COMPARATIVE STUDY OF EXPERIMENTAL AND ANALYTICAL RESULTS OF GEO POLYMER CONCRETE

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 7, Issue 1, Jan-Feb 2016, pp. 211-219, Article ID: IJCIET_07_01_018

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ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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COMPARATIVE STUDY OF

EXPERIMENTAL AND ANALYTICAL

RESULTS OF GEO POLYMER CONCRETE

D. Annapurna

Assistant Professor, Civil Engineering Department,

University College of Engineering, Osmania University, Hyderabad, INDIA

Prof. Ravande Kishore

Professor, Civil Engineering Department, University College of Engineering,

Osmania University, Hyderabad, INDIA

M. Usha Sree

P.G. Scholar, Civil Engineering Department,

University College of Engineering, Osmania University, Hyderabad, INDIA

ABSTRACT

Geo polymer concrete is a recently developed construction material which

is environment friendly and perhaps best alternative to conventional concrete.

In the present scenario, where global warming is a big issue due to Co2

emissions, no cement concrete like Geo Polymer Concrete is the big boon for

construction industry. The research work carried out on Geo Polymer

Concrete and documented in the present paper is a step forward in the

direction to encourage the development of Geo Polymer Concrete for its wide

application in construction industry. The present paper describes

experimental work and analytical work pertaining to Finite Element Analysis

using ANSYS software to simulate the flexural behavior of Reinforced Geo

Polymer Concrete Beams. The alkaline solution used for present study was the

combination of sodium silicate and sodium hydroxide solution with the varying

ratio of 2.50. NaoH solids with 97 - 98% purity is purchased from commercial

source and mixed with water to make solution with a concentration of 16

molarity. The standard test specimens viz., cube, cylinder and prism were cast

to understand compressive strength, flexural strength, stress-strain behavior,

Poisson’s ratio. These properties are incorporated for modeling the flexural

behavior of Reinforced Geo Polymer Concrete Beams using ANSYS software,

which will simulate the load-deflection behavior, crack pattern, ultimate load

etc. The model thus developed is validated using the data generated during

experimental investigations on Reinforced Geo Polymer Concrete Beams in

flexure. The results of theoretical investigations match closely with that of

D. Annapurna, Prof. Ravande Kishore and M. Usha Sree


results obtained from experimental work, thus making the developed model

useful for predicting the flexural behavior of Reinforced Geo Polymer Concrete

Beams.

Key words: Geo Polymer Concrete, Fly Ash, Molarity, Sodium Silicate,

Sodium Hydroxide, ANSYS.

Cite this Article: D. Annapurna, Prof. Ravande Kishore and M. Usha Sree,

Comparative Study of Experimental and Analytical Results of Geo Polymer

Concrete, International Journal of Civil Engineering and Technology, 7(1),

2016, pp. 211-219.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=1

1. INTRODUCTION

Concrete is the most widely used material in the world, with Ordinary Portland

Cement being the current most utilised concrete binder. Although there are variations

in the estimates of the total global concrete production, roughly 3 billion tones of

Portland cement was recorded to have been manufactured during last decade.

This rate of concrete usage is increasing semi-exponentially due to continuous global

industrialization. The current usage is estimated at 4 tones per capita. Concrete’s

environmental impact, especially during the manufacturing process, is ranked as one

of the worst in the world as 1 tone of Portland cement production results in 1 tonne of

CO2 emissions. Portland cement manufacture therefore accounts for 5-8% of global

man-made CO2 emissions.

Pozzolans such as blast furnace slag and fly ash may be activated using alkaline

liquids to form a binder and hence totally replace the use of OPC in concrete. In this

scheme, the alkalinity of the activator can be low to mild or high. In the first case,

with low to medium alkalinity of the activator, the main contents to be activated are

silicon and calcium in the by-product material such as blast furnace slag. The main

binder produced is a C-S-H gel, as the result of a hydration process. In the later case,

the main constituents to be activated with high alkaline solution are mostly the silicon

and the aluminium present in the by-product material such as low calcium (ASTM

Class F) fly ash (Palomo, Grutzeck et al. 1999). The binder produced in this case is

due to polymerization. Davidovits in 1978 named the later as Geo polymers, and

stated that these binders can be produced by a polymeric synthesis of the alkali

activated material from geological origin or by-product materials such as fly ash and

rice husk ash. In the case of geo polymers made from fly ash, the role of calcium in

these systems is very important, because its presence can result in flash setting and

therefore must be carefully controlled. The source material is mixed with an

activating solution that provides the alkalinity (sodium hydroxide or potassium

hydroxide are often used) needed to liberate the Si and Al and possibly with an

additional source of silica (sodium silicate is most commonly used).

1.1. Need of present research

Construction industry requires huge amount of Concrete which in turn consumes

tones of Cement. However the production of Cement causes environmental

degradation in view of huge amount of co2 emissions during the production of Cement. It is therefore desired that the dominant construction material like Concrete

needs to be manufactured using the least amount of Cement. Research in that

direction has resulted into development of Fly Ash Concrete with partial replacement

Comparative Study of Experimental and Analytical Results of Geo Polymer Concrete


of Cement. But in view of the fact that the demand for Concrete production is rising

in geometric proportion, production of no Cement Concrete, such as Geo Polymer

Concrete is the need of the hour. Several pozzolanic materials can be considered for

producing Geo Polymer Concrete. Fly Ash is one of the pozzolanic material which is

abundantly available. It is a byproduct from thermal power plants and considered to

be marginal material posing disposal issue. Hence Fly Ash based Geo Polymer

Concrete is a construction material of huge potential providing solution to the

environment related issues. Considerable research is being carried out on Fly Ash

based Geo Polymer Concrete. While properties and performance of Geo Polymer

Concrete to a limited extent has been understood, the critical review of the related

literature reveals that very limited published results are available for Geo Polymer

Concrete with higher alkaline liquid ratio above 0.5. Further, very little work seems to

have been carried out on the flexural behavior of Reinforced Geo Polymer Concrete

(RGPC) analytically. Hence, an attempt is made to study the effect of alkaline liquid

ratio of 0.55 and 0.6 with 16 molarity NaOH on mechanical properties and flexural

behavior of Reinforced Geo Polymer Concrete beams both experimentally and

analytically.

2. RESEARCH METHODOLOGY

In this project fly ash is used as the base material for making geo polymer concrete.

NaOH of 16 molarity and alkaline liquid ratios of 0.55 and 0.6 are used in the present

work. Standard specimens were cast to know the mechanical properties of Geo

Polymer Concrete. ANSYS software is used to model the flexural behavior of

Reinforced Geopolymer Concrete Beams. Ultimate load carrying capacity, Maximum

deflection and crack pattern are observed. Reinforced Geo Polymer Concrete Beam

model results will be validated with experimental results.

3. EXPERIMENTAL PROGRAM

3.1. Materials

The materials used for making fly ash-based geo polymer concrete specimens are dry

fly ash as the source material, aggregates, alkaline liquids, water, and super plasticizer

if necessary.

Fly Ash

Chemical analysis of fly ash is shown in Table 3.1 and is within the limits specified

by IS 3812(Part 1)-2003.

Table 3.1 Properties of Fly ash

Characteristics Results /% by mass

Loss on Ignition 1.80

Silica, SiO2 53.36

Alumina, Al2O3 35.93

Iron, Fe2O3 4.36

Magnesium, MgO

Nil

Calcium, CaO 4.55



Sodium Hydroxide: Sodium hydroxide solids in the form of flakes with 97% purity

were used in the preparation of alkaline activator.

Sodium Silicate: Sodium silicate in the form of solution was used in the preparation

of alkaline activator.

3.2. Mix Design and concrete production

Design of Geo Polymer mixtures have been carried out by considering coarse

aggregate and fine aggregate together as 75% of total mixture by mass with 30% of it

being fine aggregate. This is similar to the aggregate content required for design of

conventional concrete. Further, assuming design of Geo Polymer Concrete same as

that of conventional concrete and following the guidelines of mix design given by

Rangan [2010], the mixture proportions are arrived at and the same is tabulated at

Table 3.2.

Table 3.2 Mix proportion of different alkaline liquid ratios

Alkaline

liquid ratio

Na2Sio3

(kg/m3)

NaOH

(kg/m3)

Water for

NaOH

(kg/m3)

Fly ash

(kg/m3)

Fine Agg.

(kg/m3)

Coarse Agg.

(kg/m3)

0.55 152.074 27.00 33.829 387.096 540 1260

0.6 160.714 28.54 35.745 375 540 1260

3.3. Mechanical properties

Standard specimens were cast to determine the mechanical properties and the same

are tabulated in Table 3.3.

Table 3.3 Mechanical properties of geo polymer concrete for 0.55 and 0.6 alkaline liquid

ratios

3.4. Reinforced Geo polymer Concrete Beam

Reinforced geo polymer beams were cast with the dimensions of

1500mmx230mmx150mm. All beams were reinforced with 16mm of main

reinforcement at the bottom face with the yield strength of 420 N/mm2.

Testing were

carried out to find out the first crack load and ultimate load at the central deflection

using Universal Testing Machine.

4. ANALYTICAL MODELING USING ANSYS

As stated above, the details of modeling are described in the following text.

4.1. Geometry and Modeling

The Finite Element Analysis included modeling of geo polymer composite reinforced

concrete beams with the dimensions and properties corresponding to beams tested

experimentally in the laboratory. By taking the advantage of the symmetry of the

beam and loading, one quarter of the full beam was used for finite element modeling.

S.No

.

Alkaline

liquid ratio

Compressive

strength (N/mm2)

Flexural strength

(N/mm2)

Modulus of Elasticity,

MPa

1 0.55 34 5.16 25000

2 0.6 35.62 5.17 25500



This approach reduces computational time and Computer disk space requirements

significantly.

4.2. Element Types

Eight noded solid brick elements (Solid 65) were used to model the concrete. This

solid element has eight nodes with three degrees of freedom at each node –

translations in x, y, and z directions. The element is capable of plastic deformation,

cracking in three orthogonal directions, and crushing. Flexural and shear

reinforcements were modeled as discrete reinforcement by using beam188 as shown

in Figure 4.1.

Figure 4.1 Beam model showing solid 65 and beam188 elements

4.3. Real Constants

Real Constant Set 1 is used for the Solid 65 element. Real Constant Sets 2 and 3 are

defined for the beam188 element.

4.4. Material properties

The Solid65 element with reference to ANSYS software requires linear isotropic and

multi-linear isotropic material properties to model concrete. As required for modeling

using ANSYS software the material properties such as compressive strength, Modulus

of Elasticity etc. obtained from the experimental work on mechanical properties of Geo

Polymer Concrete given in Table 3.3 has been used as input data.

4.5. Meshing

To obtain satisfactory results from the Solid 65 element, a rectangular mesh was

considered. Further beam 188 is considered for discretization of reinforcement such

that the concrete and reinforcement share the same node. For concrete and

reinforcement the assigned Mesh attributes are 1, 2.

4.6. Loads and Boundary Condition

Displacement boundary conditions are needed to constraint the model to get a unique

solution.

To ensure that the model acts the same way as the experimental beam boundary

conditions need to be applied at points of symmetry, and where the support exist. The

symmetry boundary conditions were set first. Since this is a simply supported beam so

constraints given at one support is in UX, UY and at the other supports UY is given.

The loads and boundary conditions applied to the model are shown in Figure 4.2



Figure 4.2 Loads and boundary conditions

5. RESULTS AND DISCUSSIONS

The results of Reinforced Geo Polymer Concrete beam obtained both experimentally

and analytically are discussed in the following text.

5.1. Displacement and crack pattern

For the nonlinear analysis, automatic time stepping in the ANSYS program predicts

and controls the load step sizes. The longitudinal displacement at ultimate load is

shown in

Figure 5.1. Final Crack patterns observed in experimental and theoretical studies

are found to have similar pattern, which is depicted in Figure 5.2 and 5.3

Figure 5.1 Longitudinal Displacement vector sum at ultimate load



Figure 5.2 Final crack pattern at ultimate load

Figure 5.3 Experimental cracks at ultimate load

From Table 5.1 clearly reveal that, at first, second and third cracks, the load

predicted by theoretical model are 15%, 14% and 13% higher than the experimental

values. This implies that the theoretical model overestimating the load for the model

therefore warrants further refinement for estimation of crack loads. However, for

crack at ultimate load the theoretical model underestimates the load marginally by

3%. Hence, for ultimate load condition the model can be carried as reliable and

dependable. Further, at first, second and third cracks, the deflection predicted by

theoretical model are 6, 10 and 14% higher compared to experimental results. Hence

the theoretical model which overestimates the results pertaining to deflection is

acceptable. However for deflection at ultimate load the theoretical model is



underestimating the result marginally by 3%. Hence, this model could be refined or

the theoretical results are to be cautiously considered.

In general the model to predict the results for loads at different crack and

deflection at different stages of loading, there is a scope for improvement in the model

to satisfy all the requirements simultaneously.

Table 5.1 Comparison between Experimental and Theoretical results

Beam

ID First crack Second crack Third crack Ultimate load

GPC Load

(KN)

Def.

(mm)

Load

(KN)

Def.

(mm)

Load

(KN)

Def.

(mm)

Load

(KN)

Def.

(mm)

Exp. 6.5 0.255 7 0.269 8 0.302 19.5 0.863

Ana. 7.5 0.2700 8 0.2956 9 0.3446 19 0.836

5.2 Load deflection curves of reinforced geo polymer concrete beam

Load deflection curves are plotted using experimental and theoretical results and in

shown in Fig. 5.4. From this figure, it is observed that both curves representing

experimental and theoretical results are very close and at some points overlapping to

each other.

Figure 5.4 Load Deflection curve

6. CONCLUSIONS

At various stages of cracking except, at the final crack theroretical model

overestimates the loads in the range of 13 to 15%.

The theoretical model estimates the load at final crack within acceptable limit of -3%.

At different stages of cracking except at failure the theoretical model overestimates

the deflection in the range of 6 to 14%. Thus enabling the use of theoretical model for

prediction of deflection.

The predicted and experimental deflection profile match closely, indicating the

dependability of theoretical model.

0

2

4

6

8

10

12

14

16

18

20

0 0.2 0.4 0.6 0.8 1

Load

in

KN

Deflection in mm

EXP

ANSYS



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COMPARATIVE STUDY OF EXPERIMENTAL AND ANALYTICAL RESULTS OF GEO POLYMER CONCRETE