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A comprehensive overview about the influence of different admixtures

and additives on the properties of alkali-activated fly ash

Alaa M. Rashad

Building Materials Research and Quality Control Institute, Housing & Building National Research Center, HBRC, Cairo, Egypt

a r t i c l e i n f o

Article history:

Received 18 May 2013Accepted 22 July 2013Available online 31 July 2013

Keywords:

Alkali-activated fly ashFibersAdmixturesAdditives

a b s t r a c t

The development of new binders, as an alternative to Portland cement (PC), by alkaline activation, is acurrent researchers interest. Alkali-activated fly ash (AAFA) binder is obtained by a manufacturing pro-cess less energy-intensive than PC and involves lower greenhouse gasses emission. Utilizing AAFA systemas binder material can limit the consumption of virgin materials (limestone and sand) required in PCmanufacture. AAFA belongs to be prospective material in the field of Civil Engineering where it can resistaggressive acids, resist sulfate attacks, resist aggregate alkali reaction, and resist elevated temperatures.Researchers have employed different fibers, chemical admixtures, mineral admixtures, additives andother materials in AAFA system aiming to modify special properties of this system. This paper presentsa comprehensive overview of the previous works carried out on using different admixtures and additivesin AAFA system.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

Currently, PC is still the leading material for industrial concretedemand worldwide, fulfilling a demand of over 1.6 billion tonnesannually [1]. The production of cement is increasing about 3%annually [2]. The projections for the global demand of PC show thatin the next 40 years it will have a twofold increase reaching 6 Gt/year[3]. The cement industry is the second largest producer of thegreen house gas[1]. Among the green house gases, CO2contributesabout 65% of global warming. Additionally, cement production andresulting emissions are expected to increase by 100% from the cur-rent level by 2020[4]. On the same line with this, the global de-mand will have increased almost 200% by 2050 from 2010 [3].Beside the emission of CO2, cement industry launches SO3 andNOxwhich can cause the greenhouse effect and acid rain[5,6]. Thisis particularly serious in the current context of climate change

caused by CO2 emissions worldwide, causing a rise in sea leveland the occurrence of natural disasters and being responsible forfuture meltdown in the world economy[7,8]. Not only CO2, SO3and NOxare launched into the atmosphere from cement industry,but also about 5% to 10% of the by-products. These by-productsare dusts from the dryers, mills, kilns, coolers and transportationfacilities. These dusts arise from different sources; altogether,600014,000 m3 dust-containing airstreams are generated per1 tonne cement which contains 0.7 and 800 g/m3 of dust (depend-ing on source and technology)[9].

In addition to consuming considerable amounts of virgin mate-rials (limestone and sand) and energy (energy demand about

17001800 MJ/tonne clinker[10,11]), producing each tonne of PCof which about 1.5 tonnes of raw material is needed [6]. The ce-ment production account about 5% of worldwide industrial energyconsumption [12,13]. The PC industry ranks third in the sector(after aluminum and steel) for the energy consumption[14]. Fur-ther, concrete made from PC is subjected to certain durability prob-lems that are difficult to solve. In the light of these problems, thescientific community has undertaken to seek new processes, tech-nologies and materials to provide the construction industry withalternative binders. One avenue that is expected to significantreduce cement is use of blended cement [1522]. The secondalternative is use new cementless binder material based on theby-products as FA, slag[11,2326]or burned clay[27]and otheraluminosilicate materials [28,29]. The new binder materials that

can replace PC, by alkali activation, can generate less carbon diox-ide than PC [6,3036]. Comparison to PC concrete, the globalwarming potential of alkali-activated concrete is 70% lower [37].The energy consumption of alkali activation system is calculatedto be approximately 60% less than that of PC [38].

FA is a by product of thermal power plants resulting from thecombustion of pulverised coal in the coal-fired furnaces. Aroundone billion tonnes of FA are produced annually worldwide incoal-fired steam power plants[3942]. The environmental impactof FA in terms of its massive generation, large usage of land dis-posal with short and long term impact on surrounding areas is amajor concern for everyone. One option to eliminate this ash inan ecologically sensitive manner is to reuse it. FA can replace

0261-3069/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.matdes.2013.07.074

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Materials and Design 53 (2014) 10051025

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cement content up to 30%. The current European standard ENv197(2000) allows a replacement level up to 55% cement by FA in ce-ment mixture CEM IV. FA can replace 5070% cement in high vol-ume fly ash (HVFA) concrete. However, the best option to eliminateFA disposal is to reuse it as a binder material, without PC, activatedwith alkaline activators.

The alkali activation of aluminosilicamaterials is a chemicalpro-

cess that transforms partially or wholly vitreous structures intocompact cementitious skeletons. Researchers reported that AAFAconcretes can achieve compressive strength over 60 MPa after ther-mally curing [43,44]. The AAFA concrete is durable, can resistaggressive acids, resist aggregate alkali reaction[45,46]resist sul-fate attacks[47,48]and resist elevated temperatures[6]. This sys-tem performs better than PC mortars in reinforcement steelbonding[49]. AAFA can protect steel reinforcement from corrosion[50]and can be used to fix toxic elements[5155]. The dry shrink-age of AAFA binders can belowered than thatof PC binders [5659].On the other hand, AAFA requires rather long heat curing to obtainreasonable strength development at early age. The long heat curingperiod limits the application of the AAFA. To achieve comparablestrength to PC concrete, it is necessary to provide geopolymer con-crete with elevated temperature curing between 40 and 80Cforatleast 6 h [41,60,61].Further, the question of whether geopolymerconcretes are durable remains the major obstacle to recognitionin standards for structure concrete, and hence to their commercialadoption. Geopolymer cannot possibly have the availability of dec-ades of in-service testing and durability data to prove its long-termstability. Most standard methods of testing paste and concretedurability involve exposing small samples to very extreme condi-tions for short periods. Higher-risk application such as high risebuilding, which constitutes a smaller fraction of total concrete mar-ket, will follow only when the market is comfortable with the real-world track record of the material in low risk application [62]. Inaddition, in some countries as UK, FA production does not exceedits consumption in cement, which limits the wider adoption of geo-polymer technology until this bottleneck is resolved [62]. However,

researchers tried to modify special properties of AAFA by addingdifferent admixtures and additives aiming to produce blendedmaterials have more advantages than the neat AAFA. Differentadmixtures and additives were employed in AAFA and investigatedby numerous researchers.

Although there are numerous numbers of review papers in theliterature regarding to AAFA system[43,51,63,64]there is no pub-lished literature review paper that reviewed the previous workscurried out on AAFA modified with different types of admixturesand additives. However, in this investigation, the author conducteda comprehensive literature review focused on the effect of differentadmixtures and additives on some special properties of AAFA sys-tem. A review on fibers, chemical admixtures, mineral admixturesand additive materials that were added into FA in alkali activation

system was presented.

2. Fibers

Yunsheng et al. [6567] investigated the behavior of shortpolyvinyl alcohol (PVA) fibers reinforced FA-metakaolin (MK)geopolymer boards manufactured by extrusion technique. Fiberlength was 6 mm with average diameter of 14 lm and a densityof 1300 kg/m3. The average tensile strength and elastic modulusof the fiber were 1500 MPa and 36 GPa, respectively. MK, inmortars, was partially replaced with FA at levels of 0%, 10%,30% and 50%, by weight. Fibers volumes were 0%, 1% and 2%in neat MK geopolymer, whilst they were 2% in FA-MK geopoly-mers. NaOH was used as alkaline activator. The fresh geopoly-

mer composites were fed into the pugmill chamber of

single-screw vacuum extruder. After mixing, de-airing and com-paction, the composites were pushed through a thin sheet diewith a cross-sectional size of 75 6 mm. The specimens werecured at 20 C and 99% RH. They concluded that the additionof high volume fraction PVA fibers changed the impact failuremode of FAMK-geopolymer boards from brittle pattern to duc-tile pattern, resulted in great increase in impact toughness.

Short PVA fibers reinforced geopolymer boards without or withlow percentage of FA possessed very high impact strength andstiffness, but when much FA was incorporated, the impactresistance was reduced.

Vaidya and Allouche[68]added carbon fibers to geopolymerconcrete to enhance its electrical conductivity. They employedcarbon fibers at level of 0.4%, by dry weight of FA. The FA to sandto coarse aggregate was 1:2:2. The activator was a solution of so-dium silicate and NaOH. Specimens of cylinders and rectangularbeams were cast and cured at 60 C for 24 h, then at room tem-perature. The results showed that the electrical resistance fol-lowed a descending trend with the increase in bending stresses.Electrical resistance appeared to fluctuate with the applicationof axial compressive stresses. This behavior could be attributedto densification of the geopolymer paste on one hand, and thedevelopment of micro-cracks within the matrix on the other.They concluded that the conductive geopolymer could serve asa smart material in health monitoring applications of concretestructures.

Puertas et al.[69]modified AAFA mortars with polypropylenefibers at levels of 0%, 0.5% and 1%, by mortar volume. The resultsshowed higher compressive and flexural strengths at age of 2 daysin AAFA mortar with the increase in fiber content, whilst lowercompressive and flexural strengths were obtained at age of28 days. The compressive and flexural strengths decreased as thefiber content increased. Puertas et al. [69]used 4 4 16 cm pris-matic specimens to determine the elastic modulus of AAFA mortarsmodified with 0% and 1% polypropylene fibers, by mortar volume.The results showed that the presence of polypropylene fibers re-

duced the elastic modulus. The polypropylene fibers had a lowmodulus of elasticity; they were easily deformed and reducedthe compatibility of the material. They also studied the impactstrength of AAFA mortars before and after 50 wet/dry cycles; andbefore and after 50 cycles of freezing/thawing. Mortars were mod-ified with polypropylene fibers at levels of 0% and 0.5%, by mortarvolume. The results showed an increase in fracture with the inclu-sion of fibers either before or after 50 wet/dry cycles. On the sameline with this, the results showed an increase in both compressiveand flexural strengths with the inclusion of fibers before and after50 cycles of freezing/thawing. They also studied the drying shrink-age of alkali-activated FA/slag without or with 1% polypropylene fi-bers under two different curing conditions of humidity condition(95% RH) and laboratory condition (21C and 50% RH). The results

showed that the specimens modified with fibers cured in labora-tory condition gave lower drying shrinkage than that specimenswithout fibers. On the contrary, at humidity curing condition, thespecimens modified with fibers gave higher drying shrinkage thanthat without fibers (Fig. 1).

Li and Xu[70,71] prepared sodium silicate activated FA/slagblends with less than 0.3% basalt fibers. Tests using a split Hop-kinson pressure bar (SHPB) system revealed no change in dy-namic compressive strength, but improvements in energyabsorption were observed. 0.3% was estimated to be the optimalfiber loading based on energy absorption. Strain hardening wasnot observed. The composite properties (energy absorbed etc.)were determined to be strain rate dependent under impact load-ing.Table 1summarizes the previous studies about the effect of

different types of fibers on some properties of AAFA system.

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3. Chemical admixtures

Criado et al.[72]investigated the rheological behavior of AAFApastes under the effect of chemical admixtures. FA was activatedwith 85% of 12.5 M NaOH solution and 15% of waterglass. Somecommercial chemical admixtures as lignosulphonates, melamines(first and second generation products) and polycarboxylates (latestgeneration) were employed. The flow table spread results showedthat the polycarboxylates admixture gave the highest spread, AAFAwithout admixture came in the second place, melamines admix-ture came in the third place, whilst lignosulphonates admixture

came in the last place.Memon et al. [73], Demie et al. [74]and Nuruddin et al. [75]prepared SCC from FA-geopolymers. Sodium silicate and NaOHsolution was employed as alkaline activator. Different dosages ofcommercial superplasticizer (Sika Viscocrete-3430) of 3%, 4%, 5%,6% and 7% were used. Concrete specimens were cured at 70 Cfor 48 h. The results of slump flow showed higher flow with higherdosage of superplasticizer. On the same line with this, the com-pressive strength at ages of 1, 3, 7 and 28 days increased as thedosage of superplasticizer increased. Demie et al.[74]cured somespecimens of the previous mixtures, that had 7% superplasticizer,at 60 and 80 C for 48 h. The compressive strength results showedthat specimens cured at 70C gave the highest compressivestrength, specimens cured at 80C came in the second place, whilstspecimens cured at 60 C came in the last place. Nuruddin et al.

[75] employed different molarities of 8, 10, 12 and 14 in somespecified mixtures of the previous mixtures, that containing 6%superplasticizer and cured at 70 C for 48 h. The slump flow resultsshowed that mixture containing 10 M gave the highest flow, mix-ture containing 8 M or 12 M came in the second place. Finally, mix-ture containing 14 M came in the last place. On the other hand,specimens containing 12 M gave the highest compressive strength,

specimens containing 14 M came in the second place, whilst spec-imens containing 10 M came in the third place.Reddy et al.[76]activated low lime based FA geopolymer con-

crete with a mixture of NaOH and sodium silicate solution. 1.5%superplasticizer (CONPLAST SP-430) was employed, by FA weight.They reported that the addition of high-range water reducer hadslightly impact on the compressive strength of the hardened con-crete, but improved workability of fresh geopolymer concrete.Puertas et al.[77]studied the effect of two superplasticizers basedon vinyl copolymers and polycarboxylates on alkaline-activatedaluminum silicate FA. NaOH was used as alkaline activator withconcentration of 8 M. The dosage of the admixtures was constantand equivalent 2% in solid mass of FA. They concluded that thepresence of vinyl copolymers and polycarboxylates in activatedFA mortars did not cause any substantial modifications to thestrength behavior of these mortars, compared to that which didnot contain any admixture. The two types of admixtures did not in-crease the fluidity of AAFA pastes. Wallah and Rangan [78] re-ported that the addition of more than 2% superplasticizer basedon naphthalene in FA geopolymer mixtures had a few benefits interm of workability and deleterious for the compressive strength.Montes et al. [79] reported that the addition of superplasticizerbased on naphthalene sulfonate in FA paste goepolymers increasedthe paste viscosity and induced flash set, whilst the addition ofsuperplasticizer based on polycarboxilate slightly decreased theviscosity of the paste.Table 2summarizes the previous researchesthat studied the effect of chemical admixtures on the workabilityand compressive strength of AAFA system.

4. Slag

4.1. Workability

Yang and Song[80]studied the workability of AAFA and alkali-activated slag (AAS) activated with a combination of sodium sili-cate and NaOH powders. They noted that lower initial flow inAAS than that in the AAFA. Yang et al.[81]reported that AAS mor-tars exhibited slightly lower flow than AAFA mortars, for the samemixing condition. Yang et al.[82]used sodium silicate powder toactivate either FA or slag mortars. They used constant w/b ratioof 0.5 and sand to binder of 3. They reported that AAS mortarshad lower workability than AAFA mortars. Collins and Sanjayan[83] reported that pure AAS concrete activated with powdered

Fig. 1. Effect of 1% polypropylene fibers on alkali-activated FA/slag mortars underdifferent curing conditions[69].

Table 1

Effect of different types of fibers on some properties of AAFA system.

Author Fiber type Positive effects No or negative effects

Yunsheng et al.[6567]

PVA Changed the impact failure mode from brittle pattern to ductilepattern Great increase in impact toughness

Vaidya andAllouche[68]

Carbon Enhanced the electrical conductivity

Densification the geopolymer pastePuertas et al.[69] Polypropylene Increased the compressive and flexural strengths at age of 2 days Decreased the compressive and flexural strengths

at age of 28 days Increased the fracture before and after 50 wet/dry cycles Reduced the elastic modulus Increased the compressive and flexural strengths before and after 50freezing/thawing cycles

Higher drying shrinkage of FA/slag, in the case ofhumidity curing

Lower drying shrinkage of FA/slag, in the case of laboratory curing

Li and Xu[70,71] Basalt Improved energy absorption No change in dynamic compressive strength

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sodium metasilicate and hydrated lime gave lower workabilitythan the composite of 90% slag plus 10% ultrafine FA concrete.Rashad [84] studied the workability of alkali-activated FA/slagconcretes. The ratios of FA/slag were 100/0, 95/5, 90/10 and 85/15, by weight. A mixture of NaOH and sodium silicate was usedas alkaline activator. The results showed higher workability withhigher FA content.

Talling and Brandstetr[85]reported that FA may improve theworkability of a fresh mixture of AAS cement. Wang et al. [86]re-ported that an addition of FA (below 10%) had little effect onimproving the workability of the AAS mixture. On the contrary,Parameswaran and Chatterjee[87]reported that an Indian FA didnot improve the workability even at 40%, by weight of total binder,implying that the characteristics of FA were important. However,in general, the workability of FA/slag mixture is influenced byFA/slag fineness.Table 3summarizes the previous researches thatstudied the effect of slag on the workability of AAFA system.

4.2. Setting time

Sugama et al. [88]studied the setting time of alkali-activatedClass F FA/slag. FA was replaced with slag at levels of 50%, 60%,70%, 80%, 90% and 100%, by weight. Sodium silicate was used asalkaline activator with molar ratios (SiO2/Na2O) of 3.22, 2.50 and2.00. The results indicated that the setting time decreased withthe increase in slag content, when sodium silicate had molar ratiosof 3.22 and 2.50. Kumar et al.[89]partially replaced FA with slag atlevels of 0%, 5%, 15%, 25%, 35% and 50%, by weight, in FA/slag-based

geopolymers. They reported that the setting time decreased as thecontent of slag increased.

4.3. Strength

Goretta et al.[90]measured the compressive strength of Class C

FA, slag and sodium silicate alkali-activated concrete. The aggre-gate constituted 52% and an alkali activator 11.2% of the total

Table 2

Effect of chemical admixtures on workability and compressive strength of AAFA system.

Author Activator concentration Admixture Positive effects No or negative effects

Criado et al.[72]

85% of 12.5 M NaOH and15% waterglass

Superplasticizer(lignosulphonates)

Improved the workability

Superplasticizer(melamines)

Reduced theworkability

Superplasticizer

(polycarboxylates)

Reduced the

workabilityMemon

et al.[73]

12 M NaOH + 143 kg/m3

sodium silicateSuperplasticizer (SikaViscocrete-3430)

Improved the workability

-Increased the compressive strength at ages of 1, 3, 7 and 28 daysDemie et al.

[74]12 M NaOH + 143 kg/m3

sodium silicateSuperplasticizer (SikaViscocrete-3430)

Specimens cured at 70 C gave the highest strength, followed byspecimens cured at 80 C, followed by specimens cured at 60 C

Nuruddinet al.[75]

8, 10, 12, 14 MNaOH + 143 kg/m3

sodium silicate

Superplasticizer (SikaViscocrete-3430)

The best workability was obtained when 10 M of activator wasused, followed by 8 M or 12 M and followed by 14 M

The highest compressive strength at 12 M of activator was used,followed by 14 M and followed by 10 M

Reddy et al.[76]

10 M NaOH + 171.42 kg/m3 Na2SiO3

Superplasticizer (CONPLASTSP-430)

Improved the workability No much impact onthe compressivestrength

Puertaset al.

[77]

8 M NaOH Superplasticizer (vinylcopolymers and

polycarboxylates)

No increase in theworkability

No much impact onthe compressivestrength

Wallah andRangan[78]

816 M NaOH Superplasticizer(naphthalene)

No much impact onthe workability

Deleterious for thecompressive strength

Monteset al.[79]

Activator/FA = 0.35 Superpalsticizer(naphthalene sulfonate)

Increased theviscosity

Induced flash setSuperplasticizer(polycarboxilate)

Slightly decreased the viscosity

Table 3Effect of slag on the workability of AAFA system.

Author Increasedworkability

Decreasedworkability

Fineness Notes

Yang and Song[80]

p FA: 3000 cm2/g,

slag: 4000, 6000,8000 cm2/g

AAS had lessworkabilitythan AAFA

Yang et al.[81]

p FA: 3388 cm2/g,

slag: 4204 cm2/gAAS had lessworkabilitythan AAFA

Yang et al.[82]

p FA: 4200 cm2/g,

slag: 4400 cm2/gAAS had lessworkabilitythan AAFA

Collins andSanjayan[83]

p UFA:

90% < 13.7 mm,slag: 4600 cm2/g

Rashad[84] p FA: 3500 cm2

/g,slag 3200 cm2/gTalling and

Brandstetr[85]

p Unavailable

Wang et al.[86]

p Unavailable Litt le

improvementParameswaran

andChatterjee[87]

p Unavailable


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mass; the mass ratio of silicate to FA + slag was 0.29. 50 mm diam-eter cylinders having a 1:2 diameter-to-length ratio were used fortesting compressive strength. They reported that compressivestrength of 35 MPa could be obtained at 14 days. Smith and Os-borne[91]and Bijen and waltje[92]found that waterglass-acti-vated FA/slag blends showed very low strength, but NaOHactivation gave higher strengths. On the contrary, Dai and Cheng

[93]found that waterglass was much more effective than NaOH.Weiguo et al. [94]replaced FA with slag at levels of 0%, 30%,60%, 50%, 40%, 70% and 100%, by weight, in alkali-activated FA/slagcements. Waterglass with SiO2/Na2O ratio of 2.4 and NaOH whichused to adjust the SiO2/Na2O ratio to 1.0, was used as alkaline acti-vator. The results showed that the compressive and flexuralstrengths increased as the slag content increased. Puertas et al.[95] alkali-activated FA/slag pastes with NaOH solution. Theparameters of this study were: activator concentration (NaOH:2 M and 10 M), curing temperature (25 and 65 C) and FA/slag ra-tios of 100/0, 70/30, 50/50, 30/70 and 0/100, by weight. In the cur-ing temperature process, the pastes were maintained at 65 Cduring the first 5 h. for the rest of the curing time, the specimenswere maintained at ambient temperature and 98% RH; the sameas the specimens cured at 25 C. The compressive strength resultsat 1 day showed an increase in strength with the increase in slagcontent. 65C coupled with 10 M of NaOH gave the higheststrength. At 7 days, 30/70 gave the highest strength at 25 C cou-pled with 10 M of NaOH. In the remaining conditions, the strengthincreased with the increase in slag content. At age of 28 and90 days, as the slag content increased as the compressive strengthincreased. 25 C coupled with 10 M of NaOH seemed to be the opti-mum condition, followed by 65 C coupled with 10 M of NaOH, fol-lowed by 25C coupled with 2 M of NaOH. 56C coupled with 2 Mof NaOH came in the last place.

Gara et al.[96]studied the compressive strength of the alkali-activated FA/slag composites. The FA/slag ratios were 100/0, 75/25,50/50, 25/75 and 0/100, by weight. Sodium silicate with modulus(SiO2/Na2O) of 0, 0.75, 1, 1.5 and 2 was used as alkaline activator.

The %Na2O was added at 4%, 6% and 8%, related to the binderweight. The pastes were cured at 75 C for 24 h and then at 20 Cup to 28 days. The results indicated that for 0/100 pastes, the high-est strengths were for 4% Na2O (8085 MPa); the optimum modu-lus was 1.5. For 100/0 pastes, the higher %Na2O, the better thestrength, whereas the highest strength of 25 MPa was reachedusing modulus 1. For the composite of 25/75, the strengths were(5660 MPa) at 4% Na2O and the modulus 1 and 1.5. For the com-posite of 50/50 paste, the strengths were (4548 MPa) at 4% Na2Oand the best modulus was 11.5. For the composite of 75/25pastes, the strength reached 3035 MPa at 4% Na2O and modulus1.5. Guerrieri and Sanjayan [97] presented the compressivestrength of geopolymer pastes made of composites FA/slag. The ra-tios of FA/slag were 100/0, 65/35, 50/50, 35/65 and 0/100, by

weight. The alkaline activators were mixtures of sodium silicate li-quid and 8 M NaOH. The activators were mixed in proportions sothat Ms were 0, 0.5, 1.0, 1.5 and 2.0. Industrial grade-powdered so-dium metasilicate with hydrated lime was also used. The activatorsconcentrations were 4% and 8% Na. After casting, the specimenswere kept at 23 1C and 50 5% RH for 2 h and then were curedat 80 1 C and 95 3% RH for 22 h, after that the specimens wereallowed to cool down to room temperature. The compressivestrength was measured at 24 h after curing period. The resultsshowed that the composite of 65/35 achieved the highest compres-sive strength at 8% Na and Ms 1.01.5, followed closely by the 35/65, followed by 0/100 and 50/50. Chi and Huang[98]presented thecompressive strength and flexural strength, at ages of 7, 14 and28 days, of geopolymer mortars made of different combinations

of FA/slag ratios of 100/0, 70/30, 50/50, 30/70, 0/100, by weight.Sodium silicate with modulus ratio of 1 was used as alkaline

activator. Two concentrations of Na2O of 4% and 6%, by cementi-tious weight, were employed. The results showed that the compo-sition of 50/50 achieved the highest compressive strength andflexural strength followed by 30/70, 0/100, 70/30 and 100/0,respectively, at both 4% and 6% Na2O.

Yang et al.[99]activated FA/slag pastes with alkaline activatorwith modulus of 1.2, 1.4 and 2.0. The ratios of FA/slag were 100/0,

80/20, 60/40, 40/60, 20/80 and 0/100, by weight. The pastes weredemoulded after curing for 24 h in room temperature, then theywere cured at 50 C for 48 h. After that, they were cured at roomtemperature until testing. The compressive strength of the pasteswas measured at ages of 3, 7 and 28 days. The results showed thatthe composition of 20/80 gave the highest compressive strengthfollowed by 40/60, 0/100, 60/40, 80/20 and 100/0, respectively, atMs of 1.2 and 1.4. At Ms of 2.0, the composition of 20/80 also gavethe highest compressive strength followed by 40/60 or 60/40, 0/100, 80/20 and 100/0, respectively. Kim and Kim[100]replacedFA with slag at levels of 0%, 50% and 100%, by weight, in FA/slag-based geopolymers. 2.78 M NaOH was used as activator. The com-pressive strength results of the mortars, at ages of 1, 7 and 28 days,increased as the content of slag increased. Aydn [101] activatedFA/slag mortars with NaOH and sodium silicate. The ratios of FA/slag were 40/60, 20/80 and 0/100, by weight. The specimens werecured at 20 C and 90% RH for 5 h, then in steam at 70 C for 6 h.The results showed an increase in the compressive strength withthe inclusion of slag. The compressive strength increased as thecontent of slag increased. Smith and Osborne[91]investigated ce-ment made of the combination of 40% FA and 60% finely slag acti-vated with 7% NaOH. They found that the early strength propertieswere good but there was a little gain in strength beyond 28 days;though improved strength might be obtained by varying the pro-portions of slag and FA or by increasing the fineness of the slag. Ku-mar et al. [89]partially replaced FA with slag at levels of 0%, 5%,15%, 25%, 35% and 50%, by weight, in FA/slag-based geopolymers.An increase in the compressive strength was observed with theinclusion of slag. As slag content increased as the compressive

strength increased. Zhang et al. [102] solidified municipal solidwaste incinerator (MSWI) FA with the Na2SiO3-activated slag.The Na2SiO3 activated slag was added to MSWI FA at 25%, 30%,35% and 45%, by weight. The compressive strength results showedthat 45% gave the highest compressive strength at age of 7 days,whilst 35% gave the highest compressive strength at ages of 28and 60 days. Rashad[84]studied the compressive strength, split-ting tensile strength and flexural strength of alkali-activated FA/slag concretes. The ratios of FA/slag were 100/0, 95/5, 90/10 and85/15, by weight. A mixture of NaOH and sodium silicate was usedas activator. The results showed that the compressive strength,splitting tensile strength and flexural strength increased as the slagcontent increased.

Wang et al.[103]studied the compressive strength and porosity

of alkali-activated FAslagMK cementitious materials preparedby hydrothermal method. Waterglass was used as alkaline activa-tor with the modulus adjusted to 1.0 by dissolving NaOH. The ratioof water to solid was about 0.35. Different mixtures with differentcontents of slag, MK and FA were employed. The slag contentsranging from 16.2% to 31.33%, the FA contents ranging from20.46% to 73.52%, and MK contents ranging from 7.22% to49.39%. The compressive strength results indicated that this typeof material had higher mechanical strength. The highest compres-sive strength value reached nearly 80 MPa. They suggested that thehigher compressive strength was attributed to the addition of slag.The more contents of slag in the system, the more hydration prod-ucts of CSH and hydrated aluminates calcium were obtained. Li andLiu[104]utilized 4% slag, presented by weight of dry powders, as

additive to 90% FA + 10% MK-based geopolymer. Na2SiO3 andNaOH solution was used as alkaline activator. The paste specimens


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were cured at 30 or 70 C for 14 days. After 14 days, the specimenswere tested in compression. The results showed 51.96% and 25.72%increases in compressive strengths, due to the inclusion of 4% slag,cured at 30 C and 70 C, respectively. 4% slag addition also influ-enced pore structure of the geopolymer significantly. A refinedpore size and reduced porosity volume were exhibited after 4% slagaddition. On the contrary, Puertas et al. [69] investigated both

compressive and flexural strengths of mortar consisted of 50% FAcoupled with 50% slag activated with 8 M NaOH versus neat FAmortar activated with 8 M NaOH. The specimens were cured at85C during the first 24 h. The results showed lower compressiveand flexural strengths at ages of 2 and 28 days with the inclusion of50% slag.Table 4summarizes the previous researches that studiedthe effect of slag on the strength of AAFA system.

4.4. Durability

Sugama et al.[88]exposed FA/slag-based geopolymers to CO2-laden H2SO4with pH value of 1.1 for 15 days at 90 C, after auto-claving at 100, 200 and 300 C. The paste specimens were preparedby varying two parameters, FA/slag weight ratios of 0/100, 10/90,30/70 and 50/50, by weight, and SiO2/Na2O molar ratios, in the so-dium silicate, of 3.22, 2.50 and 2.00. The weight loss resultsshowed that the proportion of 50/50 mixture had the lowestweight loss among the all studied molar ratios, followed by 30/70 and followed by 10/90, whilst the mixture of 0/100 came inthe last place. Ismail et al.[105]studied the performance of alka-li-activated FA/slag geopolymer binders to different forms of sul-fate exposure immersed in 5 wt% MgSO4 or 5 wt% Na2SO4solutions for 3 months. Sodium metasilicate was used as alkalineactivator at concentration of 8 wt%. They reported that MgSO 4was more aggressive to geopolymer paste than Na2SO4. The pres-ence of magnesium led to decalcification of the Ca-rich gel phasespresented in the blended FA/slag geopolymer system, causing deg-radation of the binder system and the precipitation of gypsum. Theproducts of magnesium sulfate attack were poorly cohesive and

expansive, led to dimensional instability and loss mechanical per-formance. On the contrary, immersion of geopolymer pastes inNa2SO4 did not lead to any apparent degradation of the binderand no conversion of the binder phase components into sulfate-containing precipitates. Chi and Huang[98]studied the percentageof water absorption of geopolymer mortars made of different com-binations of FA/slag ratios of 100/0, 70/30, 50/50, 30/70, 0/100, byweight. Sodium silicate with modulus ratio of 1 was used as alka-line activator. Two concentrations of Na2O of 4% and 6%, by cemen-titious weight, were employed. The results showed a reduction inthe percentage of water absorption with increasing slag contentat both concentrations.

4.5. Fire resistance and metal leaching

Guerrieri and Sanjayan[97]studied the high temperature per-formance up to 800 C, for 1 h, of alkali-activated FA/slag pastesactivated with a combination of sodium silicate and 8 M NaOH.FA was replaced with slag at levels of 0%, 50%, 65% and 100%, byweight. They reported that the specimens with very low initialstrengths (

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Table 4

Effect of slag on the strength of AAFA system.

Author % incorporation Positive effects Negativeeffects

Fineness Notes

Weiguo et al.[94] 0, 25, 50, 75 and 100 p

0.08 sieve residue was controlledbelow 2%

100% optimal

Puertas et al.[95] 0, 30, 50, 70 and 100 p

FA: 3980 cm2/g, slag: 4600 cm2/g Cured at 65C coupled with 10 M, at age of1 day

100% optimalp Cured at 25C coupled with 10 M, at age of

7 days70% optimalp

For the remaining conditions, at age of7 days

100% optimalp At ages of 28 and 90 days

100% optimal

Gara et al.[96] 0, 25, 50, 75 and 100 p

FA: 2600 cm2/g, slag: 3700 cm2/g At 4% Na2O, Ms = 1.5100% optimalp

At 4% Na2O, Ms = 11.575% secondplacep

At 4% Na2O, Ms = 11.550% third place

Guerrieri andSanjayan[97]

0, 35, 50, 65 and 100 p

Unavailable At 8% Na2O, Ms = 11.5

35% optimalp At 8% Na2O, Ms = 11.5

65% secondplacep

At 8% Na2O, Ms = 11.5100% thirdplacep

At 8% Na2O, Ms = 11.550% fourthplace

Chi and Huang[98] 0, 30, 50, 70 and 100 p

FA: 2370 cm2/g, slag: 4350 cm2/g50% optimump

100% second

placep

30% Thirdplace

Yang et al.[99] 0, 20, 40, 60, 80 and100

p Unavailable At Ms = 1.2 or 1.4

80% optimalp

60% secondplacep

100% thirdplacep

40% fourthplacep

20% fifth place

Kim and Kim[100] 0, 50 and 100 p

FA: 1050 lm, slag: less than 20 lm100% optimump

50% Secondplace

Aydn[101] 60, 80 and 100 p

FA: 3230 cm2/g, slag: 4100 cm2/g100% optimump

80% Secondplace

Smith and Osborne[91]

60 p

FA: 3980 cm2/g, slag: 4600 cm2/g At early ages, but little strength gainbeyond 28 days

Kumar et al.[89] 0, 5, 15, 25, 35 and50

p FA: 13,000 cm2/g, slag: 9200 cm2/g

50% optimal

(continued on next page)

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The ratios of FA/MK were 50/50, 30/70, and 10/90, by weight. 2%short polyvinyl alcohol (PVA) fibers were used as reinforcements.The fiber length was 6 mm, whilst its average diameter was14 lm. Solution of NaOH and sodium silicate was used as alkalineactivator. Extrusion method was used to manufacture the geopoly-mers. The experimental results showed that the inclusion of high

content of MK in the geopolymer gave good fibermatrix bond.This led to a higher flexural strength. On the other hand, the inclu-sion of small MK content in the geopolymer, led to lower flexuralstrength. Zhang et al.[111]studied some properties of alkali-acti-vated FA/MK. The ratios of FA/MK were 70/30, 50/50, 30/70, 10/90and 0/100, by weight. Chemical-grade NaOH and sodium silicatesolution were used as alkaline reagents. The compressive and flex-ural strengths at 2 days showed that the composite 0/100 gave thehighest compressive strength and flexural strength followed by 30/70, 10/90 and 50/50, respectively, whilst the composite of 70/30came in the last place. The incorporation of FA increased the elec-trical resistivity of geopolymeric pastes, whereas FA content had alittle impact on the electrical resistivity.

Aguilar et al. [112] produced lightweight concretes based on

binders of FA/MK activated with 15.2% of Na2O using sodium sili-cate of modulus SiO2/Na2O = 1.2. The ratios of FA/MK were 25/75and 0/100. Concretes with densities of 1200, 900 and 600 kg/m 3

were obtained by aeration by adding aluminum powder, in someformulations lightweight aggregate of blast furnace slag was addedat a ratio binder: aggregate 1:1; curing was carried out at 20 and75C. The compressive strength development was monitored for180 days. They concluded that it is possible to produce concretebased on geopolymers of different densities. The substitution ofFA with 75% MK was viable to form reactive cementitious pastes.The increment in the curing temperature from 20 to 75 C acceler-ated the development to the compression strength during the firstday; in the long term curing at 20 C similar results were obtained.

Yunsheng et al.[66]studied the durability of FA/MK-based geo-

polymers reinforced with short PVA fibers. Sodium silicate andNaOH solution was used as alkaline activator. The incorporationsof MK in FA were 50%, 70%, 90% and 100%, by weight. They reportedthat impact strength, impact stiffness and impact toughness ofcontrol specimens, specimens exposed to acid solution attack andspecimens exposed to 20 freeze/thaw cycles increased with theinclusion of MK. 10% FA coupled with 90% MK showed the bestmixture followed by 30/70 and 50/50, respectively. They also re-ported that the 10/90 gave lower porosity. Table 5summarizesthe previous researches that studied the effect of MK on the work-ability, setting time, strength and durability of AAFA system.

5.2. Immobilization

Bankowski et al.[113]activated FA/MK with solution of sodiumsilicate and NaOH. The solution had 0.76 M and the sodium silicate

concentration was 4.25 M. This geopolymer was used to encapsu-late brown coal FA containing high concentrations of heavy metals.The results indicated that leaching of calcium and potassium hasbeen reduced by this geopolymer. Significant reductions in leach-ing were found for calcium, arsenic, strontium, selenium and bar-ium. The geopolymer was effective at stabilizing low percentages

of FA, but effective as the percentage of FA increased. Phair et al.[114] studied the effect of incorporation of Al sources, such asmetakaolinite, kaolinite and K-Feldspar, with FA geopolymers onsolidification stabilization of heavy metals. They reported that forincreasing the efficiency of immobilisation, it was suggested thatthe metal waste be pre-treated with the Al source/clay beforebeing added to the geopolymer mixture. This would maximizethe sportive capacities of the Al source. They also reported thatall matrices were generally found to be highly efficient in retainingPb within the matrix with the order of effectiveness: FA > kaolin-ite > K-feldspar > metakaoline.

Xu et al. [115]studied some factors affecting the immobiliza-tion of heavy metals in FA/MK-based geopolymers. They used asolution of KOH and K2SiO3 as activator. The results showed that

the heavy metals could be effectively immobilized into the geo-polymeric matrices. The concentrations of alkali activator and dif-ferent types of heavy metals had impact on the immobilizationbehavior to one metal in the same system. Yunsheng et al. [109]studied the immobilization behavior of FA/MK mortars activatedwith NaOH and sodium silicate solution. The ratios of FA/MK were70/30, 50/50, 30/70, 10/90 and 0/100, by weight. They concludedthat the synthesized geopolymer could effectively immobilize Cuand Pb heavy metals. Van Jaarsveld[116]reported that the inclu-sion of MK affected the propensity of the geopolymer matrix toimmobilize heavy metals effectively. The inclusion of MK activelyimproved the stability of the geopolymer matrix against chlorideattack.

6. Silica fume

Nuruddin et al.[117]partially replaced FA, in geopolymer con-cretes, with SF at levels of 0%, 3%, 5% and 7%, by weight. Sodium sil-icate and NaOH solution was used as alkaline activator. Sugarbased material was incorporated, 3% of total binder, to increasethe setting time of concrete. There were three different curing con-ditions named hot gunny, ambient and external exposure curing. Inhot gunny curing, specimens were covered with gunny sack,dipped in warm water which removed in the third day. In ambientcuring, specimens were placed in the shade. In external exposurecuring, specimens were put in plastic coated shelve and exposedto direct sunlight. The compressive strength results showed thatthe optimal replacement level with SF that gave the highest com-

pressive strength depended on curing condition. In hot gunny cur-ing, 3% SF was the optimal. In ambient temperature curing, 7% SF

Table 4(continued)

Author % incorporation Positive effects Negativeeffects

Fineness Notes

Zhang et al.[102] 25, 30, 35 and 45 p

Unavailable At age of 7 days45% optimalp

At ages of 28 and 60 days35% optimal

Rashad[84] 0, 5, 10 and 15 p FA: 3500, slag: 320015% optimal

Wang et al.[103] 16.231.33 p

FA, slag and MK: particle size lessthan 74 lm

Li and Liu[104] 4 p

Particle size (lm) FA: 11.69, slag: 0.94Puertas et al.[69] 0 and 50

p FA: 3980 cm2/g, slag: 4600 cm2/g

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was the optimal, whilst 100% FA was the optimal at the externalexposure curing. Dutta et al.[118]and Thokchom et al.[119]par-tially replaced FA with SF, in pastes and mortars, at levels of 0%,2.5% and 5%, by weight. Sodium silicate and NaOH solution wasused as activator. The activator concentration was 8% Na2O, whilemolar ratio was 1. The specimens were cured at 85 C for 48 h thenallowed to cool inside the oven. The compressive strength resultsindicated that as the SF content increased in the pastes as the com-pressive strength marginally decreased. On the contrary, as the SFcontent increased in the mortars as the compressive strength in-creased. The water absorption results showed an increase withintroduction of SF in the pastes, whilst they showed a reductionwith introduction of SF in the mortars.

Wu and Sun[108]prepared activator from sodium silicate solu-tion by mixing predetermined amounts of NaOH flake and SF in

distilled water. The mixture was sealed and placed in a furnaceat 75C for approximately 12 h, to achieve a complete reaction be-tween NaOH and SF, and then left to be cooled at room tempera-ture. They partially replaced FA, in mortars, with MK at levels of0%, 10%, 20% and 30%, by weight, in which SF/(FA + MK) ratios of0%, 5%, 7.5%, and 10% and NaOH/(FA + MK) ratios of 5%, 7.5%, 10%and 12.5% were obtained. The experimental results showed an in-crease in slump with increasing SF content from 0% to 12.5%. In thecase of NaOH/(FA + MK) ratio of 5%, the 7 days compressivestrength increased as SF increased from 5% to 7.5%, then decreasedas SF further increased to 10%, whereas the 28 days compressivestrength increased monotonically as SF increased from 5% to 10%.In case of NaOH/(FA + MK) ratio of 7.5%, both the 7 and 28 dayscompressive strengths increased as SF increased from 5% to 10%,

with the exception of 10% MK. Both the 7 and 28 days compressivestrengths decreased as SF increased from 10% to 12.5% in the caseof 20% MK. For NaOH/(FA + MK) ratio of 10%, 7 and 28 days com-pressive strengths increased with SF from 0% to 7.5%, followed bya reduction as SF/(FA + MK) further increased from 7.5 to 10% forthe same MK content except 0%. They concluded that the optimalSF content depended on NaOH content, where optimal SF contentshifted from 10% to 7.5% when NaOH was increased from 7.5% to10% or higher. Songpiriyakij et al. [120]partially replaced FA withSF, in pastes at levels of 0%, 10%, 20%, 30% and 40%, by weight. Mix-ture of Na2OSiO2and NaOH was used as activator. The NaOH con-centration was 10 M or 18 M. The Na2OSiO2/NaOH ratio was 2.5.The compressive strength and bonding strength, at ages of 1, 3,7, and 28 days, increased with increasing SF content and NaOH

concentration. They also studied the initial and final setting times

of the paste mixture containing 40% SF and 10 M NaOH versus con-trol mixture. The results showed that the inclusion of SF increasedinitial setting time by about 17.86%, but decreased final settingtime by about 20%. Table 6summarizes the previous researchesthat studied the effect of SF on the workability, compressivestrength and water absorption of AAFA system.

7. Portland cement

Lohani et al.[121]replaced FA, in concretes, with PC at levels of0%, 10%, 25%, 40%, 60% and 100%, by weight. NaOH was used asalkaline activator. The slump results indicated higher workability

Table 5

Effect of MK on the workability, setting time, strength and durability of AAFA system.

Author %incorporation

Fineness Effects Notes

Zhang et al.[107]

33.3, 50, 66.7and 100

FA: 0.787 m2/g, MK:1.37 m2/g

Increased the workability 66.7% optimal, steamcuring for 6 days

Prolonged the setting time Increased the compressive strength

Wu and Sun[108]

0, 10, 20 and30

Unavailable Increased the workability

Increased the compressive strength

Yunshenget al.[109]

50, 70, 90 and100

FA: 4000 cm2/g, MK:3500 cm2/g

Incr eased the compr essive and flexur al strengths 70% optimal

Li et al.[110] 50, 70 and 90 FA: 4000 cm2/g, MK:3500 cm2/g

Increased the flexural strength 90% optimal

Zhang et al.[111]

30, 50, 70, 90and 100

FA: 26.7 m2/kg, MK:65.1 m2/kg

100% MK gave the highest compressive and flexural strengths, followed by70%, 90%, 50%, and 30%, respectively

Yunshenget al.[66]

30, 50, 70, 90and 100

FA: 4000 cm2/g, MK:3500 cm2/g

Increased the impact strength, impact stiffness and impact toughness 90% optimal

Resist acidic solution attach Resist 20 freeze/thaw cycles Lowered the porosity

Table 6

Effect of SF on the workability, compressive strength and water absorption of AAFAsystem.

Author %Incorporation

Effects Notes

Nuruddin et al.[117]

0, 3, 5 and 7 Increased the compressivestrength, 3% optimal

Hot gunnycuring

Increased the compressivestrength, 7% optimal

Ambientcuring

Increased the compressivestrength, 0% optimal

Externalexposurecuring

Dutta et al.[118]andThokchomet al.[119]

0, 2.5 and 5 Increased the compressivestrength, 5% optimal

In mortars

Reduced the waterabsorption Decreased thecompressive strength

In pastes

Increased the waterabsorption

Wu and Sun[108]

0, 5, 7.5, 10and 12.5

Increased the workability

Increased the compressivestrength at SF levels 7.510%

Dependedon NaOHcontent

Songpiriyakijet al.[120]

0, 10, 20, 30,40 and 50

Increased the compressiveand bonding strengths withincreasing SF content

40 Increased the initialsetting time, but decreasedthe final setting time

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with decreasing PC content. On the other hand, compressivestrength increased with increasing PC content. Palomo et al.[122] partially replaced FA with PC clinker at level of 30%, byweight. The composite was activated with either NaOH solutionor waterglass + NaOH solution. Mixture hydrated with deionisedwater was employed for comparison. The compressive strength re-sults showed that the highest compressive strength was obtained

when waterglass + NaOH was used as activator. Mixture mixedwith deionised water came in the second place, whilst mixtureactivated with NaOH came in the last place.

Guo et al.[123]studied the compressive strength, at ages of 3, 7and 28 days, of FA/PC-based geopolymers activated with NaOHsolution and sodium silicate solution. FA was partially replacedwith PC at levels of 0%, 10%, 20%, 30%, 40% and 50%, by weight.The specimens were cured at 23 C. They reported that the 40%PC gave better mechanical performance compared to the bindersusing other mixture ratios. In another investigation, Guo et al.[124] partially replaced Class C FA with PC at levels of 0%, 10%,20%, 30%, 40% and 50%, by weight. NaOH solution and sodium sil-icate solution were used to activate the composites in which theamount of Na2O was fixed at 10 wt%. The pastes were cured at75C for 4, 8 and 24 h or at 23 C for 3, 7 and 28 days. At curingtemperature of 75C, the compressive strength increased withincreasing PC content up to 40%. The composition of 60% FA plus40% PC gave the highest compressive strength at ages of 4, 8 and24 h. At curing temperature of 23 C, the compressive strength in-creased with increasing PC content up to 40% at ages of 3 and7 days, whilst it increased with increasing PC content up to 50%at age of 28 days. However, the composition of 60% FA plus 40%PC gave the highest compressive strength at ages of 3 and 7 days.The composition of 50/50 gave the highest compressive strengthat age of 28 days, whilst the composition of 60/40 (FA/PC) camein the second place (Fig. 2). They concluded that specimens madeof 60/40 had better mechanical performance compared to bindersusing other mixture ratios.

Owens et al.[125]studied the early ages compressive strength

of FA/PC pastes activated with different activators and cured ateither 20 C up to testing date or at 60 C for initial 24 h and thenat 20C for the remaining period. The activators were 1% sodiumsulfate, 10% calcium sulfate (anhydrite), from binder weight and1 M NaOH. The FA was partially replaced with PC at level of 50%,by weight. Neat FA/PC paste without activator was employed forcomparison. At 20 C curing temperature, the compressive strengthresults showed that 1% sodium sulfate, which used as activator,gave the highest compressive strength at age of 1 day, followedby 1 M NaOH, followed by neat FA/PC without activator and fol-lowed by 10% calcium sulfate. At ages of 3 and 7 days, the neatFA/PC without activator gave the highest compressive strength,

followed by 1% sodium sulfate, followed by 1 M NaOH, whilst10% calcium sulfate came in the last place. At 60 C curing temper-ature for 1 day and then 20 C for the remaining period, 10% cal-cium sulfate gave the highest compressive strength at age of1 day, followed by 1% sodium sulfate, followed by neat FA/PC with-out activator, whilst 1 M NaOH came in the last place. At ages of 3and 7 days, 10% calcium sulfate gave the highest compressive

strength, followed by neat FA/PC without activator, followed by1% sodium sulfate. Finally, pastes activated with 1 M NaOH camein the last place. They concluded that sodium sulfate seemed tobe the optimum activator when curing temperature was 20 C,whilst calcium sulfate seemed to be the optimum activator whencuring temperature was 60 C for 1 day and then 20 C for theremaining period.

Saraswathy and Song[126]studied the corrosion performanceof steel embedded in different FA/PC concrete mixtures. The ratiosof FA/PC were 10/90, 20/80, 30/70 and 40/60, by weight. The mix-tures were activated with NaOH and calcium oxide. They also acti-vated the mixtures with physical activation and thermal activation.The results showed that FA/PC ratios of 20/80 and 30/70 improvedthe corrosion resistance properties of concrete. The FA/PC chemi-cally activated gave the lowest corrosion rate, lower absorptionand lower coulomb values compared to either physical activationor thermal activation.

Fernndez-Jimnez et al.[127] studied the residual compressivestrengths, after exposure to elevated temperatures, of differentthree types of binders. These binders were PC, AAFA and alkali-activated FA/PC. The neat AAFA binder was activated with a mix-ture of 15% liquid sodium silicate and 85% NaOH solution. Thecomposite of FA/PC (59/25) was activated with 16% solid activator(8% solid sodium silicate + 8% Na2CO3). They concluded that neatAAFA performed better than PC. Residual compressive strengthwas maintained or even raised in this material after exposure toelevated temperatures. The hybrid FA/PC exhibited intermediatebehavior between the neat AAFA and PC.

Wu and Nail[128]studied the effect of sulfate attack and ASR

on blended cements consisted of 2060% Type I cement, 4080%Class C FA and spray-dryer ash (SDA) activated with 24% sodiumsulfate. Neat Type I cement was employed as a control. They con-cluded that the blended cements showed superior resistance tosulfate attack. With 60% cement replacement, the 1-year mortarbar expansion was significantly lower than limit of 0.1% specifiedin ASTM C 1157 for Type high sulfate resistance blended cement.The mortar bar expansion of blended cements in alkali solutionwas lower than the control Type I cement. The expansion valueswere still beyond the limit that is considered safe for ASR. Theaddition of sodium sulfate depleted Ca2+, increased the pH valuein cement past and promoted the dissolution of PC minerals andpozzolan minerals. It also accelerated the formation of early ages.Table 7summarizes the previous researches that studied the effect

of PC on some properties of AAFA system.

8. Cement kiln dust

Wang et al.[129]studied the effect of curing temperature andNaOH addition on the compressive strength of FA blended with ce-ment kiln dust (CKD) binders. The ratio of FA/CKD was 50/50.NaOH was used as alkaline activator with two different concentra-tions of 2% and 5%. The curing temperatures were 14, 38 and 50 C.The results indicated that curing temperature was more effectivefor FA/CKD binder strength improvement than NaOH addition.Addition of 2% NaOH increased the strength of the binder at bothearly and later ages, whilst addition of 5% NaOH increased the

strength only at early age when the pastes cured at 24 C or38C. 2% NaOH reduced the strength when curing temperatureFig. 2. Compressive strength of FA/PC binders [124].


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was 50C(Fig. 3). Wang et al. [130]investigated three differentmethods and their effects on the strength development of nonclin-ker cements made of 50% Class F FA and 50% CKD. These activationmethods included ball mill cogrinding, chemical addition and ele-vated temperature curing. In chemical addition method, FA/CKDwas activated with 2% or 5% NaOH, by weight. The compressivestrength results showed that the inclusion of 2% NaOH was moreeffective than the inclusion of 5% NaOH, to improve the compres-sive strength (Fig. 4).

9. Lime

Shi[131]prepared FA/lime at ratio of 80/20 without activationor with activation by 4% Na2SO4. The water to solid ratio of 0.35was used to produce a paste with normal consistency. Paste spec-imens were cured in fog room at temperature of 23 C, up to test-ing date. The results indicated that the addition of Na 2SO4did notaffect the initial setting time, but shortened the final setting time.Activated pastes showed much higher strength than un-activatedpastes at ages of 3 and 28 days. The addition of Na 2SO4 raisedthe alkalinity of pore solutions, accelerated initial pozzolanic reac-tion and resulted in the formation of AFt, which gave the high earlystrength of the FA/lime paste. Shi and Day [132]studied the effectof addition of lime on the strength development and hydration of

FA/slag mixtures activated with NaOH and sodium silicate. Theyconcluded that the addition of a small amount of hydrated limesignificantly increased the early-age strength, but slightly de-creased the later-age strength of the cements. Fan et al. [133]pre-sented new method of FA activation with addition of lime and asmall quantity of Na2SiO3. FA/lime pastes without or with smallquantity of Na2SiO3 were tested in compression at ages of 3, 14,28, 56, 90 and 120 days. The results indicated that the inclusionof Na2SiO3 increased the compressive strength at ages of 3, 14and 28 days, whilst no effect on the compressive strength at ageof 56 days. On the other hand, the inclusion of Na2SiO3decreasedthe compressive strength at ages of 90 and 120 days, in comparisonwith FA/lime without Na2SiO3. Table 8summarizes the previous

Table 7

Effect of PC on some properties of AAFA system.

Author Replacement levels (%) P ositive effects Negativeeffects

Studied property and notes

Lohani et al.[121] 0, 10, 25, 40, 60 and 100 p

Workabilityp Compressive strength

Palomo et al.[122] 30 p

Compressive strength (activator: waterglass + NaOH)Guo et al.[123] 0, 10, 20, 30, 40 and 50

p Compressive strength

40% optimalGuo et al.[124] 0, 10, 20, 30, 40 and 50


40% optimal at ages of 3, 7 days, whilst 50% optimal at age of 28 daysOwens et al.[125] 50


20 C curing 1% Na2SO4optimal at age of 1 dayp Compressive strength

20 C curing At ages of 3, 7 daysp Compressive strength

60 C then20 C

10% calcium sulfate optimal at ages of 1, 3, 7 days

Saraswathy and Song[126] 60, 70, 80 and 90 p

Corrosion resistance 7080% optimal

Fernndez-Jimnez et al.[127]

0 and 25 p

After exposure to elevated temperatures

Wu and Nail[128] 2060 p

Sulfate attack resistance

Fig. 3. Effect of curing temperature on alkali-activated FA/CKD compressivestrength (a) 2% NaOH (b) 5% NaOH[129]. Fig. 4. Effects of NaOH addition on strength of FA/CKD[130].

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researches that studied the effect of lime on the compressivestrength of AAFA system.

10. Natural pozzolan

Nazari et al.[134]partially replaced FA with rice husk-bark ash(RHBA) at levels of 20%, 30% and 40%, by weight, in geopolymersactivated with waterglass + NaOH. The compressive strength re-sults showed that 30% RHBA combined with 70% FA gave the high-est compressive strength at 7 and 28 days. The composition of 20%RHBA coupled with 80% FA came in the second place, whilst thecomposite of 40% RHBA coupled with 60% FA came in the last place.In another investigation, Nazari and Rohani[135]studied the flex-ural strength of the same mixtures and concluded similar conclu-sions. Riahi et al. [136] measured the percentage of waterabsorption of the same mixtures that activated with the solutionof waterglass and NaOH. The SiO2/Al2O3 ratios were 2.38, 2.99and 3.81. The experimental results showed that SiO2/A2O3 ratioof 2.99 gave the lowest water absorption percentage, the SiO2/Al2O3 ratio of 2.38 came in the second place, whilst the ratio of3.81 came in the last place. The 30% RHBA coupled with 70% FAgave the lowest water absorption, the combination of 20% RHBAwith 80% FA came in the second place, whilst the combination of40% RHBA with 60% FA came in the last place.

Songpiriyakij et al. [120]partially replaced FA with RHBA, inpastes at levels of 0% and 40%, by weight. The ratio of RHBA was70:30. The treated temperature was around 400 C. Mixing of Na2-OSiO2 and NaOH was used as activator. The NaOH concentrationwas 10 M or 18 M. The Na2OSiO2/NaOH ratio was 2.5. The resultsshowed an increase in the compressive strength and bondingstrength, at ages of 1, 3, 7 and 28 days, with the inclusion of RHBA.The specimens activated with 18 M NaOH exhibited lowerstrengths, at ages of 1 and 3 days, in comparison with that acti-vated with 10 M NaOH. On the other hand, the specimens activatedwith 18 M NaOH showed higher strengths, at ages of 7 and 28 days,than that activated with 10 M NaOH. They also studied the initialsetting time and final setting time of the paste mixture containing40% RHBA and 10 M NaOH compared to control mixture. The re-

sults showed that the inclusion of RHBA increased both initialand final setting times by about 21.43% and 6.67%, respectively.

Kusbiantoro et al.[137]partially replaced FA, in concretes, withmicrowave incinerated rice husk ash (MIRHA) at levels of 0%, 3%and 7%, by weight. The composites were activated with solutionof sodium silicate and NaOH. The geopolymer concrete specimenswere exposed to three different curing conditions that were ambi-ent, external exposure and oven curing. In ambient curing, thespecimens were placed at the shaded area with maximum temper-ature of 35 + 1 C. In external exposure curing, the specimens wereplaced in plastic chamber exposed to direct sunlight with maxi-mum temperature of 55 + 1 C. In oven curing, the specimens wereplaced, after casting by 1 h, in an oven at temperature of 65 C for24 h, then in ambient temperature. The results showed that the

improvement in the compressive strength of MIRHA-based geo-polymer concrete was up to 22.34% higher than that of non-MIR-

HA-based geopolymer concrete at ambient temperature, whilstthe inclusion of MIRHA in FA had adversely impact on compressivestrength at external exposure curing. In oven curing, the inclusionof MIRHA in FA had significantly improvement in compressivestrength. 3% MIRHA had compressive strength up to 14.17% higherthan that of non-MIRHA concrete, whilst 7% gave 19.41% higher, re-lated to non-MIRHA concrete. They also studied the bondingstrength between FA-MIRHA based geopolymers and steel. Theyfound that 3% MIRHA had marginal improvement in bondingstrength, whilst 7% had significant improvement which reached38.31% higher than that of non-MIRHA, at ambient curing

(Fig. 5). In external exposure curing, the non-MIRHA geopolymermixture gave the highest bonding strength, followed by 7% MIRHAand 3% MIRHA (Fig. 6). The 7% MIRHA presented only 4.29% lowerbonding strength than that of non-MIRHA concrete. In oven curing,the 3% MIRHA gave the highest bonding strength at 3 and 7 days,whilst the bonding strength of all mixtures was comparable atage of 28 days. Nuruddin et al. [138]presented the compressivestrength development (from age of 3 days up to 56 days) throughpolymerization process of alkaline solution and FA blended withMIRHA. FA was blended with MIRHA at levels of 3%, 5% and 7%.A solution of NaOH and Na2SiO3 was used as alkaline activator.Concrete specimens were cured at three different conditionsnamed hot gunny curing (3338 C), ambient curing (2732C)and external exposure curing (3944 C). At hot gunny and ambi-

ent curing, the results indicated that the addition of 5% MIRHAgave the highest compressive strength, followed by 0%, followedby 3% and 7%. At external exposure curing, the results indicatedthat the addition of MIRHA at level of 0% gave the highest compres-sive strength, followed by 7%, followed by 3% and 5%.Table 9sum-marizes the previous researches that studied the effect of RHBAand MIRHA on some properties of AAFA system.

11. Nanoparticles

Riahi and Nazari[139]studied the compressive strength of ash-based geopolymers containing rice husk ash + FA and nanoalumi-

Table 8

Effect of lime on the compressive strength of AAFA system.

Author %incorporation

Positive effects No or negative effects

Shi[131] 20 Increased early strengthShi and Day[132] Small amount Increased early strength Slightly decreased the later strengthFan et al.[133] Increased the compressive strength at ages of 3, 14 and 28 days No effect on the strength at age of 65 days

Decreased the compressive strength at ages of 90 and

120 days

Fig. 5. Bonding strength of FA-MIRHA-based geopolymer concrete in ambientcuring[137].


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na + nanosilica. Four factors including the percentage of nanosilica(at 3 levels of 1, 2 and 3 wt%), oven curing temperature (at 3 levelsof 25, 70 and 90 C), oven curing time (at 3 levels of 2, 4 and 8 h)

and NaOH concentration (at 3 levels of 5, 8 and 12 M) were consid-ered. The alkali activating was done by a mixture of NaOH and so-dium silicate solutions. The experimental results showed that theoven curing time was not important factor affecting the compres-sive strength. The optimum NaOH concentration of 8 M showedthe most effect on the compressive strength. Utilizing of 3 wt%SiO2 nanoparticles resulted in obtaining the highest strength.Al2O3 nanoparticles had no effect on the compressive strength.The optimum level of nano silica, oven curing temperature andoven time were 3 wt%, 90C and 8 h, respectively. Rodrguezet al.[140]assessed the effect of the use of an alternative activatorbased on nanosilica/MOH (M = K+ or Na+) blended solutions on theperformance of AAFA binders. Sodium silicate and potassium sili-cate were used as reference soluble silica sources. They reported

that the production of high mechanical strength and low perme-ability could be achieved using alternative activators based onmodified nanosilica. These binders showed an extent of reactionwhich was slightly lower than that of binders produced from usingsodium silicate activators, but mechanical strengths were similar.The water demand and porosity of the samples prepared withthe nanosilica-based activators were lower than for the case of sil-icate activators, which was attributed to the slightly delayed re-lease of silica from the solid nanosilica particles, which remain in

suspension in the solution during the early ages of reaction andthen released silica later in the reaction process.

Chindaprasirt et al.[141]investigated the effect of silica derivedfrom nanosilica and rice husk ash and alumina (nanoalumina) onthe setting time and compressive strength of Class C FA geopoly-mers. Sodium silicate and NaOH were used as alkaline activators.The setting and compressive strength were investigated by adjust-

ing SiO2/Al2O3ratio of the starting mixture, via series of mixturesformulated with varying SiO2 or Al2O3 contents. The resultsshowed that the increasing in both alumina and silica, acceleratedthe setting. The control specimen with SiO2/Al2O3= 4 had com-pressive strength of 62.6 MPa. The compressive strength decreasedwith the addition of silica content from 4.8 to 5.8 (SiO2/Al2O3from4 to 4.79). On the other hand, the increasing Al2O3content did notshow any significant effect on the compressive strength. Table 10summarizes the previous researches that studied the effect ofnanoparticles on some properties of AAFA system.

12. Bottom bed and fluidized bed combustion

Boonserm et al.[142]studied the improvement of the geopoly-

merization of bottom ash (BA) by incorporating FA. The ratios ofFA/BA were 100/0, 75/25, 50/50, 25/75 and 0/100, by weight. NaOHsolution at 10 M concentration and sodium silicate solution wereused as alkaline activators. The results indicated that the compres-sive strength decreased with increasing BA content. Chindaprasirtet al. [143] presented utilization of FA obtained from fluidizedbed combustion (FBC) as a source material for geopolymer. FBCFA has low reactivity and high content of CaO and CaSO 4 whichlimits its use. However, they blended FBC FA with pulverized coalcombustion (PCC) FA in different contents. The ratios of PCC/FBCwere 100/0, 80/20, 60/40, 20/80 and 0/100, by weight. A solutionof NaOH and Na2SiO3was used as alkaline activator. They reportedthat the compressive strength decreased with increasing FBC FAcontent (Fig. 7).

Chindaprasirt and Rattanasak[144]blended FBC FA with BA atratio of 60/40. The blended FBC/BA was partially replaced with PCCFA at levels of 50%, 60%, 70% and 80%, by weight. Sodium silicateand 10 M NaOH solutions were used as alkaline activators. The re-sults indicated that the inclusion of 60% PCC FA gave the highestcompressive strength. Xu et al. [145] investigated compressivestrength, at age of 7 days, of low-reactive circulating FBC FAblended with different contents of MK activated with sodium sili-cate solution. The ratios of FBC FA/MK were 30/70, 40/60, 50/50,

Fig. 6. Bonding strength of FA-MIRHA-based geopolymer concrete in externalexposure curing[137].

Table 9

Effect of RHBA and MIRHA on some properties of AAFA system.

Author % incorporation Studied property Positiveeffects

Negativeeffects

Notes

Nazari et al.[134] 20, 30 and 40RHBA

Compressive strength p 30% optimal, followed by 20%

Nazari and Rohani[135]

20, 30 and 40RHBA

Flexural strength p

30% optimal, followed by 20%

Riahi et al.[136] 20, 30 and 40RHBA

Water absorption p

30% optimal, followed by 20%

Songpiriyakij et al.[120]

0 and 40 RHBA Compressive and bondingstrength

p

Kusbiantoro et al.[137]

0, 3 and 7 MIRHA Compressive and bondingstrength

p Ambient curing

p External exposure curingp

Oven curingNuruddin et al.[138] MIRHA Compressive strength

p Hot gunny and ambient curing

5% optimal, followed by 0%, 3% and 7%,respectivelyp

External exposure curing 0% optimal, followed by 7%, 3% and 5%,

respectively

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60/40 and 70/30, by weight. The ratio of 40/60 gave the highestcompressive strength, the ratio of 30/70 came in the second place,the ratio of 50/50 came in the third place, whilst the ratio of 60/40came in the fourth place. Finally, the ratio of 70/30 came in the lastplace.

13. Zeolite

Huang et al. [146]studied the compressive strength and efflo-rescence extent of the FA/5A zeolite geopolymer pastes. FA waspartially replaced with 5A zeolite at levels of 0%, 5%, 10% 15%

and 20%, by weight. NaOH solution and sodium silicate solutionwere mixed to prepare liquid activator with Na2O/SiO2= 2.0 andH2O/Na2O = 10. The specimens were cured at 80 C for 24 h thenat ambient temperature. The results showed that the addition of5A zeolite served to increase the compressive strength (Fig. 8),which resulted from micro-aggregate effect of fine zeolite particleson one hand and the enhancement of geopolymerization extent onthe other hand. The Ca2+ diffused from 5A zeolite through ion ex-change with Na+ in activator solution was assumed to be incorpo-rated into the alumino-silicate framework as a charge-balancingcation to form a new fiber-like phase in the zeolite-contained geo-polymer specimens. The fiber-like phase was suggested to be theamorphous zeolite-like hydrate products and the formation of this

phase improved the geopolymerization through the mechanism ofproviding nucleation sites for geopolymer formation. However, the15% 5A zeolite gave the highest compressive strength. The efflores-cence extent geopolymer specimen decreased with 5A zeolite addi-

tion, which by the reason of the Na+ fixation into the zeolitestructure through Ca2+/Na+ exchange and the lesser pore volumeof macrospores. Mingyu et al. [147]synthesized geopolymers byusing FA as the main starting material, zeolite as supplementarymaterial, and NaOH and CaO together as activator. An orthogonalarray testing protocol was used to analyze the influence of the mix-ture proportion on some properties of the geopolymer mortars. Theresults indicated that the concentration of NaOH solution and theCaO content played an important role on the strength of the mate-rials. Zeolite as additive, the geopolymer showed the higheststrength and the best sulfate resistance.

14. Gypsum and flue gas desulfurization

Boonserm et al. [148] studied the compressive strength ofblended FBC FA and PCC FA geopolymers containing gypsum asan additive. The gypsum additions were 0%, 5% and 10%, by weight.NaOH and Na2SiO3 were used to activate the aluminosilicatesources. The results indicated that the inclusion of 5% gypsum gavethe highest compressive strength, whilst the inclusion of 10% camein the second place. Boonserm et al. [142]studied the improve-ment of the geopolymerization of FA/BA that used as the blendedsource materials at ratios of 50/50, 25/75 and 0/100, by weight.The source materials were then partially replaced with 0%, 5%,10% and 15%, by weight, with the flue gas desulfurization gypsum(FGDG). The results indicated that the compressive strength in-creased with increasing FGDG content up to 10%, then decreased

beyond this level. Boonserm et al.[142]studied the improvementof the geopolymerization of FA incorporating FGDG as additive. FAwas partially replaced with FGDG at levels of 0%, 5%, 10% and 15%,by weight. The results indicated that the compressive strength de-creased as the content of FGDG increased. Guo et al.[124]partiallyreplaced Class C FA with flue FGDG and water treatment residual(WTR) at levels of 0%, 10%, 20%, 30%, 40% and 50%, by weight. NaOHand sodium silicate solution were used to activate the composi-tions in which the amount of Na2O was fixed at 10 wt%. The pasteswere cured at 75 C for 4, 8 and 24 h or at 23 C for 3, 7 and28 days. The results showed a reduction in the compressivestrength with the inclusion of either FGDG or WTR in FA matrix.They concluded that specimens made of either 10% FGDG or 10%WTR had better mechanical performance compared to binders

using other mixture ratios, but neat AAFA was still gave thehighest compressive strength.Table 11summarizes the previous

Table 10

Effect of nanoparticles on some properties of AAFA system.

Author Nanopar ticlestype

Positive effects No or negativeeffects

Riahi andNazari[139]

Nanosilica Increased thecompressivestrength

Nanoalumina No effect on the

compressivestrength

Rodrguezet al.[140]

Nanosilica (asactivator)

Reduced thepermeability Decreased waterdemand

Chindaprasirtet al.[141]

Nanosilica andrice husk ash

Accelerated thesetting Decreased thecompressivestrength

Nanoalumina Accelerated thesetting No effect on thecompressivestrength

Fig. 7. Compressive strength of geopolymer mortars at age of 7 days[143].

Fig. 8. Compressive strength of geopolymer specimens with different zeolitecontents[146].


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researches that studied the effect of gypsum and FGDG on the com-pressive strength of AAFA system.

15. Other materials

Mingyu et al.[147]synthesized geopolymers by using FA as themain starting material, bentonite as supplementary material, and

NaOH and CaO together as activator. An orthogonal array testingprotocol was used to analyze the influence of the mixture propor-tion on some properties of the geopolymer mortars. The resultsindicated that the concentration of NaOH solution and the CaOcontent played an important role on the strength of the materials.Bentonite simply acted as filler in which led the geopolymer to bemore contact, but did not show improvement on the compositionsand the microstructures of the geopolymer. Srinivasan and Sivak-unar[149]studied setting time and compressive strength of theFA/bentonite-based geopolymer mortars. The ratios of FA/benton-ite were 30/70, 20/80, 10/90 and 0/100, by weight. NaOH was usedas alkaline activator. They reported that the inclusion of bentoniteincreased the initial and final setting times. The compressivestrength values at ages of 1, 3, 7, 14 and 28 days decreased with

increasing bentonite content.Zhang et al.[150]replaced FA with mine tailings, waste materi-als produced from mining and screening operations, at levels of 0%,25%, 50%, 75% and 100%, by weight. NaOH was used as alkalineactivator with different concentrations of 5, 10 and 15 M. The spec-imens were cured at 60 C. Unconfined compressive strength (UCS)was measured at different ages of 2, 7, 14 and 28 days. The resultsshowed a reduction in the UCS with the inclusion of the mine tail-ings. The reduction in the UCS increased as the mine tailings con-tent increased (Fig. 9). Higher activator concentration led to highercompressive strength.

Jiao et al.[151]replaced FA with silica-rich vanadium tailing atlevels of 50%, 60%, 70%, 80%, 90% and 100%, by weight. Sodium sil-icate was used as alkaline activator. The specimens were cured atroom temperature. The test results showed that the mass ratio of30/70 (FA/vanadium tailing) corresponded to the highest compres-sive strength. This mixture was selected and subjected to elevatedtemperatures of 150, 300, 450, 600, 750, 900 and 1050 C for 1 h,after curing for 7 days. The results showed that the residual com-pressive strength did not change substantially before 600 C. From600 to 900 C, the residual compressive strength increased andreached its peak at 900 C. From 900 to 1050 C, the residual com-pressive strength sharply decreased.

Oh et al.[152]partially replaced two types of Class C FA withtwo levels of Na-aluminate, by weight. The first type of FA was par-tially replaced with 18%, whilst the second type was partially re-placed with 10%. Solution of 10 M NaOH was used as alkaline

activator. The specimens were cured at 80 C and 100% RH, up totesting time. Compressive strength was measured at 6 h, 1 day, 7,14 and 32 days. They reported that the inclusion of Na-aluminate

reduced the compressive strength of the specimens, with thereduction magnitude relatively constant regardless of length ofcuring period (Fig. 10). Rovnank[153]activated FA pastes with so-dium silicate. Calcium aluminate C12A7 (mayenite) was added atdifferent incorporations of 0.1%, 0.15% and 0.2%, by weight. Theyreported that the inclusion of C12A7accelerated the setting times.The 24 h compressive strength increased, whilst 28 days compres-sive strength reduced with the inclusion of C12A7.

Ahmari et al. [154] replaced FA with ground waste concrete(GWC) powder, in concretes, activated with NaOH and sodium sil-icate solution. The GWC powder was obtained by crushing andgrinding the tested PC concrete specimens. FA was replaced withGWC at levels of 0%, 25%, 50%, 75% and 100%, by weight. They con-cluded that the inclusion of GWC improved the UCS of the geopoly-mer binder up to 50% replacement level. Further increase of GWCcontent led to decrease the UCS (Fig. 11). Increased NaOH concen-tration resulted in higher UCS, especially at GWC content less than50%. Addition of sodium silicate also improved the UCS due to pro-vision of additional SiO2and delayed setting. The optimum initialSi/Al (the Si/Al ratio at the highest UCS for the FA/GWC geopolymerwas around 3.38). Lampris et al. [155]manufactured geopolymerfrom grind silt which was used as source material. Silt powderwas partially replaced with PFA at levels of 0% and 20%, by weight.The grind silt without or with FA were activated with NaOH andsodium silicate solution. The paste specimens were cured at roomtemperature or at 60 C for three days and then at room tempera-ture for four days. The compressive strength results at 7 daysshowed an increase in strength with the inclusion of FA. The inclu-sion of 20% FA raised the compressive strength by 17.11% and

4.63% for specimens cured at room temperature and 60 C for3 days then at room temperature for 4 days, respectively. Yanand Sagoe-Crentsil[156]partially replaced sand in AAFA mortarswith wastepaper sludge. Dry wastepaper sludge ranging from 0%to 10% was added as sand replacement. NaOH and sodium silicatewas used as alkaline activator. Both fresh and hardened geopoly-mer mortars properties were evaluated. The results showed thatthe addition of wastepaper sludge to geopolymer mortars reducedflow properties and compressive strength. These reductions in-creased with increasing wastepaper sludge content. On the otherhand, the addition of wastepaper sludge decreased the dryingshrinkage. The drying shrinkage decreased as the content of waste-paper sludge increased (Fig. 12).

Lee and van Deventer[157]synthesized alkali-activated cement

systems to study the effect of the inorganic salts (KCl, K2CO3, KNO3,

Table 11Effect of gypsum and FGDG on the compressive strength of AAFA system.

Author % incorporation Positive effect Negativeeffect

Boonserm et al.[148]

0, 5 and 10 (gypsum) p

5% optimalfollowed by 10%


0, 5, 10 and 15 (FGDG) p p

up to 10% beyond10%


0, 5, 10 and 15 (FGDG) p

Guo et al.[124] 0, 10, 20, 30%, 40 and

50 (FGDG)

p

Fig. 9. Unconfined compressive strength of geopolymer specimens with differentmine tailings contents at10 M NaOH concentration[150].

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KOH, CaCl2, Ca(OH)2, CaCO3, CaSO3, CaO, MgCl2.6H2O, Mg(NO3)2.6-H2O and MgO) on some properties of control mixture did not con-

tain these inorganic salts. FA and kaolin of the appropriate ratiowere mixed (FA/kaolinite ratios were 2.02, 4 and 9). Potassium

hydroxide solution of 15 M was mixed with sodium silicate. Thissolution was used to activate the source materials. They concludedthat ionic contamination during manufacturing of AAFA cementswas found not to adversely affect the product early strength. Thesetting and rheological properties of the early pastes were changedsignificantly by Ca and Mg salts through heterogeneous nucleationeffects. Setting was accelerated by these salts once the right solu-

tion composition was achieved through solid dissolution. Potas-sium salts were found to delay setting only when the initialsolution for solid activation was low in soluble silicate concentra-tion. The anions of Cl, CO23 and NO

3 could affect the alkalinesolution to achieve the right composition and thus retardedsetting.

Ariffin et al.[158]replaced the pulverized fuel ash with palm oilfuel ash. The ratios of pulverized FA/palm oil fuel ash were 70/30,50/50, 30/70 and 0/100, by weight. The compositions were acti-vated with sodium silicate and NaOH solution. The results indi-cated that the composition of 70/30 gave the highestcompressive strength, the composition of 50/50 came in the sec-ond place and the composition of 30/70 came in the third place. Fi-nally, the composition of 0/100 came in the last place. Srivastavaet al. [159] investigated experimental study related to inorganicspecies in sludge generated from Common Effluent TreatmentPlant contaminated with hazardous wastes at relatively high con-centration. The environmental sensitive metals studied in thesludge were Pb, Fe, Ni, Zn and Mn. The solidification/stabilization(S/S) of heavy metals within FA-cement-based matrix was con-ducted for low cost treatment and reuse of sludge. The sludge con-tents ranging from 0% to 50%, cement contents ranging from 30% to15%, whilst low calcium FA contents ranging from 70% to 35%. Asolution of NaOH and sodium silicate was used as alkaline activa-tor. The results indicated that with increasing sludge from 14.2% to25% the UCS was almost the same. The mixture containing 56% FA,20% sludge and 24% cement cured at 28 days showed increase instrength as well as rate of stabilization within range of 9599%for zinc, iron and manganese at pH 7. The order of fixation of toxic

metals in the alkali-activated matrix was Zn > Mn > Fe > Ni > Pb.Criado et al.[160]evaluated the inhibitive of two mixtures of or-ganic compounds, disodium b-glycerol phosphate (GPH) withsodium 3-aminobenzoate (3AMB) and GPH with sodium N-pheny-lanthranilate (PhAMB), on the corrosion of carbon steel reinforce-ment bars embedded in carbonated chloride-polluted AAFAmortars. Mortar carbonation was achieved by maintaining thespecimens in CO2 atmosphere for 60 days at room temperatureand 65% RH. The mortars were partially immersed in water solu-

Fig. 10. Compressive strength development of alkali-activated FA/Na-aluminate (a)first type FA, (b) second type FA[152].

Fig. 11. UCS versus GWC content in FA/GWC geopolymers at age 7 days[154].

Fig. 12. Variation of drying shrinkage with curing time and wastepaper sludgecontent[156].


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tion containing 1% NaCl, both in the absence and in the presence ofthe inhibitors. The results achieved in synthetic solution suggestedthat the mixtures of 0.05 M GPH with 0.05 M 3AMB and, particu-larly, 0.05 M GPH with saturated PhAMB exhibited good inhibitiveeffects on rebar corrosion. Dutta and Ghosh[161]studied the com-pressive strength and the percentage of water absorption, at age of28 days, of AAFA pastes modified with lime stone dust. FA was par-tially replaced with lime stone dust at levels of 0%, 10% and 15%, byweight. A mixture of NaOH and sodium silicate solution was usedas activator. The silicate modulus was fixed at 1. Specimens werecured along with the molds at 65 C for 48 h and allowed to coolbefore being removed and stored at room temperature at dry placebefore testing. The compressive strength results of the pastesshowed 20% and 44% enhancement with the inclusion of 10% and15% lime stone dust, respectively. On the same line with this, the

inclusion of 10% and 15% lime stone dust reduced the percentageof water absorption by 16% and 40.1%, respectively.Table 12sum-marizes the previous researches that studied the effect o

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