.
Arezoumandi, M., Wolfe, M., Volz, J., 2013. A comparative study of the bond Dunstan, E., 1984. Fly Ash and Fly Ash Concrete. Report No. REC-ERC-76. U.S. Bureau
strength of reinforcing steel in high-volume fly ash concrete and conventional of Reclamation, Denver, CO, USA, 23. 42 pp.
concrete. Constr. Build. Mater. 40, 919e924. Dunstan, M., 1986. Fly Ash as the ‘Fourth Ingredient’ in Concrete Mixtures, Fly Ash,
ASTM - C618e8a, 2009. Standard Specification for Coal Fly Ash and Raw or Calcined Silica Fume, Slag, and Natural Pozzolanics in Concrete. ACI SP-91 39, 171e197.
Natural Pozzolan for Use in Concrete. ASTM International, USA. Detroit.
Babu, K.G., Rao, G.N., 1996. Efficiency of fly ash in concrete with age. Cem. Concr. Durdzinski, P.T., Dunant, C.F., Haha, M.B., Scrivener, K.L., 2015a. A new quantification
Res. 26, 465e474. method based on SEM-EDS to assess fly ash composition and study the reaction
Belie, N., Baert, G., Schutter, G., 2011. Modelling of microstructure of Portland of its individual components in hydrating cement paste. Cem. Concr. Res. 73,
cement: fly ash binders based on calorimetric and thermogravimetric experi- 111e122.
ments. In: 13th International Congress on the Chemistry of Cement. Consejo Durdzinski, P.T., Snellings, R., Dunant, C.F., Haha, M.B., Scrivener, K.L., 2015b. Fly ash
Superior Investigaciones Cientificas (CSIC), Madrid, pp. 1e7. as an assemblage of model Ca-Mg-Naealuminosilicate glasses. Cem. Concr. Res.
Bendapudi, S.C.K., 2011. Contribution of fly ash to the properties of mortar and 78 (Part B), 263e272.
concrete. Int. J. Earth Sci. Eng. 04 (06 SPL), 1017e1023. Embong, R., Kusbiantoro, A., Shafiq, N., Nuruddin, M.F., 2016. Strength and micro-
Bentur, A., Goldman, A., 2011. A curing effects, strength and physical property of structural properties of fly ash based geopolymer concrete containing high-
high strength silica fume concretes. Mater Civ. Eng. ASCE 1, 46e58. calcium and water-absorptive aggregate. J. Clean. Prod. 112, 816e822.
Bentz, D., 2006. Modeling the influence of limestone filler on cement hydration EPA, 2008. Study on Increasing the Usage of Recovered Mineral Components in
using CEMHYD3D. Cem. Concr. Compos. 29, 124e129. Federally Funded Projects Involving Procurement of Cement or Concrete.
Bentz, D., Ferraris, C., la Varga, I.D., Peltz, M., Winpigler, J., 2010. Mixture propor- Environmental Protection Agency, 2008.
tioning options for improving high volume fly ash concretes. Int. J. Pavement EPRI, 1991. Mechanistic Basis for Cementing Action. EPRI GS-7122, Project 2708e4.
Res. Technol. 3, 234e240. Erdogdu, K., Turker, P., 1998. Effects of fly ash particle size on strength of Portland
Bentz, D.P., Ferraris, C.F., Galler, M.A., Hansen, A.S., Guynn, J.M., 2012. Influence of cement fly ash mortars. Cem. Concr. Res. 28, 1217e1222.
particle size distributions on yield stress and viscosity of cement fly ash pastes. Escalante-Garcia, J., Sharp, J., 1998. Effect of temperature on the hydration of the
Cem. Concr. Res. 42, 404e409. main clinker phases in Portland cements: Part II, blended cements. Cem. Concr.
Berry, E., Hemmings, R., Cornelius, B., 1990. Mechanisms of hydration reactions in Res. 28, 1259e1274.
high volume fly ash pastes and mortars. Cem. Concr. Compos. 12, 253e261. Feldman, R., Carette, G., Malhotra, V., 1990. Studies on mechanics of development of
Berry, E.E., Hemmings, R.T., Zhang, M.H., Cornelius, B.J., Golden, D.M., 1994. Hy- physical and mechanical properties of high-volume fly ash-cement pastes. Cem.
dration in high-volume fly ash concrete binders. ACI Mater. J. 91, 382e389. Concr. Compos. 12, 245e251.
Bijen, J., Selst, R.V., 1993. Cement equivalence factors. Cem. Concr. Res. 23, Fernandez-Jimenez, A., Palomo, A., Lopez-Hombrados, C., 2006. Engineering prop-
1029e1039. erties of alkali-activated fly ash concrete. ACI Mater. J. 106e112.
Bilodeau, A., Malhotra, V.M., 2000. High-volume fly ash system: concrete solution Fernandez-Jimenez, A., Palomo, A., 2003. Characterisation of fly ashes. potential
for sustainable development. ACI Mater. J. 97, 41e48. reactivity as alkaline cements. Fuel 82, 2259e2265.
Bisaillon, A., Rivest, M., Malhotra, V., 1994. Performance of high-volume fly ash Frany, A., Bijen, J., Haan, Y.D., 1989. The reaction of fly ash in concrete, a critical
concrete in large experimental monoliths. ACI Mater. J. 91, 178e187. examination. Cem. Concr. Res. 19, 235e246.
Bleszynski, R., Thomas, M., 1998. Microstructural studies of alkali silica reaction in Fung, W.W.S., Kwan, A., 2010. Role of water film thickness in rheology of CSF mortar.
fly ash concrete immersed in alkaline solutions. Adv. Cem. Based Mater. 7, Cem. Concr. Compos. 32, 255e264.
66e78. Georgescu, M., Saca, N., 2009. Properties of blended cement with limestone filler
Blissett, R., Rowson, N., 2012. A review of the multi-component utilisation of coal fly and fly ash content. Sci. Bull. 71 (3). ISSN 14542331.
ash. Fuel 97, 1e23. Ghosh, S.N., Sarkar, L.S., 1993. Mineral admixtures in cement and concrete. In:
Bouzoubaa, N., Zhang, M., Bilodeau, A., Malhotra, V., 1997. The effect of grinding on Progress in Cement and Concrete, first ed. ABI Books, New Delhi, p. 565.
the physical properties of fly ashes and a Portland cement clinker. Cem. Concr. Giaccio, G., Malhotra, V., 1988. Concrete incorporating high volumes of ASTM Class F
Res. 27, 1861e1874. fly ash. Cem. Concr. Aggreg. 10, 88e95.
Bouzoubaa, N., Zhang, M., Malhotra, V., Golden, D., 1999. Blended fly ash cements a Gopalakrishnan, S., 2005. Demonstration of Utilising High Volume Fly Ash Based
review. ACI Mater. J. 96, 641e650. Concrete for Structural Applications. Structural Engineering Research Centre,
British Standards Institution, 1997a. BS 5328: Part 1, Guide to Specifying Concrete. Chennai, India.
British Standards Institution, 1997b. BS 8110: Part I, Structural Use of Concrete: Code Gopalan, M., Haque, M., 1985. Design of fly ash concrete. Cem. Concr. Res. 15,
of Practice for Design and Construction. 694e702.
Bukhari, S.S., Behin, J., Kazemian, H., Rohani, S., 2015. Conversion of coal fly ash to Guneyisi, E., Gesoglu, M., zbay, E., 2010. Strength and drying shrinkage properties of
zeolite utilizing microwave and ultrasound energies: a review. Fuel 140, self-compacting concretes incorporating multi-system blended mineral ad-
250e266. mixtures. Constr. Build. Mater. 24, 1878e1887.
Caijun Shi, Krivenko, Pavel V., Roy, Della, 2006. Alkali-activated Cements and Hassett, D., Eylands, K., 1997. Heat of hydration of fly ash as a predictive tool. Fuel
Concretes. Taylor and Francis, London and New Tork. 76, 807e809.
Cao, C., Sun, W., Qin, H., 2000. The analysis on strength and fly ash effect of roller Hemalatha, T., 2011. Studies on Characterization of Self Compacting Concrete:
compacted concrete with high volume fly ash. Cem. Concr. Res. 30, 71e75. Microstructure, Fracture and Fatigue. Ph.D. thesis. Department of Civil Engi-
Celik, K., Jackson, M., Mancio, M., Meral, C., Emwas, A.H., Mehta, P., Monteiro, P., neering, Indian Institute of Science, Bangalore, India.
2014. High-volume natural volcanic pozzolan and limestone powder as partial Hemalatha, T., Ramaswamy, Ananth, Chandra Kishen, J.M., 2015. Simplified mix
replacements for Portland cement in self-compacting and sustainable concrete. design approach of self compacting concrete. ACI Mater. J. 112, 277e285.
Cem. Concr. Compos. 45, 136e147. Hemalatha, T., Mapa, M., George, N., Sasmal, S., 2016. Physico-chemical and me-
Chan, Y., Liu, C., Lu, Y., 1998. Effect of slag and fly ash on the autogenous shrinkage of chanical characterization of high volume fly ash incorporated and engineered
high performance concrete. In: International Workshop on Autogenous cement system towards developing greener cement. J. Clean. Prod. 125,
Shrinkage of Concrete. JCI, Hiroshima, Japan, pp. 221e228. 268e281.
Chancey, R., 2008. Characterization of Crystalline and Amorphous Phases and Hemmings, R., Berry, E., 1988. On the glass in coal fly ashes: recent advances. In:
Respective Reactivities in a Class F Fly Ash. Ph.D. Dissertation. The University of Presented at the MRS Symposium, Pittsburg,USA, p. 3.
Texas at Austin, TX, pp. 887e890. Hobbs, D., 1982. Influence of pulverized-fuel ash and granulated blast furnace slag
Chindaprasirt, P., Chotithanorm, C., Cao, H., Sirivivatnanon, V., 2007a. Influence of upon expansion caused by the alkalisilica reaction. Mag. Concr. Res. 34, 83e94.
fly ash fineness on the chloride penetration of concrete. Constr. Build. Mater. 21, Holt, E., Leivo, M., 2004. Cracking risks associated with early age shrinkage. Cem.
356e361. Concr. Compos. 26, 521e530.
Chindaprasirt, P., Homwuttiwong, S., Sirivivatnanon, V., 2004. Influence of fly ash Hosino, S., Ohba, Y., Sakai, E., Daimon, M., 1995. The fluidity of cement paste with
fineness on strength, drying shrinkage and sulfate resistance of blended cement various classified lime stones and prepared lime stone. JCA Proc. Cem. Conc.
mortar. Cem. Concr. Res. 34, 1087e1092. 484e489.
Chindaprasirt, P., Jaturapitakkul, C., Sinsiri, T., 2007b. Effect of fly ash fineness on Hosino, S., Ohba, Y., Sakai, E., Daimon, M., 1996. Relation between the properties of
microstructure of blended cement paste. Constr. Build. Mater. 21, 1534e1541. inorganic powders and the fluidity of cement pastes. JCA Proc. Cem. Conc.
Cross, D., Stephens, J., Vollmer, J., 2005. Structural Applications of 100 Percent Fly 186e191.
Ash Concrete. Montana State University, Bozeman, MT, USA. IS-1489, 2000. IS 1489 (Part I): 1991 Portland-Pozzolana Cement Specification. In-
Dananjayan, R.R.T., Kandasamy, P., Andimuthu, R., 2016. Direct mineral carbonation dian Standards, India. Amendment no.3.
of coal fly ash for CO2 sequestration. J. Clean. Prod. 112, 4173e4182. Itskos, G., Itskos, S., Koukouzas, N., 2010. Size fraction characterization of highly-
Dhir, R., McCarthy, M., Bai, J., 2012. Harnessing fly ash potential for developing high calcareous fly ash. Fuel Process. Technol. 91, 1558e1563.
strength and high durability concrete. Indian Concr. J. 86, 17e25. Ivan Odler, 2009. Special Inorganic Cements. E and FN SPON. Taylor and Francis
Diamond, S., 1981. Effects of two Danish fly ashes on alkali contents of pore solu- group, London.
tions of cement-fly ash pastes. Cem. Concr. Res. 11, 383e394. Jaarsveld, J.V., Deventer, J.V., 1999. Effect of the alkali metal activator on the prop-
Diamond, S., 1983. On the glass present in low-Ca and high-Ca fly ash. Cem. Concr. erties of fly ash based geopolymers. Ind. Eng. Chem. Res. 38, 3932e3941.
Res. 13, 459e464. Jo, B., Kim, C., Lim, J., 2007. Characteristics of cement mortar with nano-SiO2 par-
Dunstan, E., 1976. Performance of Lignite and Sub-bituminous Fly Ash in Concrete. ticles. Constr. Build. Mater. 21, 1351e1355.
558 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559

Jones, M., McCarthy, A., Booth, A., 2006. Characteristics of the ultrafine component 42, 570e578.
of fly ash. Fuel 85, 2250e2259. Nazari, A., Riahi, S., 2011. The effects of zinc dioxide nanoparticles on flexural
Joshi, R.C., Lohtia, R.P., 1997. Fly Ash in Concrete Production, Properties and Uses. strength of self-compacting concrete. Compos. Part B Eng. 42, 167e175.
Gordon and Breach Science Publishers, Netherlands. Nochaiya, T., Wongkeo, W., Chaipanich, A., 2010. Utilization of fly ash with silica
Kakali, G., Tsivilis, S., Aggeli, E., Bati, M., 2000. Hydration products of C3A, C3S and fume and properties of Portland cement-fly ash-silica fume concrete. Fuel 89,
Portland cement in the presence of CaCO3. Cem. Concr. Res. 30, 1073e1077. 768e774.
Kashani, A., Nicolas, R.S., Qiao, G.G., Deventer, J.S.V., Provis, J.L., 2014. Modelling the Palomo, A., Alonso, S., Nez, A.F.J., Sobrados, I., Sanz, J., 2004. Alkaline activation of fly
yield stress of ternary cement-slag-fly ash pastes based on particle size distri- ashes. A 29Si NMR study of the reaction products. J. Am. Ceram. Soc. 87,
bution. Powder Technol. 266, 203e209. 1141e1145.
Kawashima, S., Hou, P., Corr, D.J., Shah, S.P., 2013. Modification of cement-based Palomo, A., Grutzeck, M., Blanco, M., 1999. Alkali-activated fly ashes a cement for
materials with nanoparticles. Cem. Concr. Compos. 36, 8e15. the future. Cem. Concr. Res. 29, 1323e1329.
Khan, M., Ayers, M., 1995. Minimum length of curing of silica fume concrete. Pane, I., Hansen, W., 2005. Investigation of blended cement hydration by isothermal
J. Mater. Civ. Eng. ASCE 7, 134e139. calorimetry and thermal analysis. Cem. Concr. Res. 35, 1155e1164.
Kim, J.H., Noemi, N., Shah, S.P., 2012. Effect of powder materials on the rheology and Papadakis, V., 1999. Effect of fly ash on Portland cement systems, Part I: low calcium
formwork pressure of self-consolidating concrete. Cem. Concr. Compos. 34, fly ash. Cem. Concr. Res. 29, 1727e1736.
746e753. Paris, J.M., Roessler, J.G., Ferraro, C.C., DeFord, H.D., Townsend, T.G., 2016. A review
Kobayakawa, M., Hwang, K., Hanehara, S., Tomosawa, F., 1998. Influence of several of waste products utilized as supplements to Portland cement in concrete.
factors on pozzolanic reaction of fly ash. Summ. Tech. Pap. Annu. Meet. Archit. J. Clean. Prod. 121, 1e18.
Inst. Jpn A-1, 633e 634. Pera, J., Husson, S., Guilhot, B., 1999. Influence of finely ground limestone on cement
Kovtun, M., Ziolkowski, M., Shekhovtsova, J., Kearsley, E., 2016. Direct electric curing hydration. Cem. Concr. Compos. 21, 99e105.
of alkali-activated fly ash concretes: a tool for wider utilization of fly ashes. Pereira, C.F., Luna, Y., Querol, X., Antenucci, D., Vale, J., 2009. Waste stabilization/
J. Clean. Prod. 133, 220e227. solidification of an electric arc furnace dust using fly ash-based geopolymers.
Kumar, S., Kumar, R., Alex, T., Bandopadhyay, A., Mehrotra, S., 2007. Influence of Fuel 88, 1185e1193. Selected Papers from the 2007 World of Coal Ash
reactivity of fly ash on geopolymerisation. Adv. Appl. Ceram. 106, 120e127. Conference.
Kwan, A., Chen, J., 2013. Adding fly ash microsphere to improve packing density, Ponikiewski, T., Golaszewski, J., 2014. The influence of high-calcium fly ash on the
flowability and strength of cement paste. Powder Technol. 234, 19e25. properties of fresh and hardened self-compacting concrete and high perfor-
Kwan, A., Wong, H.H.C., 2008. Packing density of cementitious materials: Part 2- mance self compacting concrete. J. Clean. Prod. 72, 212e221.
packing and flow of OPCþPFAþCSF. Mater. Struct. 41, 773e784. Poon, C., Kou, S., Lam, L., Lin, Z., 2001. Activation of fly ash/cement systems using
Lam, L., Wong, Y., Poon, C., 1998. Effect of fly ash and silica fume on compressive and calcium sulfate anhydrite (CaSO4). Cem. Concr. Res. 31, 873e881.
fracture behaviors of concrete. Cem. Concr. Res. 28, 271e283. Poon, C., Lam, L., Wong, Y., 2000. A study on high strength concrete prepared with
Lam, L., Wong, Y.L., Poon, C.S., 2000. Degree of hydration and gel/space ratio of high- large volumes of low calcium fly ash. Cem. Concr. Res. 30, 447e455.
volume fly ash/cement systems. Cem. Concr. Res. 30, 747e756. Poon, C., Wong, Y., Lam, L., 1997. The influence of different curing conditions on the
Langley, W., Carette, C., Malhotra, V., 1989. Structural concrete incorporating high pore structure and related properties of fly-ash cement pastes and mortars.
volumes of ASTM Class F fly ash. ACI Mater. J. 86, 507e514. Constr. Build. Mater. 11, 383e393.
Lee, C.Y., Lee, H., Lee, K., 2003. Strength and microstructural characteristics of Qian, J., Shi, C., Wang, Z., 2001. Activation of blended cements containing fly ash.
chemically activated fly ash-cement systems. Cem. Concr. Res. 33, 425e431. Cem. Concr. Res. 31, 1121e1127.
Li, G., 2004. Properties of high volume fly ash concrete incorporating nano-silica. Rao, G.A., 2001. Long-term drying shrinkage of mortar influence of silica fume and
Cem. Concr. Res. 34, 1043e1049. size of fine aggregate. Cem. Concr. Res. 31, 171e175.
Lothenbach, B., Scrivener, K., Hooton, R., 2011. Supplementary Cementitious Mate- RILEM 73-SBC Committee, 1988. Siliceous by-products for use in concrete. Mater.
rials. Cement and Concrete Research, 41, 1244 e 1256. Conferences Special: Struct. 69.
Cement Hydration Kinetics and Modeling, Quebec City, 2009 and amp; CON- Sahmaran, M., Yaman, I., Tokyay, M., 2007. Development of high volume low-lime
MOD10, Lausanne, 2010. and high-lime fly-ash-incorporated self consolidating concrete. Mag. Concr.
Malhotra, V., 1986. Superplasticized fly ash concrete for structural applications. Res. 59, 97e106.
Concr. Int. 8, 28e31. Sahmaran, M., Li, V.C., 2009. Durability properties of micro-cracked ECC containing
Malhotra, V.M., 1990. Durability of concrete incorporating high-volume of low- high volumes fly ash. Cem. Concr. Res. 39, 1033e1043.
calcium (ASTM Class F) fly ash. Cem. Concr. Compos. 12, 271e277. Said, A., Zeidan, M., 2009. Enhancing the reactivity of normal and fly ash concrete
Maltais, Y., Marchand, J., 1997. Influence of curing temperature on cement hydration using colloidal nano-silica. Am. Concr. Inst. 267, 75e86.
and mechanical strength development of fly ash mortar. Cem. Concr. Res. 27, Sakai, E., Miyahara, S., Ohsawa, S., Lee, S., Daimon, M., 2005. Hydration of fly ash
1009e1020. cement. Cem. Concr. Res. 35, 1135e1140.
Malvar, L., Lenke, L., 2006. Efficiency of fly ash in mitigating alkali-silica reaction Sanchez, F., Sobolev, K., 2010. Nanotechnology in concrete a review. Constr. Build.
based on chemical composition. ACI Mater. J. 103, 319e326. Mater. 24, 2060e2071.
Maslehuddin, M., Saricimen, H., Al-Mani, A., 1987. Effect of fly ash addition on the Sato, T., Diallo, F., 2010. Seeding effect of nano-CaCO3 on the hydration of tricalcium
corrosion resisting characteristics of concrete. ACI Mater. J. 84, 42e50. silicate. Transp. Res. Rec. 2141, 61e67.
McCarthy, G., Solem, J., Manz, O., Hassett, D., 1989. Use of a database of chemical, Shaheen, S.M., Hooda, P.S., Tsadilas, C.D., 2014. Opportunities and challenges in the
mineralogical, and physical properties of North American fly ash to study the use of coal fly ash for soil improvements A review. J. Environ. Manag. 145,
nature of fly ash and its utilization as a mineral admixture in concrete. In: 249e267.
Materials Research Society Symposium Proceedings. Materials Research Society, Shaikh, F., Supit, S., 2014. Mechanical and durability properties of high volume fly
Boston, p. 178. ash (HVFA) concrete containing calcium carbonate (CaCO3) nanoparticles.
McCarthy, G., Solem-Tismack, J., 1994. Hydration mineralogy of cementitious coal Constr. Build. Mater. 70, 309e321.
combustion byproducts. In: Advances in Cement and Concrete, Proceedings of Shaikh, F., Supit, S., Sarker, P., 2014. A study on the effect of nano silica on
an Engineering Foundation Conference, Materials Engineering Division. ASCE, compressive strength of high volume fly ash mortars and concretes. Mater. Des.
Durham, NH, pp. 24e29. 60, 433e442.
Medhat, H., Michail, D., 2000. The effect of fly ash composition on the expansion of Shehata, M., Thomas, M.D.A., Bleszynski, R., 1999. The effects of fly ash composition
concrete due to alkali silica reaction. Cem. Concr. Res. 30, 1063e1072. on the chemistry of pore solution in hydrated cement pastes. Cem. Concr. Res.
Mehta, P., 1985. Influence of fly ash characteristics on the strength of Portland-fly 29, 1915e1920.
ash mixtures. Cem. Concr. Res. 15, 669e674. Shehata, M., Thomas, M.D.A., 2000a. Alkali release characteristics of blended ce-
Mehta, P., 1998. Role of pozzolanic and cementitious materials in sustainable ments. Cem. Concr. Res. 36, 1166e1175.
development of the concrete industry. In: Proceedings of the 6th CANMET/ACI Shehata, M., Thomas, M., 2000b. The effect of fly ash composition on the expansion
International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural of concrete due to alkali-silica reaction. Cem. Concr. Res. 30, 1063e1072.
Pozzolans in Concrete, pp. 1e20. ACI SP-178. Shehata, M., Thomas, M., 2002. Use of ternary blends containing silica fume and fly
Maslehuddin, Mohammed, Abdulaziz, I., Al-Mana, M.S., Saricimen, H., 1989. Effect of ash to suppress expansion due to alkali-silica reaction in concrete. Cem. Concr.
sand replacement on the early-age strength gain and long-term corrosion- Res. 32, 341e349.
resisting characteristics of fly ash concrete. ACI Mater. J. 86, 58e62. Shi, C., 1996. Early microstructure development of activated limeefly ash pastes.
Mokarema, D.W., Weyers, R., Lane, D., 2005. Development of a shrinkage perfor- Cem. Concr. Res. 26, 1351e1359.
mance specifications and prediction model analysis for supplemental cemen- Shi, C., 1998. Pozzolanic reaction and microstructure of chemical activated limeefly
titious material concrete mixtures. Cem. Concr. Res. 35, 918e925. ashes. ACI Mater. J. 95, 537e545.
Nagataki, S., Sakai, E., Takeuchi, T., 1984. The fluidity of fly ash-cement paste with Siddique, R., 2004. Performance characteristics of high-volume Class F fly ash
superplasticizer. Cem. Concr. Res. 14, 631e638. concrete. Cem. Concr. Res. 34, 487e493.
Nanthagopalan, P., Haist, M., Santhanam, M., Mller, H., 2008. Investigation on the Slanicka, S., 1991. The influence of fly ash fineness on the strength of concrete. Cem.
influence of granular packing on the flow properties of cementitious suspen- Concr. Res. 21, 285e296.
sions. Cem. Concr. Compos. 30, 763e768. Smith, I., 1967. Design of fly ash concretes. In: Proc Inst Civil Eng, pp. 769e790.
Narmluk, M., Nawa, T., 2011. Effect of fly ash on the kinetics of Portland cement Smith, R., 1988. Is the available alkali test a good durability predictor for fly ash
hydration at different curing temperatures. Cem. Concr. Res. 41, 579e589. concrete incorporating reactive aggregate. In: Presented at the MRS Sympo-
Nazari, A., Riahi, S., 2010. The effects of SiO2 nanoparticles on physical and me- sium, Pittsburg, USA, pp. 249e256.
chanical properties of high strength compacting concrete. Compos. Part B Eng. Sobolev, K., Vivian, I.F., Saha, R., Wasiuddin, N.M., Saltibus, N.E., 2014. The effect of
 T. Hemalatha, A. Ramaswamy / Journal of Cleaner Production 147 (2017) 546e559 559

fly ash on the rheological properties of bituminous materials. Fuel 116, 471e477. ashes based on their origin, composition, properties, and behaviour. Fuel 86,
Sua-iam, G., Makul, N., 2015. Utilization of coal- and biomass-fired ash in the 1490e1512.
production of self-consolidating concrete: a literature review. J. Clean. Prod. Wang, K., Shah, S., Phuaksuk, P., 2001. Plastic shrinkage cracking in concrete
100, 59e76. materials-Influence of fly ash and fibers. ACI Mater. J. 98, 458e464.
Sumer, M., 2012. Compressive strength and sulfate resistance properties of con- Wang, S., Zhang, C., Chen, J., 2014. Utilization of coal fly ash for the production of
cretes containing Class F and Class C fly ashes. Constr. Build. Mater. 34, glass-ceramics with unique performances: a brief review. J. Mater. Sci. Technol.
531e536. 30, 1208e1212.
Supit, S., Shaikh, F., Sarker, P., 2013. Effect of nano silica and ultrafine fly ash on Ward, C.R., French, D., 2005. Relation between Coal and Fly Ash Mineralogy, Based
compressive strength of high volume fly ash mortar. Appl. Mech. Mater on Quantitative X-ray Diffraction Methods. World of Coal Ash (WOCA), Lex-
368e370, 1061e1065. ington, Kentucky, USA.
Supit, S.W.M., Shaikh, F.U.A., 2015. Durability properties of high volume fly ash Weerdt, K., Justnes, H., Kjellsen, K., Sellevoid, E., 2010. Fly ash-limestone ternary
concrete containing nano-silica. Mater. Struct. 48, 2431e2445. composite cements: synergetic effect at 28 days. Nord. Concr. Res. 42, 51e70.
Tangtermsirikul, S., 1998. Effect of chemical composition and particle size of fly ash Wesche, 1991. Fly Ash in Concrete Properties and Performance. E and FN SPON.
on autogenous shrinkage of paste. In: International Workshop on Autogenous RILEM, London.
Shrinkage of Concrete. JCI, Hiroshima, Japan, pp. 175e186. Wong, H., Kwan, A., 2008. Rheology of cement paste: role of excess water to solid
Teixeira, E.R., Mateus, R., Cames, A.F., Bragana, L., Branco, F.G., 2016. Comparative surface area ratio. J. Mater. Civ. Eng. 20, 189e197.
environmental life-cycle analysis of concretes using biomass and coal fly ashes Xu, A., Sarkar, S., 1991. Microstructural study of gypsum activated fly ash hydration
as partial cement replacement material. J. Clean. Prod. 112 (Part 4), 2221e2230. in cement paste. Cem. Concr. Res. 21, 1137e1147.
Temuujin, J., Van Riessen, A., 2009. Effect of fly ash preliminary calcination on the Xue, B., Pei, J., Sheng, Y., Li, R., 2015. Effect of curing compounds on the properties
properties of geopolymer. J. Hazard. Mater. 164, 634e639. and microstructure of cement concretes. Constr. Build. Mater. 101, 410e416.
TIFAC. Technology, information, forecasting and assessment council. http://www. Yao, Z., Ji, X., Sarker, P., Tang, J., Ge, L., Xia, M., Xi, Y., 2015. A comprehensive review
tifac.org.in/. (Accessed 6 January 2017). on the applications of coal fly ash. Earth Sci. Rev. 141, 105e121.
Thomas, M., Shehata, M., Shashiprakash, S., Hopkins, D., Cail, K., 1999. Use of ternary Yazici, H., Aydin, S., Yigiter, H., Baradan, B., 2005. Effect of steam curing on Class C
cementitious systems containing silica fume and fly ash in concrete. Cem. high-volume fly ash concrete mixtures. Cem. Concr. Res. 35, 1122e1127.
Concr. Res. 29, 1207e1214. Yazici, S., Arel, H.S., 2012. Effects of fly ash fineness on the mechanical properties of
Tixier, R., Mobasher, B., 2003. Modeling of damage in cement-based materials concrete. Sadhana 37, 389e403.
subjected to external sulfate attack. II: comparison with experiments. J. Mater. Ye, Q., Zhang, Z., Kong, K.D., 2007. Influence of nano-SiO2 addition on properties of
Civ. Eng. 15, 314e322. hardened cement paste as compared with silica fume. Constr. Build. Mater. 21,
Tkaczewska, E., 2014. Effect of size fraction and glass structure of siliceous fly ashes 539e545.
on fly ash cement hydration. J. Ind. Eng. Chem. 20, 315e321. Zeng, Q., Li, K., Fen-chong, T., Dangla, P., 2012. Determination of cement hydration
Ukwattage, N., Ranjith, P., Yellishetty, M., Bui, H., Xu, T., 2015. A laboratory-scale and pozzolanic reaction extents for fly-ash cement pastes. Constr. Build. Mater.
study of the aqueous mineral carbonation of coal fly ash for CO2 sequestration. 27, 560e569.
J. Clean. Prod. 103, 665e674. Zhang, M., 1995. Microstructure, crack propagation, and mechanical properties of
Uysal, M., Akyuncu, V., 2012. Durability performance of concrete incorporating Class cement pastes containing high volumes of fly ashes. Cem. Concr. Res. 25,
F and Class C fly ashes. Constr. Build. Mater. 34, 170e180. 1165e1178.
Varga, I.D. la, Castro, J., Bentz, D., Weiss, J., 2012. Application of internal curing for Zhang, M., Islam, J., 2012. Use of nano-silica to reduce setting time and increase
mixtures containing high volumes of fly ash. Cem. Concr. Compos. 34, early strength of concretes with high volumes of fly ash or slag. Constr. Build.
1001e1008. Mater. 29, 573e580.
Varga, I.D. la, Spragg, R.P., Bella, C.D., Castro, J., Bentz, D.P., Weiss, J., 2014. Fluid Zhang, M., Islam, J., Peethamparan, S., 2012. Use of nano-silica to increase early
transport in high volume fly ash mixtures with and without internal curing. strength and reduce setting time of concretes with high volumes of slag. Cem.
Cem. Concr. Compos. 45, 102e110. Concr. Compos. 34, 650e662.
Vargas, J., Halog, A., 2015. Effective carbon emission reductions from using upgra- Zhao, H., Sun, W., Wu, X., Gao, B., 2015. The properties of the self-compacting
ded fly ash in the cement industry. J. Clean. Prod. 103, 948e959. concrete with fly ash and ground granulated blast furnace slag mineral ad-
Vassilev, S.V., Vassileva, C.G., 2007. A new approach for the classification of coal fly mixtures. J. Clean. Prod. 95, 66e74.