Construction and Building Materials 37 (2012) 758–765

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Construction and Building Materials

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Comprehensive study of fly ash binder developed with fly ash – alpha gypsumplaster – Portland cement

Mridul Garg ⇑, Aakanksha PundirEnvironmental Science & Technology Division, CSIR-Central Building Research Institute, Roorkee 247 667, India

h i g h l i g h t s

" A high strength fly ash binder is developed using fly ash and other industrial wastes." Hydration process and morphological behavior of binder studied by DTA, XRD and SEM." Strength development of binder takes place through formation of AFt and CSH phases." Durability studies show absence of leaching of the matrix in the binder." Binder used in masonry mortars, bricks and concrete by partial replacement of cement with it.

a r t i c l e i n f o

Article history:Received 27 July 2012Received in revised form 14 August 2012Accepted 17 August 2012Available online 13 September 2012

Keywords:Fly ashHydrationCompressive strengthScanning electron microscopyX-ray diffractionDurability

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.conbuildmat.2012.08.018

⇑ Corresponding author. Tel.: +91 1332 283298; faxE-mail address: mridul_est@rediffmail.com (M. Ga

a b s t r a c t

In this study, a new type of fly ash binder has been developed using fly ash, hydrated lime sludge andPortland cement, as well as a-gypsum plaster as stimulator. The hydration process and microstructureof the fly ash binder was investigated with differential thermal analysis, X-ray diffraction and scanningelectron microscopy. These studies showed that the strength development of binder takes place throughformation of ettringite and tobermorite. The durability of fly ash binder was assessed by its performancein water by immersion and by alternate wetting and drying cycles at 27–50 �C. The results reveal absenceof leaching of the matrix in fly ash binder as well as reduction in strength and enhancement in weight losswith the increase in temperature and cycles. The fly ash binder is found suitable for use in masonry mor-tars, concrete and bricks.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

In developing countries, the consumption of Portland cementmust be limited as it consumes high energy, destroys the ecologicalenvironment and brings us a serious green house effect. Largequantities of industrial by-products are produced every year bychemical industries in India. Among various industrial wastes pro-duced so far, the utilization of waste products such as fly ash, phos-phogypsum, fluorogypsum, and lime sludge, as cementitiousmaterial is to be encouraged to reduce the environmental impactsof waste accumulation and CO2 emission from the production ofPortland cement. The wastes with potential to replace Portland ce-ment in various applications should be investigated to take benefitof the economical and environmental advantages involved.

In India, about 100 million tones of fly ash is produced as finelydivided by-product from the combustion of pulverised coal in sus-

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: +91 1332 272272.rg).

pension fired furnaces of thermal power plants. It is collected byelectrical or mechanical precipitators or cyclones and comprisesof rounded glassy particles of variable chemicals and mineralogicalcompositions. The properties of fly ash show variation and dependupon numerous factors, such as the composition of coal, flametemperature, oxidation conditions and mode of collection of flyash. Several countries and organisations have their own standardspecifications and requirements for fly ash to be used as mineraladmixture or as pozzolana. ASTM C 618-89 [1], defines the pozzo-lana as ‘‘siliceous or siliceous and aluminuous materials whichthemselves possess little or no cementitious value but in finely di-vided form and in the presence of moisture chemically react withCa(OH)2 at ordinary temperature to form compounds possessingcementitious properties’’. Physical and chemical properties of flyash play an important role in imparting the pozzolanic reactivityand in the production of cement mortar and concrete. Most ofthe fly ash particles are glassy or amorphous. Yet the minerals likequartz, mullite, magnetite, crystoballite, haematite and calciumcompounds including calcium sulphate may be present as crystal-

Table 2Physical properties of fly ash and Portland cement.

No. Property Fly ash Portland cement

1 Fineness (m2/kg Blaine) 320 3302 Lime reactivity (N/mm2) 4.8 –3 Setting time (min)

Initial – 96Final – 240

4 Compressive strength (MPa)3 days – 25.07 days – 39.628 days – 50.5

5 Soundness, Lechatlier expansion (mm) – 1.5

Fig. 1. XRD of fly ash sample (Q: Quartz, Mu: Mullite, H: Hematite, M: Magnetite,AN: Anhydrite, L: Lime).

M. Garg, A. Pundir / Construction and Building Materials 37 (2012) 758–765 759

line compounds constituting about 15.0% by weight of the fly ash.Some of the carbon in coal particles does not burn properly andthus fly ashes also possess unburnt carbon. Not more than 25% offly ash is being used in India at present. The major reasons for lim-ited utilization of fly ash in India may be due to non-availability ofquality grade fly ash and its less reactivity compared to foreign flyashes.

A number of studies using different activating methods includ-ing alkali activation and sulphate activation had been carried outfor the activation of fly ash [2–5]. Among different ways of flyash activation [6], the addition of gypsum was found suitable forfly ash–cement blends. The use of fly ash in concrete has attractedmuch research interest in recent years and various workers [7–11]suggested that interaction between sulphate and fly ash formsdenser structure of ettringite and monosulphoaluminate hydratethat fills pores in the paste and enhance the sulphate ressistanceof concrete. Considerable work has been done in China and otherplaces [12–16] to improve water resistance of binders based onfly ash, phosphogypsum/fluorogypsum and cement. Some compos-ite binders and prefabricated building elements based on chemicalgypsum and pozzolanic materials were studied for use in construc-tion [17–19]. Yan and Yang have suggested that a binder contain-ing low quality fly ash, fluorogypsum and Portland cement couldbe used in the manufacture of wall elements [20].

Besides fly ash, phosphogypsum; fluorogypsum; H-acid gypsumand lime sludge are known industrial wastes generated by thephosphatic fertilizer, hydrofluoric acid, intermediate dye industriesand sugar, paper manufacturing units in India. Extensive R&D stud-ies have been done at CSIR-Central Building Research Institute,Roorkee on the utilization of these wastes for making cementitiousbinders and building products [21–23].

Earlier studies have been carried out on b-hemi hydrate plasterand its use in the production of gypsum binder and plaster prod-ucts. However, the present study was focused on use of autoclavedgypsum plaster (a-hemi hydrate plaster) in combination with highfly ash content (up to 60%), cement and lime sludge for making flyash binder. In the present study, the physico-chemical propertiesand durability of fly ash binder was tested and discussed. Thestrength development and the formation of hydraulic productswas evaluated with the help of X-ray diffraction (XRD), differentialthermal analysis (DTA) and scanning electron microscopy (SEM).The suitability of fly ash binder for making masonry mortars, con-crete and bricks was studied and discussed.

2. Materials and characterization

2.1. Raw materials

The chemical composition of phosphogypsum, fly ash, Portland cement andlime sludge and physical properties of cement and fly ash used in the productionof fly ash binders are shown in Tables 1 and 2 respectively. The chemical composi-

Table 1Chemical composition of fly ash, phosphogypsum, lime sludge and Portland cement.

Constituents(%)

Flyash

Phosphogypsum Limesludge

Portlandcement

P2O5 – 0.24 3.60 –F – 0.20 1.00 –Organic matter – 0.02 – –Cl – – 0.10 –Na2O + K2O 0.76 0.03 – –SiO2 66.2 0.85 3.10 22.50Al2O3 + Fe2O3 28.35 – 0.50 9.60CaO 1.50 32.0 52.0 61.50MgO 0.80 0.05 0.31 2.65SO3 0.20 45.10 0.16 1.75LOI 1.50 20.5 41.0 2.00

tion of fly ash indicate that this fly ash can be classified as a low calcium fly ash(class F, according to IS: 3812-2003) [24]. This fly ash satisfies the chemical require-ments for use as a pozzolana because the content of pozzolana oxides (SiO2 + Al2-

O3 + Fe2O3) in it (94.55%) is greater than the minimum content (70%) for theseoxides required by IS: 3812. The mineral composition of fly ash determined by X-ray diffraction (Fig. 1) showed that the main crystalline phase in fly ash is quartz(SiO2) and other crystalline phases in small amounts are mullite, hematite and mag-netite. The lime sludge was calcined at 1000 �C for a period of 4 h to form limewhich was used after complete hydration.

2.2. Preparation and testing of alpha-gypsum plaster

Garg et al. [25] produced high strength a-gypsum plaster from phosphogypsumin which crystal modifier such as sodium succinate, potassium citrate and sodiumsulphate (less than 0.5% of the weight of phosphogypsum) were added during theautoclaving of gypsum followed by immediate filtration and drying at 130 �C. Withactivator, the optimum pressure and duration of autoclaving was found to be as 35psi and 2.0 h. respectively. The cubes of alpha plaster of size 25 mm were cast at35% consistency tested for different physical properties as per IS: 2542-2007 [26].The a-plaster attained a compressive strength 27–30 MPa, setting time 25–30 min and bulk density 1.2–1.3 g/cc.

2.3. Preparation of fly ash binder, its testing and evaluation

The fly ash binders were prepared by blending the fly ash with alpha-plaster,Portland cement and hydrated lime sludge according to the proportions shown inTable 3 followed by inter-grinding in a ball mill to a fineness of 400 m2/kg (Blaine).The fly ash binders were tested and evaluated for physical properties such as con-sistency, setting time, compressive strength and soundness as per methods speci-fied in Indian Standards [27,28]. The 25 mm cubes of fly ash binders were curedunder high humidity (>90%) at 27 ± 2 �C for different hydration periods up to28 days. The major hydration products responsible for strength development inthe fly ash binder with curing period were monitored by X-ray diffraction (RigakuD-Max 2200), scanning electron microscopy (LEO 438 VP, UK) and differential ther-

Table 3Mix proportions of fly ash binders.

Designation Mix composition (% by wt.)

Fly ash a-Plaster

Hydrated lime sludge Portland cement

B1 56 8 16 20B2 60 15 5 20B3 55 15 15 15B4 60 10 15 15

Table 4Physical properties of fly ash binders.

Properties B1 B2 B3 B4

Consistency (%) 37 35 37.5 38

Setting time (min)Initial 25 22 23 26Final 45 38 40 42

Compressive strength (MPa)1 day 5.8 8.8 9.5 7.23 days 7.7 14.2 13.1 11.37 days 11.5 18.3 16.1 12.728 days 24.7 27.5 22.3 17.3

Bulk density (gm/cc)1 day 1.45 1.48 1.46 1.503 days 1.47 1.49 1.48 1.527 days 1.48 1.50 1.50 1.5328 days 1.51 1.53 1.51 1.55

Soundness mm 2.0 1.80 2.1 2.3

Table 5Properties of masonry mortars prepared using fly ash binder ‘B2’.

Mix proportion (by wt.) Compressive strength(MPa)

Water retentivity(%)

3 days 7 days 28 days

Binder Sand (F.M 1.28)1 3 3.1 4.1 7.7 62.01 4 2.1 2.9 3.5 60.51 5 1.0 1.0 2.3 56.0Binder Sand (F.M 1.90)

1 3 3.6 4.9 10.0 67.01 4 2.8 3.6 6.7 62.51 5 1.0 1.6 3.4 59.0

Cement Sand (F.M 1.28)1 5 1.2 1.8 3.7 15.01 6 1.0 1.5 2.0 10.0

Cement Sand (F.M 1.90)1 5 1.4 2.7 4.2 22.01 6 1.0 2.5 3.8 16.5

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mal analysis (Stanton Red Croft, UK). The binder samples hydrated for different cur-ing periods were collected from the middle portion of the compressive strengthspecimens, dried and ground to pass 150-lm IS sieve for XRD, DTA and SEM studies.

2.4. Durability of fly ash binder

The 25 mm fly ash binder cubes hardened in over 90% relative humidity at27 ± 2 �C for a period of 28 days were subjected to durability test by determiningits behavior in (1) water and (2) wetting and drying cycles.

2.4.1. WaterThe cubes were dried to a constant weight at 42 �C and then immersed in tap

water for different periods. The water absorption was calculated using the followingequation as per the method given in IS: 2542.

Water absorption ¼ w1 �ww

� 100

where w is the weight of the specimen before and w1 is the weight of the specimenafter immersion in water. The following relation described by Singh et al. [29] is usedfor determination of porosity of fly ash binder:

Porosity ¼ w dsdw

where W is the weight loss, ds is the dry density of gypsum cement and dw is thedensity of water. The dry density in kg/m3 was obtained by dividing the weight ofthe specimen before water immersion by the overall volume (calculated on the basisof the dimension of specimen).

2.4.2. Wetting and drying cyclesThe hardened fly ash binder cubes were subjected to alternate wetting and dry-

ing cycles at different temperatures from 27 �C to 50 �C. One cycle of wetting anddrying comprises of heating the cubes for 16 h at different temperatures followedby cooling for 1 h and then immersing them in water for a period of 7 h [30]. Aftera certain number of cycles, the compressive strength and weight loss of dry cubeswere determined.

2.5. Preparation of masonry mortars

The fly ash binder was mixed with sand (fineness modulus 1.28 and 2.0) in dif-ferent proportions according to Table 5. The cubes of size 5 cm � 5 cm � 5 cm werecast at 105 ± 5% flow for compressive strength test and water retentivity of the mor-tar determined as per Indian Standard [28].

2.6. Preparation of concrete

Suitability of fly ash binder as partial replacement of Portland cement was stud-ied. In this regard, concrete cubes (150 mm) were cast as per Indian Standard [31],using 10% and 20% replacement of Portland cement by the fly ash binder, gravel(40% passing 20 mm and retaining 10 mm IS sieve plus 60% passing 10 mm andretaining 4.75 mm IS sieves) and Badarpur sand (fineness modulus 2.0) in the pro-portions 1:2:4 and 1:3:6. The water cement ratio was fixed at 0.5. The concretecubes were cured in water and tested for compressive strength.

2.7. Preparation of fly ash binder bricks

The bricks of size 190 mm � 90 mm � 90 mm were cast at 30% consistency byreplacing fly ash binder with different percentage of fly ash by vibration-compac-tion technique (vibration time 20 s). The bricks were cured at 27 �C under morethan 90% relative humidity, up to a period of 28 days, dried at 42 ± 2 �C and testedfor compressive strength, bulk density and water absorption.

3. Results and discussion

3.1. Properties of fly ash binder

The physical properties of fly ash binders are given in Table 4.Data show increase in strength and bulk density with increase incuring period in all the compositions. The strength developmentin binder ‘B2’ is higher than other compositions, probably due tolow consistency of binder ‘B2’. Although the fly ash binders possesslow strength in early ages, but with a satisfactory strength increaserate. The development of early age strength can be ascribed to thehydration of a-plaster to the gypsum and latter development ofstrength may be due to the pozzolanic reaction of fly ash andhydration of Portland cement. The metastable silicate present infly ash reacts with Ca2+ ions contributed by the hydration of Port-land cement and lime and form water insoluble calcium silicates(C–S–H), C4AH13 and aluminate hydrate compounds. Besides flyash, the cementitious binders contain a-gypsum plaster whichon addition of water releases SO2�

4 ions which further combineswith Al2O3 and CaO available in the aqueous phase and formsettringite (C3A�3CaSO4�32H2O). The interaction of fly ash with themoist lime and gypsum to form cementitious materials is shownbelow:

Fig. 2. X-ray diffractogram of fly ash binders ‘B1’ and ‘B2’ hydrated for 28 days.G = gypsum, E = ettringite, T = tobermorite, CH = calcium hydroxide, Q = quartz.

M. Garg, A. Pundir / Construction and Building Materials 37 (2012) 758–765 761

CaOþ fly ashþH2O! CaaAlb �CH2OCalcium aluminate hydrate

þ CaxSiy �2H2OCalcium silicate hydrate

ð1Þ

CaaAlb:CH2OCalcium aluminate hydrate

þCaSO4:2H2O!Gypsum

C3A � 3CaSO4:32H2OEttringite

ð2Þ

In the above equations a, b, c, x, y and z are the variables that aredependent on the temperature, pressure and molar ratios of thereactants. These hypothesis corroborate the findings of Yanget al. [32]. The fly ash binders were found sound as the cold expan-sion complied with maximum specified value of 5 mm given in IS:6909. The formation of C–S–H, gypsum and ettringite compounds,responsible for strength development have been monitored by X-ray diffraction, Differential thermal analysis (DTA) and Scanningelectron microscopy of the hydrated fly ash binder.

Fig. 3. Differential thermograms of fly ash binder ‘B2’ hydrated for (a) 7 days and(b) 28 days.

3.2. Hydration process of fly ash binder

The X-ray diffractogram of fly ash binders ‘B1’ and ‘B2’ hydratedfor 28 days are shown in Fig. 2. The XRD data showed quartz peakin both the fly ash binders, which is inherent to fly ash as well asnew crystals that result from the hydration reactions. The mostprominent peaks in the fly ash binders ‘B1’ and ‘B2’ were of ettring-ite at 21.5�, 28.5�, 41� and tobermorite at 29.8�, 35.5�, 43� and 51�.The peaks of gypsum were observed at 10.5�, 23�, 55� along withpeaks of calcium hydroxide at 18.5� and 39�. The intensity of cal-cium hydroxide peak is very less in binder ‘B2’ as compared to bin-der ‘B1’. It amply demonstrated that most of the lime in binder ‘B2’has been consumed by the pozzolanic reaction of fly ash. It can beseen that the intensity of peaks of tobermorite and ettringite of flyash binder ‘B2’is higher than binder ‘B1’.

The DTA of fly ash binder ‘B2’ hydrated for 7 and 28 days areshown in Fig. 3a and b respectively. Fig. 3a and b clearly indicatesthat endothermic peaks at 110–130 �C and 150 �C appear due toformation of ettringite and gypsum dehydration respectively.These ettringite endotherms are increased with curing and thegypsum endotherms are reduced probably due to the consumptionof gypsum by the increased formation of ettringite endotherms.Further, formation of small endotherms at 480–520 �C at 7 daysof curing are due to Ca(OH)2 which disappear at 28 days curing.The appearance of endotherms at 695–730 �C may be ascribed tothe decomposition of CaCO3. The formation of calcium silicate hy-

drate (CSH) peak is not visible possibly due to overlapping with theettringite endotherms. These results confirm that strength devel-opment in fly ash binder is due to ettringite, gypsum and probablydue to CSH phases.

3.2.1. Microstructural studies of fly ash binderThe SEM images of fly ash binders ‘B1’ and ‘B2’ hydrated for 7

and 28 days are shown in Fig. 4a and b and Fig. 5a and b respec-tively. In Fig. 4a it can be seen that at 7 days hydration, large quan-tity of agglomerated irregular euhedral to subhedral bodies ofrounded fly ash particles are coated with lime particles. In Fig. 4bthe fly ash spheres can be seen partially smeared with lime andgypsum crystals of prismatic and tabular shaped and the formationof euhedral CSH crystals coated with partially hydrated fly ashspheres. Fig. 5a illustrate the formation of subhedral to anhedralcrystals of tobermorite, agglomerated with cubic crystal ofCa(OH)2. Occasionally, gypsum crystals of prismatic and columnar

Fig. 4. Micrographs fly ash binder ‘B1’ hydrated for (a) 7 and (b) 28 days.

Fig. 5. Micrographs of fly ash binder ‘B2’ hydrated for (a) 7 and (b) 28 days.

Fig. 6. Effect of water immersion on the water absorption of fly ash binders.

Fig. 7. Effect of water immersion on the porosity of fly ash binders.

762 M. Garg, A. Pundir / Construction and Building Materials 37 (2012) 758–765

habit are conjugated with rounded bodies of fly ash. Fig. 5b showedthat the smooth surface of fly ash spheres are intermingled withlath, columnar and prismatic shaped crystals of gypsum andettringite and enhance the conjunctures of the different solid par-ticles in the binder. The inert crystalline phases of dendritic mullitecrystals can be seen on the surface layer that retain the sphericalshape of fly ash during hydration. The similar findings was ob-served by other workers [33,34].

3.3. Durability of fly ash binder

3.3.1. Performance of fly ash binder in waterThe fly ash binder cubes hardened for 28 days were dried and

then immersed in water to measure their water absorption and

porosity after different immersion periods. The effect of immersionin water on the water absorption and porosity of fly ash binders‘B1’, ‘B2’, ‘B3’ and ‘B4’ are illustrated in Figs. 6 and 7 respectively.It can be seen that water absorption and porosity increased withthe increase in immersion period for all the hardened binder cubes.The results show that the level of increase in the water absorptionand porosity in binder ‘B2’ is lowest than other binders withimmersion period in the following order:

fly ash binder‘ B2’ < fly ash binder‘ B1’ < fly ash binder‘B 3’

< fly ash binder‘ B4’

Fig. 8. Effect of water immersion on compressive strength of fly ash binders ‘B1’and ‘B2’.

Fig. 9. Effect of wetting and drying cycles on compressive strength of fly ash binder‘B2’ at different temperatures.

Fig. 10. Effect of wetting and drying cycles on weight loss of fly ash binder ‘B2’ atdifferent temperatures.

Fig. 11. Differential thermograms of fly ash binder ‘B2’ exposed to alternate wettingand drying cycles at 50 �C (a) 5 Cycles and (b) 45 Cycles.

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These findings clearly indicate the absence of leaching for all the flyash binders. However, fly ash binder ‘B2’ possess better water resis-tance than other binders. The effect of different immersion periodson compressive strength of fly ash binder B1 and B2 was studiedand exhibited in Fig. 8. The data show that compressive strength

of binder ‘B2’ is higher than that of ‘B1’ with immersion period.The results show that after 28 days immersion of cubes in water,the fly ash binder ‘B2’ retained 92% and binder ‘B1’ retained 87%of the original strength.

3.3.2. Wetting and drying cyclesThe effects of alternate wetting and drying cycles on the com-

pressive strength and weight loss of the fly ash binder ‘B2’ keptat temperatures from 27 �C to 50 �C are shown in Figs. 9 and 10respectively. It can be seen from Fig. 9 that initially up to 15 cyclesthe strength of the binder at 27 �C is higher than the originalstrength of the binder and afterwards decreased. At 27 �C, thecubes retained 88% of the original strength after 45 cycles. How-ever, on increasing the temperature and wetting and drying cyclesthe compressive strength was reduced. The maximum fall instrength occurred at 50 �C and no cracks were observed even after45 cycles. At 40 �C and 50 �C, the cubes after 45 cycles retained 83%and 74% strength of the pristine value, respectively. It can be de-picted from Fig. 10 that the weight loss increased from 27 �C to50 �C with an increase in wetting and drying cycles and maximum

Fig. 12. Effect of wetting and drying cycles on compressive strength of fly ashbinder ‘B1’ at different temperatures.

Fig. 13. Effect of wetting and drying cycles on weight loss of fly ash binder ‘B1’ atdifferent temperatures.

Table 6Compressive strength of concrete prepared from binder ‘B2’.

No. Material (% bywt.)

Mix design (% by wt.) Compressivestrength (MPa)

Cement-

binderB2

Cement -binder B2

Sand Coarseaggregate

7 days 28 days

1 90 10 1 2 4 13.8 22.52 80 20 1 2 4 10.3 20.83 90 10 1 3 6 6.5 11.74 80 20 1 3 6 4.8 10.25 100 – 1 2 4 20.2 31.56 100 – 1 3 6 9.5 15.5

764 M. Garg, A. Pundir / Construction and Building Materials 37 (2012) 758–765

weight loss was observed at 50 �C. The reduction in strength andenhancement in the weight loss of the binder cubes beyond27 �C can be correlated with the decomposition of the AFt (C3-

A�3CaSO4�32H2O) phase into gypsum and calcium carbonate,formed during the hydration of the fly ash binder. This phenome-non is amply demonstrated by DTA studies. Some typical thermo-grams of 5 and 45 wetting and drying cycles of the fly ash binder at50 �C are shown in Fig. 11a and b respectively. Fig. 11a exhibits theformation of three endotherms at 110–135 �C, 150 �C and 735–780 �C due to the presence of ettringite, gypsum and calcium car-bonate respectively. It can be seen from Fig. 11b that as the alter-nate wetting and drying cycles increased, reduction in the intensityof endotherm of ettringite was observed. Simultaneously, anenhancement in the intensity of endotherms of gypsum and cal-cium carbonate was noticed. This finding is in agreement withthe studies carried out by other workers [35,36]:

Table 7Properties of fly ash binder bricks.

C3A:3CaSO4:32H2Oþ 3CO2

! 3CaSO4:2H2Oþ 3CaCO3 þ 2AlðOHÞ3 þ 23H2O

Mix design (%by wt.)

Bulkdensity(gm/cc)

Compressivestrength 28 days(MPa)

Waterabsorption(%)

Dryingshrinkage(%)

BinderB2

Flyash

40 60 1.40 8.4 18.3 0.1350 50 1.45 10.5 16.5 0.1160 40 1.48 11.8 15.3 0.11

Similar effect of alternate wetting and drying cycles on the com-pressive strength and weight loss of the fly ash binder ‘B1’ kept attemperatures from 27 �C to 50 �C were noticed and exhibited inFigs. 12 and 13 respectively. The data revealed that at 27 �C, 40 �Cand 50 �C, the cubes after 45 cycles retained 81% and 77% and72% strength of the original value, respectively.

3.4. Applications of fly ash binder

3.4.1. Masonry mortarsThe suitability of optimum mix composition of fly ash binder

‘B2’ was tested and evaluated for making masonry mortars. The re-sults are shown in Table 5. The data reveal that on increasing sandcontent, compressive strength and water retentivity are reduced. Amix proportion of 1:3 and 1:4 binder sand (fineness modulus 1.28and 1.90) mortar show higher values of compressive strength andwater retentivity than the mix 1:6 cement–sand mortar and com-ply with the minimum specified strength of 2.5 and 5.0 N/mm2 at 7and 28 days and water-retentivity of 60.0% laid down in IndianStandard [37]. Therefore, these binder–sand mortar proportionscan be used in place of 1:6 cement:sand mortars for the construc-tion of brick walls and for plaster work.

3.4.2. ConcreteThe compressive strength of the concrete made with 10 and 20%

replacement of cement with fly ash binder ‘B2’ are given in Table 6.It can be seen that by replacing the cement with 10.0% and 20.0%by the fly ash binder ‘B2’, the compressive strength of the concretereduced than the 1:2:4 and 1:3:6 plain concrete. However, 28 daysstrength complied with the requirement of 15.0 and 10.0 MPa for1:2:4 and 1:3:6 concrete mix respectively given in IS: 456 [38].

3.4.3. Fly ash binder bricksThe properties of fly ash binder bricks (size: 190 mm �

90 mm � 90 mm) made by vibration-compaction technique usingfly ash binder ‘B2’ with different percentage of fly ash are givenin Table 7. The results show that the compressive strength of bricksdecreased and water absorption increased with increase in fly ashconcentration. However bulk density decreased with fly ash con-centration. The properties of fly ash binder bricks complied withthe requirement as given in IS: 12894 [39]. The drying shrinkageof the fly ash binder bricks tested according to method describedin IS: 4139 [40] lies within the maximum specified value of0.15%. The photographs of fly ash binder bricks are shown inFig. 14.

Fig. 14. Photographs of fly ash binder bricks.

M. Garg, A. Pundir / Construction and Building Materials 37 (2012) 758–765 765

4. Conclusions

The following conclusions can be drawn based on the experi-mental study:

1. A new binder with good strength and volume stability has beendeveloped by mixing fly ash, alpha gypsum plaster, hydratedlime sludge and Portland cement.

2. The attainment of strength with hydration in the binders is dueto the formation of tobermorite and ettringite.

3. The fly ash binders are durable as they do not show leaching ofthe matrix when subjected to long term immersion in water.

4. The strength of the fly ash binder is decreased and the weightloss increased with the increase in temperature and alternatewetting and drying cycles. The maximum fall in strengthoccurred at 50 �C.

5. The fly ash binder ‘B2’ is suitable for use in masonry mortarsand for concrete by partial replacement of cement with it.

6. The high strength and stability of fly ash binders has been uti-lized in making prefabricated building materials such as bricksand blocks.

7. Utilization of high volume fly ash in combination with otherindustrial wastes, i.e. phosphogypsum and lime sludge in con-struction materials contribute much to the environment protec-tion and to reduce pollution and health hazards produced bythem.

Acknowledgement

The work reported in this paper forms a part of the normal re-search programme at the CSIR-Central Building Research Institute,Roorkee (India). The authors are grateful to Prof. S.K. Bhattachar-yya, Director, Central Building Research Institute, Roorkee for giv-ing the permission for publication of the paper.

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