addtitive

ueg

Rese

rous were markedly improved with the addition of steel bres.mproved workability and compressive.and increased compressive strength.

e strength and the lowest drying shrinkage.ge, set

m.

Panel on Climate Change) [1]. Major CO producing sectors, such

culprit [2]. Each year, the concrete industry produces approxi-mately 12 billion tonnes of concrete and uses about 1.6 billion ton-nes of PC worldwide [3]. The production of cement is increasingabout 3% annually [4]. Indeed, with the manufacture of 1 tonneof cement approximately 0.94 tonnes of CO2 are launched intothe atmosphere [5]. The IEA (International Energy Authority) holdsthe cement industry responsible for emitting between 6% and 7% of

crease by 100% from the current level by 2020 [8]. On the same lineost 200% by 2050cement inhouse effee current c

of climate change caused by CO2 emissions worldwide, caurise in sea level and the occurrence of natural disasters andresponsible for future meltdown in the world economy [11].

In many countries around the world cement production con-sumes huge amounts of energy, in particular, arising from the cal-cination of raw materials at around 1500 C and the grinding ofraw materials, cement clinker and gypsum [12]. The energy de-mand associated with PC production is about 17001800 MJ/tonneclinker [1315], which is the third largest use of energy, after alu-minium and steel manufacturing industries [6,13]. The cement

Tel.: +20 1228527302; fax: +20 233351564.

Construction and Building Materials 47 (2013) 2955

Contents lists available at

B

evE-mail address: [email protected]

as power generation, transportation, oil rening and manufactur-ing of steel and concrete are under pressure to adopt measures thatwould drastically reduce the global CO2 emission rate by 2030.Within the concrete industry, cement manufacturing is the main

with this, global demand will have increased almfrom 2010 [7]. Beside the emission of CO2,launches SO3 and NOx which can cause the greenacid rain [9,10]. This is particularly serious in th0950-0618/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.04.011dustryct andontextsing abeingFibresChemical admixturesMineral admixturesOther admixtures

2013 Elsevier Ltd. All rights reserved.

1. Introduction

Practices in the delivery of build infrastructure, there are spe-cic concerns over atmospheric CO2 concentrations which at390 ppm reached record breaking levels (U. N. Intergovernmental

all the CO2 emission into the atmosphere [6]. The projections forthe global demand of PC show that in the next 40 years it will havea twofold increase reaching 6 Gt/year [7]. Among the green housegases, CO2 contributes about 65% of global warming. Additionally,cement production and resulting emissions are expected to in-Keywords:Alkali-activated slag

ent additives in AAS systeWater absorption and permeability po Superplasticizer (naphthalene-based) i SF in AAS matrix decreased workability 10% PC in AAS gave higher compressiv Gypsum in AAS reduced drying shrinka

a r t i c l e i n f o

Article history:Received 29 January 2013Received in revised form 1 April 2013Accepted 3 April 2013Available online 28 May 2013ting time and increased compressive strength.

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 slag (AAS) binder is obtained by a manufacturing processless energy-intensive than PC and involves lower greenhouse gasses emission. AAS belongs to prospectivematerials in the eld of Civil Engineering. Researchers have employed bres, chemical admixtures, min-eral admixtures and other materials as additives in AAS system aiming to modify some properties of thissystem. This paper presents a comprehensive overview of the previous works carried out on using differ-h i g h l i g h t sA comprehensive overview about the inthe properties of alkali-activated slag A

Alaa M. Rashad Building Materials Research and Quality Control Institute, Housing & Building National

Construction and

journal homepage: www.elsnce of different additives onuide for Civil Engineer

arch Center, HBRC, Cairo, Egypt

SciVerse ScienceDirect

uilding Materials

ier .com/locate /conbui ldmat

some properties of AAS system. A review on bres, chemical admix-tures, mineral admixtures and other additive materials that were

uildproduction account about 5% of worldwide industrial energy con-sumption [16,17]. In addition, cement production consumes con-siderable amounts of virgin materials (limestone and sand),producing each tonne of PC of which about 1.5 tonnes of rawmate-rial is needed [14]. Further, concrete made of PC is subject to cer-tain durability problems that are difcult to solve. In the light ofthese problems, the scientic community has undertaken to seeknew processes, technologies and materials to provide the construc-tion industry with alternative binders. One avenue that is expectedto signicant reduce cement is use of blended cement [1825]. Thesecond alternative is to recycling in cement industry [2634]which has become indispensable processes in some countries.The third alternative is the use alkali-activation of slag, y ash(FA), burned clay and other aluminosilicate materials. The new bin-der materials that can replace PC, by alkali activation, can generateabout 8090% less carbon dioxide than PC [35]. Comparison to PCconcrete, the global warming potential of alkali-activated concreteis 70% lower [36]. In addition, there are numerous advantages ofthis system as lower heat of hydration [37], the development ofearlier and higher mechanical properties [38,39], low heat release[40], better resistance of chemical attack [41,42], freezethawresistance [43], re resistance [44,45], higher reduction in chloridediffusion [46] and stronger aggregate-matrix interface formation[47,48]. On the contrary, the AAS system presents some problemssuch as rapid setting periods [49], higher shrinkage values [50],higher formation of salt eforescences [39], higher carbonation[51] and tendency to crack during curing [52,53]. However, theseadvantages and disadvantages are depended on the types of PCand blended cement, and AAS and not always in the case. For spe-cic problems, adequate solutions have been established.Researchers have been tried to solve some of these problems byusing different additives in AAS system.

The most commonly used activators are sodium silicate, sodiumhydroxide, sodium carbonate or a mixture of sodium - potassiumhydroxide (NaOH, KOH) with sodium silicate - potassium silicate,the mixture of sodium hydroxide with sodium silicate has beengenerally agreed to be the most effective activator and providesthe best formulation for high strength and other advantageousproperties. However, both the sodium hydroxide and sodium sili-cate do not exist naturally and they are obtained from energyintensive manufacturing processes. This is particularly the casefor sodium silicate, which is produced by melting sand and sodiumcarbonate at 13501450 C, followed by dissolving in an autoclaveat 140160 C under suitable steam pressure [54]. As a result, eventhough AAS could potentially be considered as a low energy andlow carbon cement system. Other uncommon activator as Na2SO4can be obtained either from natural occurring sodium-sulfate-bearing brines, crystalline evaporate deposits or as a by-productduring the manufacture of various products such as viscose rayon,hydrochloric acid and silica pigments [13]. However, in general theenergy consumption of alkali activation system is calculated to beapproximately 60% less than that of PC [55].

Ground granulated blast furnace slag (denoted as slag) is a by-product obtained in the manufacturing of iron in a blast furnacewhere iron ore, limestone and coke are heated between 1400 Cand 1600 C. Quenching process of molten slag by water is convert-ing it into a ne (no larger than 5 mm diameter), granulated slag ofwhitish colour. The rapid cooling prevents the formation of largercrystals. The resulting granular material comprises some 8595%non-crystalline calcium-aluminosilicates (glassy materials) thathigher in energy than the crystalline material [56]. Slag is com-monly utilized in the cement industry for preparation of blendedcement CEM II, CEM IV and CEM V where cement clinker substitu-

30 A.M. Rashad / Construction and Btion by slag range from 6 to 95 wt% [57]. This may be a partiallysolution to the disposal problem. Despite this use, the vast majorityof this slag is still disposed in landlls [58]. One option to eliminateadded into slag in alkali activation system is presented.

2. Fibres

In the literature, there are few references concerning the inu-ence of bres on the mechanical properties of alkali-activated ce-ments. However, the available references can be summarized asfollowing: Bernal et al. [86] activated slag concretes with water-glass. They added steel bres in amounts of 40 kg/m3 and120 kg/m3 into the AAS concrete mixtures. They reported thatthe water absorption and permeable porous quantity were mark-edly improved with the addition of the bres. Both splitting tensileand exural strengths were largely improved with increasing brevolume. On the other hand, a reduction in compressive strengthwith bre incorporations was observed. Aydn and Baradan [87]studied the effects of length and volume fraction of steel breson the mechanical and drying shrinkage behaviour of steel brereinforced alkali-activated slag/silica fume (SF) mortars. Steel -bres with two different lengths of 6 mm and 13 mm, and four dif-ferent volume fractions of 0.5%, 1.0%, 1.5% and 2.0% were used. Thecomposite ratio of slag/SF was 80/20. This composite was activatedwith waterglass and NaOH solution. The results showed a reduc-tion in the workability and drying shrinkage with the inclusionof bres. As bres content increased as the workability and dryingshrinkage decreased. Compressive strength (Fig. 1) and exuralstrength as well as toughness increased with the increase in brescontents and bres lengths (Fig. 2). Bernal et al. [88] modied AASconcretes by steel bres. The steel bres contents were 0%, 0.1%and 0.3%, by weight. Waterglass was used as alkaline activator.They reported that the inclusion of bre increased the splittingtensile strength, exural strength and toughness, at ages of 7, 14this disposal of the slag in an ecologically sensitive manner is to re-use it as cementing material by alkali activation.

The alkali activation system is a chemical process that trans-forms partially or wholly vitreous structures into cementitiousskeletons. In this context, the idea of applying alkali activationwas put forward in the researchers priorities. Thus, AAS cementand concrete were invented in the USSR in 1957 by Glukhowsk ofthe Kiev Institute of Civil Engineering, Ukraine [59], although thepossibility of using alkaline activation of slag can be traced backto the 1940s [60]. In recent years AAS cement and concrete have re-ceived great attention worldwide, with applications in the Far East[61,62] and Europe [6365]. A variation of AAS cement has beenused in the USA since 1987 [66,67]. Today the focus is no longeron obtaining new binders, but on developing materials with sus-tainably high mechanical strength and other characteristics. Oneoption to improve some special properties of AAS system is toadd one or more additives into this system. Already the literaturehas abundant of review papers in alkali activation system [6878]. In addition, the previous authors reviewed the opportunitiesand challenges of AAS system [58]; historical background, termi-nology, reaction mechanisms, hydration products and materialsand binders manufacture [79,80]; reinforced geopolymer compos-ites [81]; durability [82]; geopolymers with recycled aggregate[83]; effect of various chemical activators on pozzolanic reactivity[84] and the pursuit of an alternative of PC [85]. Indeed, there isno published literature review paper which reviewed the previousworks curried out on AASmodiedwith different types of additives.However, in this investigation, the author conducted a comprehen-sive literature review focused on the effect of different additives on

ing Materials 47 (2013) 2955and 28 days. Water absorption was reduced with the inclusion ofbre, at ages of 7, 14 and 28 days. 0.3% bre content showed betterperformance than 0.1%.

BuildA.M. Rashad / Construction andPuertas et al. [43] modied alkali-activated mortars by polypro-pylene bres. The bres contents were 0%, 0.5% and 1%, by mortarvolume. The source binder materials consisted of 100% slag or 50%slag coupled with 50% FA. Neat slag was activated with a mixtureof Na2SiO3 and NaOH with 4% concentration of Na2O, by slag mass.The composite of slag/FA was activated with 8 M NaOH. The resultsshowed that the incorporation of the bre did not affect positivelythe mechanical behaviour and freezing/thawing resistance of themortars. The modulus of elasticity decreased with the inclusionof 1% bres. The impact resistance of the mortars after wet/dry cy-cles increased with the inclusion of the bre. 1% bre increased thedrying shrinkage of the specimens that cured at 95% RH, whilst 1%bre reduced the drying shrinkage of the specimens cured at 21 Cand 50% RH. Lee et al. [89] presented a feasibility study of strain-hardening bre reinforced cementless composite using AAS basedmortar and polyvinyl alcohol (PVA) bre. Test results showed thefeasibility of attaining tensile strain up to 4.7% in bre reinforcedAAS composite, compared to 0.02% for the mortar matrix alone. Al-caide et al. [90] reported that the inclusion of carbon bres in AAS

Fig. 1. The inuence of bre length and content on th

Fig. 2. The effect of bre length and contenting Materials 47 (2013) 2955 31mortars failed to improve the compressive strength. On the otherhand, using bres caused a reduction in the drying shrinkage. Puer-tas et al. [91] reported that the inclusion of glass bres in AAS mor-tar caused a reduction in the drying shrinkage with no adverseeffect on its mechanical properties.

Li and Xu [92,93] prepared sodium silicate activated slag/FAblendswith less than0.3%basalt bres. Tests using a splitHopkinsonpressure bar (SHPB) systemrevealed no change in the dynamic com-pressive strength, but improvements in energy absorptionwere ob-served. 0.3% was estimated to be the optimal bre loading based onenergy absorption. Strain hardeningwas not observed. The compos-ite properties (energy absorbed, etc.) were determined to be strainrate dependent under impact loading. Silva and Thaumaturgo [94]presented the fracture toughness inmortarsmadeof PSS (slag + MK)cement matrix reinforced by wollastonite microbres (Ca(SiO3)).The bres volumes were 1%, 2%, 3% and 5%. They reported that wol-lastonite microbres improved the fracture toughness of the geo-polymer. The best volume of the bre was 2%. The betterreinforcing efciency obtained by the geopolymer was related to

e compressive strength of activated mortars [87].

on toughness of activated mortars [87].

the nature of the bond between bre and matrix, and consequentlythe toughening mechanism in operation. PSS cement compositesshowed debonding and bre pullout as the main tougheningmech-anisms. The bre contributed to stiffness and increased the peakload.

Natali et al. [95] modied some properties of the slag/MK geo-polymer by adding different types of dispersed short bres. So-dium silicate solution, with a SiO2:Na2O ratio of 1.99, and 8 MNaOH solution were used as alkaline activators. The used breswere: HT-carbon bres (average bre diameter 10 lm, tensilestrength 5490 MPa), commercial E-glass bres (average brediameter 10 lm, tensile strength 2500 MPa), PVA bres (averagebre diameter 18 lm, tensile strength 1800 MPa) and PVC bres(average bre diameter 400 lm, tensile strength 215 MPa).Regardless the bres type, the same content of bres (1 wt% frac-tion on the total mixture) was added to MK/slag mixture. Theused bres were cut to obtain a 7 1 mm length. They concludedthat all different types of bres had good adhesion properties, mi-cro-cracks propagation along the matrix and created a favourablebridging effect. 1 wt% of reinforcing bre embedded in the geo-polymer matrix was able to increase the exural strength from30% up to 70% depending on bre type. Geopolymers added withPVC and carbon bres exhibited signicantly post-crack improved,resulted more enhancements in ductility after reaching the rstcrack load.

From the above review of literature of this part, it can be notedthat the main advantage of employing steel or polypropylene orcarbon or glass bres in AAS system is reducing the drying shrink-age that AAS system suffers. On the same line with this, the ten-

3. Chemical admixtures

Douglas and Brandstetr [96] reported that the addition of so-dium lignosulfonate or sulfonated naphthalene-based superplasti-cizer did not improve the workability of AAS mortars. Wang et al.[97] studied the inclusion of water-reducing admixtures, such assodium lignosulphonate and naphthalene-based superplasticizerin AAS mortars. They concluded that such admixtures caused a de-crease in the compressive strength without improving the work-ability. Puertas et al. [98] studied the effect of twosuperplasticizer admixtures, based on vinyl copolymers and poly-carboxylates, on waterglass-activated slag mortars and pastes.The dosage of the admixtures was constant and equivalent 2%, insolid mass of slag. They concluded that the vinyl copolymer-basedadmixture decreased mortar mechanical strength after 2 and28 days without increasing paste workability, whilst the polycar-boxylate admixture had no effect on the mechanical performanceof the mortar but did not improve the workability. The calorimetricresults revealed that with the admixture vinyl copolymer, the slagactivation was delayed. This delay in the reaction process ac-counted for the lower mechanical strength of this mortar after2 days. Polyacrylate copolymer had not a signicant effect on theactivation process of the slag, which explained why its mechanicalstrength level was about the same as that for admixture-free mor-tar. Palacios and Puertas [99] investigated how several superplast-icizers (polycarboxylates, vinyl copolymers, melamine andnaphthalene-based) and shrinkage-reducing (polypopylenglycolderivatives) admixtures affect the mechanical and rheologicalproperties and setting times of AAS pastes and mortars. Two alka-

ve e

roveabirovethsrovethsucedeaseal stucedrovery cuceden

roveuceducedrove

easess arovero-cx an

tedeaserovecem

32 A.M. Rashad / Construction and Building Materials 47 (2013) 2955dency of the post cracks was reduced by employing HT-carbon orcommercial E-glass or PVA or PVC bres. On the contrary, theinclusion of steel bres in AAS matrix decreased the workabilityand compressive strength. However, Table 1 summarizes the effectof different type of bres on some properties of AAS system.

Table 1Effect of different types of bres on some properties of AAS system.

Author Fibre type Positi

Bernal et al. [86] Steel Impperme Impstreng

Aydin and Baradan [87] Steel Impstreng Red

Bernal et al. [88] Steel Increxur Red

Puertas et al. [40] Polypropylene Impwet/d RedspecimRH

Lee et al. [89] Polyvinyl alcohol ImpAlcaide et al. [90] Carbon RedPuertas et al. [91] Glass RedLi and Xu [92,93] Basalt Imp

Silva and Thaumaturgo [94] Wollastonite microbers (Ca(SiO3)) Incrstiffne

Natali et al. [95] HT-carbon, commercialE-glass, PVA and PVC

Imp Micmatrieffect Crea Incr Impenhan

the rst cbres)line activator solutions, waterglass and NaOH, were used; alongwith two concentrations of 4% and 5% of Na2O, by slag mass. Theresults indicated that all admixtures reduced liquid/solid ratio.The greatest reduction induced when the activator was NaOHand the admixture was naphthalene derivative. The admixtures

ffects No or negative effects

d the absorption, andlity porous quantity

Decreased the compressive strength

d the splitting and exural

d the compressive, exuralas well as toughness

Decreased the workability

the drying shrinkaged the splitting tensile strength,rength and toughness

Decreased the compressive strength

the waster absorptiond the impact resistance afterycles

No positively effects on the mechanicalbehaviour and freeze/thawing resistance

the drying shrinkage of thes that cured at 21 C and 50%

Decreased the modulus of elasticity Increased the drying shrinkage of thespecimens that cured at 95% RH

d the tensile strainthe drying shrinkage No effect on the compressive strengththe shrinkage No effects on the mechanical propertiesments in the energy absorption No effect on the dynamic compressive

strengthd the toughness, contributed tond increased peak loadd the adhesion propertiesracks propagation along thed created a favourable bridging

a favourable bridging effectd the exural strengthd the post-crack, resulted moreents in ductility after reaching

rack load (for PVC and carbon

Superplasticizer admixture showed very uid concrete with slumpmore than 200 mm, but the concrete lost its uidity after 10 min.The AAS concrete activated with sodium carbonate and NaOH andcontaining 10 ml/kg of water-reducing exhibited a slump exceeded200 mm. However, they recorded that using water-reducing andAEA admixtures were the most effective for improving workability.The compressive strength results showed that using superplasticiz-er admixture caused 25% loss of 28 days strength, the use of water-reducing (based on lignosulphonates) reduced the early strength upto 14 days. AEA had some effect on early strength up to 7 days, afterthat strength development was similar to AAS concrete withoutadmixtures (Fig. 3). The drying shrinkage results showed that thespecimens with superplasticizer exhibited the highest drying

Building Materials 47 (2013) 2955 33did not increase the slump of the pastes when waterglass was usedas activator. When the activator was NaOH, owability increasedslightly in polycarboxylate, melamine-based and vinyl copolymeradmixtures, whilst the naphthalene-based admixture increasedow rate signicantly. The shrinkage-reducing admixture had noimpact on paste slump. In the case of waterglass-AAS pastes with4% of Na2O, the admixtures had no signicant effect on setting,with the exception of the vinyl copolymer. In the case of water-glass-AAS pastes with 5% of Na2O, the vinyl copolymer acceleratedthe initial set slightly, but lengthened the nal setting time. Theadmixtures based on melamine and polycarboxylate retarded theinitial and nal sets. The naphthalene-based admixture shortenedboth initial and nal setting times. However, they concluded thatnaphthalene-based admixture combined with NaOH-AAS mortarsraised mechanical strength values compared to slag mortar withno admixtures. Naphthalene-based admixture combined withNaOH-AAS pastes improved workability and retarded the initialand nal setting times compared to slag paste with no admixtures.

Palacios et al. [100] studied the effect of different types ofsuperplasticizers (naphthalene-based, melamine-based and vinylcopolymer) on the yield stress and plastic viscosity of AAS pastes.Slag was activated with NaOH solutions at pH of 11.7 and 13.6.PC paste mixtures were employed for comparison. They reportedthat the dosages of the superplasticizers required to attain similarreduction in the yield stress were 10-fold higher for PC than for11.7-pH NaOH-activated slag pastes. Vinyl copolymer admixtureinduced the highest reduction of the yield stress in 11.7-pHNaOH-activated slag pastes. The only admixture observed to affectthe rheological parameters in 13.6-pH NaOH-activated slag wasnaphthalene-based admixture due to its structural stability in suchextremely alkaline media. Dosages as low as 1.26 mg naphthalene/g slag were observed to induce the maximum reduction in yieldstress (98%). The presence of the three types of superplasticizerslowered the plastic viscosity in the 11.7-pH NaOH-AAS pastesand only naphthalene-based admixture in 13.6-pH NaOH-AASpastes. Palacios et al. [101] established the effect of HRWR on therheology and setting of AAS pastes andmortars. Two different alka-line activators were used. The activators were waterglass solutionwith SiO2/Na2O = 1 and NaOH solution with 4% Na2O, by mass. Fivedifferent chemical admixtures were employed four HRWR: poly-carboxylate-based, melamine formaldehyde derivative, naphtha-lene formaldehyde derivative and vinyl copolymer; andshrinkage reducing agent. The dosages of admixtures were 0%,0.3%, 0.5%, 1.0%, 1.5% and 2.0%, by mass of the binder. They re-ported that the greatest drop in the yield stress in AAS cementswas found when naphthalene-derivative HRWR was added toNaOH-activated slag pastes and mortars because of its inherentstability in alkaline media. The other admixtures incorporated inAAS pastes and mortars did not signicantly modify their rheolog-ical parameters. Increasing the mixing time could dramatically re-tard the setting of waterglass-activated slag pastes, with initial andnal setting times of approximately 3 and 10 h, respectively.

Bakharev et al. [102] studied the effect of superplasticizer, air-entraining agent (AEA) and water-reducing on some properties ofAAS concretes. The activators were liquid sodium silicate (47%Na, mass of slag) and a multi-compound activator of NaOH + Na2-CO3 (8% Na, mass of slag).The superplasticizer based on modiednaphthalene formaldehyde polymers, water-reducing based onlignosulphonates and AEA with a soluble salt of an alkyl aryl sul-phonate. The slump results showed that sodium silicate activatedslag concrete with 4% Na, had a slump of 55 mm immediately aftermixing. The same concrete with water-reducing of 6 ml/kg had aslump of 80 mm and had better workability than concrete without

A.M. Rashad / Construction andwater-reducing.Water-reducing admixture of 10 ml/kg in the sameconcrete mixture produced a slump of 200 mm. AEA at a dosage of6 ml/kg produced a considerable improvement in workability.shrinkage, AAS specimens without admixtures came in the secondplace and the specimens admixed with water-reducing came inthe third place, whilst the specimens admixed with AEA came inthe fourth place. They concluded that AEA admixture was the mostsuitable for use in AAS concretes and it was not desirable to usesuperplasticizer admixture in AAS concretes.

Bilim et al. [103] studied the effect of shrinkage-reducing (SHR)and superplasticizing and set-retarding admixtures (SSR) on someproperties of slag pastes and mortars activated with alkaline acti-vator. Liquid sodium silicate was used to activate the slag at twosodium concentrations of 4% and 6%, by mass of slag. Liquid so-dium silicate and NaOH were blended to obtain 0.75 and 1 modu-lus of SiO2/Na2O. SHR based on polypropylenglycol and SSR basedon modied polymer liquid were used as chemical additives. 1% ofeach admixture, by binder mass, was added to the activator solu-tion. Fixed water/binder (w/b) ratio of 0.5 was used to preparepaste and mortar specimens. The results indicated that both SSRand SHR admixtures generally did not have an impact on settingtimes of the pastes, with the exception for the sodium silicate acti-vated slag paste with Ms = 0.75 and 4% Na, where SSR caused long-er initial and nal setting times in comparison with those mixturewithout admixture. Both SSR and SHR chemical admixtures re-duced compressive and exural strengths of the AAS mortars atage of 2 days. After 2 days, SSR had no impact on the compressiveand exural strengths, whereas SHR increased the exural strengthof AAS without changing in the compressive strength. SSR admix-ture had no impact on AAS mortars after carbonation, whilst SHRadmixture somewhat decreased the carbonation depths of AASmortars. Both SSR and SHR reduced the drying shrinkage of AASmortars, but these shrinkages were still higher than that of PC.

Collins and Sanjayan [53] studied the drying shrinkage of AASconcretes without or with 1.5% shrinkage-reducing chemicaladmixture, compared to PC concrete. The slag was supplied withgypsum (2% SO3), whichwas blendedwith slag. The activators werepowdered sodium metasilicate and hydrated lime. The resultsshowed that AAS concrete had 1.6 times greater drying shrinkagethan PC concrete at 56 days. The AAS concrete containing 1.5%Fig. 3. Compressive strength of AAS concrete prepared using different admixtures[102].

shrinkage reducing showed lower drying shrinkage compared topure AAS concrete (Fig. 4). Palacios and Puertas [104] studied the ef-fect of shrinkage-reducing admixture, based on polypropylenglycol,on the compressive strength, exural strength and dimensional sta-bility of waterglass-activated slag mortars. The concentrations ofshrinkage-reducing were 0%, 1% and 2%, by slag mass. Specimenswere cured at 20 2 C and 99% RH for 48 h. Then, the specimenssubsequently removed from the moulds and cured until testingdate at either 99% or 50% RH. The results showed that the additionof 1% shrinkage-reducing did not signicantly modify the compres-sive strength or the exural strength for the specimens cured ateither 99% or 50% RH, although after 28 days, the exural strength

34 A.M. Rashad / Construction and Buildof the specimens cured at 99% RH was 25% higher than recordedfor the mortars without admixture. The addition of 2% shrinkage-reducing increased the compressive strength and exural strengthat both curing conditions, although more signicantly in the mor-tars cured at 99% RH: exural strength was increased by approxi-mately 75% at 7 days and by more than 100% at 28 days related tothe mortars without shrinkage-reducing. The shrinkage resultsindicated that the shrinkage-reducing reduced the shrinkage byup to 85% and 50% when the AAS mortar specimens were cured at99% and 50% RH, respectively. They reported that the mechanismprimarily involved in shrinkage reduction was the decrease in thesurface tension of pore water prompted by the admixture.

From the above review of literature of this part, it can be notedthat the main advantage of employing some chemical admixturesas shrinkage-reducing (based on polypropylenglycol) or air-entraining (with a soluble salt of an alkyl aryl sulphonate) orwater-reducing (based on lignosulphonates) in AAS matrix reducedthe drying shrinkage that AAS system suffers. Other chemicaladmixtures as superplasticizer (based on polycarboxylate) orsuperplasticizer (based on vinyl copolymer) or superplasticizer(based on melamine) or superplasticizer (based on naphthalene)retarded the setting time that AAS suffers, but depending on acti-vator type and Na2O concentration. Shrinkage-reducing (based onpolypropylenglycol) somewhat decreased the carbonation depththat AAS suffers. On the contrary, some chemical admixtures assuperplasticizer (based on lignosulfonate) or superplasticizer(based on sulfonated naphthalene) or superplasticizer (based onvinylcopolymer) decreased the compressive strength and had noeffect on the workability of AAS system. However, Table 2 summa-rizes the previous researches that studied the effect of chemicaladmixtures on some properties of AAS system.

4. Mineral admixtures

4.1. Silica fume and quartz powder

4.1.1. WorkabilityCollins and Sanjayan [105] partially replaced slag with 10% con-

densed silica fume (CSF) in alkali-activated concrete activated withFig. 4. Drying shrinkage of concrete prisms subjected to sealed curing at 23 C for24 h followed by exposure to 23 C and 50% RH [53].powdered sodium metasilicate and hydrated lime. They showedthat alkali-activated slag/CSF concrete had signicantly less work-ability than neat AAS concrete.

4.1.2. StrengthRashad et al. [106] partially replaced slag with quartz powder

(QP) at replacement levels of 0%, 5%, 10%, 15%, 20%, 25% and 30%,by weight, in alkali-activated pastes. Sodium silicate was used asactivator. The results showed that the compressive strength value,at age of 28 days, increased with increasing QP content (Fig. 5). Thecomposite of 30% QP coupled with 70% slag gave the highest com-pressive strength. Rashad and Khalil [44] activated slag with so-dium silicate. The slag was partially replaced with SF at levels of0%, 5%, 10% and 15%, by weight. The paste specimens were curedat 20 1 C and 90 5% RH. They concluded that the inclusion ofSF in slag enhanced and increased the compressive strength. Theoptimal content of SF that gave the highest compressive strengthat ages of 7 and 28 days was 5% (Fig. 6). Escalante-Garca et al.[107] activated slag mortars with 6 wt% Na2O equivalent of NaOH.The slag was partially replaced with SF at levels of 0%, 5%, 10%, 15%and 20%, by weight. The compressive strength increased with thepresence of SF up to 15%, then decreased with the replacement le-vel of 20%. The replacement levels of SF at 510% gave the highestcompressive strength. In another investigation Escalante-Garcaet al. [108] reported that partially replacing 10% of slag with geo-thermal silica waste in mortar specimens, activated with 6 wt%Na2O equivalent of NaOH and waterglass, enhanced the formationof hydration products and produced denser microstructure in com-parison with the mortar containing neat slag. Aydn [109] activatedslag mortars with NaOH and sodium silicate. Slag was partially re-placed with SF at levels of 0%, 10% and 20%, by weight. The speci-mens were cured at 20 C and 90% RH for 5 h, then in steam at70 C for 6 h. The results showed that 10% SF enhanced the com-pressive strength by 4.24%, whilst 20% SF reduced the compressivestrength by 15.42%. On the contrary, the exural strength de-creased by 29.59% and 32.65% with the inclusion of 10% and 20%SF, respectively.

Collins and Sanjayan [105] reported that partially replacing 10%of slag with condensed SF in concrete specimens, activated withsodium metasilicate powder and hydrated lime, improved theone-day compressive strength by 10% higher than that of AAS con-crete without SF. Rousekov et al. [110] reported that the NaOHactivated pastes prepared with the proportion of slag: SF of 1:2and 1:1 gave higher strength at age of 56 days than the proportionsof 2:1 when NaOH/SF was 20%. Roy and Silsbee [66] reported high-er early and later strength of alkali-activated pastes containing

Table 2Effect of chemical admixtures of some properties of AAS system.

Author Admixture Positive effects No or negative effects

Douglas and Brandster [96] Superplasticizer (sodiumlignosulfonate or sulfonatednaphthalene-based

No effect on the workability

Wang et al. [97] Superplasticizer (sodiumlignosulfonate or sulfonatednaphthalene-based)

No effect on the workability. Decreased the compressive strength

Puertas et al. [98] Superplasticizer(vinylcopolymer-based)

No effect on the workability Decreased the compressive strength Delayed slag activation process

Superplasticizer(polycarboxylate-based)

No effect on the workability No effect on the mechanical performance No signicant effect on the slag activationprocess

Palacios and Purtas [99] Superplasticizer(polycarboxylate-based)

Reduced the liquid/solid ratio No effect on the workability whenwaterglass was used as activator

Improved the workability when NaOH wasused as activator

No signicant effect on the setting timewhen waterglass with 4% Na2O was used asactivator Retarded the initial and nal setting times

when 5% Na2O of waterglass was used asactivator

Superplasticizer (vinylcopolymer-based)



Slightly accelerated the initial settingtime when waterglass with 5% Na2O wasused as activator Lengthened the nal setting time when

waterglass with 5% Na2O was used asactivator

Superplasticizer (melamine-based)



No signicant effect on the setting timewhen waterglass with 4% Na2O was used asactivator Retarded the initial and nal setting times

when 5% Na2O of waterglass was used asactivator

Superplasticizer (naphthalene-based)



No signicant effect on the setting timewhen waterglass with 4% Na2O was used asactivator

Retarded the initial and nal setting timeswhen NaOH was used as activator

Shortened the initial and nal settingtimes when 5% Na2O waterglass was usedas activator Improved the compressive strength when

NaOH was used as activatorShrinkage-reducing(polypopylenglycol derivatives)

Reduced the liquid/solid ratio No effect on the workability whenwaterglass was used as activator No signicant effect on the setting timewhen waterglass with 4% Na2O was used asactivator

Palacios et al. [100] Superplasticizer(naphthalene-based)

Lowered the yield stress when either of11.7-pH or 13.6-pH NaOH was used asactivator Improved the uidization when 13.6-pHNaOH was use as activator Lowered the plastic viscosity when eitherof 11.7-pH or 13.6-pH NaOH was used asactivator

Superplasticizer(melamine-based)

Lowered yield stress when 11.7-pH NaOHwas used as activator

No effect on the owability when 13.6-pH NaOH was used as activator

Lowered plastic viscosity when 11.7-pHNaOH was used as activator

Superplasticizer (vinylcopolymer-based)

Lowered (the highest reduction) yieldstress when 11.7-pH NaOH was used asactivator

No effect on the owability when 13.6-pH NaOH was used as activator

Lowered plastic viscosity when 11.7-pHNaOH was used as activator

Palacios et al. [101] HRWR(polycarboxylate-based) Did not signicantly modify itsrheological parameter

HRWR (melamine formaldehydederivative)

Did not signicantly modify itsrheological parameter

HRWR (naphthaleneformaldehyde derivative)

Lowered (the highest reduction) the yieldstress when NaOH was used

HRWR (vinyl copolymer-based) Did not signicantly modify itsrheological parameter

Shrinkage reducing Did not signicantly modify its

(continued on next page)

A.M. Rashad / Construction and Building Materials 47 (2013) 2955 35

e ef

ovedity

roveve)cedroveve acedionase

ewh

ced the drying shrinkage No impact on the compressive strengthafter age of 2 days

uildTable 2 (continued)

Author Admixture Positiv

Bakharev et al. [102] Superplasticizer (naphthaleneformaldehyde polymers)

Imprits ui

Water-reducing (based onlignosulphonates)

Impeffecti Redu

Air-entraining (with a solublesalt of an alkyl aryl sulphonate)

Impeffecti Redureduct

Bilim et al. [103] Shrinkage-reducing (based onpolypropylenglycol)

Incre2 days Somdepth Redu

36 A.M. Rashad / Construction and BRashad and Khalil [44] partially replaced slag with SF at levelsof 0%, 5%, 10% and 15%, by weight, in alkali-activated pastes thatdesignated as SF0, SF5, SF10 and SF15, respectively. Sodium silicatewas used as activator. The specimens were cured at 20 1 C and90 5% RH. After 28 days, some specimens were crushed directlyin compression without exposure to elevated temperatures. Otherspecimens were exposed to 400, 600, 800 and 1000 C, for 2 h. Theresults indicated that the compressive strengths after ring in-creased with the presence of SF up to 800 C, then decreased at1000 C in comparison with neat AAS specimen. Both residualstrength and relative strength of hardened neat AAS paste at1000 C were signicantly higher than that of hardened alkali-acti-vated slag/SF. They concluded that neat AAS was more efcient toresist elevated temperature, especially at 1000 C, than alkali-acti-vated slag/SF. They found that the volume of the specimens madeof neat slag did not exhibit any change in their dimensions andshowed volume stability. On the contrary, the specimens made ofslag/SF mixtures exhibited slightly volume instability after expo-sure to elevated temperatures. This volume instability marginally

Superplasticizer set retarder(based on modied polymer)

Longer twhen sodiMs = 0.75 Reduced

Collins and Sanjayan [53] Shrinkage-reducing ReducedPalacios and Puertas [104] Shrinkage-reducing (based on

polypropylenglycol) 2% imprstrengths Reduced

Fig. 5. Compressive strength development versus QP content [106].fects No or negative effects

rheological parameterd the workability, but mixture lostafter 10 min

Reduced the compressive strength Increased the drying shrinkage (thehighest increase in the drying shrinkage)

d the workability (the most Reduced the early compressive strengthup to 14 days

the drying shrinkaged the workability (the mostdmixture)

No effect on the compressive strengthafter 7 days

the drying shrinkage (the lowestin drying shrinkage)d the exural strength after age of No effect on the setting times

at decreased the carbonation Reduced the compressive and exuralstrengths at age of 2 days

ing Materials 47 (2013) 2955increased as the content of SF increased. Rashad and Khalil [44]also studied the repeated thermal shock resistance of the previousmixtures. After drying, the specimens were exposed to 800 C for40 min, then quenched into water at room temperature for5 min. This called one cycle. Such cycles were repeated until thespecimens were broken, damaged or deteriorated. The resultsshowed that the hardened neat AAS paste had thermal shock1.75 times greater than other hardened alkali-activated slag/SFpastes (Fig. 7). They concluded that neat AAS exhibited more resis-tance of sudden thermal shock than alkali-activated slag/SF.

Aydn [109] studied the percentage of permeable volume anddrying shrinkage of activated slag mortars with NaOH and sodiumsilicate. Slag was partially replaced with SF at levels of 0%, 10% and20%, by weight. The specimens were cured at 20 C and 90% RH for5 h, then in steam at 70 C for 6 h. After that, the specimens werekept at 20 C and 55% RH. The results showed a reduction in thepercentage of permeable volume by 11.4% and 17.93% with theinclusion of 10% and 20% SF, respectively. The measurement of

he initial and nal setting timesum silicate with 4% Na2O andwas used

No effect on the setting times

the drying shrinkage Reduced the compressive and exuralstrengths at age of 2 days No impact on the compressive andexural strengths after age of 2 days No impact on the carbonation depth

the drying shrinkageoved the compressive and exural 1% did not signicantly modify the

compressive and exural strengthsthe drying shrinkage

Fig. 6. Compressive strength development versus SF content [44].

drying shrinkage of the specimens started from the end of heattreatment up to 4 months. The results showed a reduction in thedrying shrinkage with the inclusion of SF. The inclusion of 10% SF

compressive strength and signicant increase in the resistance towater (improve the hydraulicity of the binder). Further, the im-proved properties of the composites containing the alkali activatorover those prepared with NaOH conrmed the higher effectivenessof SF activator over the NaOH. Brew and Mackenzie [111] exploitedsolgel type condensation reactions between sodium silicate,formed in situ by alkaline dissolution of SF, and a solution of sodiumaluminate. They concluded that the specimens prepared from thisactivator showed good compressive strength, indicated that theproducts displayed all the characteristics of typical aluminosilicategeopolymers. Bernal et al. [112] activated slag/metakaolin (MK)blended binderswith NaOHwhichmixedwith either SF or rice huskash (RHA), as alternative silica-based activators. The results indi-cated thatpasteswithNaOH/SForNaOH/RHAshowedsimilar trendsinmechanical strength development as a function of activation con-ditions compared with pastes obtained using commercial silicatesolutions as activator. All activating solutionspromotedhigher com-pressive strength development with the increase contents of slag inthe binders, which promoted the coexistence of aluminosilicatereaction products along with calcium silicate hydrate gel.

Zivica [113] studied the acidic resistance of slag/PC with chem-ically modied silica fume (MSF). The results of this study indi-

Fig. 7. Thermal shock resistance of hardened neat AAS and alkali-activated slag/SFpastes [44].

A.M. Rashad / Construction and Building Materials 47 (2013) 2955 37showed the lowest drying shrinkage.From the above reviewof literature of this section, it can be noted

that the main advantage of employing SF and QP in AAS system isenhancing the compressive strength and producing denser micro-structure. On the same line with this, the inclusion of SF in AAS ma-trix can reduce the drying shrinkage that AAS system suffers. On thecontrary, the inclusion of SF in AAS matrix decreased the residualcompressive strength after exposure to 1000 C. On the same linewith this, the inclusion of SF in AAS matrix reduced the thermalchock resistance by about 42.85%, related to the neat AAS paste.The inclusion of SF and QP in AAS matrix is still needs more investi-gations that studying the effect of these materials on setting time,formation of salt eforescences, carbonation resistance and the ten-dency to cracks during curing. However, Table 3 summarizes the ef-fect of SF and QP on some properties of AAS system.

4.1.4. As activatorRousekov et al. [110] explored new type of alkali activatorman-

ufactured from SF. The data obtained showed that the optimal pro-portion of slag and SF alkali activator allowed an increase in the

Table 3Effect of SF and QP on some properties of AAS system.Author Content Positive effects

Collins and Sanjayan [105] 10% CSFRashad et al. [106] Up to 30% QP Increased the comRashad and khalil [44] Up to 15% SF Increased the comEscalante-Garca et al. [107] Up to 20% SF Increased the com

Escalante-Garca et al. [108] 10% geothermal silicawaste

Gave denser micro

Aydn [109] Increased the comCollins and Sanjayan [105] 10% CSF Increased 1 day coRousekov et al. [110] Slag: SF of 1: 2 and 1:

1 Increased the comslag: SF of 1: 1

Roy and Silsbee [66]

4.2.1. Workability

tained at ambient temperature and 98% RH; the same as the spec-

Table 4Effect of SF as activator on AAS system.

Author Activator Effects

Rousekov et al. [110] SF Increased the compressive strength Increased the resistance to water (improved the hydraulicity of the binder)

Brew and Mackenzie [111] SF Increased compressive strengthBernal et al. [112] SF or

RHA Similar trends of mechanical strength development as a function of activation compared with specimensactivated with commercial silicate solution

Zivica [113] ModiedSF

Higher acidic resistance of slag/PC

peciOHpecitergctio

38 A.M. Rashad / Construction and Building Materials 47 (2013) 2955Yang and Song [116] studied the workability of AAS and alkali-activated y ash (AAFA) activated with a combination of sodiumsilicate and NaOH powders. They noted that higher initial ow inAAFA than that in the AAS. Yang et al. [117] reported that AAS mor-tars exhibited slightly less ow than AAFA mortars for the samemixing condition. Yang et al. [118] used sodium silicate powderto activate either slag or FA mortar. They used constant w/b ratioof 0.5 and sand to binder of 3. They reported that the AAS mortarhad lower workability than FA-based alkali-activated mortar. Col-lins and Sanjayan [105] explained that partial replacement slagwith 10% ultrane FA in AAS concrete activated with powdered so-dium metasilicate and hydrated lime, showed higher workabilitythan neat AAS concrete. Talling and Brandstetr [119] reported thatFA might improve the workability of the fresh mixture of AAS ce-ment. Rashad [120] studied the workability of slag/FA-based geo-polymer concrete mixtures. The ratios of slag/FA were 15/85, 10/90, 5/95 and 0/100, by weight. The results indicated that as FA con-tent increased as the workability increased. Wang et al. [97] re-ported that an addition of FA (below 10%) had little effect onimproving the workability of the mixture. On the contrary, Para-meswaran and Chatterjee [121] reported that an Indian FA didnot improve the workability even at 40% by weight of total binder,implying that the characteristics of FA are important. Table 5 sum-marizes the previous researches about the effect of FA on the work-ability of AAS system.

4.2.2. Setting timeSugama et al. [122] studied the setting time of alkali-activated4.2. Fly ash

Zivica [114] SF At slag/PC ratio of 100/0, sspecimens activated with Na At slag/PC ratio of 30/70, sspecimens activated with wa

Zivica [115] SF Intensication of the produslag/Class F FA. Slag was partially replaced with FA at levels of0%, 10%, 20%, 30%, 40% and 50%, by weight. Sodium silicate wasused as alkaline activator with SiO2/Na2O molar ratios of 3.22,2.50 and 2.00. The results indicated that the setting time increasedwith the increase in FA content when using sodium silicate withmolar ratios of 3.22 and 2.50. On the contrary, using sodium sili-

Table 5Effect of FA on the workability of AAS system.

Author Increased workability

Yang and Song [116]p

Yang et al. [117]p

Yang et al. [118]p

Collins and Sanjayan [105]p

Talling and Brandstetr [119]p

Rashad [120]p

Wang et al. [97]p

Parameswaran and Chatterjee [121]imens cured at 22 C. The results showed that higher compressiveand exural strengths of the specimens cured at 22 C at ages of 7and 28 days compared to those specimens cured at 65 C.

Lu [127] produced waterglass-activated slag/FA concrete withstrength of 36 MPa at 7 days and 56 MPa at 28 days when curedin a fog room in the temperature range of 1020 C. Smith and Os-cate with a 2.00 SiO2/Na2O ratio led to rapid setting. An increasein the proportion of FA shortened the setting time. Kumar et al.[123] replaced slag with FA at levels of 50%, 65%, 75%, 85%, 95%and 100% in slag/FA-based geopolymers. They reported that thesetting time increased as the content of FA increased.

4.2.3. StrengthPuertas et al. [124] investigated both compressive and exural

strengths of mortar consisted of 50% slag coupled with 50% FA acti-vated with 8 M NaOH versus neat slag mortar activated with amixture of Na2siO3 and NaOH with 5% concentration of Na2O, byslag mass. The results showed lower compressive and exuralstrengths at ages of 2 and 28 days with the inclusion of 50%FA.Shi and Day [125] partially replaced slag with FA at levels of 0%and 50%, by weight. They activated the mixtures with either so-dium silicate or NaOH. They reported that when NaOH was usedas an activator, the slag replacement with FA did not show a signif-icant effect on compressive strength. The compressive strength de-creased with the inclusion of FA in the slag matrix, when sodiumsilicate was used as an activator. Puertas and Fernndez-Jimnez[126] activated the composite of 50% slag/50% FA with 10 M NaOH.The liquid/solid ratio was 0.35. Two curing temperatures of 22 and65 C were used. The pastes were maintained at 65 C during therst 5 h. For the rest of the curing time, the specimens were main-

mens activated with SF gave higher compressive strength at 7 days age than

mens activated with SF gave higher compressive strength at 28 days age thanlassn of CSHborne [128] and Bijen and Waltje [129] found that waterglass-acti-vated slag/FA blends showed very low strength, but NaOHactivation gave higher strength. On the contrary, Dai and Cheng[130] found that waterglass was much more effective than NaOH.Smith and Osbrone [63] investigated comprised of nely slag, FAand NaOH. They found good early strength values, but there was

No effect Notes

AAS had less workability than AAFAAAS had less workability than AAFAAAS had less workability than AAFA

Little improvementp

Buildlittle gain in the later ages. On the same line with this, Douglas andBrandstetr [96] activated slag mortars with sodium silicate. Theymodied the mortars by 2% lime, 2% lime + 5% FA and 2%lime + 10% FA. The w/b ratio was xed at 0.41. The results indi-cated that the inclusion of 5% FA gave lower strength at age of1 day in comparison with the mixture did not include FA, whistit gave higher strength at ages of 7 and 28 days. The inclusion of10% FA gave lower strength at ages of 1 day and 7 days, whist itgave higher strength at age of 28 days in comparison with thosecontaining 5% FA. On the contrary, Collins and Sanjayan [105] ex-plained that partial replacement slag with 10% ultrane FA inAAS concrete activated with powdered sodium metasilicate andhydrated lime, showed 24% better 1-day strength, but lower thestrength at ages beyond 28 days, compared to neat AAS concrete.Other authors as Talling and Brandstetr [119] reported that partialsubstitution slag with 10% FA, by weight, might result in an in-crease in strength. On the contrary, Wang et al. [97] reported thatthe addition of FA (below 10%) in AAS mortar often cause slightreduction in compressive strength under normal curing. However,substitution slag with FA at higher proportions reduced thestrength noticeably [61,121]. On the same line with this, Rashad[120] reported that substitutions slag with higher proportions ofFA (i.e. 85%, 90%, 95% and 100%) in slag/FA-based geopolymer con-cretes activated with mixture of NaOH and sodium silicate, re-duced the compressive strength, splitting tensile strength andexural strength. The compressive strength, splitting tensilestrength and exural strength decreased as the content of FAincreased.

Garci9a et al. [131] prepared pastes of slag and FA in proportionsof 100/0, 75/25, 50/50, 25/75 and 0/100, by weight, activated withsodium silicate. The used moduli (SiO2/Na2O) were 0, 0.75, 1, 1.5and 2. 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 an increase in the compressivestrength with increasing slag content. The highest compressivestrength was noted for the neat slag (8085 MPa) when 4% ofNa2O and 1.5 SiO2/Na2O were used. For 0/100 paste, the higher%Na2O, the better the strength, whereas the highest strength of25 MPa was reached using modulus 1. For the composite of 75/25, the strengths were (5660 MPa) at 4% Na2O and the modulus1 and 1.5. For the composite of 50/50 paste, the strengths were(4548 MPa) at 4% Na2O and the best modulus was 11.5. Forthe composite of 25/75 paste, the strength reached 3035 MPa at4% Na2O and modulus 1.5. Weiguo et al. [132] replaced slag withFA at levels of 0%, 30%, 40%, 50%, 60%, 70% and 100%, by weight.Waterglass with SiO2/Na2O ratio of 2.4 and NaOH which used toadjust the SiO2/Na2O ratio to 1.0 was used as alkaline activator.The results showed that the compressive and exural strengths de-creased as the FA content increased. Kumar et al. [123] replacedslag with FA at levels of 50%, 65%, 75%, 85%, 95% and 100%, byweight, in slag/FA-based geopolymers. The specimens were curedat either 27 C or 60 C. The reduction in compressive strengthwas observed with the inclusion of FA. As FA content increasedas the compressive strength decreased. Kim and Kim [133] re-placed slag with FA at levels of 0%, 50% and 100%, by weight, inslag/FA-based geopolymers. 2.78 M NaOH was used as activator.The compressive strength results of the mortars, at ages of 1, 7and 28 days, decreased as the content of FA increased. Puertaset al. [134] activated slag/FA pastes with NaOH solution. Theparameters of this study were: activator concentration (NaOH 2and 10 M), curing temperature (25 and 65 C) and slag/FA ratio(100/0, 70/30, 50/50, 30/70 and 0/100). In the curing temperatureprocess, the pastes were maintained at 65 C during the rst 5 h.

A.M. Rashad / Construction andfor the rest of the curing time, the specimens were maintained atambient temperature and 98% RH; the same as the specimenscured at 25 C. The compressive strength results at 1 day showedan increase in strength with the increase in slag content. 65 C cou-pled with 10 M of NaOH gave the highest strength. At 7 days, 70/30gave the highest strength at 25 C coupled with 10 M of NaOH,whilst the strength increased with the increase in slag content, inthe remaining conditions. At age of 28 and 90 days, as the slag con-tent increased as the compressive strength increased. 25 C cou-pled with 10 M of NaOH seemed to be the optimum condition,followed by 65 C coupled with 10 M of NaOH, followed by 25 Ccoupled with 2 M of NaOH. 56 C coupled with 2 M of NaOH camein the last place.

Bakharev et al. [38] studied the alkali-activated Australian slagmortar using different activators. In addition, they prepared mix-ture of alkali-activated slag/FA. The ratio of slag/FA was 30/70.They concluded that FA introduced in AAS at 30% reduced the com-pressive strength of the mortar. Smith and Osborne [63] investi-gated cements made of the combination of 60% nely slag and40% FA activated with 7% NaOH. They found that early strengthproperties were good but there was little gain in strength beyond28 days. Aydn [109] activated slag mortars with NaOH and sodiumsilicate. Slag was partially replaced with FA at levels of 0%, 20% and40%, by weight. The specimens were cured at 20 C and 90% RH for5 h, then in steam at 70 C for 6 h. The results showed a reductionin the compressive strength with the inclusion of FA. The reductionin the compressive strength was 3.11% and 13% with the inclusionof 20% and 40% FA, respectively. Zhang et al. [135] solidied muni-cipal solid waste incinerator (MSWI) FA with the Na2SiO3-activatedslag. 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 7 days, whilst35% gave the highest compressive strength at 28 and 60 days.

Guerrieri and Sanjayan [136] presented the compressivestrength of geopolymer pastes made of different combinations ofslag/FA ratios. The ratios of slag/FA were 100/0, 65/35, 50/50, 35/65 and 0/100, by weight. The alkaline activators were mixtures ofsodium silicate liquid and 8 M NaOH. The activators were mixedin the proportion so that Ms were 0, 0.5, 1.0, 1.5 and 2.0. Industrialgrade-powdered sodium metasilicate with hydrated lime was alsoused. The concentrations of the activators were 4% and 8% Na. Aftercasting, the specimens were kept at 23 1 C and 50 5% RH for 2 hand then were cured at 80 1 C and 95 3% RH for 22 h, after thatthe specimenswere allowed to cool down to room temperature. Thecompressive strengthwasmeasured at 24 h after curing period. Theresults showed that the composite of 35/65 achieved the highestcompressive strength at 8% Na and Ms 1.01.5, followed closely bythe 65/35, followed by 100/0 and followed by 50/50. Chi and Huang[137] presented the compressive strength and exural strength, atages of 7, 14 and 28 days, of geopolymer mortars made of differentcombinations of slag/FA ratios of 100/0, 70/30, 50/50, 30/70, 0/100,byweight. Sodium silicatewithmodulus ratio of 1was used as alka-line activator. Two concentrations of Na2O of 4% and 6%, by cemen-titious weight, were employed. The results showed that thecomposition of 50/50 achieved the highest compressive strengthand exural strength followed by 70/30, 100/0, 30/70 and 0/100,respectively, at both 4% and 6% Na2O. Goretta et al. [138] measuredthe compressive strength of Class C FA, slag and sodium silicate al-kali-activated concrete. The aggregate constituted 52% and an alkaliactivator 11.2% of the total mass; the mass ratio of silicate to FA + s-lag was 0.29. 50 mm diameter cylinders having a 1:2 diameter-to-length ratio were used for testing compressive strength. They re-ported that compressive strength of 35 MPa could be obtained at14 days. Table 6 summarizes the pervious researches that studiedthe effect of FA on the strength of AAS system.

ing Materials 47 (2013) 2955 394.2.4. Durability and drying shrinkageSugama et al. [122] exposed alkali-activated slag/Class F FA to

CO2-laden H2SO4 with pH value of 1.1 for 15 days at 90 C, after

ects

ala)

uildTable 6Effect of FA on the strength of AAS system.

Author % incorporation Positive eff

Puertas and Chatterjee [121] 50Shi and Day [125] 50Smith and Osborne [128] pBijen and Waltje [129] pDouglas and Brandstetr [96] 5 p

10 pCollins and Sanjayan [105] 10

p

Talling and Brandstetr [119] 10p

Wang et al. [97] Below 10Wang [61] Higher proportionsParameswaran and Chatterjee [121] Higher proportionsRashad [120] 85, 90, 95 and 100Garca et al. [131] 0, 25, 50, 75 and 100

p0% optim

(8085 MP

40 A.M. Rashad / Construction and Bautoclaving at 100, 200 and 300 C. The paste specimens were pre-pared by varying two parameters, slag/FA weight ratios of 100/0,90/10, 70/30 and 50/50 and SiO2/Na2O molar ratios, in the sodiumsilicate, of 3.22, 2.50 and 2.00. For all autoclaved temperatures, theweight loss results showed that the proportion of 50/50 mixturehad the lowest weight loss among all studied molar ratios, fol-lowed by 70/30 and followed by 90/10. The mixture of 100/0 camein the last place. Ismail et al. [139] studied the performance of al-kali-activated slag/FA geopolymer binders to different forms of sul-fate exposure immersed in 5 wt% MgSO4 solution or 5 wt% Na2SO4solution for 3 months. Sodium metasilicate was used as alkalineactivator at concentration of 8 wt%. They reported that MgSO4was more aggressive to geopolymer paste than Na2SO4. The pres-ence of magnesium led to decalcication of the Ca-rich gel phasespresented in the blended slag/FA geopolymer system, causing deg-radation of the binder system and the precipitation of gypsum. Theproducts of magnesium sulfate attack were poorly cohesive andexpansive, 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 [137] studied the percent-

Weiguo et al. [132] 0, 30, 40, 50, 60, 70 and 100p

0% optimalKumar et al. [123] 50, 65, 75, 85, 95 and 100

p0% optimal

Kim and Kim [133] 0, 50 and 100p

0% optimalPuertas et al. [134] 0, 30, 50, 70 and 100 p

30% optimalp0% optimal

Bakharev et al. [38] 30Smith and Osborne [63] 40

pAydn [109] 20 and 40Zhang et al. [135] 55, 65, 70 and 75

p55% optimalp65% optimal

Guerrieri and Sanjayan [136] 0, 35, 50, 65 and 100p

65% optimalp35% second

placep0% third placp50% fourth p

Chi and Huang [137] 0, 30, 50, 70 and 100p


placep0% third placp100% last plaNegativeeffects

Notes

ppp

Activated with waterglassActivated with NaOHpActivated with waterglassActivated with NaOHpAt 1 dayAt 7 and 28 dayspAt 1 and 7 daysAt 28 daysAt 1 daypBeyond 28 days

pppp

4% Na2O, 1.5 SiO2/Na2O

ing Materials 47 (2013) 2955age of water absorption of geopolymer mortars made of differentcombinations of slag/FA ratios of 100/0, 70/30, 50/50, 30/70, 0/100, by weight. Sodium silicate with modulus ratio of 1 was usedas alkaline activator. Two concentrations of Na2O of 4% and 6%,by cementitious weight, were employed. The results showed areduction in the percentage of water absorption with increasingslag and decreasing FA content at both concentrations. Aydn[109] studied the percentage of permeable volume of activated slagmortars with NaOH and sodium silicate. Slag was partially replacedwith SF at levels of 0%, 20% and 40%, by weight. The results showedan increase in the percentage of permeable volume by 3.8% and3.26% with the inclusion of 20% and 40% FA, respectively.

As known, shrinkage is the reduction in volume at constanttemperature without external loading. It is as important materialproperty that signicant effects on long-term performance of de-signed structures. It also inuences structural properties and dura-bility of the material. However, Rashad [120] reported thatsubstitutions slag with higher proportions of FA (i.e. 85%, 90%,95% and 100%) in slag/FA-based geopolymer mortars activatedwith mixture of NaOH and sodium silicate reduced the dryingshrinkage. The drying shrinkage decreased as the content of FA in-creased. On the same line with this, Chi and Huang [137] prepared

p25% optimal

(5660 MPa)4% Na2O, 1 and1.5 SiO2/Na2O

p50% optimal

(4548 MPa)4% Na2O, 11.5 SiO2/Na2O

p75% optimal

(3035 MPa)4% Na2O, 1.5 SiO2/Na2O

As FA content increased as strength decreasedAs FA content increased as strength decreased

pCuring 65 C for 5 h, then in room. 10 M NaOH at 1 dayCuring 25 C for 5 h, then in room. 10 M NaOH. at 7 daysAt 28 and 90 dayspGood at early ages and little gain beyond 28 dayspAt 7 daysAt 28 and 60 days8% Na2O, 11.5 SiO2/Na2O

elace

4% or 6% Na2O, 1 SiO2/Na2O

ece

and reduced the heat release. Cheng and Chiu [143] studied someproperties of slag geopolymer blended with metakaolinite. The re-sults indicated that the more metakaolinite added in the system,the slower setting time. Other author [144] reported that MK orMK doped with sodium could be successfully used as heat evolu-tion/hydration accelerating addition in AAS mixtures. Buchwaldet al. [145] studied some properties of slag blended with MK-based

Building Materials 47 (2013) 2955 41geopolymer mortars made of different combinations of slag/FA ra-tios of 100/0, 70/30, 50/50, 30/70, 0/100, by weight. They measurethe drying shrinkage at ages of 7, 14 and 28 days. They reportedthat the drying shrinkage decreased as the content of FA increased.Aydn [109] activated slag mortars with NaOH and sodium silicate.Slag was partially replaced with FA at levels of 0%, 20% and 40%, byweight. The specimens were cured at 20 C and 90% RH for 5 h,then in steam at 70 C for 6 h. After that, the specimens were keptat 20 C and 55% RH. The measurement of drying shrinkage of thespecimens started from the end of heat treatment up to 4 months.The results showed a reduction in the drying shrinkage with theinclusion of FA. The drying shrinkage decreased as the content ofFA increased.

4.2.5. Fire resistance and metal leachingGuerrieri and Sanjayan [136] studied the high temperature per-

formance up to 800 C, for 1 h, of alkali-activated slag/FA pastesactivated with a combination of sodium silicate and 8 M NaOH.Slag was replaced with FA at replacement levels of 0%, 35%, 50%and 100%, by weight. They reported that the specimens with verylow initial strength (

uildwith a combination of sodium silicate and NaOH. They reportedthat the inclusion of MK in AAS matrix decreased the compressivestrength. Bernal et al. [149] activated slag/MK mortars with blend-ing sodium silicate and NaOH to reach the overall molar ratios of1.6, 2.0 or 2.4. The ratios of slag/MK were 100/0, 90/10 and 80/20, by weight. The binder/sand ratio was 1:2.74 and water/(slag + MK + anhydrous activator) of 0.47 was employed. The re-sults showed that the neat slag mixture gave the highest compres-sive strength, for all Ms ratios. The compressive strength decreasedwith increasing MK content. Chen et al. [150] manufactured differ-ent compositions of slag/MK pastes. The ratios of slag/MK were 50/50, 40/60, 30/70, 20/80 and 0/100, by weight. The compositionswere activated with NaOH solution. The ratio of liquid to solidwas 0.45. The pastes were cured hydrothermally at 90, 120 and180 C. The results showed a reduction in compressive strengthwith increasing MK content, at all curing conditions.

Buchwald et al. [151] studied the compressive and bendingstrengths of neat AAS paste and alkali-activated slag/MK pastes.Slag was replace with MK at levels of 0%, 25%, 50% and 100%, byweight. The results showed that as MK content increased as thecompressive strength and bending tensile strength decreased.The neat slag gave the highest compressive and bending tensilestrengths, whilst neat MK gave the lowest. Wang et al. [152] stud-ied the compressive strength and porosity of alkali-activated slag-FA-MK cementitious materials prepared by hydrothermal method.Waterglass was used as alkaline activator. The modulus of water-glass was adjusted to 1.0 by dissolving NaOH. The ratio of waterto solid was about 0.35. Different mixtures with different contentsof slag, MK and FA were employed. The slag contents ranging from16.2% to 31.33%, whilst the FA contents ranging from 20.46% to73.52% and MK contents ranging from 7.22% to 49.39%. The com-pressive strength results indicated that this type of material hadhigher mechanical strength. The highest compressive strength va-lue reached about 80 MPa. They suggested that the higher com-pressive strength was attributed to the addition of slag. The morecontents of slag in the system gave more hydration products(CSH and hydrated aluminates calcium).

Burciaga-Di9az et al. [153] studied the compressive strength ofAAS pastes activated with a combination of sodium silicate andNaOH. They used different concentrations of Na2O (i.e. 5%, 10%and 15%). Slag was replaced with MK at levels of 0%, 20%, 50%,80% and 100%, by weight. The neat slag pastes gave the highestcompressive strength at 5% of Na2O, whilst neat MK and slag/MKof 20/80 pastes required 15% Na2O to reach the highest compres-sive strength. The replacement levels of 20% and 50% with MK re-quired 10% Na2O to reach the highest compressive strength. Bernalet al. [154] partially replaced slag with MK at levels of 0%, 10% and20%, by weight, in alkali-activated concretes. The alkaline activat-ing solutions were formulated by blending sodium silicate andNaOH to reach the overall molar ratios (SiO2/Al2O3) of 3.6, 4.0and 4.4. They used different activator concentrations. They re-ported that at high activator concentration, the inclusion of MK en-hanced the compressive and exural strengths at early age. Chengand Chiu [143] studied slag geopolymers blended with metakaoli-nite. The results indicated that the compressive strength increasedwith increasing metakaolinite content, whilst the density de-creased with increasing metakaolinite content.

Yip et al. [155] blended slag/MK at ratios of 0/100, 20/80 and40/60, by weight. Commercial sodium silicate solution and NaOHpearl at molar ratios (SiO2/Na2O) of 2.0, 1.5 and 1.2 were used toactivate the slag/MK. The compressive strength results showedthat slag/MK at ratio of 20/80 gave the highest compressivestrength at 2 and 1.2 M ratios, whilst slag/MK = 0/100 gave the

42 A.M. Rashad / Construction and Bhighest compressive strength at 1.5 M ratio. Yunsheng et al.[156] tested the mechanical strength of slag/MK-based geopoly-mer mortars. NaOH and sodium silicate solution with the molarratio (SiO2/Na2O) of 3.2 were used as alkaline reagents. The ratiosof slag/MK were 0/100, 10/90, 30/70, 50/50 and 70/30, by weight.The specimens were cured at 20 C and 100% RH for 28 days. Theresults showed that geopolymer mortar containing 50/50 of slag/MK gave the highest compressive strength, followed by 70/30and followed by 30/70. The geopolymer mortar containing 100%MK gave the lowest compressive strength. The results of exuralstrength showed a similar tendency as compressive strength.Table 8 summarizes the pervious researches that studied the effectof MK on the strength of AAS system.

4.3.3. DurabilityShen et al. [157] partially replaced slag with zeolites or MK in

alkali activation pastes. They reported that replacement slag withzeolites or MK increased the porosity of the hardened pastes, butthe leaching fraction of Ca + and Sr2+ were decreased. The decreasein leaching fraction might be attributed to the formation andadsorption properties of (Al + Na) substituted CSH and self gener-ated zeolite precursor. Zhang et al. [158] studied the permeability,measured by Darcy method, of slag/MK-based geopolymers. Differ-ent liquid/solid ratios of 0.55 and 0.6 were employed. They re-ported that the inclusion of slag could reduce permeability,particularly at liquid/solid ratio of 0.6. The existence of slag hadonly a slight effect on permeability of geopolymer at liquid/solidratio of 0.55. When the slag content was P10%, geopolymer hada relatively steady and low permeability, suggesting slag had apacking inuence on geopolymer structure [146].

Bernal et al. [154] studied water absorption, capillary sorptivityand rapid chloride permeability test (RCPT) of alkali-activated slag/MK concrete. The ratios of slag/(slag + MK) were 0.8, 0.9 and 1.0.The alkaline activating solutions were formulated by blending so-dium silicate and NaOH to reach the overall molar ratios (SiO2/Al2O3) of 3.6, 4.0 and 4.4. They concluded that the increase in MKcontents and higher activator concentrations led, in most cases,to reduce water absorption (Fig. 8) and water sorptivity and gavelower chloride permeability (Fig. 9). Wang et al. [152] studiedthe porosity of alkali-activated slag-FA-MK cementitious materialsprepared by hydrothermal method. Waterglass was used as alka-line activator with the modulus adjusted to 1.0 by dissolvingNaOH. The ratio of water to solid was about 0.35. The porosity re-sults indicated that this type of material had compact structure.The porosity was less than 36%, after hydrothermal process.

4.3.4. Carbonation resistanceThe accelerated carbonation test was used to induce the car-

bonation of alkali-activated slag/MK mortars activated with blend-ing sodium silicate and NaOH to reach the overall molar ratios of1.6, 2.0 or 2.4 [149]. The binder/sand ratio was 1:2.74. Thewater/(slag + MK + anhydrous activator) of 0.47 was employed.The specimens were exposed to an accelerated carbonation witha concentration of 3.0 0.2% at temperature of 20 2 C and RHof 65 5%. The specimens were exposed to these conditions for340 or 540 h. After 340 h of carbonation at Ms = 2.4, the mortarbased on neat slag showed the lowest carbonation depth. The car-bonation depth increased with the increase in MK content. After540 h of carbonation at any Ms, all specimens were fully carbon-ated. The results also showed that the compressive strength de-creased after carbonation. In another investigation [154] theaccelerated carbonation test was used to induce the carbonationof alkali-activated slag/MK concretes activated with blending so-dium silicate and NaOH to reach the overall molar ratios of 3.6,4.0 and 4.4 [154]. The ratios of slag/slag + MK were 1, 0.9 and0.8, by weight, were employed. Carbonation concentration was

ing Materials 47 (2013) 29553.0 0.2% at temperature of 20 2 C and RH of 65 5%. The spec-imens were exposed to carbonation for 250, 500, 750 and 1000 h.The results, after carbonation, showed increases in the total pore

BuildA.M. Rashad / Construction andvolumes of the specimens and decreases in the compressivestrengths with the increase in MK content.

Table 8Effect of MK on the strength of AAS system.

Author Replacement levels (%) Positive effects

Yip et al. [146] 0, 20, 40, 60, 80 and 100p

20% optimalBernal et al. [147] 20, 40, 60, 80 and 100


Bernal et al. [148] 20, 40, 60 and 100p


Bernal et al. [142] 0, 10 and 20Bernal et al. [149] 0, 10 and 20Chen et al. [150] 50, 60, 70, 80 and 100Buchwald et al. [151] 0, 25, 50 and 100Wang et al. [152] 7.2249.39Burciaga-Di9az et al. [153] 0, 20, 50, 80 and 100 p

100% optimalp80% optimalp20% and 50%

Bernal et al. [154] 0, 10 and 20p

At early ageCheng and Chiu [143] Different contents

pYip et al. [155] 60, 80 and 100


Yunsheng et al. [156] 30, 50, 70, 90 and 100p

50% optimalp30% second pp70% third pla

Fig. 8. Water absorption in the rst 48 h of alkali-activated slag/MK concretes with28 days of curing [154].

Fig. 9. Rapid chloride permeability test results for 28 days cured activated slag/MK[154].4.3.5. Fire resistanceBernal et al. [147] studied the effect of elevated temperatures of

200, 400, 600, 800 and 1000 C, for 2 h, on the geopolymers formu-lated with an overall SiO2/Al2O3 molar ratio of 3, slag/(slag + MK)ratios of 0.0 and 0.2 (i.e. slag/MK ratios of 0/100 and 20/80). Con-stant H2O/Na2O ratio of 12 and Na2O/SiO2 ratio of 0.25 were em-ployer. The results indicated that the geopolymers formulatedwith MK and slag had higher residual compressive strength thanthe neat MK-based geopolymer up to 800 C. On the other hand,the neat MK system showed a much higher residual strength uponcooling from 1000 C to room temperature, indicating that the ex-tent of glass formation from the geopolymer gel at 1000 C is re-duced by the incorporation of Ca into the gel, as a consequence offormation of CSH type gel that coexisted with the aluminosilicategeopolymer gel. Cheng and Chiu [143] studied re resistance of slaggeopolymer blendedwithmetakaolinite, when a 10 mm thick panelof geopolymer exposed to 1100 C ame. The measured reverse-

Negative effects Notes

SiO2/Al2O3 = 3SiO2/Al2O3 = 3.4, 3.8 and 4Na2O/Al2O3 = 3 at age 7 daysNa2O/Al2O3 = 3.8 at age 7 daysp

ppppp

Na2O = 5%Na2O = 15%Na2O = 15%

optimal Na2O = 10%At higher activator concentrationIncreased with increasing MK contentMolar = 2 and 1.2Molar = 1.5

lacece

ing Materials 47 (2013) 2955 43side temperature reached 240283 C after 35 min. They observedthat the re characteristics could be improved by increasing theKOH or the alkali concentration and amount of MK. Table 9 summa-rizes the previous researches that studied the effect of MK on dura-bility, carbonation resistance and re resistance of AAS system.

4.3.6. ImmobilizationGuangren et al. [159] evaluated the effects of MK on simulated

radioactive Sr or Cs immobilizing behaviour of AAS matrix by cat-ion exchange capacity, distribution ratio of selective adsorption,leaching test and porosity analyses. PC matrix was used as a refer-ence. The alkaline activators were waterglass and sodium carbon-ate. The addition of alkaline activator was adjusted to 5%, by Na2O,of slag in weight. Slag was partially replaced with MK at levels of0%, 5%, 10% and 15%, by weight. The pastes containing 0.5 wt%Cs+ (CsCl) or Sr2+ (SrCl2.6H2O) were cast in a cylindrical mould,with a diameter of 2.5 cm and a height of 5 cm which was curedin fog room at 25 C for 28 days. Ratio of water to solid in thepastes was 0.3. The effects of MK on Sr or Cs ion selective adsorp-tion of AAS matrix were evaluated by the distribution ratio (Kd)which dened as the ratio of the amounts of ions adsorbed by aunit mass of solid adsorbent to the equilibrium concentration ofion in the aqueous phase. The results of the Kd showed that PChad the lowest Kd, whilst Kd of AAS matrix was highly increasedby 38% and 151% for Sr ion and Cs ion, respectively. This indicatedthat the improvement of AAS matrix on selective adsorption

m.

Sr2+

orpt

res

highme

g M

uildbehaviour for Cs ion was much more effective than for Sr ion. Addi-tions of MK into AAS matrix had positive effect to further enhancetheir selective adsorption on Sr and Cs ions. As MK content in-creased in AAS matrix, as the Kd increased. For slag/MK ratio of85/15, its Kd was larger than that of neat AAS matrix by about40% and 56% for Sr ion and Cs ion, respectively. The results ofleachability showed that the leaching rate for Sr or Cs ion de-creased in the order PC > neat AAS > alkali-activated slag/MK. Theporosity results showed that PC matrix had the largest porosity.Neat AAS matrix and alkali-activated slag/MK matrix possessedsimilar pore structure. Their pore size distributions were concen-trated on small pores (

Buildwith PC at level of 30%. The compressive strength results at 1, 3 and28 days were conducted. The results revealed that the neat AASpaste gave higher strength than 70/30 slag/PC paste at all ages.

Indeed, the results of Douglas and Brandstetr [96] contrast withthe above results. However, they activated slag mortars with so-dium silicate. The mortars were modied with some additives asPC. In some mortar mixtures, 2% PC and 8% PC were added in theAAS mortars. The w/b ratios were 0.38 and 0.48. The activator con-centration was 4.6 g Na2O/100 g binder. For specimens preparedwith w/b ratio of 0.38, the results showed that the mortars con-taining 2% PC gave higher compressive strengths than that contain-ing 8% PC at ages of 3, 7 and 28 days. At 0.48 w/b ratio, thecompressive strength value of 8% PC was higher than that of 2%PC, at ages of 3 and 7 days. On the other hand, the compressivestrength of 2% PC was higher than that of 8% PC at age of 28 days.On the same line with this, Zivica [164] activated different compo-sitions of slag/PC with alkali-silicate admixture. The ratios of slag/PC were 100/0, 90/10 and 70/30, by weight. The results showedthat replacing slag with 10% PC gave the highest compressive

Fig. 10. Strength development of different types of mortars [46].

A.M. Rashad / Construction andstrength at ages of 28 and 90 days. Replacing slag with 30% PCcame in the second place. Fu-Sheng et al. [161] studied the com-pressive strength of blended alkali-activated slag/PC activated withNa2SiO3. Slag was partially replaced with PC at levels of 0%, 10%,20% and 30%, by weight. Neat PC mixture was employed for com-parison. The results showed that partially replacing slag with 10%PC gave strength higher than neat PC or those of 20% or 30%replacements. Also, partially replacement slag with 10% PC gavehigher strength than that of neat AAS at ages of 1 and 28 days,whilst it gave lower strength at age of 3 days, compared to neatAAS.

Zivica [115] partially replaced slag, in mortars, with PC at levelsof 10% and 30%, by weight. The composites were non-activated oractivated with SF activator. The compressive strength resultsshowed that the activated slag/PC at ratio of 90/10 gave higherstrength than that of activated 70/30 at age of 28 days, whilst theactivated 70/30 gave higher strength than that of activated 90/10at ages of 1 and 90 days. Both the activated composites gave higherstrength than either un-activated composites or traditional neat PCmortars. In another investigation Zivica [114] activated differentcomposites of slag/PC mortars with SF activator. The ratios ofslag/PC were 100/0, 90/10 and 70/30, by weight. The resultsshowed that 70/30 composite gave the highest compressivestrength at age of 28 days, followed by 90/10 and followed by100/0. Acevedo-Martinez et al. [165] activated different compos-ites of slag/PC, in mortars, with waterglass at 010 wt% of Na2O.The ratios of slag/PC were 100/0, 80/20, 50/50, 30/70 and 0/100,by weight. The compressive strength results showed that the com-posite of 0/100 gave the highest strength at 0% Na2O, followed by30/70 and followed by 50/50. At each of 4%, 6% or 10% Na2O, thecomposite of 80/20 exhibited the highest compressive strength,followed by 50/50 and followed by 30/70. Singh et al. [166] re-ported that the use of 4% Na2SO4 signicantly increased thestrength of slag with 50% PC. Table 10 summarizes the pervious re-searches that studied the effect of PC on the strength of AASsystem.

4.4.3. DurabilityRoy et al. [46] studied porosity, median pore size and density of

65/35 slag/PC without or with alkali activation. The alkaline activa-tor was 4 M NaOH. They reported that the alkaline activator re-duced the porosity and median pore size, whilst density wasincreased. The porosity, median pore size and the density of acti-vated slag/PC were higher than that of neat AAS, whilst the poros-ity and median pore size of activated slag/PC were lower than thatof neat PC without alkaline activator. On the same line with this,Zivica [114] activated the composites of slag/PC mortars with SFactivator. The ratios of slag/PC were 100/0, 90/10 and 70/30, byweight. The results of total porosity and pore median decreasedas the content of PC increased. Veiga and Gastaldini [167] partiallyreplaced slag, in mortars, with either 50% white PC or grey PC, byweight. The composites were non-activated or activated with 4%Na2SO4, by total binder weight. Also, neat white PC and neat greyPC without activator were employed as references. The hardenedspecimens were exposed to 5% Na2SO4 for 2 years according toASTM C1012/04. The expansion results, after 2 years, indicated thatthe composition of 50% slag/50% white PC activated with Na2SO4 orwithout activation presented expansion reductions of 95.2% and94.9%, respectively, in comparison with neat white PC. The compo-sition of 50% slag/50% grey PC activated with Na2SO4 or withoutactivation presented expansion reductions of 96.9% and 95.7%,respectively, in compression with neat grey PC. These mean thatthe activated 50% slag blend had higher capability to resist sodiumsulfate attack and classied as high sulfate resistance. Zivica [113]studied the acidic resistance of slag/PC activated with chemicallyMSF. The ratios of slag/PC were 100/0, 90/10 and 70/30, by weight.The results showed that as the cement content increased as theacidic resistance decreased.

Roy et al. [46] investigated the steady state chloride diffusionthrough the hardened pastes. The pastes were manufactured fromslag/PC at different levels ranging from 0/100 to 100/0. The differ-ent mixtures of slag/PC were non-activated or activated with alka-line activator. The results showed a clear trend of decreasingdiffusion rate with decreasing PC content (Fig. 11). In addition,the activated hardened pastes showed lower diffusion rate thanthat of un-activated hardened pastes. Table 11 summarizes theprevious researches that studied the effect of PC on the durabilityof AAS system.

4.4.4. Drying shrinkageFu-Sheng et al. [161] studied the drying shrinkage of blended

alkali-activated slag/PC mortars activated with Na2SiO3. Slag wasreplaced with PC at levels of 0%, 10%, 20% and 30%, by weight. PCmortar mixture was employed as a reference. The results showedthat the neat AAS specimen exhibited higher drying shrinkage atage of 35 days, whilst the blend of 10% PC specimen gave lowerdrying shrinkage which similar to the drying shrinkage of PCspecimen.

ing Materials 47 (2013) 2955 45From the above review of literature of this part, it can be notedthat the main advantage of employing PC in AAS matrix is decreas-ing the drying shrinkage that the AAS system suffers as well as

ativcts

uildTable 10Effect of PC on the strength of AAS system.

Author Replacementlevels (%)

Positive effects Negeffe

Wu et al. [160] 70p

p

46 A.M. Rashad / Construction and Bdecreasing the total porosity and pore median. The inclusion of PCin AAS matrix, in most cases, increased the compressive strength.On the same line with this, the inclusion of PC in AAS matrix hadhigher capacity to resistance sodium sulfate attack and increasedthe acidic resistance. On the contrary, the inclusion of PC in AASmatrix increased the chloride diffusion rate as reported by Royet al. [46]. However, the inclusion of PC in AAS matrix is still needsmore investigations that studying the effect of this material on for-

Roy et al. [46] 40p

Talling and Brandstetr [119] Undeterminedp

Bilim and Atis [163] 0, 20, 40 and 80 p

Bakharev et al. [38] 0 and 30p

Douglas and Brandstetr [96] 2 and 8p

2% higherthan 8%p

8% higherthan 2%p

2% higherthan 8%

Zivica [164] 0, 10 and 30p


placeFu-Sheng et al. [161] 0, 10, 20 and 30

p10% optimal p

Zivica [115] 10 and 30p


Zivica [114] 0, 10 and 30p


placep0% third

placeAcevedo-Martinez et al. [165] 0, 20, 50, 70 and

100

p100%

optimalp70% second

placep50% third

placep20% optimalp50 % second

placep70% third

placeSingh et al. [166] 50

p

Fig. 11. The effective diffusion coefcient of activated and un-activated slag/PChardened pastes [46].e Notes

At 3 and 7 days, compared to PCAt 28 and 90 days, compared to PCCompared to slag/PC of 60/40 without alkali activation

Compressive and exural strengths decreased as PC content increased. 0%gave the highest strength0% gave the highest strengthw/b = 0.38 at ages of 3, 7 and 28 days

w/b = 0.48 At ages of 3 and 7 days

w/b = 0.48 At age of 28 days

At ages of 1 and 28 daysAt age of 3 days, 0% gave

addtitive

Documents

Transcript of addtitive