Revista Română de Materiale / Romanian Journal of Materials 2015, 45 (2), 105 – 116 105

PROPRIETĂŢILE ŞI CARACTERISTICILE MICROSTRUCTURALE ALE UNOR LIANŢI MICŞTI CU ZGURĂ, ACTIVAŢI ALCALIN

PROPERTIES AND MICROSTRUCTURAL CHARACTERISTICS OF ALKALI-ACTIVATED SLAG-BLENDED CEMENTS

N.R. RAKHIMOVA∗, Kazan State University of Architecture and Engineering, Department of Building Materials

420043, Russian Federation, Kazan, Zelenaya Str. 1

The effects of ground used sand (GUS), ground fly ash (GFA) (class F), and microsilica (MS) on water requirement, setting

time, and compressive and bending strength development of alkali-activated slag-blended cements (AASBC) were studied. Siliceous blending materials were found to be able to replace up to 50% of ground granulated blast furnace slag (GGBFS) and contributed to up to 90% improvement of strength of AASBCs, The granulation for GUS, granulation, curing conditions, and basicity of GGBFS for GFA, and curing conditions for MS have effects on the development of the properties of the AASBCs.

Keywords: Blast furnace slag, alkalis, activators, binding composite materials, setting time, mechanical properties 1. Introduction

Sustainable development in the construction

industry requires effective blended cements and materials based on these blended cements. The introduction of supplementary cementitious materials (SCM) in traditional and alternative cements, in addition to solving imperious ecological problems, also improves the performance capabilities of the cement.

Extensive literature on the research and application of blended ordinary Portland cements (OPC) is available; however, the potential of the combination of various types of SCMs and OPC are yet to be exhaustively studied and reported. Further, sustainability in this field is associated with an increasing use of known SCMs, development and use of new SCMs, and the development and use of different clinker types. This requires a scientific approach to understand the reactions and performance of such materials combination [1].

SCMs are classified into two types, inert and active, which are the most frequently used classifications in building materials science. It is usually to name mineral powders that react with OPC and water as reactive SCMs, and those that do not form hydration products with binding properties as inert SCMs or simply fillers because of the insignificant interaction of the cement paste with such materials. This distinction is clearly relative because all types of mineral powders have some degree of effect on the structure and properties of mixed binders and therefore, in addition to being active, they are also multifunctionally active, differing only in the mechanism of influence on the structure and

properties of the filled binders. Therefore, it seems reasonable to classify mineral blending materials based on whether they are “chemically active” i.e. they form hydration products with cementitious properties or are “physically active” i.e. they do not form hydration products. The “physically active” mineral blending materials affect the physical structure and properties of blended binders, i.e. they are “physically active and reactive” supplementary materials and they combine both “filler” and “modifier” effects [2].

This approach is very reasonable for alkali-activated slag-blended cements (AASBC). The substitution and modifications represent the most promising trend for alkali-activated slag cements (AASC). Alkali activation allows for effective interaction between the AASC paste, fillers, and modifiers and enhances the compatibility with mineral blending materials of various compositions and structures. Hence, a much wider range of various mineral materials are usable with AASBCs than with blended OPCs. Therefore, the properties of AASCs are dependent on many more factors than OPCs. In addition to the influencing factors common to all powdery binders, i.e. chemical and mineralogical composition, fineness, water/binder ratio, and curing conditions, the influencing factors related to the alkaline component, its composition, and concentration, have a significant effect on the properties and structure of the AASCs.

Influencing factors of blending materials for AASBC are similarly to those for OPCs, and they include composition, fineness, and the amount of glassy phase. Due to the diverse range of SCMs used, generic relations between the composition,

∗ Autor corespondent/Corresponding author, E-mail: rahimova.07@list.ru

106 N.R. Rakhimova / Properties and microstructural characteristics of alkali-activated slag-blended cements

particle size, and exposure conditions, such as temperature or relative humidity become increasingly crucial [3].

Some of the main influencing factors controlling AASBC and their significance have been investigated. In this aspect, alkali-activated slag-fly ash systems have been most extensively researched.

Smith and Osborne [4] were the first which reported on alkali-activated slag-fly ash systems. A combination of 60% slag and 40% fly ash with 7% NaOH (relative to the combined mass of slag and fly ash) showed good early mechanical strengths and a small strength gain after 28 days.

Tang [5] investigated the effect of slag/fly ash ratio, water/binder ratio and activator (waterglass and NaOH) dosage on the strength development of alkali-activated slag-fly ash cements using the factoral design method. He found that these factors affected the strength of the cement in the following order: slag/fly ash ratio > water/binder ratio > waterglass dosage > NaOH dosage.

The activation of fly ash/slag pastes with NaOH solutions have been studied by Puertas [6]. The ratio of fly ash/slag and the activator concentration were found to be significant influence factors. The influence of curing temperature on the development of the strength of the pastes was lower than the contribution of other factors.

The effect of the fineness of ground fly ash with a specific surface area 400 m2/kg on the properties of alkali-activated mortars was studied by Lu C. [7]. Mixed AASC showed a 28-day strength of 76 MPa for a fly ash content of 60%. When non-ground fly ashes were used, the 28-day strength was only approximately 12.9–16.2 MPa.

Partial replacement of the ground granulated blast furnace slag GGBFS by fly-ash gives positive results in improvement of performance capabilities and substitution of slag. Proper slag/fly ash ratio was found to have an effect of a mutual complement to the superiority supplement [8]. Alkali-activated slag-fly ash cements showed very good resistance to acidic, sulphate, and seawater attacks, and corrosion resistance increased with increase in the fly ash replacement [9], which also improved the mechanical strength and pore structure [8, 10-12].

Many studies have demonstrated the complex microstructure and chemical composition of alkali-activated slag-fly ash cements binder gels. Shi and Day [13] and Puertas and Fernandez-Jimenez [14, 15] reported that the main hydration products of alkali-activated slag-fly ash cements were C–S–H and alkali aluminosilicate hydrate gels. Yang found that the microstructure and chemical composition of such blended binders fall between those of the aluminosilicate gel formed in the silicate-activated fly ash and those of calcium

silicate hydrate gel formed in silicate-activated granulated blast furnace slag (GBFS) [16].

Thus, the microstructure, composition, properties, slag/fly ash ratio, water/binder ratio, alkali activator dosage, grinding fineness up to 400 m2/kg, and curing temperature have been investigated as influencing factors for alkali-activated slag-fly ash cements. The influencing factors and their significance in AASBC with “physically active” and “chemically active” blending materials, to the best of our knowledge, have not been reported. In addition, the relevance of the above mentioned influencing factors and the fineness of grinding up to specific surface areas of 800 m2/kg, GGBFS basicity, and pre-hardening time on the property evolution and their dependence on the activity of the blending materials is not completely known. In the present study, we have studied the effect of the typically physically active blending materials, such as silica sand, which is physically active and reactive, fly ash and reactive mineral additions, and microsilica on the properties of fresh and hardened pastes of AASBCs. In addition, we have also attempted to determine the significance of the influencing factors on the property evolution of AASBC. Further, we have attempted to describe the main structural characteristics of AASBCs depending on the activity type of the blending materials.

2. Experimental

The starting materials were ground granulated blast furnace slags (GGBFS) from Orsko-Khalilovsky (GGBFS 1) and Chelyabinsky (GGBFS 2). Specific surface areas (Ssp) of the GGBFS were 300 m2/kg. As the blending materials were used industrial by-products of siliceous composition, which in accordance with the proposed classification, can be considered as physically active, physically active and reactive, and reactive i.e. ground used sand (GUS), ground fly ash (GFA), and microsilica MS (Table 1, 2). The GBFSs, used sand (US), and fly ash (FA) were ground in the laboratory planetary mill.

The alkaline activation of the mixed cement was carried out using a commercial sodium carbonate solution. The addition of the alkali activator was adjusted to 5 wt% (by Na2O) of the blended cement.

The AASBC cement pastes were prepared in cubic moulds (2 × 2 × 2 cm3), cement-sand mortars in prismatic moulds (4 × 4 × 16 cm3). The compressive strength of AASBC was measured after 1, 3, 7, 28, and 365 days of storage under normal conditions (room temperature, humidity 95–100%) and after steam curing regime for 4 + 3 + 6 + 3 h (four hours of pre-hardening time at room temperature, three hours of temperature rise time, six hours of constant temperature 90–95 °C time, and three hours of temperature decrease time).

N. R. Rakhimo

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N.R. Rakhimo

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2b

2c

compressive snt of GUS, and cditions, b) GGBring.

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trength of AAScuring conditionFS1, steam cut

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F

ctural characteri ossible GUSGUS) is the

Figure 2, thmanifested Ssp(AASBC-2

ttributed to sarticle redmorphizationnergy. Secorain-size comount of pand is moreround from 2

The grain-sizef 300 m2/kg articles with

ntroduced [1ptimum distrength of effective conhe dispersionGGBFS up to

t the level oontent of GU

The pplicability

materials is tevelopment.

ndicate that GUS (Ssp = 5trength. Saardened 3–7f the referetrengths of ays are verytrengths of he referencefter one yeample and Figure 4).

ig. 3. - DeveloAASBC28 day

istics of alkali-ac

S content ande fineness ohe positive when Ssp

2,3,5-8) by several reas

duction lean and incondly, there imposition ofarticles smal than 30% 200 to 500-8e distributionis not optim

h sizes les18]. Introdupersion incrthe harden

ntent of GUSn of GUS ano 50%, whileof the refereUS = 0–50%)important

of suppltheir effect o. The resulthe substitut500 m2/kg) ramples of 7 days show ence samplethe blended

y close to ththe samples

e value. An iar is 10.8–3

18.4–48%

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ctivated slag-ble

d its influencof GUS. On

influence exceeds

1.6 times. sons. First, tds to su

creases theis an improvf the mixed ller than 5 µ[17] when

800 m2/kg (bn of the GGBmum and imsser than ction of GUreases the ned paste

S = 0–30%) dnd allows to se maintainingence sample). characteristementary

on the long-tts in Figuretion of GGBreduces the

the blendstrengths lo

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for blend

e compressive on to the refer

days (b).

ended cements

ce on AASBCthe basis oof GUS i

the GGBFSThis can bthe GUS sizurface layee superficiavement in thcement. Th

µm increasethe GUS i

by 4.5 timesBFS at an Ss

mproves whe20 µm ar

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depending osubstitute thg the strengte (permissibl

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eference, andays excee

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strength of thence up to afte

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N. R. Rakhimo

Fig. 4. - Incremdepenadmix

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AA

AA

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ASBC(MS)-0

ASBC(GFA)-0

ăţile şi caracteris

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ukhovsky [1l. [22] AASC

se and unifoween the am to indicate

Fig. 5 - Sca

of AASBC

C(GUS)-0 C(MS)-0

C(GFA)-0

Strength cha

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year of the AASions and type

19], Shi et C materials aorm interfacggregate anthat the

anning electron

Experimental cGGBFS

GGBFS1 GGBFS1 GGBFS1

racteristics of th

pressive strength(MPa)

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r lianţi micşti cu

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The efffficiency of t

> (GGBFS baGUS = 0.9–1

The comortars AAShe maintenahe level of thn the bendintrength/bend

3.2. Physical

The inresh paste

The adhe water requ

ardened AASBC

he AASBCs Conten

admixtur303

30

ASBCs mortars

ng strength (MP

7.1

6.2

10.1

10.7

zgură, activaţi a

g of the inte(GUS) wito the

. Figure 5 hardened Anterfacial zofect of the inhe GUS folloasicity, curin.14.

ompressive aBC(GUS)-0

ance of the he referenceng strength ading strength

lly active anfluence of t

dition of GFAuirement and

C(GUS) paste.

nt of re, %

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15

s (steam curing)

Pa) Compre

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erfacial transith time s

long-term shows the

AASC(GUS) ones in betwenfluencing faows the ordeng conditions

and bending(Tables 4 acompressive

e sample andand ratio of

h.

nd reactive Gthe GFA on

A results in ad this increas

Ssp of the admixture

500 000-25000

500

) essive strength/

strength

6.2

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5.8

5.3

10

sitional zone substantially

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paste, GUS een. actors on th

er: Ssp of GUSs, etc.), Fe o

g strengths oand 5) showe strength ad a decreascompressiv

GFA n the AASBC

an increase ise depends

Table 4

Table

/ bending

09

e S of

of w at e e

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110

on the amsetting timeSsp of 200, 5by up to 1.5

Influe

hardened pIn ge

basicity andof Na20 5%is added tGGBFS ispolymineralcombine thparticles of blending mdifferent sizlarge sizes and are ablended AAGFA on thon the Ssp, is shown in 200 m2/kg ("physical acincrease in(AASBC-9,10,13,16) pozzolanic

Unlik(GUS), GFAwhich is 1,5when steamThe permiswhen the comparabledepending curing is usof 200 to 50of particles the solubiliinteraction w

Fig.6 - Th

mount and fes of the AA500, and 8005, 3, and 4 tim

ence of thpaste eneral, glassd slow reacti

% compared to GGBFS, s diluted. l- and quare qualities o

glassy GFmaterial (quzes). The GF

in the first additional aASBC(GFA)ce strength ocuring condFigure 6. W

(AASBC-11,1ctivity" of n the Ssp fro12,15) and facilitates

reaction of thke physicallyA exhibits ph5 times lowem curing is ussible conten

strength e to that of thon the basic

sed. The grin00 and 800 mof sizes beloty of GFA with the mine

N.R. Rakhimo

he dependence

fineness of ASBC(GFA) w0 m2/kg was mes, respect

he GFA on

sy class F Gon to alkali ato GGBFS [2the main

However, rter-phase Gof the reactivFA) and phartz and muFA particles

stage procealuminosilicacement. Theof AASBC(Gditions, and G

When a GFA w14) is

GFA predom 200 m2/k

800 respectthe appea

he GFA. y active blenhysical activer than that osed (AASBC

nt of GFA ofof blende

he reference city of GGBFnding of FA m2/kg increaow 5 µm by min the basiceral matrix of

ova / Properties

of the strength

the GFA. Twhen GFA wused increa

tively (Table

n the AAS

GFA has a at concentra23]. When Gcomponent unequigranuGFA (Tableve additive (hysically acullite particleof medium eeds are fil

ate sources e effect of

GFA) dependGGBFS basiwith a low Ss

used, dominates. kg to 500 m2

tively (AASBarance of

nding materity at a low of GGBFS, o

C-11) (Figuref Ssp 200 m2

ed cement can reach 5

FS when steto reach an

ases the contmore than 30c medium, af the AASC

and microstruc

of AASCs (GFA

The with sed 3).

SBC

low tion

GFA i.e.

ular, 2) fine

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in the

ding icity sp of the An

2/kg BC-the

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is 50% eam

Ssp tent 0%, and

[2A(AucatethhaGcsm

pmsoTap

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ctural characteri

A) on the curing

2,23,24]. AnAASC mixed AASBC 9,10p to 62%, during conditilso become

emperatureshe incremenigher and is nd in norma

GFA contentonditions onimilar to th

materials - SCThe pr

hases in GFmineral matrixize at high tef the effect o

These factorsnd basicity roperties of b

Increasours to 16 hontent and are-hardeningf silica in Aardening, w

he thresholdxide from

ntergranular maintains theufficient higemperature,lassy phase

han the disecreases to

With increaseme from 2 tof AASBC (G

istics of alkali-ac

conditions, Ssp

n increment with GFA o

0,12,13,15,16depending onons, and Ssp

es much mothan at ro

nt in strengtup to 62% a

al conditionst of 20-25%n the stren

hat of blendCM. resence of thFA, the increax when the Gemperature iof GFA on ths contribute

and curinblended cemse in the prhours allowsaffects the stg at room teAASBC (GF

when the admd value, a ce

the GGBspace. This

e pH into tgh level. the release

e increases solution of a crucial lev

e in the durao 16 h, the GFA) increase

ctivated slag-ble

, and GFA conte

in the streof Ssp of 506) at contenn the basicitp of GFA (Fiore reactive

oom temperath after steaat GFA contes (28 days) u%. The effength of AASded OPC w

he crystallinase in the soGFA particlesnfluence the

he AASBC(Gas much asg condition

ments. re-hardening s an increasetrength (Figuemperature, FA) is low. mixture contertain amouFS liberate

s calcium oxthe binder With incre

e rate of silicsignificantly GGBFS, an

vel at lower ation of the pGFA content es (Figure 7)

ended cements

ent.

ength of th00–800 m2/knt 20-30% ity of GGBFSgure 6). GFA at elevateature; henceam curing ient of 25-30%up to 17% aect of curinSBC(GFA) iwith siliceou

e and glassolubility in ths decrease i

e dependencGFA) strengths GGBFS Sss affect th

time from e in the GFAure 7). Durin

the solubilitDuring pre

tent is belownt of calciumes into thxide probablsystem at ase of thca from GFAmore rapidl

nd pH valuGFA contenpre-hardenin

and strengt.

e g s

S, A d e, s

% at g s s

sy e n e

h. sp e

2 A g ty e-w m e y a e A y e t. g h

N. R. Rakhimo

Fig. 7 - The

(GGhar

The

(GFA) abrucontent (Fiare steam Thus, the and GFA aGGBFS, pacritical cotransformatparticles ofcaused by content of binder systAASC promglass in GFsimultaneoudepolymerizthe total reaa pH < 8, thwith an incrup to 11 to pH increaseand [Si(OHand is eapolycondenInitially, theand then wdecrease interconnecacid gel [26 OH

OH – Si – OH

OH

OH

HO - - Si – O

OH

ova / Proprietă

e dependence GBFS1, GFA 80rdening time.

strength ofuptly decreagure 6), espcured and appropriate re limited, dearticle size oncentrationtion to orthof hydrated s

the mutual glassy silica

tem of AASmotes the r

FA [25]. The sus processzation [26], waction: (SiO2he solubility orease in the 25 times. T

es because H)6]2- [27]. Oasily conve

nsation evene chain polywith an incof рН v

cted by the 6-28] accordi

OH

H + OH – Si – O

OH

O H

n+2

ăţile şi caracteris

of the stren00 m2/kg, steam

f blended ases at a pecially whewhen the Sconcentratio

etermined byof GFA, cu of silic

osilicic acid-silica. Hypoth

conditionala and pH ofBC. High-alreactivity of solubility of sses of hwhich can b2)n + 2nH2O of silica is 2

pH, the soluhe solubility of the forma

Orthosilicic aerted into an in very dycondensatiocrease in covalue, the formation o

ng to the foll

OH OH –

-H2O

sticile microstru

ngth of AASBCm curing) on the

binder AASparticular G

en the sampSsp >500 m2

ons of GGBy the basicityring conditioca, and -bound collohetically, thisity of threshf the hardenkali mediumaluminosilic

silica consisthydration be described↔ nSi(OH)4× 10-3 mol/L aubility increaof silica at h

ation of Si(Oacid is unstaa polymer dilute solutioon takes plaoncentration

chainsof a polysiliowing reacti

OH OH

– Si – O – Si – O

OH OH

cturale ale unor

C-13 pre-

SBC GFA ples /kg.

BFS y of ons,

its oidal s is hold ning

m of cate ts of and

d by 4. At and

ases high

OH)4 able

by ons. ace, or are con on.

oS8HApti

resinethodcvthccccScinbdlocreinthowFoSccmAa

OH +

r lianţi micşti cu

Undissrthosilicic ac

SiO44- is the m

–11.71 orthH3SiO4

- and wAccording to

olymerizingme accordin

O

HO – Si – OH

OH

The seactive aluignificant a

ntergranular ntrance of a

he disruptionf the liquid ecline. Wheertain level,ery short pehe hardeningolloidal partompressive omparison ontent is

Simultaneousalcium oxide

n the рН. Talance in thepend on th

owering of thontent is loequired for nsufficient fohan the criticcur and the

with the formFigure 6, it ca

f FA to achiSsp of GGBFonsiderable haracteristic

m2/kg is sufficAASBC(GFA)

ctivated by s

+nSi(OH)4 -nH2O

zgură, activaţi a

ociated H4Scid existencemajor form ohosilicic acidwith an ion H[29], monom(condensingg to the follo

H HO –

small GFA uminosilicateamount of spaces of th

an acid oxiden of the acid-

medium ofen the pH o

the silicic aeriod and theg cement pticles of hyd

strength sto the sam

lower thasly, the exe (basic oxidThus, the che liquid phas

he influencinghe рН of the ower than the silicic a

or decrease ical value, pe mixed cem

mation of a han also be oieve a Ssp >

FS is 300 mimprovem

s of GFA-AAcient and is t) based on nsodium carbo

alcalin

SiO4 is the me at pH = 8;of existence d is in equ

H2SiO42- at pH

meric H3SiO4-

g) in a very sowing schem

O O

– Si – O – Si –

OH OH

particles ce glass i

silicic acihe hardeninge (silicon ox-base balancf the ceme

of the solutioacid ions poe intergranuaste is filled

drated silicasignificantly mples in whan the cxtraction frde) promoteshanges of thse of GFA-Ag factors of medium. W

the permissacid formatithe pH at a

polymerizatioment fresh phigh-strengthobserved tha

500 m2/kg, m2/kg, fails

ment in thASC. Hence,the upper limneutral and aonate.

11

major form o; at pH = 12[27]. At pH

uilibrium witH = 11.71–12- is capable ohort period oatic process

O

– O – Si – OH

OH

consisting ointroduce id into th cement. Th

xide) leads tce and the pHnt begins t

on reaches lymerize in lar spaces od with boun. Hence, th

worsens ihich the FAcritical limiom GGBFSs an increashe acid-basAASC systemboth rise an

When the GFAsible amounon, which ia lower leveon ceases taste harden structure. It the grindinalthough thto lead to he strengt, Ssp of ~ 50mit for GFA iacid GGBFS

11

of 2, = h

2. of of .

of a e e o H o a a of d e n A t. S e e m d A nt s el o s n g e a h 0 n

S,

112

GGBFS

GGBFS 1

GGBFS 2

Content oAASB

01357

1020

With compressivintroductionstrength, aGUS (Figurthe strengthof the referyear, AASBand AASBC

Comreactive supermissibleThe resultstrength ofreplacemenin the casesupplementof the mainSsp of the depending o

For pinfluencing the followinGGBFS bas

The AASBC(GFThe additiocompressiv 3.3. Reacti

The iMS h

paste. The up to 20% 19.4% (Tabresults obtaOC-based s

Curing conditions

normal conditions

steam curing

normal conditions

steam curing

of MS in BC, %

0

3 5 7 0 0

regard to ve strengthn of GFA lealthough lessre 3). Howevh of GFA-AArence after 2BC(GFA) is sC(GUS). bining the q

upplementarye and effectivs illustrate f the AASCnt of GGBFSe of blendedts increases n constituenadditives. T

on its Ssp. physically acfactors affe

ng order: (Sssicity) > pre-

strengthFA)-0 mortarsn of 30% of

ve and bendin

ive MS influence of Mhas a plastic

water requidecreases fble 7). Thisained by Kosystems, the

N.R. Rakhimo

up to

g up

u

g u

Ch

Normal consistency,

% 24.9 23

20.8 19.5 19.0 18.8 18.7

the develoh of AASds to a dimin

ser than thatver, by introdASC is nearl28 days agesuperior tha

ualities of thy material, Gve replacem

that GFA C and can S by up to 50d OPC, the e

with increasnt, curing teThe Fe of G

ctive and react the efficiesp of FA, cuhardening tim

h characs are presenGFA to AASng strength o

MS on AASBcizing effect orement for a

from 24.9–25s is in agreeorolev [30]. e introduction

ova / Properties

Ranges of repla

effeco 40-50% (FA S

p to 50% (GFA S

p to 30% (GFA

p to 30% (GFA

aracteristics ofGGBFS1Setting ti

initial

1-20 1-10 0-45 0-45 0-40 0-40 0-45

opment of BC(GFA),nish of the et determinedduction of Gy similar to te and after on the refere

he filler and GFA can be

ment of GGBincreases

be used as% (Table 6).effectiveness

se in the basimperature,

GFA is 0.9–

active GFA,ency of GFAuring conditiome. cteristics nted in TableC increases of the mortar

BC fresh pason AASBC(Madditions of 5.8% and 18ement withAs opposed

n of MS into

and microstruc

acement of GGBRanges of the

ctive Ssp 500-800 m2/k

Ssp =200 m2/kg)

Ssp 800 m2/kg)

Ssp 200 m2/kg)

fresh paste of t

ime, hour-minut

final

3-503-402-502-302-101-502-00

the the arly d of US, that one nce

the e a

BFS. the

s a . As s of icity and

–1.6

the A in ons,

of e 5. the

rs.

ste MS) MS

8.7–the

d to

AaNwM

p

ssta

F

stchA

ctural characteri

BFS by GFA e replacement G

kg)

)

he AASBCs wit

te Noconsis

%

25 23 21 19 19 19 19

AASC doesssume that

Na2CO3 solutwater releaseMS.

The inpaste

MS, dignificant potrength of And Table 4).

ig. 8 - The dep

content For rea

trengtheningonditions, tardening tim

AASBC(MS) b

istics of alkali-ac

GGBFS by GFA p

u(GFA Ssp

u(GFA Ssp

th MS GG

rmal stency, %

S

5.8 3.9 1.5 9.9 9.7 9.5 9.4

not increathe interact

tion binder sye, leading to

nfluence of M

ue to its hositive affec

AASBC(MS)

pendence of the, curing conditio

active MS, thg effect is dhe basicity

me. The varbinders with

ctivated slag-ble

ermissible

-

up to 30% p =500-800 m2/k

-

up to 30% p =500-800 m2/k

GBFS2 Setting time, hou

initial

0-50 0-40 0-30 0-25 0-25 0-25 0-35

ase water dtions in the ystem resultso a plasticiz

MS on AASB

high reactivct on the binders (Fig

e strength of AAons, and GBFS

he optimum determined b

of GGBFSriation of thethe MS cont

ended cements

Table 6

kg)

kg)

Table

ur-minute

final

3-00 2-50 2-30 2-20 2-10 2-10 2-30

demand. WGGBFS-MS

s in the “freezing effect o

BC hardene

vity exerts compressiv

ures 8 and

ASC(MS) on Mbasicity.

addition anby the curinS, and pree strength otent

7

e S-e” of

d

a e 9

S

d g

e-of

N. R. Rakhimo

Fig. 9 - The

AAS resembles binders withThe GGBFSa 37% instrength ofconditions wis 27% wheThe upperAASBC(MSfor binderscarried out (MS) bindeunder steacompressivMPa with 4on GGBFSwith 3% MS

The sfor diminishexhibits strbinders. Foseven daysbinders arerespectivelysample. Aftof AASBC(reference AAASBC(GFstrength in the consideAASBC - (M4.1 % for cu

For hof MS, theconcentratio4% with stecuring condsolubility oencounterenormal coinfluencing MS-AASC conditions time. The va

ova / Proprietă

dependence SBC (MS)-17 on

the gradatioh GFA conteS1 is more bcrease is f MS-AASCwhen GGBFen GGBFS2 wr limit of

S) binders bs based on

under normers based oam, the adve strength in4% MS conte 2, the incre

S content). strengtheninh the dosagerengthening or early age os, the compe higher wiy, in compater 360 days(MS) bindersAASC, the

FA). Howevepercentage f

ered binders MS) cured uuring under shighly reactivere are onons. The effeam curing ditions. This of MS silicad during ste

onditions. Tfactors on tbinders fo

> basicity oalue of Fe of

ăţile şi caracteris

of the strengthn the pre-harden

on of that oent of Ssp = 5basic than Gseen in th binders cuS1 is used awas used (FMS conte

ased on GGGGBFS2 w

mal conditionon GGBFS1dition of Mncrease of uent ) and for ease is up to

g effect of Me of the alkaeffect on th

of hardeningpressive streth up to 1arison with s, the comprs outbalancebinders AASer, the incfrom 28 daysis minimum:nder normal

steam (Figurve additions,ly certain efective AASCand upto 7%is explained

a at higheeam curing tThe significthe compresollows the of GGBFS >

MS is up to

sticile microstru

h of AASBC (ning time.

of AASBC(G500–800 m2

GBFS2. Hene compressured in norand the increigures 8 andnt is 7%

GBFS1 and when curing

ns. For AASB1, when cu

MS leads top to 105% (samples ba

o 60% (98 M

MS can be uali activator. he AASBC(M three days

engths of th05 and 50

the refereressive strenes those of SBC(GUS) a

crement in s to 360 day: about 28 %l conditions ae 4). , as in the ceffective AAC quantities % under nord by the higr temperatuthan that uncance of sive strength

order cu> pre-harden1.9.

cturale ale unor

(MS)

FA) /kg. nce, sive rmal ase

d 9). for 5%

g is BC-ured o a 115 sed

MPa

sed MS

MS) and ese %,

nce ngth the

and the s of

% for and

case ASC

are rmal gher ures nder

the h of ring ning

3

3

cfrareainAc8ininasepthGmfainAinre3

cafoinOthfoztrthregmhemtr

3

FAcastcp

2(GG

r lianţi micşti cu

3.4. Structustructof the

3.4.1. AASBCDespite

hanges the rom the momn alkali activeact with alknd Na2O to

ncrease in cAASC. Introdoncentration%.The incre

ncreases then the initial stre maintainupplementarrosion of throlongs the

he eroded sGUS has a himatrix of AASacilitate the nterfacial zoAASBC (GUSndirectly conesults of AAb).

Studiesement freshctivated slag

ormation of nterfacial traOPC. Also, trhe results oormation of one. Evolutransitional zohe adhesionelease of thradual eros

mineral matrardened palements (Fig

matrix of Aransitional zo

3.4.2. AASBCPolymi

FA causes aAASBC (GFAonsisting of ffects the tages of haomponents article size a

Since G9% - quartzGFA) with an

GGBFS ratio

zgură, activaţi a

ure formatiture types, ae AASBC haC(GUS) binde the low hardening p

ment of the mvator solutionkali, the alkalo (CaO, SiOomparison w

duction of 3n of Na2O beased contee activation atages of hardned over ry alkali amohe GUS pardevelopmenurface of thgh adhesion

SC. In the prfaster form

one during S) hardenednfirmed by thASBC (GUS)

s on the inteh paste andg mortars [2

the strongansitional zoraces of che

of our studiea developin

tion of thisone over timn strength, he surface Gsion at the ix. The struaste consisgures 5, 10AASC, the one, and the

C(GFA) bindneral and p

a more comA) hardened

a larger nustructure fo

ardening andat every sta

and its structGFA containsz and mulliten alkali solutslightly incre

alcalin

ion procesand structurdened pas

ders chemical a

process of AAmixing of GUn. Because Gi solution to

O2, and Al2Owith that of t30% GUS inby GGBFS

ent of alkali and dissolutiodening and ttime. In a

ount increaserticles, and

nt of this proce mechanic

n strength witrocess, the Gation of hydthe later st paste formhe developm) up to 360

erface betwed quartz sa20, 31] haveg, dense,

ones in comemical reacties seem to ng interfacias developin

me causes awhich is be

GUS particlehigh рН o

ucture of AAsts of threa), including

developinGUS particle

ders polyphase coplicated formd paste withumber of eleormation prod the particiage dependsure. s crystalline e), when mtion, the alka

eases. This in

11

ss featuresural elementtes

activity, GUSASBC (GUS

US-AASC witGUS does noGGBFS rati

O3) the ratithe referencncreases thfrom 5% tmetal oxid

on of GGBFSthe conditionaddition, thes the surfac

the high pHcess. Clearlyally activateth the mineraGUS particledrates in thtages of thation. This i

ment strengtdays (Figur

en the AASCand in alkale showed thand uniform

mparison witions [21] an

indicate thal transitionang interfacian increase iecause of

es caused bof the AASCASBC (GUSee structurag the minerag interfaciaes.

omposition omation of thh a structurements. GFAocess at apation of th

s on the GFA

material (22ixing AASBCali solution tntensifies the

13

s, ts

S S) h ot o o e e o e S s e e H y, d al

es e e s h

re

C i-e m h d e al al n a

by C S) al al al

of e

re A

all e A

–C o e

114 N.R. Rakhimova / Properties and microstructural characteristics of alkali-activated slag-blended cements

a) b) c) Fig. 10 - Structure types and structural elements of the AASBC hardened paste with physically active (a), physically active and reactive

blending materials (b), and reactive supplements (c). 1 is GUS, 2 and 5 are the developing interfacial transitional zones, 3 is the mineral matrix of AASC, 4 is the crystalline GFA particle, 6 is the amorphous GFA particle, 7 is the interpenetrating interfacial transitional zone, and 8 is the skeleton.

gradual hydration and dissolution of GFA in the early stages of hardening and the continuation of this process during the time with GGBFS and GFA particles of larger sizes. GFA particles of sizes >5 mm, together with the crystalline GFA grains can act as nucleation sites for the reaction products. During the time, there is gradual loosening of the surface of the GFA particles, resulting in the erosion of the interfacial transitional zone, expansion of interpenetrating constituents, including the GGBFS and GFA-based hydration products. Corrosion of the surface of GFA particles after one day of hydration and hydration products at the edge around the GFA particles containing amorphous alkaline aluminosilicate hydrates have been observed before [32, 33]. Hence, the interfacial transitional zone between the AASC fresh paste and GFA particles of glass structure can be called as "interpenetrating.” The slower reaction with the alkali component in comparison with GGBFS and the strengthening over time of the two types of interfacial transitional zones (developing and interpenetrating) create favourable conditions for strength increase of AASBC(GFA) binder at long periods of time (Fig. 3b).

GFA particles with sizes < 5 µm exhibit high reactivity even for early stages of AASBC (GFA) binder hardening. It is assumed that the amorphous silica dissolved from the GFA glassy phase removes the Са2+ from the GGBFS grains. The extraction of Са2+ from GGBFS to the solid phase shifts the chemical equilibrium between the oxides in the direction of maintenance of a high concentration of Na2O, resulting in the latter continuing to activate the GGBFS to achieve the equilibrium conditions of the component concentrations, typical for reference AASC. In addition, as a result of the cation exchange 2Nа+ → Са2+ in the liquid medium, caustic alkali is formed. There is a strong possibility that this alkali reacts with amorphous silica with sodium silicate formation, the anionic constituent of which is similar to the primary products of dissolution in the alkali aluminosilicate source, which serves as their

additional reserve. Krivenko [34] has observed that the chemical activity of GGBFS is defined by the amount of vitreous phase and рН and also the presence of the additives, which are capable of reacting with the hydrolysis products of the GGBFS glass and forming a crystalline skeleton of the hardened cement hardened paste. It is probable that GFA increases the reactivity of GGBFS. The introduction of GFA may lead to the additional activation of GGBFS, increasing the concentration of dissolution products of the starting materials and the volume of low-basic calcium silicate hydrates at the early stages of the hardening process, which reinforces the mineral matrix of AASC hardened paste and results in increased compressive and bending strengths (Table 3). Thus, the structure of the GFA-AASC hardened paste consists of three structural elements (Figure 10b) including, the mineral matrix with reduced basicity of the hydration products [21], a developing interfacial transitional zone, an interpenetrating interfacial transitional zone, crystalline, and amorphous FA particles. Figure 11a shows partly reacted fly ash particles in the volume of the binder gel, interfacial zone. 3.4.3. MS-AASC binders

МS shows extremely high reactivity, showing reactivity from early stages of hardening of AASBC (MS) binders. The MS action mechanism is analogous with those of the FA fine particles consisting of aluminosilicate glass (Figs. 6–9). The reactive MS binds with Ca2+ solubilised from GGBFS in the calcium silicate hydrates [30], forming a reinforcing skeleton of AASBC(MS) hardened paste. Figures 11b,c show that this skeleton penetrates the binder gel. Hence, the AASBC(MS) binders show the highest compressive and bending strength characteristics of AASBCs from an early stage of hardening.

The structure of AASBC (MS) hardened paste consists of structural elements (Figure 10c) including the mineral matrix with reduced basicity of the hydration products and the skeleton.

1 2 3 45 6 7 8 8

N. R. Rakhimova / Proprietăţile şi caracteristicile microstructurale ale unor lianţi micşti cu zgură, activaţi alcalin 115

a

b

c

Fig. 11 - Scanning electron images of the hardened AASBC

hardened pastes a) and b) AASBC (GFA), and c) AASBC (MS).

4. Conclusions The results of the study are summarized in

the following conclusions. 1. The effect of the siliceous mineral

supplementary materials on the properties of fresh and hardened AASBCs properties depends on the activity, content and fineness of blending materials (GUS, GFA, MS), GGBFS basicity, curing conditions, and pre-hardening time.

2. The admixtures GUS, GFA (class F), and MS are effective for strength improvement of AASBC based on neutral and acid GGBFS, activated with sodium carbonate solution. The effectiveness factor values for GUS, GFA, and MS are 0.9–1.14, 0.9–1.6, and 1.9, respectively.

3. GUS and GFA are also effective for GGBFS replacement up to 50% in AASBC. Appropriate Ssp of GUS for AASBC is higher than 500 m2/kg and the upper limit of Ssp of GFA is 500 m2/kg.

4. The influencing factors affect the strength of the AASBC in the following order:

- When introducing GUS - Ssp of GUS > (GGBFS basicity, curing conditions, and pre-hardening time).

- When introducing GFA - (Ssp of GFA, curing conditions, GGBFS basicity) > the pre-hardening time.

- When introducing MS - curing conditions > basicity of GGBFS > pre-hardening time.

5. The structural elements of AASBCs hardened pastes are as follows:

- With physically active blending materials (i.e. GUS), the elements are the mineral matrix of AASC, particles of blending material, and the developing interfacial transitional zone.

- With physically active and reactive blending materials (i.e. GFA), the elements are the mineral matrix of AASC, particles of crystal and amorphous structure of the blending material, developing and interpenetrating interfacial transitional zones, and skeleton.

- With reactive admixtures (i.e. MS), the elements include the mineral matrix of AASC and the skeleton.

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