EFFECT of NaOH CONCENTRATION

on STRENGTH of GGBS and BRHA BASED

GEOPOLYMER CONCRETE

Gokulanathan V1, PrasannaVenkatesan R

2, Pazhani K.C.

3.

College of Engineering, Guindy.

Department of Civil Engineering, Anna University, Chennai 600025, INDIA.

1Email: gokulcivilions@gmail.com,

2Email: prasmyth@gmail.com

3Email: kcpazhani@annauniv.edu

ABSTRACT

This paper presents the compressive strength of

geopolymer concrete made from ground granulated

blast furnace slag (GGBS) and black rice husk

ash(BRHA). A mixture of Sodium Hydroxide

(NaOH) and Sodium Silicate (Na2SiO3) solutions

was used as the alkaline activator solution. The

experiments were conducted for varying molar

concentrations of sodium hydroxide such as 5M, 8M

and 11M and with black rice husk ash being

replaced at 10%, 20% and 30% of the total binder

content. Compressive strength test was carried out

on 150mm cube specimens at the age of 3, 7 and 28

days. The test results revealed that, as the

concentration of sodium hydroxide solution

increases, the compressive strength of geo-polymer

concrete also increases. The average strength is

approximately same for both 0% and 10%

replacement of BRHA. The average strength of

20% replacement BRHA is decreased nearly 1.1

times when compared to the 0% and 10%

replacement of BRHA. The average strength of

30% replacement BRHA is decreased nearly 1.5

times when compared to 0% and 10% replacement

of BRHA.

KEYWORDS: Scanning electron microscope (SEM)

Black Rice Husk ash (BRHA), Ground Granulated

Blast Furnace Slag (GGBS), Sodium Hydroxide

(NaOH), Sodium Silicate (Na2SiO3), Geopolymer

concrete (GPC).

I.INTRODUCTION

As a result of booming infrastructural development

around the world, the demand for cement production is

also increased. Ordinary Portland Cement (OPC) is

mainly used as a cementitious material for the concrete

production. Nowadays, concrete industry is known to

be the major consumer of natural resources, such as

water, sand and aggregates, and manufacturing

Portland cement also requires large amounts of each of

them. As a result, the energy consumption for the

cement production is high. It is estimated that the

production of cement will increase from 1.5 billion

tons in 1995 to 2.2 billion tons in 2010 [8]. For

manufacturing each tone of the Portland cement about

1.5 tons of raw materials is needed [9]. The production

of 1 tone ordinary Portland cement consumes 4GJ

energy and produces about 1 tone of carbon dioxide

(CO2) to the atmosphere [10] which leads to

environmental pollution. To reduce the environmental pollution and excess embodied energy utilization, the

alternative solution is Geo-polymer concrete.

The term geo-polymer was first coined by Davidovits in 1978 to describe a family of mineral

binders with chemical composition similar to zeolites

but with an amorphous microstructure [5]. Unlike

ordinary Portland/pozzolanic cements, geo-polymers

do not form calcium- silicate-hydrates (CSHs) gel for

matrix formation and strength, but utilize the poly-

condensation reaction of silica and alumina precursors

to attain structural strength. Two main constituents of

geo-polymers are: source materials and alkaline

liquids. The source materials should be rich in silicon

(Si) and aluminium (Al). These could be natural

minerals such as kaolinite, clays, etc. Alternatively, by-

product materials such as fly ash, silica fume, slag,

rice-husk ash, red mud, etc could be used as source

materials. The alkaline liquids are from soluble alkali

metals that are usually sodium or potassium based. The

most common alkaline liquid used in geo-

polymerization is a combination of sodium hydroxide

(NaOH) or potassium hydroxide (KOH) and sodium

silicate or potassium silicate. Till now most of the

research has been conducted on flyash based

geopolymer and in this study, industrial wastes such as

ground granulated blast furnace slag (GGBS) and agro

waste as black rice husk ash (BRHA) are used as a

source materials to prepare geopolymer concrete.

II.EXPERIMENTAL INVESTIGATION

A. Materials used

The materials used in this study are GGBS,

BRHA, fine and coarse aggregates, alkaline solution,

super plasticizer and water.

1. Ground Granulated Blast Furnace Slag

(GGBS) Geopolymer concrete is produced by

activating alumino-silicate based source material with

an alkaline solution. Ground granulated blast furnace

slags are used as one of the source material for

geopolymer binder. GGBS was obtained from JSW

cements limited. Bellari, Karnataka. It was given to

SGS India Pvt. Ltd. Laboratory, Ambattur, chennai for

testing. Table 1. shows the Chemical composition of

GGBS.

Table 1: Chemical Composition of GGBS

S.No Chemical Composition Percentage

1 Al2O3 14.06

2 Fe2O3 2.80

3 CaO 33.75

4 MgO 7.03

5 K2O 0.69

6 Na2O 0.41

7 SiO2 31.25

300m 100m

50m 10m

Fig 1. SEM images of GGBS

2. Black Rice Husk Ash (BRHA)

Black rice husk ash (BRHA) is a by-product

from the burning of rice husk. The rice husk ash is a

highly siliceous material that can be used as an

admixture in concrete if the rice husk is burnt in a

specific manner. The available Rice husk ash is black

in colour as it contains unburnt carbon. Chemical

composition of black Rice husk ash is shown in Table

2. From Table 2. silica contributes about 94% of the

BRHA.

Table 2: Chemical composition of BRHA

S.No Chemical Composition Percentage

1 Al2O3 0.56

2 Fe2O3 0.43

3 CaO 0.55

4 MgO 0.40

5 K2O 0.66

6 Na2O 0.06

7 SiO2 93.96

300m 100m

50m 10m

Fig 2. SEM images of BRHA

3. Alkaline activator solution

A combination of sodium hydroxide solution

(NaOH) and sodium silicate solution (Na2SiO3) was

used as an alkaline activator solution. The sodium

hydroxide solution was prepared by dissolving the

sodium hydroxide solids, in the form of pellets in

distilled water.In order to avoid the effect of unknown

contaminants in the mixing water, the sodium

hydroxide pellets were dissolved in distilled water.

In this study, the molar concentrations of

NaOH used are 5M, 8M and 11M. Since the molecular

weight of Sodium Hydroxide is 40g, and in order to

prepare 5M solution 5 x 40= 200 gms of Sodium

Hydroxide was dissolved in 1000 ml of distilled water.

The sodium silicate solution contained Na2O =14.7%,

SiO2 = 29.4%, and 55.6% of water, by mass. The

activator solution was prepared at least one day prior to

its use.

4. Aggregates

Granite type coarse aggregates was passed

through 20mm sieve and meets gradation

requirementsof IS 2386 -1963. Fine aggregate of

natural river sand taken from a local supplier are used

in the present study and they have the properties as

given in Table3. Its gradation meets zone ii of IS 383 -

1970 requirements.

Table 3. Properties of aggregates

S.No

Property

Coarse

aggregate Sand

20mm

1 Fineness modulus 8.14 3.45

2 Specific gravity 2.87 2.6

3 Bulk

density(Kg/m3)

1533.33 1254

Table 4. Details of mix proportions

5. Super plasticizer High-range water-reducing naphthalene based

super plasticizer was added to the mixture to improve

the workability of fresh concrete.

6. Water Extra water nearly 10% of binder is added to

increase the workability of the concrete.

B. Mix proportions

In this study, mix design procedure was

chosen from the literature by Djwantoro Hardjito, et al

(2004), showed that the aggregates occupythe largest

volume, (about 75-80 % by mass) in GPCs.The total

volume occupied by the aggregates (Coarse and fine

aggregates) is assumed to be 77%. The alkaline liquid

to GGBS ratio is taken as 0.40, Unit weight of

geopolymer concrete is 2400 kg/m3, sodium silicate to

sodium hydroxide is 2.5 [4].The details of mix

proportions are given in Table 4. In this study

conventional concrete is 100% GGBS. Three levels of

sodium hydroxide concentration i.e. 5 M, 8 M and

11 M were used.

Mix % replacement

of RHA

GGBS BRHA F.A C.A NaOH Na2SiO3 Sp

Kg/m3

GC 1

5M

0

394

0

647

1201

45

113

6

10 355 39 647 1201 45 113 6

20 315 79 647 1201 45 113 6

30 276 118 647 1201 45 113 6

GC 2

8M

0

394

0

647

1201

45

113

6

10 355 39 647 1201 45 113 6

20 315 79 647 1201 45 113 6

30 276 118 647 1201 45 113 6

GC 3

11M

0

394

0

647

1201

45

113

6

10 355 39 647 1201 45 113 6

20 315 79 647 1201 45 113 6

30 276 118 647 1201 45 113 6

C.Mixing, casting and curing of GPC

1. Mixing and casting

The alkaline activator used for the experiment was a mixture of Sodium hydroxide and Sodium

silicate solutions. These solutions were prepared 24

hours before the mixing of concrete [4].

The aggregates, GGBS and BRHA were

mixed together and the prepared alkaline solution was

added to the dry mix and thoroughly mixed.The super

plasticizer along with extra water was then added to the

mix to improve the workability of concrete.

The geopolymer concrete was placed in 150

mm cube moulds in three layers and each layer was

compacted by giving 25 blows with a 25mm tamping

rod.

2. Curing

The geopolymer concrete specimens were

then placed in a hot air oven at a temperature of 600C

for 48 hours. And then the specimens were taken

outand cured under room temperature till the time of

testing.

Material collection Addition of NaOH solution

Mixing of all ingredients GGBS cube specimen

BRHA cube specimen

Fig 3. Process of cube casting

D. Compressive Strength Test

The cube specimens were tested in a

compressive testing machine having 2000KN capacity

in accordance with the Bureau of IS 516-1959

procedures. The compression test results are tabulated

in Table 5.

Table 5. Average Compressive Strength Results

S.NO Molarity % replacement of BRHA Average compressive strength MPa

3 Day 7 Day 28 Day

1 5M 0 56.23 60.5 62.7

10 56.2 61.0 62.95

20 51.4 55.2 57.3

30 37.2 40.7 42.0

2 8M 0 61.9 66.5 69.2

10 62.0 66.9 68.86

20 56.7 61.2 62.9

30 41.33 44.8 46.0

3 11M 0 66.96 72.2 74.86

10 67 71.96 74.9

20 61.1 65.03 68.1

30 44.5 47.5 50.3

Figure 4: compressive strength of geopolymer

concrete with different molar concentration of

sodium hydroxide (NaOH)

Figure 5: compressive strength of geopolymer

concrete with different percentage replacement of

black rice husk ash (BRHA)

Figure 6: compressive strength of geopolymer

concrete with different curing time

1II. RESULTS AND DISCUSSION

1. The average compressive strength is approximately same for both conventional and

10% replacement of BRHA.( fig 6)

2. The average compressive strength of concrete with 20% replacement BRHA is decreased nearly 1.1

times when compared to the conventional and 10%

replacement of BRHA.

3. The average compressive strength of 30% replacement BRHA is decreased nearly 1.5 times

when compared to conventional and 10%

replacement of BRHA.

4. Due to the presence of high silica content in black Rice Husk Ash (BRHA) there is a fast chemical

reaction occurred resulting quick setting of

geopolymer concrete.

5. The average compressive strength increased approximately 10 to 12% when there is increase in

molar concentration of NaOH solution between

5M and 8M.

6. Compressive strength of geopolymer concrete decreased with increase in percentage replacement

of BRHA. ( fig 5)

7. Compressive strength of geopolymer concrete increased with increase in molar concentration

from 5,8 and 11M. ( fig 4)

IV. CONCLUSIONS

In this study, it can be concluded that:

1. The strength characteristic of geopolymer concrete

depends on the molar concentration of sodium

hydroxide (NaOH). The compressive strength of

geopolymer concrete increased with increase in

molar concentration of NaOH because leaching

action of silicon and aluminium from the source

materials get increased with higher concentration

of NaOH results in higher compressive strength of

geopolymer concrete.

2. The compressive strength of GGBS and BRHA

based geopolymer concrete is higher when

compare to fly ash based geopolymer concrete of

8M concentration ( NaOH) solution [2].

3. The replacement of BRHA in GGBS based

geopolymer concrete is significant only in 10% of

BRHA and quick setting has occurred if the

percentage of BRHA content increases.

4. The ease availability of rice husk ash type is black

rice husk ash (BRHA). Further experiments are

needed to increase the strength and setting time of

GGBS and BRHA based geopolymer concrete.

0

10

20

30

40

50

60

70

80

5M 8M 11M

3 Days

7 Days

28 Days

Molar Concentration

Av

era

ge

Co

mp

ress

ive

stre

ng

th i

n M

Pa

0

10

20

30

40

50

60

70

0 10 20 30

3 days

7 days

28 days

% Replacement of BRHA

Av

era

ge

com

pre

ssiv

e st

ren

gth

MP

a

0

10

20

30

40

50

60

70

80

3 7 28

0% BRHA

10% BRHA

20% BRHA

30% BRHA

Days

Av

era

ge

com

pre

ssiv

e st

ren

gth

( M

Pa

)

ACKNOWLEDGEMENT

First and for most, thank to god for giving me

a life. I am deeply indebted to my project guide, for her

guidance, encouragement and stimulating suggestions

which enabled me to carry out this project work

successfully. Thanks also to the technician of Concrete

Laboratory, which help to me on doing my research

from mixing the concrete until the testing of the

concrete. Finally I would like to thank my parents and

friends for their encouragement and unending support.

REFERENCES

[1] Alireza NajiGivi, Suraya Abdul Rashid, Farah

Nora A. Aziz, Mohamad Amran Mohd Salleh,

(2010), Assessment of the effects of rice husk ash particle size on strength, water permeability and

workability of binary blended concrete, Construction and Building Materials., Vol. 24,

Issue 11, pp.2145-2150.

[2] Bhosale, M.A , Shinde, N.N (2012), Geopolymer concrete by using fly ash in construction, IOSR Journal of Mechanical and Civil Engineering.,

Vol. 1, Issue 3, pp.25-30.

[3] Detphan. S, and Chindaprasirt, P

(2009), Preparation of fly ash and rice husk ash geopolymer International Journal of Minerals, Metallurgy and Materials.,Vol. 16, Issue 6, pp.

720-726.

[4] Hardjito, D. and Rangan, B. V.

(2005),Development and Properties of Low Calcium Fly Ash Based Geopolymer Concrete, Research Report GC 1, Faculty of Engineering,

Curtin University of Technology.

[5] Joseph Davidovits, (1994), Development of Very Early High Strength Cement, Journal of Materials Education, Vol. 16, pp. 91-139.

[6] Joseph Davidovits, (1994), Global Warming Impact on the Cement and Aggregates Industries, World Resource Review, Vol. 8, No.2, pp. 263-

278.

[7] Kartini, K, Mahmud, H.B, Hamidah, M.S, (2006),

Strength Properties of Grade 30 Rice Husk Ash Concrete 31st Conference on Our World in Concrete & Structures.

[8] Malhotra, V. M. (1999), Making Concrete "Greener" With Fly Ash. ACI Concrete

International, pp. 61-66

[9] McCaffery, R. (2002), Climate Change and the Cement Industry, Global Cement and Lime Magazine ( Environment Special Issue), pp. 15-19.

[10] Mehta, P. K., (2001) Reducing the Environmental Impact of Concrete, ACI Concrete International, Vol 23 (10): pp. 61-66.

[11] Mohd Mustafa Al Bakri, Mohammed H,

Kamarudin H, Khairul Niza I and Zarina Y.

(2011), Review on fly ash-based geopolymer concrete without Portland Cement Journal of Engineering and Technology Research Vol. 3(1),

pp. 1-4.

[12] Zhang, M.H. and Mohan, M.V. (1996). High Performance Concrete Incorporating Rice Husk

Ash as a Supplementary Cementing Material.

ACI Materials Journal. Vol. 93(6): pp. 629-636.