Revie

A

strength." MK and blended MK with steel slag

can be used as repair materials.

g r a p h i c a l a b s t r a c t

3.2. SiO2/Al2O3 ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7543.3. Solid/liquid ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754

4. Effect of curing condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7555. Effect of ultrasound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7556. Effect of MK fineness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7557. Resistance of aggressive solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755

Mobile: +20 1228527302; fax: +20 233351564, 233367179.

Construction and Building Materials 41 (2013) 751765

Contents lists available at SciVerse ScienceDirectE-mail address: alaarashad@yahoo.comBlended alkali-activated metakaolin

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7522. Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7523. Nature, concentration of activator, SiO2/Al2O3 ratio and solid/liquid ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753

3.1. Nature and concentration of activator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753a r t i c l e i n f o

Article history:Received 10 October 2012Received in revised form 24 November 2012Accepted 19 December 2012Available online 4 February 2013

Keywords:Metakaolin alkali activationDurability0950-0618/$ - see front matter 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.conbuildmat.2012.12.030Effect of slag replacement percentages on compressive strength [90]

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 metakaolin (AAMK), belongs to prospective materials inthe eld of Civil Engineering. This paper presents a comprehensive overview of the previous works car-ried out on the use of MK in alkali activation.

2013 Elsevier Ltd. All rights reserved.20% with calcite gave higherh i g h l i g h t s

" AAMK system has better acid,seawater attack, sodium sulfateresistance than PC.

" AAMK system has very good heatresistant up to 12001400 C.

" Polypropylene and short bersincrease AAMK exural, strength andimpact energy.

" Replacing 10% MK with FA or lime orFlexural strength of MK-based geopolymer at different NaOH concentrations [32] Building Materials Research and Quality Control Institute, Housing & Building National Research Center, HBRC, Cairo, EgyptAlaa M. Rashad

lkali-activated metakaolin: A short guide for civil Engineer An overviewwConstruction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmatll rights reserved.

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

presented.

lerc[1pmtipec

product of greatest crystallinity. The addition of sodium silicate

ted regarding the nanostructure of NASH gel is: the NASH

ildiThe dissolutionreprecipitation reactions occurring during theaching of MK with alkaline hydroxide or silicate solutions wereelatively well described in terms of the conditions under whichertain zeolitic products will form [11,12]. Granizo and Blanco3] studied the reaction of MK with NaOH solutions. They re-orted that the alkaline activation of MK to yield a cementitiousaterial was an exothermic process involving three steps: an ini-al and very fast process of dissolution, followed by an induction

gel structure was that of a charge-balance aluminosilicate, whichwas inuenced by the Si/Al ratio and the alkali cations presented.In the structure, Al trended to be surrounded by four Si neighborsin a 4-coodinated geopolymer framework. The charge-balanced al-kali metal would not associate the Al atom, but rather would asso-ciate with one or more negatively-charged oxygen atomssurrounding the aluminum. As in the case for CSH gel, NASHgels were difcult to characterize with XRD due to their amor-2. Hydration

in addition to NaOH signicantly reduced crystallite formation.

However, Li et al. [22] reported that it could be condently sta-8. Resistance of elevated temperature and fire . . . . . . . . . . . . . . . . . . .9. Fibers effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10. MK blended with FA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11. MK blended with slag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12. MK blended with calcium hydroxide . . . . . . . . . . . . . . . . . . . . . . . . .13. MK blended with other materials . . . . . . . . . . . . . . . . . . . . . . . . . . . .14. Special applications of MK based geopolymer . . . . . . . . . . . . . . . . . .15. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction

Concrete is one of most extensively used construction materialsin the world. Each year, the concrete industry produces approxi-mately 12 billion tonnes of concrete and uses about 1.6 billion ton-nes of PC worldwide [1]. Indeed, with the manufacture of 1 tonneof cement approximately 0.94 tonnes of CO2 are launched intothe atmosphere [2]. The cement industry accounts for 58% ofworldwide CO2 emission [3]. Not only CO2 releases from cementmanufacture but also SO3 and NOx which can cause the greenhouseeffect and acid rain [4,5]. These cause serious environmental im-pact. To reduce the environmental impact of cement industries,MK and other cementitious materials are used to replace part ofcement or as a source of new cementless materials. MK reactschemically with hydrating cement to form modied paste micro-structure. In addition, to its positive environmental impact, MK im-proves concrete mechanical properties and durability. The term ofMK pozzolan refers to a silecious material which, in the presence ofwater, will react chemically with calcium hydroxide to formcementitious compounds. On the same line, to reduce the environ-mental impact resulting from cement industries, AAMK (futurecement) is recently used.

Investigations in the eld of alkali activation had an exponentialincreased after the research results of the French author Davidovits[6] that developed and patented binders obtained from alkali acti-vation of MK. Alkali activation of MK and other materials can beclassied this new kind of binders as the third generation cementafter lime and PC. The alkali activation of MK is a way to reducecarbon dioxide lunched into the atmosphere. The alkali activationof MK yields strong [710] and durable cementitious materials thatharden at temperatures under 100 C [7,9,10]. The composition,structure and properties of the reaction product obtained in alkaliactivation of MK are directly impacted by the specic surface andcomposition of the initial kaolin and the activator type and its con-centration. However, in this investigation, the author conducted aliterature review focused on AAMK. Hydration, natural of activa-tors, curing condition, resistance of aggressive solutions and reresistance of AAMK were reviewed. In addition, a review onblended MK with other materials, in alkali activation system was

752 A.M. Rashad / Construction and Bueriod in which the heat exchanged rate decreased and nally anxothermic step of reaction in which cementitious materials pre-ipitated and after which the heat exchanged rate decreased. Based. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760

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on calorimetric results, they also reported that the induction peri-od was lengthened as the NaOH solution concentration and liquidpercentage increased. The induction period was shortened as thetemperature increased. The total heat increased as the liquid per-centage and the NaOH concentration increased.

Granizo et al. [14] reported that the reaction product of MK acti-vation with sodium silicate + NaOH solutions is an amorphous hy-drated sodium aluminosilicate. Some authors [9,15] have found theproduct of MK activation with NaOH solutions is NASH gel withgood mechanical properties. Granizo et al. [16] studied differentconcentrations of NaOH (from 12 to 18 M) to activate two differenttypes of MK with variable solution/solid ratios. They concludedthat the material obtained after MK alkaline activation is mainlyan amorphous sodium aluminosilicate. The total heat released in-creased as Na2O concentration increased as well as the nenessof MK increased. The insoluble residues (IR) of the samples madefrom coarse MK are higher than those of ne MK. IR decreasedexponentially as Na2O in solution increased. So, reaction degree in-creased as NaOH concentration increased.

Davidovits [17] described the alkali activation of MK using apolymerization model similar to that proposed to describe the for-mation of zeolites [18] or zeolite precursors from alkali alumunos-ilicate solutions. Madani et al. [12] reported that the MK activationinvolved a dissolution step followed by a step of polycondensationthat could be assigned to those described for zeolites which formwhen kaolinites or metakaolinites are attacked by NaOH solution.Rahier et al. [19] reported that when the activator is a NaOH andwaterglass mixture, the material formed is amorphous and cemen-titious, but its structure and composition are different from theproduct formed if NaOH is used alone. The amorphous NASHgel had thus similar chemical composition as natural zeolitic mate-rials but without the extensive crystalline zeolitic structure [20].Zhang et al. [21] studied the effect of the NaOH content and thepresence of sodium silicate activators on the formation of crystal-line phases from MK-based geopolymers. They reported that geo-polymers activated with NaOH alone with Si/Na ratios of 4/4 orless formed the crystalline zeolite NaA (Na96Al96Si96O384.216H2-O), but at ratios > 4/4 nanosized crystals of another zeolite (Na6[-A1SiO4]6.4H2O) were formed. The Si/Na ratio of 4/4 produced a

ng Materials 41 (2013) 751765phous or nanocrystalline nature. Valuable information about gelnanostructure and composition could be nished using techniquesof FTIR, SEM or TEM [23].

Yunsheng et al. [24] studied the hydration process of MK geo-polymer activated with potassium silicate solution, KOH. Theyreported that at the early stage of hydration the MK particlespack loosely together resulting in the existence of many largevoids. As hydration progressed, sponge like gel products weregradually produced and precipitated on the surface of these par-ticles and extended outwards. As a result, these voids were fullylled. At the later stage, the MK particles were covered by athick gel layer, and the microstructure of geopolymeric paste be-came very compacted. Sum et al. [25] and Zhang et al. [26] stud-

Granizo et al. [15] investigated MK and mixtures of (MK + cal-cium hydroxide) with a 1:1 ratio activated with 5 and 12 M NaOHsolutions cured at 45 C. They concluded that CSH gel was pro-duced readily with a low NaOH concentration in the presence ofcalcium hydroxide. The main product formed both with and with-out calcium hydroxide was the same network structure, with thegeneral approximate formula: Si2Al2Na2H4O10. The rate of alkalimaterial formation was very low in the presence of calciumhydroxide. The reaction rate of alkali material formation was verylow in the presence of calcium hydroxide. Table 1 summarizes the

polymers, i.e. low concentrations result in the formation of dense

geopolymers increased linearly by approximately 400% from Si/Al = 1.15 to Si/Al = 1.9, where it obtained its maximum value,

A.M. Rashad / Construction and Building Materials 41 (2013) 751765 753ied MK geopolymer activated with potassium solution. Theyconcluded that at early stage, the MK particles pack loosely to-gether resulting in the existence of many large voids. As hydra-tion preceded, gel products gradually precipitated on the surfaceof these particles and extended outsides; as a result, these voidswere fully lled. At later stage, the MK particles were wrappedby a thick gel layer, and the microstructure of geopolymer pastebecame very denser.

Alonso and Palomo [27] believed that when MK activation wascarried out with highly concentration of alkaline solutions (NaOH)in the presence of calcium hydroxide, the main reaction productwas a sodium aluminosilicate similar to that obtained when MKwas activated in the absence of calcium hydroxide and the forma-tion of CSH gel as product was observed as a secondary reactionproduct. This system was inuenced by parameters such as curingtemperature, alkali concentration, initial solids content, etc. Whenthe activator concentration increased, a delay in polymer forma-tion was produced, whereas temperature accelerated its formation.The solids ratio did not inuence the rate of aluminosilicate forma-tion. In another study, Alonso and Palomo [28] did the calorimetricstudy of alkaline activation of calcium hydroxideMK solid mix-tures. A series of MK and calcium hydroxide mixtures were acti-vated in 1:1 proportion, with different NaOH concentrations (5,10, 12, 15 and 18 M) at 45 C during 24 h. The activation stepsand reaction products were examined through isothermal conduc-tion calorimetry and the reaction products characterizations werecarried out by means of chemical analysis and instrumental tech-niques (XRD, FTIR and nuclear magnetic resonance NMR). Basedon the investigation, they concluded that: (a) when NaOH concen-tration was 5 M or lower in the MK activation in calcium hydroxidepresence, the main product formed was CSH gel; (b) when the acti-vation was 10 M or higher the main reaction product was the alka-line aluminosilicate with polymeric character similar to the oneobtained in the MK activation with the same activator but in cal-cium hydroxide absence. As secondary reaction product (between20% and 30%), CSH gel was obtained; (c) a threshold OH concen-tration existed above which, the alkaline polymer was mainlyformed, and beneath which, the CSH gel was the main reactionproduct; (d) a high hydroxyl group concentration impeded the cal-cium hydroxide dissolution, Ca2+ concentration was small and thedissolved silicates were xed as sodium aluminosilicate, whenOH was not so high, Ca2+ in solution increased and it precipitatedas hydrated calcium silicate.

Table 1Hydration product versus activator type.

Author Activator

Granizo et al. [14] Sodium silicate + NaOHGranizo et al. [9] NaOHGranizo et al. [15] NaOHMadani et al. [12] NaOHZhang et al. [21] NaOHAlonso and Palomo [27] NaOH

Alonso and Palomo [28] NaOHGranizo et al. [15] NaOHbefore decreasing again at the highest Si/Al ratio of 2.15. Higher

Hydration product Notes

Hydrated sodium aluminosilicateNASH gelNASH gelZeoliteZeoliteSodium aluminosilicategel, while high concentrations result in reduced gel skeletal densi-ties. They also reported that the compressive strength of MK basedhydration product versus activator type.

3. Nature, concentration of activator, SiO2/Al2O3 ratio and solid/liquid ratio

3.1. Nature and concentration of activator

Alkali hydroxides and waterglass or a combination of them havebeen studied for AAMK cements. Waterglass-activated cements of-ten give much higher strength than alkali hydroxide-activated ce-ments. However, high curing temperature and high concentrationof alkalis are also required to achieve high strength from the acti-vation of MK [2931]. Wang et al. [32] studied MK geopolymeractivated with NaOH. They reported that mechanical propertiesof the geopolymers were greatly dependent on the concentrationof NaOH solution. Flexural strength (Fig. 1), compressive strengthand apparent density of the geopolymer increased along withincreasing of NaOH concentration within 414 mol/l. This attrib-uted to the enhanced dissolution of the metakaolinite particulatesand hence the speeded condensation of the monomer in the pres-ence of NaOH with higher concentration.

Granizo et al. [14] supported the idea that the alkali activationof MK using solution containing sodium silicate and NaOH resultsin the production of materials exhibiting higher mechanicalstrength compared to the activation with only NaOH. Moreover,the exural strength increased when the concentration of Na in-creased. Pinto [33] studied AAMK and found that mechanicalstrength increased when using a 12 M concentration of NaOH acti-vator and calcium hydroxide percentage from 0% to 20%. However,for a concentration of 15 M it was noticed that the calcium hydrox-ide percentage did not inuence strength. Also the alkali activationof MK was studied and reported that the used of an alkaline activa-tor with waterglass caused an increase in mechanical strength,from 30 to 60 MPa in compression and from 5 to 7 MPa in exuralstrength. Duxson et al. [34] reported that the concentration of sol-uble silicon affected the distribution of porosity in MK-based geo-Alkaline aluminosilicateCSH MK + lime

strength was higher for a molar ratio Si/Al/Na of 2.5:1:1.3, Provis

and a solid content of 37%. The silicon content was increased bythe addition of SF with 95% or higher SiO2 content to compensatefor the shortage of silicon in MK. The mole ratios were varied:5.5 6 SiO2/Al2O3 6 6.5, 0.8 6 Na2O/Al2O3 6 1.2, 7.0 6 H2O/Na2-O 6 10. The levels for each of the factors were set at three grades(low, intermediate and high). They concluded that Na2O/Al2O3and H2O/Na2O had signicant impact on the compressive strength.The highest compressive strength (34.9 MPa) was achieved at SiO2/Al2O3 = 5.5, Na2O/Al2O3 = 1.0 and H2O/Na2O = 7.0.

Temuujin et al. [41] studied the effect of Si:Al variation on theadhesion strength of MK geopolymers to stainless and mild steels.Sodium silicate was employed to activate MK. They used differentSi:Al ratios of 1. 2 and 2.5 with water/binder (w/b) ratios of 0.61,0.45 and 0.74, respectively, at xed Na:Al ratio of 1. They reportedthat adhesion strength > 3.5 MPa to stainless and mild steels forgeopolymer with Si:Al = 2.5 and Na:Al = 1 while for compositionswith Si:Al = 1 and 2 the adhesion to the metal substrates was very

ilding Materials 41 (2013) 751765and van Deventer [38] used potassium, sodium and mixed (1:1) so-dium/potassium silicate solutions that prepared by dissolvingamorphous silica in KOH solution with H2O/M2O = 11 (M = K and/strength was recorded when the ratios of SiO2/Al2O3 and Na2/Al2O3were 3.03.8 and about 1, respectively.

3.2. SiO2/Al2O3 ratio

Pinto [33] studied AAMK based mixtures and found that somemixtures with calcium hydroxide and an atomic ratio of SiO2/Al2O3 = 5.1 led to higher compressive strength performance. Otherauthors [35] working with high SiO2/Al2O3 molar ratio MK. Theyfound out that hydration products developed during geopolymer-ization have lower SiO2/Al2O3 molar ratio than in the original pre-cursor material. De Silva et al. [36] studied the early-stage reactionkinetics of MK/sodium silicate/NaOH geopolymer system. The set-ting time and early strength development characteristics of mix-tures containing varying SiO2/Al2O3 ratios, cures at 40 C for upto 72 h were studied. They concluded that (a) increasing SiO3/Al2O3 ratio led to longer setting times; (b) increasing SiO3/Al2O3molar ratios up to 3.43.8 was responsible for the high-strengthgained observed at later stages; (c) increasing in Al led to lowerstrengths with increasing NaAlSi grained rather than amorphousNaAlSi containing geopolymers. Rowles and OConnor [37] stud-ied the alkali-activation of MK, noticing that the mechanical

Fig. 1. Flexural strength of MK-based geopolymer at different NaOH concentrations[32].

754 A.M. Rashad / Construction and Buor Na), giving solutions with composition SiO2/M2O = 0.02.0.These solutions were then mixed with MK. They investigated theeffects of sample SiO2/Al2O3 ratio, Na/(Na + K) ratio and reactiontemperature. The results obtained indicated that the initial gelphase formed during geopolymerisation was later transformed toa second, more-ordered gel phase, and provided detailed informa-tion of the rst gel phase during the rst 3 h of reaction. Increasingthe SiO2/Al2O3 ratio generally decreased the initial rate reaction.

Zhang et al. [39] studied the effect of SiO2/Al2O3, K2O/Al2O3 andH2O/K2O on the compressive strength of K-PSS geopolymer. Theyprepared K-PSS geopolymer with different SiO2/Al2O3, K2O/Al2O3and H2O/K2O ratios by activation the mixture of MK, silica fume(SF) and NaAlO2 with potassium silicate (KOH) solution. The spec-imens were cured at temperature of 20 C and 95% RH. They con-cluded that the SiO2/Al2O3 had a signicant impact on thecompressive strength. The highest compressive strength was ob-tained when SiO2/Al2O3 = 4.5, K2O/Al2O3 = 0.8 and H2O/K2O = 5.0.Yunsheng et al. [40] studied the inuence of three key parametersof SiO2/Al2O3, M2O/Al2O3 and H2O/M2O on the synthesis of MK-based geopolymer cement. MK was activated with NaOH and so-dium silicate solution with the mole ratio of SiO2/Na2O of 3.2weak. Aquino et al. [42] studied some of mechanical properties ofgeopolymers synthesized by alkali (NaOH or KOH) activation MKand SiO2 mixture. Samples with K/Al or Na/Al atomic ratios equalto 1, Si/Al atomic ratios in the 1.252.5 range and H2O/Al2O3 molarratios of 11 or 12 were cured at 80 C for 24 and 48 h. The resultsindicated that the density of the geopolymers increased withincreasing Si/Al ratios for NaOH and KOH activators. Increasingdensity of the geopolymers with increasing Si/Al ratios had signif-icant effect on increasing Youngs modulus, Vickers hardness, frac-ture toughness and strengths only at lower Si/Al ratios (below Si/Al = 1.52). At higher Si/Al ratios, all mechanical properties de-creased regardless of increasing density of the geopolymers. Thesamples cured for 48 h gave higher strength than those cured for24 h.

3.3. Solid/liquid ratio

Strength decreases as the water/solid ratio increases. This trendis analogous to water/cement ratio in the compressive strength inPC system. Mostowicz and Berak [43] mentioned the tendency ofzeolitic synthesis mixtures to form larger crystals when the totalamount of water in the reaction mixture is increased. Yao et al.[44] reported that high solid/liquid (S/L) ratios resulted in low vis-cosity of slurry and the lower S/L ratios increased the geopolymer-ization period. On the other hand, Zuhua et al. [45] stated that lowS/L ratios could accelerate the dissolution of source materials.Zhang et al. [46] activated MK/granulated ground blast-furnaceslag (donated as slag)-based geopolymers with alkaline activator.Different L/S ratios were employed. Permeability was measuredFig. 2. Effect of L/S ratio on permeability of air curing geopolymer [46].

uildiby using Darcy method. They reported that the permeability coef-cient (k) increased along with increasing L/S ratio (Fig. 2). Themore connective pores exist in the geopolymer matrix preparedat higher L/S ratio. When the L/S ratio was 0.6, k was1.0 106 lm2, almost twice that of 0.55.

Kong et al. [47] reported that S/L ratio of 0.8 gave nearly opti-mum strength and provided good workability. Higher S/L ratiothan 0.8 had very low workability and deteriorated the propertiesof the paste produced. Liew et al. [48] activated MK pastes with al-kali activation solution at S/L ratios, by mass, ranging between 0.40and 1.20. The alkali activation solution was Na2SiO3/NaOH withdifferent ratios. The results of bulk density and compressivestrength showed that the S/L of 0.8 gave the highest values at Na2-SiO3/NaOH ratio of 0.20. Lin et al. [49] activated MK with alkalineactivator. The alkaline activator was a NaOH solution and sodiumsilicate. The effects of S/L ratios ranging from 0.4 to 1.0 (donatedas: SL04, SL06, SL08 and SL10 for S/L ratios of 0.4, 0.6, 0.8 and1.0, respectively) and SiO2/Na2O ratios ranging from 0.8 to 2.0 onthe compressive strengths at ages of 1, 7, 28 and 60 days werestudied. The results indicated that after 1 day of curing, a S/L ratioof 0.4 yielded the lowest strength. After 60 days, the strength in-creased to only 27.7 MPa. The specimen with a S/L ratio of 0.8was the strongest and its strength increased continuously during60 days of curing (Fig. 3). The silica and alumina reaction in theMK-based geopolymer system caused the increase in strength. Asthe S/L ratio approached 1.0, the paste stiffened with low workabil-ity. Therefore, the SiO2/Na2O ratio was set to 2, and the S/L ratio

Fig. 3. Compressive strength of MK-based geopolymers with various S/L ratios [49].A.M. Rashad / Construction and Bwas set to 0.8. Other authors as Zivica et al. [50] studied the effectsof the combination of low L/S ratio and pressure compaction of thefresh pastes on the properties of hardened MK geopolymer pastes.The AAMK pastes were prepared with activator solution/MK ratioof 0.08 and compacted by pressure of 300 MPa. The prepared spec-imens were 20 mm-edge cubes. The reference specimens were pre-pared with L/S of 0.7 using the compaction by hand. NaOH wasused as alkali activator. The results indicated that the use of L/S0.08 and 300 MPa compaction pressure produced very densenear-nano-pore structure with the degree of the homogeneityand the compressive strength overcoming 500 times referencehardened paste.

4. Effect of curing condition

Muiz-Villarreal et al. [51] studied the effect of curing temper-atures on the geopolymerization process, physical, mechanical andoptical properties of MK-based geopolymer activated with NaOHand sodium silicate. The inuence of different curing temperaturesof 30, 40, 50, 60, 75 and 90 C was studied. They reported that theoptimum curing temperature was 60 C which gave the best geo-polymerization process. Perera et al. [52] studied the curing atambient and controlled RH with mild heating (4060 C) of aMK-based geopolymer of molar ratios Si/Al and Na/Al of 2 and 1,respectively. They monitored the effect of curing condition onthe open porosity. They concluded that the curing in the absenceof rigorous sealing, in an oven in which the RH was held at 3070% did not offer any advantage over curing at ambient followedby mild heating (4060 C).

Rovnank [53] studied the effect of curing temperatures of 10,20, 40, 60 and 80 C and time on the compressive strength, exuralstrength and pore distribution of MK-based geopolymer mortars.Alkaline silicate solution with modulus (SiO2/Na2O) of 1.39 wasused as activator. This alkaline was prepared by dissolving of solidhydroxide in sodium silicate. The results showed that the treat-ment of fresh mixture at higher temperature accelerated thestrengths development, but the 28 days mechanical propertieswere deteriorated in comparison with results obtained for mix-tures that were treated at room or slightly decreased temperature.The results also showed that there is an increase in pore size andcumulative pore volume with rising temperature.

5. Effect of ultrasound

Feng et al. [54] studied the feasibility of using ultrasound to en-hance the geopolymerisation of metakaolinite/sand and y ash(FA)/metakaolinite mixtures. They found that the introduction ofultrasonication into the geopolymerisation systems increased thecompressive strength of the formed geopolymers and the strengthincreased with increasing ultrasonication up to certain time. Thedissolution of metakaolinite and FA in alkaline solutions was en-hanced by ultrasonication, hence releasing more Al and Si intothe gel phase for polycondensation. They also found that the ultra-sonication improved the distribution of the gel phase in the geo-polymeric matrices and strengthened the binding between theparticle surfaces and the gel phases. The ultrasonication enhancedthe formation of semi-crystalline to crystalline phases in theformed geopolymers. They also concluded that the improved per-formance of the ultrasonically formed geopolymers in term ofcompressive strength could be attributed to the accelerated disso-lution of the AlSi source materials, the strengthened bonds at thesolid particle/gel phase interfaces, the enhanced polycondensationprocess and the increased semi-crystalline and crystalline phases.

6. Effect of MK neness

Weng et al. [55] studied different specic surface areas of MKactivated with sodium silicate and NaOH They concluded thathigher specic surface area of MK powders were characterizedby quicker setting time, higher compressive strength and morehomogeneous microstructure.

7. Resistance of aggressive solutions

Davidovits [56] studied the acid corrosion resistance of severaldifferent cements in 5% H2SO4 and HCl indicated that AAMK ce-ment had the best acid resistance. PC and Portland slag cementwere destroyed easily in acidic environments. Calcium aluminatelost 3060% of the mass, while AAMK lost only 58% mass. Otherauthors [57] investigated the MK when exposed to aggressive solu-tions. The alkali activation of MK is a way of producing highstrength cementitious materials. Prisms of mortar made of sand

ng Materials 41 (2013) 751765 755and AAMK were immersed in deionized water, ASTM seawater, so-dium sulfate solution (4.4 wt.%) and sulfuric acid solution(0.001 M). The prisms were removed from the solutions at 7, 28,

56, 90 180 and 270 days. Their microstructure was characterizedand their physical, mechanical and microstructural propertieswere investigated. It was observed that: (a) the nature of theaggressive solution had little negative effect on the evolution ofmicrostructure and the strength of these materials; (b) 90-dayand older specimens experienced a slight increase in their exuralstrengths with time. This tendency was most pronounced in sam-ples cured in sodium sulfate solutions; and (c) the resultant hydro-ceramic demonstrated good stability for up to 270 days whensubmerged in aggressive liquids of various types.

8. Resistance of elevated temperature and re

Kuenzel et al. [58] investigated some properties of MK derivedgeopolymer mortars containing 50%, by weight, silica sand afterexposure to elevated temperatures up to 1200 C, for 2 h. The acti-

that compressive strength of geopolymer that had Si/Al = 1.54, M/Al = 0.66 higher than those had Si/Al = 1.4, M/Al = 0.42. Thestrength deterioration due to temperature exposure reduced withincreasing Si/Al ratio up to 1.5 then the deterioration began to in-crease. Potassium-based geopolymer (synthesized with potassiumsilicate and hydroxide) exhibited less strength regression after ele-vated temperature exposure compared to equivalent sodium-based geopolymer systems. Activator/MK around 1.11 seemed tobe the optimum that gave higher compressive strength beforeand after exposure to elevated temperature.

Lin et al. [65] studied the effect of addition a-Al2O3 particles tothe MK geopolymer activated with potassium silicate solution ex-posed to 400, 600 C, 800, 1000, 1200 and 1400 C. They reportedthat no further change until 1400 C. The addition of a-Al2O3 par-ticle ller into MK geopolymers increased the onset crystallinetemperature and reduced the crystalline velocity. The thermal

756 A.M. Rashad / Construction and Building Materials 41 (2013) 751765vating solution was mixing sodium silicate, water and NaOH. Thespecimens were cured at 22 3 C for 77 days. The used sand hadthree different grades of coarse, medium and ne. The results indi-cated that the compressive strength, porosity and microstractureof the geopolymer mortar specimens were not signicant affectedby temperatures up to 800 C. Nepheline (NaAl/SiO4) and carnegie-ite (NaAlSiO4) formed at 900 C. After exposure to 1000 C, themortar specimens were transformed into polycrystalline nephe-line/quartz ceramics with relatively high compressive strength. Be-tween 1000 and 1200 C, the specimens softened with gasevolution causing the formation of closed porosity that reducedspecimen density and limited mechanical properties. Also, the re-sults indicated that as the grade of sand ner as the higher com-pressive strength, before or after exposure to elevatedtemperature (Fig. 4). On the other hand, Kong et al. [59] studiedthe behaviour of AAMK activated with waterglass and potassiumhydroxide after exposure to 800 C at an incremental rate of4.4 C /min, with re duration 1 h, versus alkali-activated FA. Theresults indicated that the strength of MK-based geopolymer de-creased after exposure to 800 C. On the contrast, the strength ofthe corresponding FA-based increased after exposed to 800 C.Whilst Davidovits [60], Davidovits et al. [61], Barbosa and Macken-zie [62,63] reported very good heat resistant properties of materi-als prepared using sodium silicate, potassium silicate and MK,having thermal stability up to 12001400 C.

Kong et al. [64] studied the MK geopolymer binder system ex-posed to elevated temperatures. The combinations of sodium/potassium silicate and sodium/potassium hydroxide were used assource of activators. They studied different parameters as Si/Al ra-tio, activator/MK ratio and alkali cation type. The results indicatedFig. 4. Compressive strength of geopolymer/sand mortar specimens as a function ofthe heat treatment temperature [58].shrinkage of MK geopolymers increased with increasing in the heattreatment temperature. The increase in content of a-Al2O3 parti-cles could reduce the thermal shrinkage and maintain a relativelylower density and higher porosity. The increase in content of a-Al2O3 particles had no distinct inuence on the exural strengthafter heat treatment despite an increase in the porosity of the geo-polymers. Barbosa and Mackenzie [66] synthesized potassiumpolysialte (K-PS) and potassium polysialate disiloxo (K-PSDS) geo-polymers from metakaolinite and found these kind of geopolymershad excellent thermal stability, especially, the K-PS which showedlittle sign of melting up to 1400 C. Bernal et al. [67] studied the ef-fect of elevated temperatures of 200, 400, 600, 800 and 1000 C, for2 h, on geopolymers formulated with an overall SiO2/Al2O3 molarratio of 3, slag/(slag + MK) ratios of 0.0 and 0.2, constant H2O/Na2O ratio of 12 and Na2O/SiO2 ratio of 0.25. The results indicatedthat the geopolymers formulated with MK and slag had higherresidual compressive strength than the pure MK-based geopoly-mer up to 800 C. On the other hand, the pure MK system showeda much higher residual strength upon cooling from 1000 C toroom temperature, indicating that the extent of glass formationfrom the geopolymer gel at 1000 C is reduced by the incorporationof Ca into the gel, as a consequence of formation of CSH type gelthat coexisted with the aluminosilicate geopolymer gel. Chengand Chiu [68] studied re resistance of slag geopolymer blendedwith metakaolinite. They reported that when a 10 mm thick panelof geopolymer is exposed to 1100 C ame: the measured reverse-side 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.

He et al. [69] studied the effect of elevated temperatures of1000, 1100, 1200, 1300 and 1400 C, for 90 min in an argonFig. 5. Variations of exural strength and work of fracture of the carbon bersreinforced MK geopolymer composite [69].

atmosphere, on some mechanical properties of MK geopolymerand MK/carbon bers. Composites without and after heat treat-ment were denoted as C-W, C-1000, C-1100, C-1200, C-1300 andC-1400. Potassium silicate solution was used as activator. The con-tent of carbon bers was 20 vol.% for the composites without heattreatment and 25 vol.% for composites after heat treatment. Whenthe composites were heated in a temperature range from 1100 to1300 C, it is found that mechanical properties were improved(Fig. 5). The improvement could be attributed to the densiedand crystallized matrix, and enhanced bers/matrix bonding basedon ne-integrity of carbon bers. On the contrary, for compositeheat treated at 1400 C, the strengthening effect of carbon berswas dramatically decompensated. It was resulted strong bers/ma-trix interface bonding strength. The composite showed substan-tially decreased in mechanical properties and fractures in a verybrittle manner. He et al. [70] prepared unidirectional carbon bers

eter 18 lm, tensile strength 1800 MPa) and PVC bers (average -ber diameter 400 lm, tensile strength 215 MPa). Regardless thebers type, the same content of bers (1 wt.% fraction on the totalmixture) was added to MK/slag mixture. The used bers were cutto obtain a 7 1 mm length. They concluded that all different typesof bers had good adhesion properties, micro-cracks propagationalong the matrix and created a favourable bridging effect. 1 wt.%of reinforcing bers embedded in the geopolymer matrix was ableto increase exural strength from 30% up to 70% depending onbers type. Geopolymers added with PVC and carbon bers exhib-ited signicantly post-crack improved, resulted more enhance-ments in ductility after reaching the rst crack load.

Li et al. [75] manufactured MK geopolymer composites rein-forced with short PVA bers using the extrusion technique. NaOHand sodium silicate solution with a ratio of SiO2 to Na2O of 3.2were used as reagents. Two types of silica sand (300600 and90150 lm in diameter) with weight ratio of 3:2 were used asaggregates. The total sand was 32.5%, by weight of the binder.Short PVA bers were used as reinforcements. They concluded thatthe addition of PVA bers into geopolymer increased extrusion

A.M. Rashad / Construction and Buildireinforced MK geopolymer composite by ultrasonic-assisted slurryinltration method and heat treated at 1100 C. Then it wasimpregnated with SolSiO2 to seal the cracks and pores formedduring heat treatment. Composites before and after Sol-SiO2impregnation were denoted as HC and ImHC, respectively. Overan elevated temperatures ranging from 700 to 900 C, the strengthof the two composites showed anomalous gained and reachedtheir maximum values at 900 C, 322.1 and 425.1 MPa, respec-tively, (Fig. 6). These values were 19.8% and 16.8% higher than theirambient ones. At 1100 C, the impregnated composite showedsuperior high-temperature properties.

Bernal et al. [71] studied the mechanical performance of MK-based geopolymer reinforced with refractory aluminosilicate parti-cles and bers after exposed to elevated temperatures of 600, 800and 1000 C. The aluminosilicate particles were obtained by mill-ing the commercial refractory brick. The aluminasilicazirconiabers were used. The alkali activator was formulated in order toobtain overall matrix SiO2/Al2O3 molar ratios of 3.0 and 3.4 at aconstant Na2O/SiO2 ratio of 0.25. The quantity of water was ad-justed to achieve an H2O/Na2O ratio of 12. The compressivestrength and exural strength results indicated that the inclusionof refractory particles, both with and without additional refractorybers, improved post-exposure compressive and exural strengthscompared with sample without reinforcement. The inclusion ofhigher contents of refractory particles and bers reduced shrinkageof exposed specimens.

9. Fibers effect

Lin et al. [72] used short bers (2, 7 and 12 mm) to strengthenMK-based geopolymer. Potassium silicate solution was used asFig. 6. Flexural strength versus temperature of HC and InHC [70].activator. The results of exural strength and work of fractureshowed that the composites geopolymer with 7 mm short carbonbers length gave the maximum exural strength and work of frac-ture values, which were increased by 4.4 times and 118 times,respectively, (Fig. 7). Lin et al. [73] studied the effects of bers con-tent on mechanical properties and fracture behaviour of short car-bon bers reinforced MK-based geopolymer matrix. MK powderactivated with potassium silicate solution. Different volume frac-tions of short carbon bers (from 3.5 to 7.5 vol.%) were prepared.Specimens were cured at 80 C for 24 h. At the early stage of curing,a pressure of 0, 0.2, 1.2 or 2.0 MPa was loaded to obtain compositesreinforced geopolymers. The results showed that short carbon -bers had a great strengthening and toughening effect at low vol-ume contents of bers (3.5 and 4.5 vol.%). With the increase inbers content, the strengthening and toughening effect of shortcarbon bers reduced.

Natali et al. [74] modied some properties of the MK/slag geo-polymer with different types of dispersed short bers. Sodium sil-icate solution, with a SiO2:Na2O ratio of 1.99, and 8 M NaOHsolution were used as alkaline activators. The used bers were:HT-carbon bers (average ber diameter 10 lm, tensile strength5490 MPa), commercial E-glass bers (average ber diameter10 lm, tensile strength 2500 MPa), PVA bers (average ber diam-

Fig. 7. Variation of exural strength and work of fracture of geopolymer matrix andbers reinforced MK geopolymer [72].

ng Materials 41 (2013) 751765 757pressures. Extruded geopolymer thin sheets reinforced withmicrobers showed a good exural strength and reasonable tough-ness. Yunsheng et al. [76] studied the impact behaviour and

The NaOH and sodium silicate were used as source of activation.MK was partially replaced with FA at levels of 0%, 10%, 30% and

tion of MK with 25% FA was viable to form reactive cementitiouspastes. The increment in the curing temperature from 20 to 75 C

ildi50%, by weight. The results indicated that 10% replacement levelof MK with FA gave the lower porosity and higher impact strengthbefore and after 20 freezethaw cycles. Zhang et al. [77] modiedMK-based geopolymer with FA. The MK was partially replacedwith FA at levels of 0%, 33.3%, 50% and 66.7%, by weight. NaOHand water were mixed into sodium silicate to adjust the mole ratio(SiO2 to Na2O) of 1.2. Curing conditions were either in steam at80 C or in air at 20 C for 1, 3 and 6 days. They concluded thatproper addition of FA (33.3%) increased the uidity of fresh paste,prolonged its setting time and improved compressive strength ofhardened geopolymer. The compressive strength of the geopoly-mer containing 33.3%, FA by steam curing for 6 days, was improvedby 35.5%.

Bankowski et al. [79] activated MK blended with different per-centages of FA with solution of sodium silicate and NaOH. Thesolution had 0.76 M and the sodium silicate concentration was4.25 M. This geopolymer was used to encapsulate brown coal FAcontaining high concentrations of heavy metals. The results indi-cated that leaching of calcium and potassium has been reducedby this geopolymer. Signicant reductions in leaching were foundfor calcium, arsenic, strontium, selenium and barium. The geopoly-mer was effective at stabilizing low percentages of FA, but effectiveas the percentage of FA increased. Phair et al. [80] used sodium sil-icate and NaOH as activator solutions to activate FA blended withAl sources (such as metakaolinite, kaolinite and K-Feldspar) on thesolidication stabilization of heavy metals. They reported that forincreasing the efciency of immobilization, it is suggested thatmicrostructural characteristics of PVA bers reinforced MK/FA geo-polymer boards. They used NaOH and sodium silicate solution withmolar ratio of SiO2 to Na2O = 3.2 to activate MK and FA mortars inboth cases (separate and blended). Short PVA bers were used asreinforcement materials. The results indicated that the 90% MKblended with 10% FA containing 2% bers, by volume, gave thelowest porosity. The addition of high volume fraction PVA berschanged the impact failure mode of MK/FA geopolymer boardsfrom a brittle pattern to ductile pattern, resulting in a great in-crease in impact toughness.

Zhang et al. [77] studied the effect of polypropylene bers onthe mechanical properties and volume stability of geopolymer. Dif-ferent contents of polypropylene bers were acted in geopolymermatrices. NaOH and water were mixed into sodium silicate to ad-just the mole ratio of SiO2 to Na2O of 1.2. The results showed thatthe 3-day compressive strength, exural strength and impactingenergy of geopolymer containing 0.05% bers increased by 67.8,36.1 and 6.25%, respectively, while shrinkage and modulus of com-pressibility decreased by 38.6% and 31.3%, respectively. Polypro-pylene bers offered a bridging effect over the harmful pores,defected and changed the expanding ways of cracks, resulting ina great improvement of strength and toughness. Zhang et al. [46]reported that the large shrinkage problem of the MK with the addi-tion of 10% slag geopolymer, activated with NaOH and sodium sil-icate, could be solved by appropriate addition of polypropylenebers and MgO as expansion agent as well as careful curing at earlyage.

10. MK blended with FA

Yunsheng et al. [78] studied the durability of alkali-activatedblended MK-FA mortars modied with PVA short bers in whichthe composites manufactured by extrusion technique (SFRGC).

758 A.M. Rashad / Construction and Buthe 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 thataccelerated the development to the compression strength duringthe rst day; in the long term curing at 20 C results in similarresults.

11. MK blended with slag

Buchwald et al. [84] studied the activation of MK blended withslag using NaOH as alkali activator. The activator concentration forthe pure MK was higher than that for the pure slag, in order toreach the same Na/Al value of 0.4. The water content was adjustedto give the same workability. They concluded that both type ofreaction products CSH from slag and aluminosilicate networkfrom MK were able to coexist. The alkaline activation of MKslagmixtures yields a binder blend containing CSH system and geo-polymer system and a mixture of both phases due to interactionat their contact surface. In another investigation, Buchwald et al.[85] studied blended slag with MK activated with two differentconcentrations of NaOH solution. One with low NaOH concentra-tion (916 wt.%) and the other with high NaOH concentration of25 wt.%. They measured the reaction progressed of the alkali-activated pastes by isothermal calorimetry and ultrasonic mea-surements. They reported that the condensation reaction wasaccelerated by blending slag and MK but the inuence was muchapparent at higher concentrations of activator. This explained bya higher amount of dissolution of both slag and MK, but it is moresignicant on MK dissolution.

Cheng and Chiu [68] studied slag geopolymer blended withmetakaolinite. The results indicated that the more metakaoliniteadded in the system, the slower setting time. The compressivestrength increased with increasing in metakaolinite content. Thereason could be that the more metakaolinite added, the more Algel formed in the system, therefore, giving a higher degree of geo-all matrices were generally found to be highly efcient in retainingPb within the matrix with the order of effectiveness: FA > kaolin-ite > K-feldspar > metakaoline. Xu et al. [81] studied factors affect-ing the immobilization of heavy metals in FA-based geopolymers.They used a solution of KOH and K2SiO3 to activate the mixtureof MK and FA. The results showed that the heavy metals can beeffectively immobilized into the geopolymeric matrices. The con-centrations of alkali activator and different types of heavy metalshad impact on the immobilization behaviour to one metal in thesame system. Yunsheng et al. [82] studied the immobilizationbehaviour of MK/FA (100/0, 90/10, 70/30, 50/50 and 30/70), mor-tars, activated with NaOH and sodium silicate solution with themolar ratio of, SiO2/Na2O, of 3.2. There were different curing con-ditions. They concluded that geopolymer containing 70% MK and30% FA that was synthesized at steam curing (80 C for 8 h), exhib-ited higher mechanical strength. The compressive and exuralstrengths were 32.2 and 7.15 MPa, respectively. The synthesizedgeopolymer can effectively immobilise Cu and Pb heavy metals.

Aguilar et al. [83] produced lightweight concretes based onbinders composed of MK with 0 and 25% FA activated with 15.2%of Na2O using sodium silicate of modulus SiO2/Na2O = 1.2. Con-cretes with densities of 1200, 900 and 600 kg/m3 were obtainedby aeration by adding aluminum powder, in some formulationslightweight aggregate of blast furnace slag was added at a ratiobinder: aggregate 1:1; curing was carried out at 20 and 75 C.The compressive strength development was monitored for180 days. They concluded that it is possible to produce concretebased on geopolymers of MK of different densities. The substitu-

ng Materials 41 (2013) 751765polymer reaction. The density results showed a decrease with theincrease in metakaolinite content. Shen et al. [86] partiallyreplaced slag with zeolites or MK in alkali activation. The

replacement slag with zeolites or MK increased the porosity of thehardened pastes, but the leached fraction of Ca+ and Sr2+ were de-creased. The decrease in leached fraction may be attributed to theformation and adsorption properties of (Al + Na) substituted CSHand self-generated zeolite precursor. Yip et al. [87] blended slagwith MK using MK/(MK + slag) mass ratios of 1, 0.8 and 0.6 inalkali-activated system activated with commercial sodium silicatesolution and NaOH pearls at molar ratios of 2, 1.5 and 1.2. The com-pressive strength results showed that at MK/(MK + slag) = 0.8 gavethe higher strength when molar ratios were 2 and 1.2. At molarratio of 1.5, MK/(MK + slag) = 1 gave the higher strength.Burciaga-Diaz et al. [88] studied the strength development on alka-line activation of MK/slag pastes. The main parameters were MK/slag weight ratios of 100/0, 80/20, 50/50, 20/80 and 0/100, modu-lus of the alkaline solutions of sodium silicate (MSiO2/NaO2 at 0,1, 1.5 and 2), % Na2O (5%, 10% and 15%) and curing time. Cubes

evident in geopolymers formulated with SiO2/Al2O3 ratios of 3.8and 4.0.

Chen et al. [90] studied the compressive strength of alkali-acti-vated MKslag hydroceramics (AMSHC). The mixtures were madefrom MK and slag with a pure alkali solution of NaOH and a simu-lated high-alkaline waste (SAW) liquid via of hydrothermal curingfor 24 h. The affecting factors including curing temperature, con-tent of slag and dosage of simulated highly-alkaline waste on theproperties of AMSHC. The results indicated that the compressivestrength of AMSHC matrixes improved effectively by the additionof slag and the elevated curing temperature. Structural evolutionin pastes produced from alkali silicate-activated slag/MK blendswas assessed by Bernal et al. [91]. They reported that in the initialperiod of the reaction, the addition of MK led to an increase in thetotal setting time, reduced the heat release and affected the reac-tion mechanism by introduction of a large quantity of additionalAl. This effect was more signicant when an activating solution

A.M. Rashad / Construction and Building Materials 41 (2013) 751765 759were cured at 20 C for 360 days. The results indicated that thecomposition of 20% slag plus 80% MK at 10% Na2O gave the highestcompressive strength. The modulus of 11.5 was sufcient to pro-mote an adequate activation of binders of slag and MK and theirbinary mixtures.

Yunsheng et al. [89] tested the mechanical strength of MK/slaggeopolymer mortars. NaOH and sodium silicate solution with themolar ratio (SiO2/Na2O) of 3.2 were used as alkaline reagents.The ratios of MK/slag were 100/0, 90/10, 70/30, 50/50 and 30/70,by weight. The specimens were cured at 20 C and 100% RH for28 days. The results showed that geopolymer mortar containing50% slag gave the highest compressive strength followed by 70%slag and followed by 30% slag (Fig. 8). The results of exuralstrength showed a similar tendency as compressive strength. Theyused 50/50 mixture cured at 80 C for 8 h to study the immobiliza-tion behaviours of MK/slag based geopolymer in presence of Pband Cu. They concluded that leaching tests showed that MK/slagbased geopolymer could effectively immobilized Cu and Pb heavymetal and the immobilization efciency exceeded 98.5% whenthe amount of heavy metals contained in slag based geopolymericmatrix was in the range of 0.10.3%, by mass of the binder. The Pbshowed better immobilization efciency than Cu in the case oflarge dosages of heavy metals. Bernal et al. [67] studied the com-pressive strength of alkali silicate-activated blends of MK and slagpastes. The parameters were slag/(slag + MK) ratios and SiO2/Al2O3molar ratios. Alkaline activating solutions were prepared by blend-ing sodium silicate solution with solid analytical-grade NaOH toreach the desired modulus values. The results indicated that theaddition of slag to MK-based geopolymers led to an increase incompressive strength compared with reference specimensproduced using MK as the sole precursor. This effect was moreFig. 8. Effect of slag replacement percentages on compressive strength [89].with a higher silicate modulus was used, and led to a slight reduc-tion in the nal mechanical strength. However, the alkaline acti-vating solutions were formulated by blending a commercialsodium silicate solution together with 50% NaOH solution to reachmodulus (Ms = molar SiO/Na ratio) of 1.6, 2.0 or 2.4. A constantactivator concentration of 5% Na2O by mass of (slag + MK) wasused. Mortar samples were formulated with a constant water/(slag + MK + anhydrous activator) ratio of 0.47 and a binder/sandratio of 1/2.75. Different amounts of MK were blended with slag,the slag/(slag + MK) were 1.0, 0.9 and 0.8. The compressivestrengths were measured up to 180 days. The compressivestrength results showed that the increase of MK content in thebinders led to a reduction of compressive strength, this effect beingmore signicant when a higher Ms activator was used. The Ms 2.0specimens were consistently stronger than the Ms 2.4 specimensat all ages and at each level of MK substitution.

Bernal et al. [92] studied the effects of activation conditions onsome engineering properties (as compressive, exural strength andaccelerated carbonation) of alkali-activated slag/MK blends. Theconcrete mixtures were formulated with SiO2/Al2O molar ratiosof 3.6, 4 and 4.4, slag/(slag + MK) ratios of 0.8, 0.9 and 1.0 (i.e.20%, 10% and 0% MK, respectively) and a constant Na2O/SiO2 molarratio of 0.25. They used sodium silicate solution with 50 wt.%NaOH solution as alkali activators. They concluded that the higheralkali activator content gave satisfactory early strength develop-ment. The inclusion of MK enhanced exural strength at laterage. Accelerated carbonation showed rather rapid carbonationaccompanied by a loss in strength, this occurred faster at highMK content. Wang et al. [93] studied the compressive strengthFig. 9. Effects of slag content on permeability of air curing geopolymer prepared atL/S ratios of 0.55 and 0.60 [46].

and porosity of alkali-activated slagFAMK cementitious materi-als prepared by hydrothermal method. The activator used waswaterglass with the modulus adjusted to 1.0 by dissolving NaOH.The ratio of water to solid was about 0.35. The compressivestrength and porosity results indicated that this type of materialhad higher mechanical strength and compact structure. The aver-age compressive strength was more than 60 MPa after hydrother-mal process. The porosity was less than 36%. Zhang et al. [46]studied the permeability, measured by Darcy method, of MK/slag-based geopolymers. Different L/S ratios of 0.55 and 0.6 wereemployed. They reported that the inclusion of slag could reducepermeability, particularly at L/S ratio of 0.6 (Fig. 9). The existenceof slag had only a slight effect on permeability of geopolymer atL/S ratio of 0.55. When the slag content was P10%, geopolymer

Pacheco-Torgal et al. [97] studied the effect of activator concen-

13. MK blended with other materials

Zhang et al. [99] blended MK and slag in the mass ratio of 1:4.Sodium metasilicate, Na2SiO3.9H2O was used as alkaline activator.The MK/slag based geopolymer reinforced by organic resins (OR)which consist of acrylic resin emulsion and polyvinyl acetate resin.The amount of OR ranging from 0% to 15%. They concluded that theexcellent compressive and exural performance was attributed tothe OR that prevented growing cracks and increased the fracturetoughness of the geopolymer composites. The geopolymer com-posites modied with 1 wt.% OR displayed the highest compressiveand exural strengths. Komnitsas et al. [100] used the frerronickelslag-based inorganic polymers that produced by mixing slag withsodium silicate solution (Na2O:SiO2 = 0.3, Na2O = 7.58.5%,SiO2 = 25.528.5%), sodium or potassium hydroxide and water.The effect of additives such as kaolin or MK and pre-curing periodon the nal compressive strength was evaluated. The results indi-cated that the presence of MK decreased the compressive strength.This is probably due to the increased porosity of the new structureas a result of thermal processing. Bignozzi et al. [101] studied thepossibility of using electric arc furnace slag (EAFS) blended with

760 A.M. Rashad / Construction and Builditration, superplasticizer content and calcium hydroxide content onthe workability, compressive strength and exural strength ofhad a relatively steady and low permeability, suggesting slag hada packing inuence on geopolymer structure [94].

12. MK blended with calcium hydroxide

The addition of a sufcient quantity of Ca to AAMK in form ofcalcium hydroxide could lead to formation of phase separated Al-substitute CSH and NASH gels [15,94,95]. This is known to bemore prevalent at relatively low alkalinity conditions system, be-cause if the OH concentration is high, the dissolution of calciumhydroxide is hindered and it is also possible that very highly alka-line conditions will lead to dissolution of any CSH type phaseswhich are formed. It has also been suggested that Ca2+ is capableof acting as charge-balancing cation within the geopolymeric bind-ing structure, but it needs to be further studied [22]. However,Alonso and Palomo [27] partially replaced MK with calciumhydroxide at levels of either 30% or 50%. The composites were acti-vated with NaOH at different concentrations of 10, 12, 15 and18 M. The specimens were cured for 24 h at different temperaturesof 35, 45 and 60 C. After curing, the specimens were tested in ex-ural. The results showed that the inclusion of 50% calcium hydrox-ide gave higher exural strength than 30% calcium hydroxide. Thestrength increased as curing temperature increased and concentra-tion of NaOH decreased (Fig. 10). Buchwald et al. [96] studied theinuence of calcium content on the compressive strength of AAMK.MK powders have been activated with 8 mol/1 NaOH solution. Thecalcium content of these model mixtures has been increased bysuccessive exchange of the pure alumosilicate powder against cal-cium hydroxide up to 40% per mass. Compressive strengths wereconducted at 28 days and 111 days. The results indicated that theoptimal calcium content seemed to be about 10%.Fig. 10. Flexural strength of MK/lime specimens cured at 24 h [27].AAMK-based mortars. The concentrations of NaOH were 10, 12,14 and 16 M, while the contents of superplasticizer dosages were1%, 2% and 3%. MK was partially replaced with calcium hydroxideat levels of 0%, 5% and 10%. The results indicated that the workabil-ity of the fresh mortars decreased with increasing NaOH concen-tration and increased with the content of calcium hydroxide andsuperplasticizer. The results also showed that the use of 3% ofsuperplasticizer, combined with 10% calcium hydroxide improvedmortar ow from less than 50% to over 90% (Fig. 11), while highcompressive and exural strengths were maintained. Yip andDeventer [94], Yip et al. [98] studied the aluminosilicates with sim-ilar SiO2/Al2O3 and Al2O3/Na2O molar ratios. They found the exis-tence of an optimum of 20% (about 9% of calcium oxide) slagcontent in alkali-activation of MK-slag mixtures, led to increasecompressive strength, which according to them could be explainedby the fact that formed CSH within the geopolymeric binders actsas microaggregates resulting in a dense and homogeneous binder.Fig. 11. Flow versus NaOH concentration and calcium hydroxide content in thepresent of 3% superplasticizer [97].

ng Materials 41 (2013) 751765MK as starting materials for geopolymers. The MK/EAFS ratioswere 40/60, 30/70 and 20/80. Sodium silicate solution with SiO2/Na2O = 1.99 and NaOH 8 M solution were used to activate the

0%, 10%, 20%, 30% and 40%, by weight. The alkaline solution usedwas a mixture of aqueous of NaOH (12 M) and sodium silicate.The mass ratio of sodium silicate/NaOH of 2.0 was employed. Theresults showed that its possibly to improve the compressivestrength by replacing MK with Al2O3 up to 30%. Beyond 30%replacement level, the compressive strength decreased, in compar-ison to pure MK. However, 20% Al2O3 plus 80% MK gave the highestcompressive strength in which the original compressive strengthincreased by 18.1%, followed by 10% Al2O3 and followed by 30%Al2O3. Rajamma et al. [106] partially replaced biomass FA withMK, in mortars, at levels of 0%, 20% and 40%, by weight, activatedwith different molar volumes of NaOH and sodium silicate solu-tions. The compressive strength results showed that the inclusionof MK improved the compressive strength values. Also, the resultsshowed that as the MK content increased, as the improvement incompressive strength increased (Fig. 13).

Lin et al. [49] partially replaced MK with thin-lm transistor li-quidcrystal display (TFT-LCD) waste glass, after crushing and

Fig. 12. Compressive strength of alkali-activated MK-ladle slag [102].

A.M. Rashad / Construction and Building Materials 41 (2013) 751765 761starting materials. They concluded that the combination of 40/60was strongly recommended where it gave better mechanical prop-erties and compact microstructure. In another investigation, Big-nozzi et al. [102] investigated alkali-activated materials based onpartial substation of MK with ladle slag, deriving from the reningprocess of steel produced by arc electric furnace technology. Thereplacement levels were 0%, 25%, 50%, 60%, 70%, 80% and 100%,by weight, donated as G-MK100, C-MK75, G-MK50, G-MK40, G-MK30, G-MK20 and G-LS100, respectively. Sodium silicate and8 M NaOH were used as activating solutions. The compressivestrength results showed that G-MK100 and G-MK75 gave the low-est values. Mixture of G-MK20 gave the highest compressivestrength followed by G-MK40 and followed by G-MK30 (Fig. 12).They also determined the porosity percentages of the studied mix-tures. They found that as compressive strength increased as theporosity percentage decreased.

Bernal et al. [103] activated MK/slag blended binders withNaOH which mixed with either SF or rice husk ash (RHA), as alter-native silica-based activators. The results indicated that pasteswith NaOH/SF or NaOH/RHA showed similar trends in mechanicalstrength development as a function of activation conditions com-pared with pastes obtained using commercial silicate solutions asactivator. All activating solutions promoted higher compressivestrength development with increasing slag contents in the binders,which promoted the coexistence of aluminosilicate reaction prod-ucts along with calcium silicate hydrate gel. Yunsheng et al. [104]used MK blended with SF activated with KOH pellet and potassiumsilicate solution with molar ratio of SiO2/K2O of 3.25 and solid con-tent of 40%. The experimental results showed that K2O/Al2O3 had asignicant impact on compressive strength. The highest compres-sive strength when SiO2/Al2O3 = 6.5, K2O/Al2O = 0.8 and H2O/K2O = 10.

Kouamo et al. [105] modied MK geopolymer with alumina-oxide (Al2O3). MK was partially replaced with Al2O3 at levels ofFig. 13. Compressive strength values of biomass FA-MK mortars [106].milling to approximately 3000 cm2/g, at replacement levels of 0%,10%, 20%, 30% and 40%, by weight. The alkaline activator was aNaOH solution and sodium silicate. The results showed that bothinitial and nal setting times increased as the replacement levelsof MK increased. The compressive strength decreased as thereplacement levels of MK increased (Fig. 14). However, the geo-polymer based on 10% waste glass and 90% MK had a compressivestrength of 62 MPa after 60 days curing. Yip et al. [87] replaced MKwith calcite or dolomite in geopolymers. The replacement levels ofcalcite were 0%, 20%, 40%, 60%, 80% and 100%. Sodium silicate solu-tion was used as alkaline activator with different molar (SiO2/Na2O) ratios of 2, 1.5 and 1.2 by addition of solid NaOH to the so-dium silicate solution. The compressive strength and shrinkagewere measured at ages of 2, 7, 28, 90, 360 and 560 days. The resultsindicated that the addition of a moderate amount (20% by mass) ofcalcite was found to have a positive effect on the compressivestrength of MK based geopolymeric binder at all ages. More than20% calcite had a deleterious effect on strength due to signicantdisruption of the geopolymer gel network and the reduced reactivealuminosilicate content. The inclusion of calcite did not induceadditional shrinkage during the rst 90 days of aging. However,Fig. 15 shows the compressive strength and relative shrinkage re-sults at age of 560 days. The results of this study also showed thatpartially replacing MK with 20% dolomite proceeded similar trendof partially replacing MK with 20% calcite.

Lampris et al. [107] investigated the production of aggregatesfrom silt produced from aggregate washing plants using theFig. 14. Development of compressive strength of waste-glass MK-based geopoly-mers [49].

SiO2/Al2O3 ratios ranging from 2.7 to 6 were selected to synthesizegeopolymer precursors, while the NaO2/SiO2 and H2O/Na2O ratios

ildiprocess of geopolymerisation. Silts have been blended with either20% MK or 20% PFA and activated by highly alkaline sodium silicateactivating solution. The activating solution was prepared by dis-solving NaOH in distilled water and sodium silicate solution wasadded. The results indicated that the replacement of silts witheither 20% MK or 20% PFA increased the compressive strength,but it was higher for MK than it in PFA. Chen et al. [108] used res-ervoir sludge as a partial replacement of MK in the production ofgeopolymers. 30% slag plus 70% MK were used as source materialsto produce the reference mixture of the geopolymer. MK was re-placed with reservoir sludge at levels of 50%, 70% and 100%, byweight. The amounts of NaOH, sodium silicate and distilled waterwere used to produce the alkaline activators. The results showedthat the compressive strengths decreased with increasing replace-ment level of MK with reservoir sludge.

Wang et al. [109] studied the compressive strength, exuralstrength and wear behaviour (sliding against AISI-1045 steel) ofmetakaolinite-based geopolymer composites containing 5%, 10%,15%, 20%, 25% and 30% (volume fraction) polyteta-uoroethylene(PTFE). The compound activator composed of aqueous NaOH andsodium silicate was used. The results showed that mechanicalstrength of the composites was lower than corresponding geopoly-mer, while the wear model became mild. The wear was dramati-cally reduced by 8699.2%. Wang et al. [110] synthesizedmetakaolinite-based geopolymer composites containing 5%, 10%,15%, 20%, 25% and 30% (volume fraction) scalelike graphite, poly-tetra-uoroethylene (PTFE) and molybdenum disulde (MOS2),respectively, in the presence of a compound activator composedof aqueous NaOH and sodium silicate at room temperature. The tri-

Fig. 15. Compressive strength and relative shrinkage at varying calcite content atMs = 1.2 [87].

762 A.M. Rashad / Construction and Bubological behaviours of the resulting composites sliding againstAISI-1045 steel were investigated on an MM-200 friction and weartester, and the bending strength and compressive strength of thecomposites were determined. The results indicated that all thethree kinds of the tested solid lubricants reduced both bendingand compressive strengths. On the other hand, the friction, wearof the composites and uctuation of the friction coefcient werereduced.

Xiangke et al. [111] employed the activated vanadium tailing(AVT) as the main source material for geopolymerisation in combi-nation with MK. The raw vanadium tailing was blended with solidNaOH at a raw vanadium tailing/NaOH mass ratio of 5/1 andheated at 450 C for 1 h. The heated tailing was cooled naturallyto room temperature, then ground in a ball mill for 5 min. TheAVT was mixed with MK at various mass ratios of 100/0, 90/10,80/20, 70/30 and 60/40. The compressive strength results showedthat the mixture of 70/30 gave the highest compressive strength.Kouamo et al. [112] improved the compressive strength of the vol-canic ash geopolymer mortars. Volcanic ash was replaced with MKat levels of 0%, 30%, 40% and 60%, by weight. An alkali fusionof 0.3 and 17.5, respectively, were maintained constant for all syn-thesized geopolymers, except that the one with a SiO2/Al2O3 ra-tio = 3.8 (M) had a modied H2O/Na2O ratio of 11.5. The resultsindicated that the tensile cracking strain of the geopolymers couldbe controlled by nely tuning the Si/Al ratios or adding appropriateaggregate llers such as sand, thus rendering the smart nature ofgeopolymers for deformation-based sensing. Geopolymers withSiO2/Al2O3 ratios P3.8 were viable adhesives that could developstrong bond to concrete, steel and glass bers.

Vasconcelos et al. [115] carried out an experimental programabout the use of MK-based geopolymers mortars for retrottingpurposes. They addressed two main situations, the use of geopoly-meric mortars as a repairing layer or as a binding agent betweenCFRP sheets and the repaired concrete. Several compositions ofMK geopolymer mortars were executed by varying the percentageof sand/binder mass ratio (30%, 60% and 90%) and concentration ofsodium hydroxide (12 M, 14 M and 16 M). The results showed thatMK geopolymer gave a high mechanical resistance and a relevantadhesion to the concrete substrate. Also, low adhesion strength be-tween CFRP and geopolymer mortars was obtained. MK geopoly-meric mortars with low sand/binder mass ratio presented lowadhesion to concrete substrate due to high shrinkage behaviourdeduced by the microcracks in the surface of the specimens. Onthe same line with this, Hu et al. [116] studied repair materialsusing MK and MK blended with steel slag activated with NaOHprocess was used. The results showed an increase in compressivestrength with the inclusion of MK content. Also the results showedthat as MK content increased, as the compressive strength of thecomposition increased. The high amount of MK in fused volcanicash increased the amount of reactive phase content in the alumi-nosilicate allowing the dissolution of silica and alumina that im-proved the polycondensation phenomena and the formation ofpolymeric binder. Consequently, the compressive strengthincreased.

Kani et al. [113] addressed methods to reduce eforescence in ageopolymer binder based on a pumice-type natural pozzolanicmaterial. This eforescence caused by excess sodium oxideremaining un-reacted in the sodium aluminosilicate geopolymers(as natural pozzolan geopolymers). The deposited alkalis can reactwith atmospheric CO2 resulting in the formation of white carbon-ate surface deposits known as eforescence. Carbonation usuallyresults in binder degradation, pH reduction and the deposition ofcarbonate reaction products in the bulk sample, which may ormay not be visible to the naked eye, whereas eforescence causesthe formation of visible surface deposits and may or may not beaccompanied by further of the binder. However, they partially re-placed the pumice with MK at levels of 2%, 4%, 6% and 8%, byweight, aiming to reduce the eforescence. They concluded thatthe additional of MK slightly reduced the eforescence and im-proved compressive strength.

14. Special applications of MK based geopolymer

He et al. [114] studied the initial efforts of explore a new appli-cation of MK-based geopolymers to structural health monitoring. Adistributed geopolymer-ber optic sensing (G-FOS) system wasprepared, where geopolymers were used as smart adhesives to af-x optical bers to existing in-service structures to form as inte-grated G-FOS sensor. Combination of sodium hydroxide andsodium silicate solution was used as activator. Totally 11 different

ng Materials 41 (2013) 751765and sodium silicate solution with SiO2/Na2O molar ratio and massconcentration of 1.14% and 38%, respectively. The compressivestrengths were measured at ages of 8 h, 1, 3, 7 and 28 days.

product is NASH gel.2. Nature of activator plays important roles in AAMK. Water-

with slag, the newcomposite has higher residual compressive

uildiglass-activated cements often give much higher strengththan alkali hydroxide-activated cements.

3. In most cases, as the activator concentration increases, asthe mechanical strengths increase, up to certainconcentration.

4. The SiO2/Al2O3 ratio has signicant effect on compressivestrength geopolymer. The optimal ratios that give higherstrength ranging from 3.5 to 5.5, depending on activatortype and curing condition.

5. Although some researchers believed that the optimum cur-ing temperature is around 60 C, but this curing temperaturedepends on many factors as MK neness, activator type anddosage, etc.

6. Although some researchers believed that S/L ratio of 0.8gives nearly optimum strength and provides good workabil-ity, but this ratio affected with SiO2/Na2O ratio.

7. As L/S ratio increases, as permeability increases.8. Ultrasonication of geopolymers up to certain time, increases

the compressive strength and improves the distribution ofgel phase in the geopolymeric matrices.

9. Higher specic surface area of MK powders in alkali activa-tion system gives quicker setting time, higher compressiveComparing MK with MKsteel slag geopolymers, it was found thatthe 8 h, 1, 3, 7 and 28 days compressive strengths increased by43%, 28%, 17%, 6.9% and 7.6%, respectively. The addition of steelslag accelerated the setting time and signicantly improved com-pressive strength, which could be due to its latent hydrauliccementitious character.

Liew et al. [117] studied the possibility of MK to produce ce-ment powder that could be an alternative to PC by applying geopo-lymerization process. Cement paste was rstly made by alkalineactivation of calcined kaolin with alkaline activator (mixture of610 M NaOH and Na2SiO3 solution), heated at 80 C forming asolidied product, followed by pulverization to xed particle sizepowder. Different parameters of SiO2/Al2O3, Na2O/SiO2, Na2O/Al2O3, H2O/Na2O molar ratios, NaOH/Na2SiO3 ratio, concentrationof NaOH, MK/activator and heating conditions were studied. Ce-ment powder was added with water and then cured to producecubes. They found that the key parameter inuenced the propertiesof the cement powder was NaOH/Na2SiO3 ratio followed by NaOHconcentration, MK/activator ratios and heating condition. The re-sults indicated that the highest compressive strength was obtainedwhen the SiO2/Al2O3, Na2O/SiO2, Na2O/Al2O3 and H2O/Na2O molarratios were 3.10, 0.37, 1.15 and 14.23, respectively.

15. Conclusions

The use of MK as source of alkali activation system has beenwidely investigated in the recent years. The conclusions of the cur-rent literature review can be summarized as following:

1. The Alkali-activated binders seem to be the alternative of PCsystem. The exact reaction mechanism of AAMK is depend-ing on the prime source materials, alkaline activator typeand concentration of activator. The main reaction productof MK activation with sodium silicate + NaOH solutions orhighly concentrated alkaline solutions in the presence of cal-cium hydroxide is an amorphous hydrated sodium alumino-silicate. When NaOH with concentration of 5 M or lower inMK activation in calcium hydroxide presence, the main

A.M. Rashad / Construction and Bstrength and more homogeneous microstructure.10. AAMK system has better acid, seawater attack, sodium sul-

fate resistance than PC system.strength than the pure MK up to 800 C. On the other hand,the pure MK system shows a much higher residual strengthupon cooling from 1000 C to room temperature.

12. Blended MK with refractory particles modied the re resis-tance of the composition. The inclusion of higher contents ofrefractory particles and bers reduced shrinkage of exposedspecimens.

13. 0.05% polypropylene bers increase the geopolymer com-pressive strength, exural strength and impacting energy.1% short bers (FT-carbon, E-glass, PVA) embedded in thegeopolymer matrix can increase exural strength from 30%up to 70%, depending on ber type. PVC and carbon berssignicant improve the post-cracks in the geopolymers andenhancement the ductility.

14. Partially replacing 10% MK with FA in alkali activation sys-tem gives lower porosity and higher impact strength. Otherresearchers believed that the inclusion of 33.3% FA in MKbased geopolymer gives the highest compressive strength,but depends on the mole ratio and curing condition.

15. 70% MK plus 30% FA based geopolymer exhibits highermechanical strength and can effectively immobilise Cu andPb heavy metals.

16. In general, the more MK adds in alkali-activated slag system,the slower setting time. The addition of slag to MK leads toan increase in compressive strength. However, someresearchers believed that 80% MK plus 20% slag gave thehighest paste compressive strength which depends on molarratio and Na2O concentration. Other researchers believedthat 50% MK plus 50% slag gave the highest mortar compres-sive strength followed by 30%MK plus 70% slag and followedby 70% MK plus 30% slag at SiO2/Na2O = 3.2 cured at 20 Cand 100% RH for 28 days.

17. Partially replacing 10% of MKwith calcium hydroxide in geo-polymer improves both workability and compressivestrength.

18. The addition of 20% calcite or dolomite has positive effect onthe strength of MK based geopolymer binder.

19. Blending 60% of electric arc furnace slag with 40%MK in geo-polymer gives better mechanical properties and compactsmicrostructure. Whilst blending 20% MK with 80% ladle slaggives the highest compressive strength and the lowestporosity. 40% MK plus 60% ladle slag comes in the secondplace.

20. Blending 20% Al2O3 with 80% MK in geopolymer results18.1% extra compressive strength related to pure MK.

21. Partially replacing volcanic ash with MK in geopolymer mor-tars increases compressive strength.

22. The inclusion of MK in geopolymer binder based on a pum-ice-type natural pozzolanic material can slightly reduce theeforescence and improves the compressive strength.

23. MK-based geopolymer mortars can be used as a repairinglayer or as a binding agent between CFRP sheets and therepaired concrete. On the same line with this, MK andblended MK with steel slag (MK/steel slag = 80/20) activatedwith NaOH and sodium silicate solution at SiO2/Na2O = 1.14can be used as repair materials.

References11. AAMK systemhas very good heat resistant, where this systemhas thermal stability up to 12001400 C. When MK blended

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