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EffectofGGBSandFlyashaggregatesonpropertiesofgeopolymerconcrete

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436 Journal of Structural EnginEEring Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

Journal of Structural EngineeringVol. 43, no. 5, December 2016 - January 2017 pp. 436-444 No. 43-37

Effect of GGbs and Fly ash aggregates on properties of geopolymer concreteg.Venkata Suresh*,, P. Pavan Kumar reddy* and J. Karthikeyan*

Email: gvsuresh74@gmail.com

*Department of civil Engineering, national institute of technology, tiruchirapalli - 620 015, inDia.

received: 23 July 2015; accepted: 04 february 2016

KEywords: Fly ash; ground granulated blast furnace slag; pelletization; sodium hydroxide (NaOH) solution; water cured fly ash aggregates; chemically cured fly ash aggregates.

concrete is a widely used building material in the construction industry. So, increasing concrete demand, in turn increases the demand for the raw materials of concrete. as of now, largely natural aggregates are used for concrete preparation. So, in the near future, there will definitely be a shortage in the availability of natural aggregates. To face this problem, fly ash aggregates are the best alternative for natural aggregates.

In recent years there has been renewed interest in fly ash aggregate concretes, specifically for the production of high strength concretes that can be used for bridge construction and other special applications like off shore structures. in this type of high strength concretes, the aggregate was considered weaker when compared to the matrix. So the mix design concepts were usually based on preparing high strength matrix with low

alkaline solution to fly ash ratio to compensate for the aggregate’s weakness.

geetha and ramamurthy1 conducted studies on the formation of fly ash pellets in the disc pelletizer with low calcium bottom ash and clay binders. the physical and mechanical properties of light weight fly ash aggregates were dependent on the type of fly ash, either class c or class f, based on its mineralogical composition. Mehmet gesoglu et al.2 stated the effects of physical and chemical properties fly ash on the characteristics of the cold bonded fly ash aggregates. The findings of the study revealed that fly ash with higher specific surface and lower calcium oxide (cao) content yielded higher strength. gomathi and Sivakumar.3 investigated the strength characterization of fly ash aggregates using alkali activator as a binder

The paper deals with the influence of Ground Granulated Blast Furnace Slag (GGBS) and concentration of sodium hydroxide (NaOH) solution on the physical and mechanical properties of the Geopolymer Concrete (GPC) with fly ash aggregates. The fly ash aggregates were prepared using class C fly ash by adopting pelletization technique without adding any binders. Two types of curing techniques were adopted for aggregates i.e water curing and chemical curing (using NaOH solution). These two types of cured aggregates are called as Water Cured Aggregate (WCA) and Chemical Cured Aggregates (CCA). The tests like compressive strength, water absorption and specific gravity were carried out on the cured aggregates. The strength of CCA was 64.93%, 49.03% more when compared to WCA for 7 and 28 days curing and the water absorption of CCA were 4.0% for 7 days and 4.2% for 28 days. The GPC mixes were cast with CCA and WCA at 0% and 30% replacement of fly ash(class F) by GGBS with different concentrations of NaOH solutions (8M, 10M, 12M). It was observed that the GPC mixes with CCA and WCA at 30% GGBS with 12M NaOH concentration attained maximum compressive strengths of 64.14 MPa and 42.13 MPa cured at room temperature. Among the GPC specimens it is observed that the GPC mixes with CCA had better workability and bonding at the interfacial transition zone.

Journal of Structural EnginEEring 437 Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

in the Pelletization process and followed controlled humidity curing, hot air oven curing for preparation of fly ash aggregates. The production efficiency is also found to be dependent on the percentage of binders, and concentration of alkali activator added to the fly ash. Harikrishnan and ramamurthy4 investigated the efficiency of pelletization on the speed of revolution, angle, moisture content, duration and their interaction effects on the strength, water absorption; and size growth of fly ash aggregates. Manikandan and ramamurthy5 investigated the fineness of fly ash influence on the aggregate pelletization process and also stated that addition of clay binders like bentonite, kaolinite, enhanced the pellatization efficiency of coarser fly ash. Abdul kareem et al6 investigated the mechanical and microstructural characteristics of light weight aggregate gPc cured at 100-800oc. the relationship between exposed temperature and residual compressive strength is statically analysed and achieved. Deb et al7 investigated the effects of ground granulated Blast furnace Slag (ggBS) and alkaline activator concentration on compressive strength and the workability of gPc. the compressive strength increases with an increase in ggBS content, whereas workability decreases with increased ggBS content. rajamane et al8 investigated on light weight aggregate concrete (LWAC) containing fly ash protect steel from corrosion or not. in accelerated corrosive exposure to sodium chloride solution indicates that light weight concrete with fly ash offers adequate protection to steel embedded in concrete. Sundar kumar et al9 conducted the experimental studies to determine the relation between the Si-al-na ratio and the compressive strength of the mix and found that the compressive strength is decreased along with workability after optimum molar ratio. rajamane et al10. the compressive strengths of fly ash aggregate (FAA) -based lightweight aggregate concretes (lWacs) depend on the volume of fraction of coarse aggregate present in the concrete; higher volume fraction of coarse aggregate causes lower densities in concretes accompanied by lower strengths. Kareem et al11 investigated the mechanical and microstructural characteristics of light weight aggregate gPc cured at 100-800oc. the relationship between exposed temperature and residual compressive strength is statically analysed and achieved. Siddique11 conducted experimental investigation dealing with concrete incorporating high volumes of class F fly ash. Portland

cement was replaced with three percentages (40%, 45%, 50%) of class F fly ash and concluded that Class F fly ash can suitably use up to 50% level of cement replacement in concrete for use in precast elements and r.c.c constructions.

In this work, fly ash aggregate is used as an alternative for normal granite aggregate in gPc. Various processes were considered between the two phases of gPc associated with the special characteristics of aggregate like surface texture, water absorption and pozzolanic activity of the aggregate constituents. rough surface texture of aggregate leads to better mechanical interlocking with the matrix. Water absorption of the aggregate depends on its porous structure. the interaction of aggregate with the gPc matrix is different from the interaction of normal granite aggregate. So the properties of these aggregate has to be improved; the structure of these aggregate is modified by adopting different curing methods. two curing methods namely; water and chemical curing techniques were adopted for curing of fly ash aggregate.

the objective of the present work is to identify the nature of such interactions and determine the influence of type of fly ash aggregate, concentration of sodium hydroxide (naoH) solution and percentage of ggBS replacement on compressive strength, Density and Workability of gPc.

ExPErIMENTAl PrOGrAM

Materials used

the materials used for this study consist of Lignite fly ash (class C) which is obtained from

neyveli lignite corporation, tamil nadu, india was used for the preparation of aggregate by using disc type pelletizer.

fly ash (class f) which is obtained from Mettur thermal power plant, tamil nadu, india was used for the preparation of gPc.

ggBS is obtained from astrra chemicals, chennai, India was used for replacement of fly ash in casting the gPc.

fly ash aggregate (class c) with water curing and chemical curing replaces for coarse aggregate.

Sodium Silicate (na2Sio3) which has 15.9 % na2o, 31.4% Sio2 and 52.7% water.

438 Journal of Structural EnginEEring Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

Sodium Hydroxide (naoH) solution with three different molar ratio concentrations. i.e 8M, 10M, 12M.

locally available river sand and conplast SP 430 super plasticizer were used for the preparation of gPc.

the physical and chemical properties of the materials are shown in table 1, 2 and 3 respectively.

taBlE 1SiEVE analySiS of tHE MatErialS

Sieve size (μm) 300 150 75 63 45 38

100 %

finer

class c fly ash 100 65.12 8.42 6.66 3.26 0.96

ggBS 100 89.4 13 3.2 1 0.4class f fly ash 100 96.6 32.8 25.8 9.4 4.6

from the table 1, it is clearly indicated that the majority of the particles are above the range of 75 µm. from the table 2, it is observed the physical properties of the material, i.e., fly ash with class C, class F, GGBS, fine aggregate and the coarse aggregates (WCA and cca).

The specific gravity of fly ash with class C, class F, ggBS determined in the laboratory by using the density bottle method whereas the specific gravity of fine aggregate (sand), coarse aggregate (Wca and cca) determined in the laboratory by using the pycnometer.

figure 1 shows that the particles present in class C fly ash are more coarse compared with GGBFS, followed by class F fly ash and the particles present in the fine aggregate are well graded, where as the particles present in the fly ash aggregate are ocuupy only in two sizes.

i.e b/w 10mm - 20mm (70%) and 4.75mm - 10mm (30%). The fineness modulus of the fine and coarse aggregates are 2.65 and 6.70

Class C Flyash

Fine aggregate Coarse aggregate (FAA)

Class F FlyashGGBFS

1009080706050403020

Perc

enta

ge o

f fin

erPe

rcen

tage

of f

iner

100

100908070605040302010

0

10

10 10010.10.01

100Sieve size in µm

Sieve size in mm

1000

fig. 1 Particle size distribution (Semi log graph)

The chemical composition of fly ash is obtained from X-ray fluorescence (Xrf) which is shown in table 3. as per aStM c61812, based on the chemical composition of fly ash, if the sum of the elemental

taBlE 2PHySical ProPErtiES of tHE MatErialS

Materialsfly ash

ggBS fine aggregatecoarse aggregate

class c class f Wca ccaSpecific gravity 2.62 2.64 2.80 2.64 1.86 1.88

Particle size Slightly less than 38 µm to 300 µm 0.15mm to 2.36mm

4.75mm to 16.0mm

4.75mm to 16.0mm

Density (kg/m3) - - - 1650.00 1235.00 1264.00compressive

strength (MPa) - - - - 3.63 4.72

Water absorption - - - 4.00 14.28 4.20

Journal of Structural EnginEEring 439 Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

oxides Sio2, al2o3 and fe2o3 present in the fly ash is more than or equal to 50%, it is classified as class C and if the same is greater than 70%, it is classified as class f.

Preparation of fly ash aggregate

A 6 kg of dry fly ash (Class-C) is fed into the pelletizer disc after fixing the angle of the drum and constant speed of the motor to assure the homogeneity of the mixer. then pour a certain percentage of water into the fly ash as the coagulant and add it to the fly ash in the disc by sprinkling it, to form spherical pellets by consolidating finer moisturized particles into larger solid material without application of external force, with the motion of the rolling disc of the agglomeration process. Proper care should be taken to avoid water film on the surface of the pellets during the preparation of the pellets. note the time taken for complete agglomeration process of fly ash and formation of the pellets inside the disc. after completing the formation of the pellets, the fly ash aggregates are allowed to air dry to get the initial handling purposes. the procedure is repeated by changing the angle, speed and the percentage of the water until maximum efficiency of the agglomeration or pelletization is reached.

it is observed that, initially the pellets are formed by consolidating finer moisturized particles into larger solid material due to thumbing force without application of external force by using the disc type pelletizer in 10 to 12 minutes. the remaining time is for compaction of the pellets for sufficient strength by the force generated by itself inside the mixer shown in fig. 2a. finally the aggregates were prepared under the disc angle is 30o with reference to horizontal and the speed of the motor used is 1500rpm. After pelletization process, the fly ash aggregates were kept for observations in different

curing methods namelya) Water curing technique: The fly ash aggregates

being cured in water for 28 days. Here onwards these types of fly ash aggregates are named Water cured aggregates (Wca).

b) Chemical curing technique: It is a new technique where the fly ash aggregates are cured in sodium hydroxide solution (8M) for 28 days. this type of fly ash aggregates are called Chemically Cured aggregates (cca) shown in fig. 2b.

(a) Pelletized aggregates (b) Chemical curing of aggregates

fig. 2 fly ash aggregates

Mix proportions

Aggregate gradation

to study the effect of these light weight aggregates on compressive strength and workability of concrete, the aggregate with sizes 12mm-16mm and 4.75mm-12mm are taken as 70% and 30% by weight of total coarse aggregate respectively. the coarse aggregate and fine aggregate proportions are taken as 68% and 32% by volume of total aggregate respectively. Due to absorption of water is more in the Wca, the aggregates are pre-soaked for 1hr before mixing into the concrete whereas the absorption of water is less in the cca, the aggregates are directly used for mixing into the concrete.

taBlE 3cHEMical coMPoSitionS of tHE MatErialS

chemical composi-tions %

Sio2 al2o3 fe2o3 cao Mgo So3 na2o K2o cl

class C fly ash 25.3 24.54 12.91 20.21 4.85 7.95 1.25 0.13 0.020

class F fly ash 60.86 24.35 3.936 1.73 0.00 0.57 4.56 1.33 0.025

ggBfS 32.84 11.01 0.89 45.67 4.28 2.69 0.00 0.26 0.004

440 Journal of Structural EnginEEring Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

Mix designation and proportions

three series of gPc mixes were used to study the effects of concentrations of naoH solution (Series a), percentage of ggBS replacement (Series B) and the type of aggregate (Wca and cca) (Series c) as shown in table 4. the mix proportions for gPc mixes are shown in table 5.

taBlE 4MiX coMBinationS

Series

naoH concen-tration

(M)

% ggBS replace-

ment

aggre-gate type

alkaline solution to fly ash

ratio

Sodium silicate to sodium

hydroxide ratio

a

8, 10, 12 0, 30

Water cured,

chemi-cal cured

0.35 2.5Bc

taBlE 5MiX ProPortionS of gPc MiXES WitH DiffErEnt fly aSH

aggrEgatES

Description Quantity (kg/m3)

Water cured aggregate gPc

chemical cured aggregate gPc

0% ggBS 30% ggBS 0% ggBS 30% ggBS

fly ash 440.36 308.46 440.36 308.46

ggBS - 131.90 - 131.90

Sodium hydroxide (for

8M, 10M, 12M)44.00 44.00 44.00 44.00

Sodium silicate 110.00 110.00 110.00 110.00

coarse aggregate 852.00 852.00 856.50 856.50

fine aggregate 568.00 568.00 568.00 568.00

Extra water(10% weight of

fly ash)44.04 44.04 44.04 44.04

Super plasticizer (1.5% weight of

fly ash)6.61 6.61 6.61 6.61

details of mixing

the naoH solution is prepared 24 hours before the concrete mixing and then is mixed with the sodium silicate solution according to their ratio just 30 minutes before concrete mixing. First fly ash (class f), ggBS and sand are added to the pan mixer and

mixed thoroughly. then alkaline solution followed by extra water and super plasticizer are added and mixing is continuous for 3 minutes until the mortar paste is uniform. the coarse aggregate is added next and allowed to mix for 2 minutes. then the fresh gPc is placed into 150 mm × 150 mm × 150 mm cube moulds in accordance with iS 516: 195913. the gPc specimens are covered with plastic sheet for 24 hours to prevent moisture loss at controlled room temperature. after 24 hours the gPc specimens are demoulded and exposed to atmosphere at room temperature till the day of testing.

details of test

Density and compressive strength

the density was determined after 28 days using the cube specimens. after the density determination, the cube specimens were tested in the compression testing machine to determine the compressive strength in accordance with iS 516:195913. the reported density and compressive strengths are the average of three samples.

Slump cone test

the slump cone test was performed for all the gPc mixes to check the workability of gPc.

rESulTS AND DISCuSSION

Compressive strength and density

the compressive strength and densities of concrete is observed after 28 days based on the concentration of naoH solution, percentage of ggBS and type of aggregates used.

Concentration of NaOH solution

The results of compressive strength of GPC with fly ash aggregate with various concentrations of naoH solution (Series a) are shown in fig. 3. it is observed that with the increase of concentration of naoH solution, the compressive strength of the gPc mixes increased. this can be explained by the activation of the reaction of the internal Si and al components caused by the increased breakage of the glassy chain of fly ash, which is provoked by the high alkalinity due to the increase of the molarity of naoH. However,

Journal of Structural EnginEEring 441 Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

the admissible amount of naoH is limited considering economic efficiency.

19.33 22.67 26.535.13 38.86 42.1334.3 36.7 39.4

55.53 59.43 64.13

0

20

40

60

80

8M 10M 12M 8M 10M 12MCom

pres

sive

stre

ngth

(M

Pa)

Concentration of NaOH solution

Water cured aggregate Chemical cured aggregate

fig. 3 compressive strength of gPc mixes

the maximum compressive strength was obtained for gPc mixes with 12M solution irrespective of type of aggregate and percentage of ggBS replacements. a maximum 28 day compressive strength values of 64.13 MPa and 42.13 MPa were obtained for gPc mixes with cca at 0%, 30 % ggBS used whereas the maximum 28 day compressive strength values of 39.40 MPa and 26.50 MPa were obtained for gPc mixes with Wca at 0%, 30% ggBS used.

the minimum compressive strength was obtained for gPc mixes with 8M solution irrespective of type of aggregate and percentage of ggBS replacements. a minimum 28 day compressive strength values of 35.13 MPa and 55.53 MPa were obtained for gPc mixes with cca at 0%, 30 % ggBS used whereas the minimum 28 day compressive strength values of 19.33 MPa and 34.30 MPa were obtained for gPc mixes with Wca at 0%, 30% ggBS used.

2130 2130 2141 2135 2140 21532190 2205 2210 2200 2204 2220

2050

2100

2150

2200

2250

8M 10M 12M 8M 10M 12M

Den

sity

in k

g/m

3

Concentration of NaOH solution

Water cured aggregate Chemical cured aggregate

fig. 4 Densities of gPc mixes

the densities of gPc mixes with various concentrations of naoH solution were similar as in fig. 4. the densities were not affected much by the concentrations of naoH solution as the densities of the liquid in the mixes were nearly similar with various concentrations of naoH solution for the mixes with similar aggregate.

Percentage of GGBS replacement

the results of compressive strength of the gPc mixes with fly ash aggregate with partial replacement of fly ash with ggBS are shown in fig. 2. the compressive strength of gPc mixes increased with the increase in ggBS replacement from 0% to 30%. the ggBS consists of 45.67 % of cao by weight is responsible for the quick setting and for the improvement of compressive strength to a great extent. it was observed that the mixes with 0% ggBS replacement took more than 24 hours to set whereas the mixes with 30% ggBS replacement set within 24 hours. Specimens were demoulded after 24 hours from casting. the maximum 28 day compressive strengths obtained was 42.13 MPa and 64.14 MPa for the gPc mixes with Wca and cca respectively. Due to the increased percentage of ggBS the GPC mixes became flash set so GGBS replacement is restricted to 30% by weight of fly ash.

taBlE 6coMPariSon of tHE DEnSitiES BEtWEEn Wca anD

cca

faa Wca ccaMole 8 10 12 8 10 12

0 2130 2130 2141 2135 2140 215330 2190 2205 2210 2200 2204 2220%

Variation2.82 3.52 3.22 3.04 2.99 3.11

average 3.19 3.05

the densities of gPc mixes change with replacement of fly ash by GGBS is observed in Table 6. The variation of the increased density is 3.19% in case of Wca with 30% ggBS used whereas the variation of the increased density is 3.05% in case of cca with 30% ggBS.

Type of aggregate

the results of compressive strength of gPc mixes with Wca and cca are shown in the fig 2. the gPc mixes with cca performed well in terms of strength, workability and had more density compared to gPc mixes with Wca. it was observed that there is a formation of thick shell around the periphery of the fly ash aggregate which was cured chemically, and is the reason for the improved strength and reduction in the water absorption for cca.

442 Journal of Structural EnginEEring Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

cca had better bonding with the interfacial transition zone because of the presence of a naoH coating on the top surface. the maximum 28 day compressive strength of 39.40 MPa and 64.14 MPa were obtained for gPc mixes with cca at 0% and 30% ggBS replacements respectively with 12M naoH solution. the maximum 28 day compressive strengths of 26.50 MPa and 42.13 MPa were obtained for gPc mixes with water cured aggregate at 0% and 30% ggBS replacements respectively with 12M naoH solution.

figures 5a and 5b show the failure pattern of the Wca and cca gPc specimens. all the aggregates in the Wca gPc specimen were not sheared due to lack of bonding between the aggregate and the gPc matrix. the Wca has lesser compressive strength than cca gPc mix due to the presence of moisture. Whereas in the cca gPc mix, the aggregates have a rich layer of naoH on the periphery which reacts with the gPc matrix, resulting in better bonding. it is also observed from fig.5.b that cca has a thick shell formation on the outer periphery due to the dissolution of fly ash by naoH solution. this shell is responsible for the strength enhancement and also protects the quality of the aggregate.

figures 5c and 5d shows the interfacial transition zone between the GPC matrix and the fly ash aggregates at the age of 28 days.

a) WCA GPC specimen

c) SEM image of WCA specimen

b) CCA GPC specimen

d) SEM image of CCA specimen

fig. 5 fractured gPc specimens and SEM images

gPc matrix appears to be uniform in colour, homogeneous and dense microstructure in both the Wca and cca gPc specimens. it is also observed that the interface transition zone had a tight and inter locking between the aggregates which is more in cca gPc specimens than in Wca gPc mixes. it also indicates a gradual transition rather than a sharp discontinuity in structure and properties which is more in Wca gPc specimen than the cca gPc specimen.

Workability

Workability is the ease of working with a freshly mixed concrete in the stages of handling, placing, compacting and finishing. The slump test is used as a common test for measuring the workability of concrete. the workability of fresh geopolymer concrete was determined immediately after mixing of the concrete by the standard slump cone test.

Concentration of NaOH solution

The spherical shape of fly ash particles combined with lubricating effect of the alkaline activator solution gives flowability to the fresh GPC. Use of sodium silicate and naoH solutions, which are more viscous than water, make gPc mix more cohesive and sticky than oPc concrete. However, a higher slump of gPc mix indicates lesser stickiness and the higher workability of the mixture.

the slump cone test results for gPc with varying naoH concentrations (Series a) are shown in the fig. 6. it was observed that the workability of the gPc mixes decreases by small extent with an increase in the concentration of the naoH solution. as naoH increases the viscosity of the gPc mix, the workability is reduced and it quickens the geopolymerisation process.

80 75 7560 55 50

80 8065

55 55

0

20

40

60

80

100

8M 10M 12M 8M 10M 12M

Slum

p (m

m)

Concentration of NaOH solution

Water cured aggregate Chemical cured aggregate

90

fig. 6 Workability of gPc mixes

the maximum slump values of 80 mm and 90 mm were obtained for the gPc mixes with 8M naoH

Journal of Structural EnginEEring 443 Vol. 43, no. 5, DEcEMBEr 2016 - January 2017

solution at 0% ggBS replacement having Wca and cca respectively.

Percentage of GGBS replacement

the slump cone test results for the gPc mixes with 0 % and 30 % ggBS replacements (series B) are shown in the fig. 4. it was observed that with the increase of ggBS from 0 % to 30 % the workability of the gPc mixes decreased drastically irrespective of naoH concentration and the type of aggregate. the maximum slump values were obtained for all the gPc mixes with 0 % ggBS replacement compared to 30 % ggBS replacement gPc mixes. the minimum slump of 50 mm was obtained for gPc mix with Wca and 12M naoH solution at 30 % ggBS replacement. the maximum slump value was obtained as 90 mm for the gPc mix with 8M naoH solution at 0% ggBS replacement having cca. So, the maximum percentage ggBS replacement is restricted to 30 %, as otherwise there will be a serious workability problem. to improve workability, we have to opt a high super plasticizer dosage, which is uneconomical.

Type of aggregate

the slump cone test results for gPc mixes with water cured and chemical cured aggregates (series C) are shown in Fig 4. The fly ash aggregate, due to its spherical shape offers good workability when compared to ordinary granite aggregate. the gPc mixes with water cured fly ash aggregate were slightly less workable compared to gPc mixes with cca. this happened due to the rough surface texture of Wca. the surface texture of chemical cured aggregate is relatively smoother.

CONCluSIONS

Based on the experimental investigations the following conclusions are drawn:1. chemically cured aggregates (cca) has less

water absorption due to the formation of a naoH layer on the periphery of the aggregates. the least water absorption obtained is 4.0 %, and Water cured aggregates (Wca) has higher water absorption of 14.28 %.

2. The specific gravities of WCA and CCA obtained were 1.87 and 1.88, which is nearly 65% of

ordinary blue granite coarse aggregate.3. The inclusion of fly ash aggregates instead of coarse

aggregate reduced the density of geopolymer concrete (gPc) mixes by 15%.

4. the compressive strength of gPc mixes increased with partial replacement of fly ash with Ground granulated Blast furnace Slag (ggBS). as the percentage of ggBS replacement increased from 0% to 30% the compressive strength of gPc mixes also increased by 40 %.

5. the compressive strength of gPc mix increased by 45-50 % for all gPc mixes with cca when compared to gPc mixes with Wca.

6. the presence of ggBS improves the setting and hardening properties of gPc. the workability of gPc mix is reduced with increased percentage of ggBS replacement.

7. the maximum slump value of 90 mm is obtained for cca gPc mix at 0% ggBS replacement with 8M- Sodium Hydroxide (naoH) solution. the minimum slump value of 50 mm is obtained for Wca gPc mix at 30% ggBS replacements with 12M naoH solution.

rEFErENCES

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2. Mehmet gesoglu., turanozturan., and ErhanHuneyisi., “Shinkage cracking of lightweight concrete made with cold-bonded fly ash aggregates”, Cem. Conc. Res.. Vol. 34, 2004, pp 1121–1130.

3. gomathi, P. and Siva Kumar, a., “fly ash based light weight aggregates incorporating clay binders”, Ind. Jl. of Engg. and Mat. Sci., Vol.21, 2014, pp 227–232.

4. Harikrishnan, K.I. and Ramamurthy, K., “Influ-ence of Pelletization Process on the Properties of fly ash aggregates”, Waste Management, Vol. 26, 2006, pp 846–852.

5. Manikandan, r. and ramamurthy, K.., “Effect of curing Method on characteristics of cold Bonded fly ash aggregate”, Cem. Conc. Compos., Vol.30,

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2008, pp 848–853.6. abdul Kareem, omar a., al Bakri abdullah, Mohd

Mustafa., Hussin, Kamarudin, ismail, chairul nizar and Binhussain, Mohammed, “Mechanical and microstructural evaluations of light weight aggregate geopolymer concrete before and after exposed to elevated temperature”, Materials, Vol. 6, 2013, pp 4450–4461.

7. Partha Sarathi Deb., Pradip nath and Prabir Kumar Sarker, “the effects of ground granulated blast-furnace slag blending with fly ash and activator content on the workability and strength properties of geopolymer concrete cured at ambient temperature”, Mat. and Des., Vol. 62, 2014, pp 32–39.

8. rajamane, n.P., annie Peter, J. and ambily., P.S., “Effect of fly ash in lightweight concrete containing sintered fly ash aggregates”, Institite of Engineers (india), Vol. 87, 2007, pp 32–36.

9. Sundar Kumar, S., ramesh, g., Jaffer Sathik, S.a. and Bharatkumar, B.H., “Effcet of naoH

concentration and molar ratios on strength development in geopolymer mortars”, Jl. of Struct. Engg., Vol. 40, (6), 2014, pp 558–564.

10. rajamane, n.P., annie Peter, J. and ambily, P.S., “Modified Bolomey equation for strengths of lightweight concretes containing fly ash aggregates”, Magazine of Conc. Res., Vol.64, no. 4, 2007, pp 285–293.

11. Siddique, R., “Performance characteristics of high volume class F fly ash concrete”, Cem. and Conc. Res., Vol. 34, 2004, pp 487–493.

12. Standard Specification for coal fly ash and raw or calcined natural pozzolan for use in concrete, aStM c618-91.

13. Indian standard method of tests for strength of concrete, iS 516:1959

(Discussion on this article must reach the editor before March 31, 2017)

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