IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613

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Study on Strength of Fly Ash Based GeoPolymer Concrete under Heat

Curing Bagwan Mustafa

1 Shaik Abdulla

2

1P.G. Student

2Lecturer

1,2Department of Civil Engineering

1,2Khaja Bandanawaz College of engineering, Gulbarga, Karnataka.

Abstract— fly ash is a noncombustible material obtained

from the various thermal power plants. Since fly ash is

available in large scale, it is disposed of in rivers and

landfills and ponds by thermal industries which are posing

danger to environment. Due to high pozzolanic activity of

fly ash, efforts are being made to use it as a cement

replacement material. GeoPolymer concrete makes 100

percent utilization of fly ash in concrete along with alkaline

solutions, as a binder. The cube specimens and beams are

casted for 2% and 4% super plasticizers and alkaline to fly

ash ratio of 0.35. The compressive strength of cubes is

compared to that of conventional cubes at 7, 14 and 28 days

.it is observed that GeoPolymer concrete is economical as

compared to normal concrete from compressive strength

point of view.

Key words: GeoPolymer concrete, fly ash, sodium silicate,

sodium hydroxide

I. INTRODUCTION

In normal concrete cement is used for hydration process to

takes place to form binders mainly silicates and aluminates

and for gel component to bond the aggregates each other,

hydration process is activated by the reaction between

cement with water which gives rise to binders. So, to invent

alternate concrete, it should form binders in anyway without

the use of cement. This gave rise to the invention of

GeoPolymer concrete. There are two main constituents of

GeoPolymer, namely the source materials and the alkaline

liquids. GeoPolymer concrete is made by using 100 % of fly

ash instead of cement. In GeoPolymer concrete fly ash is

activated using alkaline solution to form binders . The

alkaline liquids are from soluble alkali metals that are

usually Sodium or Potassium based. The most common

alkaline liquid used in geopolymerization is a combination

of sodium hydroxide (NaOH) or potassium hydroxide

(KOH) and sodium silicate or potassium silicate. The

complete geopolymerization process yields a Si-O-Al-O

bonds in an amorphous form.

II. NEED OF THE STUDY

The fact that production of cement leads to the pollution of

environment is a well-known fact to civil engineers and

environmentalists. The mass production of cement is posing

environmental hazard on one hand and unrestricted

depletion of natural resources on the other hand. It is

estimated that production of Each ton of Portland cement

production results in loading about one ton of CO2 into the

environment. To meet the infrastructure demand in real

estate and commercial industry, there is no way to stop the

cement production for more concrete. In order to overcome

this difficulty, a new decade concrete called as GeoPolymer

concrete is used in combination with admixture such as

super plasticizers.

III. OBJECTIVES OF THE STUDY

To study the effect of super plasticizer on strength

of GeoPolymer concrete at variable percentages

such as 2% and 4%.

To conduct the experiment to determine the

compressive strength of M 25 grade concrete and

8M,12Mand 16M GeoPolymer concrete at 7,14

and 28 days.

To determine ultimate loading capacity of

8M,12Mand16M GeoPolymer concrete beams at

28 days

IV. EXPERIMENTAL ANALYSIS

The present investigation involves 100% replacement of

cement by fly ash (ASTM type class F) of low calcium

content. The super plasticizer incorporated is SP430 in 2%

and 4% proportion, to increase the workability of

GeoPolymer concrete as it is very cohesive in nature, due to

mixture of alkaline solution consisting of sodium silicate

(Na2SiO3) and sodium hydroxide (NaOH) .The ratio of

sodium silicate solution to sodium hydroxide solution is

kept as 2.5.The ratio of alkaline solution to the fly ash is

maintained to 0.35 only. To examine the compressive

strength ,sodium hydroxide solutions of varying molarities

are prepared i.e. 8M,12M and 16M for instance, sodium

hydroxide solution with a concentration of 8M consists of

8x40=320grams of sodium hydroxide solids (in pellet form)

per liter of the solution, where 40 is the molecular weight of

sodium hydroxide. The mass of sodium hydroxide solids

was measured as 262grams per Kg of sodium hydroxide

solution of 8 molar concentrations. Similarly the mass of

sodium hydroxide solids per Kg of the solution for other

concentration was measured as 12 molar : 361 grams, 16

molar: 444 grams. note that the mass of sodium hydroxide

solids was only a fraction and water was the major

component .for conventional specimens of M25 grade

concrete the proportion was (1:2.20:3.90) . Among the

materials to be used, locally available river sand was used

and normal coarse aggregates of 12mm and 20mm down

size were used for concrete mix.

A. Mixing and Curing Of Geopolymer Concrete

In the laboratory, the fly ash and the aggregates were first

mixed together in dry state. The alkaline solution consisting

of sodium silicate and sodium hydroxide solution were

mixed 1 day prior to casting. The alkaline liquid was mixed

with the super plasticizer and the extra water, if any. The

liquid component of the mixture was then added to the dry

materials and the mixing continued usually for another 10 -

15 minutes. The fresh concrete could be handled up to 120

minutes without any sign of setting and without any

degradation in the compressive strength. The concrete mix

Study on Strength of Fly Ash Based GeoPolymer Concrete under Heat Curing

(IJSRD/Vol. 2/Issue 03/2014/064)

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was then used to cast cube specimens of 150x150x150mm

size. The fresh concrete was cast and compacted by the

usual methods used in the case of Portland cement concrete

(Hardjito and Rangan, 2005; Sumajouw and Rangan, 2006)

[3],[4]. fresh fly ash-based geopolymer concrete was usually

cohesive. The workability of the fresh concrete was

measured by means of the conventional slump test. The

compressive strength of geopolymer concrete is influenced

by the wet-mixing time. Test results show that the

compressive strength increased as the wet-mixing time

increased (Hardjito and Rangan, 2005) [3].The casted

specimens were wrapped by plastic sheet to avoid moisture

loss .The specimens were then placed in an oven at 60oC for

24 hours ,because geopolymerization process requires high

temperature curing initially ,then they were left to room

temperature until testing.

B. Testing Of Cubes

The cube specimens of 150mmx150mmx150mm size were

tested in compression testing machine of 200T capacity. The

cubes were tested for 7,14and 28 days compressive strength

Molarity

No of

cubes

No

of

days

Compressive strength

(N/mm2)

8M

03 7 20.78 17.06

03 14 28.35 24.16

03 28 34.0 28.92

12M

03 7 23.06 16.66

03 14 30.21 26.03

03 28 37.28 31.62

16M

03 7 29.85 23.25

03 14 41.56 38.56

03 28 43.41 39.06

M25

03 7 15.14 10.70

03 14 23.11 16.44

03 28 28.33 23.20

Table. 1: Compressive Strength At2% And 4% Super

plasticizers

C. Casting of Beams

Eight beams of size 100x150x1800mm were casted, to

determine the ultimate loading capacity of beams. Two

beams corresponding to each molarities i.e. 8M,12Mand

16M as well as conventional M25 grade beams ,all with

reinforcement details as show below were casted. Cross

sectional details of reinforcement in beams

D. Test Setup

Test was carried out in a loading frame of 1000KN capacity.

Dial gauges with least count 0.01 were fixed to measure

deflection at different load level. All beams were tested with

two point loads applied at 1/3 of span of the beam , so as to

have a pure bending zone in the middle of the beam. The

beam was placed such that the center of the beam and the

center of the loading frame lie on the same line as per the

required effective span of 1600mm.

Fig. 1: test setup in loading frame

E. Load – Deflection Behavior

The load deflection behavior is shown in figures below. The

ultimate load value for geopolymer concrete beams is higher

as compared to conventional ones, it is about 1.5 times more

than M25 grade conventional concrete beams and maximum

ultimate loading capacity is exhibited by 16M beams.

Deflections observed are also within allowable limits as per

IS 456-2000.

BEAM

DESIGNATION

CONCRETE

MIX

FIRST

CRACKING

LOAD KN

ULTIMATE

LOAD KN

CV1-1 M-25 40 80

CV1-2 M-25 43 95

B2-1 8M 42 85

B2-2 8M 45 110

B3-1 12M 43 100

B3-2 12M 47 115

B4-1 16M 46 105

B4-2 16M 52 140

Table. 2: Load Deflection Behavior

Fig. 2

Fig. 3

0

50

100

0 5 10LO

AD

IN

KN

DEFLECTION IN MM

CV1-2

Study on Strength of Fly Ash Based GeoPolymer Concrete under Heat Curing

(IJSRD/Vol. 2/Issue 03/2014/064)

All rights reserved by www.ijsrd.com 282

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

V. CONCLUSION

The increase in compressive strength is observed when

the Na2SiO3 to NaOH ratio is 2.5.

While casting it is seen that the geopolymer concrete

mix is very cohesive and sticky. As the super

plasticizer content increases from 2% to 4% the

decrease in the compressive strength is 10%. But for

2% super plasticizer content the workability of the mix

is not good as compared to 4% super plasticizer

content. And for 4% content the setting time of the

concrete is prolonged for placing specimen in

accelerated curing chamber. Due to the cohesive mix

the tamping should done very carefully and correctly

otherwise pores will be formed in the specimens that

leads to decrease in compressive strength.

Increase in concentration of NaOH from 12M to 16M

resulted in increase of 21% ultimate load of beams

For 12M and 16M conc. Of NaOH only a minimum

difference in deflections are observed. Where

deflection is the criteria for design of geopolymer

concrete beams 12M conc of NaOH can be used for

economy. Where ultimate load is the criteria for design

of geopolymer concrete beams 16M conc of NaOH can

be used.

For three conc of NaOH i.e 8M,12M and 16M the

ultimate load increased with increase in conc of NaOH.

Ultimate load of geopolymer concrete beams is 1.5

times higher than the obtained ultimate load for normal

concrete. Maximum ultimate load is represented by

16M beams.

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0

20

40

60

80

100

0 5

LO

AD

IN

KN

DEFLECTION IN MM

B2-1

0

50

100

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0 2 4LO

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KN

DEFLECTION IN MM

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0 5

LO

AD

IN

KN

DEFLECTION IN MM

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0 2 4

LO

AD

IN

KN

DEFLECTION IN MM

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0

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0 2 4 6

LO

AD

IN

KN

DEFLECTION IN MM

B4-1

0

50

100

150

0 2 4 6

LO

AD

IN

KN

DEFLECTION IN MM

B4 -2

Study on Strength of Fly Ash Based GeoPolymer Concrete under Heat Curing

(IJSRD/Vol. 2/Issue 03/2014/064)

All rights reserved by www.ijsrd.com 283

GC 3, Faculty of Engineering Curtin University of

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