Seventh Sense Research Group www.internationaljournalssrg.org Page 1

Experimental Study Of Fly Ash Based

Geopolymer Concrete with Robo Sand

V.V.S.S Chandra Sekhar1, K.Brahmani1, A.Rohit1, K.Mohan Krishna1,

C.Ravi Kumar Reddy2 1UG Student, Civil Engineering, Kallam Haranadha Reddy Institute Of Technology(KHIT), Guntur,A.P,INDIA 2Professor, Civil Engineering, Kallam Haranadha Reddy Institute Of Technology(KHIT), Guntur,A.P, INDIA

Abstract-We know that concrete is the most widely required

and used component in every construction. As concrete

requirement reach the peak, so as cement. The use of

Portland cement results in pollution to the environment due

to the release of major pollutant carbon dioxide (CO2). As

such, many alternate materials had been introduced to

exchange cement in the concrete. Fly ash which is end-

product from the coal industry is easily available material in

the world. Also, usage of fly ash is more environment-

friendly and economical compared to OPC. Fly being

sufficiently rich in silicate and aluminate reacts with

alkaline activators forming an alumino-silicate gel that

causes good binding with the aggregate resulting in the

production of good concrete. The compressive strength of

concrete increases with increase in fineness of fly ash which

leads to the decrease in permeability. Along with fly ash,

metakaolin is used. Another main component in concrete is

the fine aggregate (sand), replaced by robosand or

manufactured sand which is easily available and results in

good strength compared to normal sand. Chemicals, Sodium

Silicate (Na2SiO3) and Sodium Hydroxide (NaOH) are used

in preparing alkaline activators with a molarity of 12M. All

the cube specimens of 150X150X150 mm are cast and

cured by oven curing followed by open-air curing before

testing. These specimens are tested at different ages of 7 &

28 days.

Keywords: Geopolymerisation, fly ash, metakaolin,

robosand, alkaline activators.

I. INTRODUCTION

The present era we can observe over usage of natural

resources and environmental-friendly methods are

being developed for effective management of natural

resources which remain only 30% according to

studies. As we all know constructions now a day

reaching the sky with its advanced technologies. But

the base component of concrete remains same forever

and ever. As the requirement of concrete increases,

cement requirement increases. But the amount of

carbon dioxide produced during manufacturing

cement is 0.93 tons for a ton of cement. Hence,

definitely, an alternative material has to the used for

an eco-friendly construction. So, In 1978 Davidovits

proposed special concrete termed as "Geopolymer"

which acts as a perfect alternative for ordinary

concrete [1]. From this technology and known fact

that fly-ash, which is an end product of thermal power

plant abundantly. Tests have been made utilizing both

geopolymer technology and fly-ash. Hardjito et al

introduced the early work on fly-ash based polymer

concrete [6]. As there is an increasing demand for

high strength concrete, metakaolin came into

existence which is becomes very reactive in excess of

calcium hydroxide. High strengths can be achieved

depending upon color and quality of metakaolin. Due

to increase in construction practices demand for river

sand has been increased, as well as cost. Use of

robosand enhances the quality of concrete by reducing

the permeability as it contains perfect gradation. So, it

serves as the best alternative for river sand. Alkaline

activators are the solutions that play major role in geo

polymerization as they react with the aluminosilicates

present in fly ash.

II. LITERATURE REVIEW

G.Himali Kumari, N.Vidya Sagar et.al

studied the Strength characteristics of

concrete by partially replacing fine aggregate

with robo sand. The study is focused on

evaluating workability and strength by

incorporating robosand in proportions of

0%,50%,75% &100% for concrete grades

M25 and M35.It has been confirmed that the

strength resulted due to replacement is 8-

12% more than the similar mix with

conventional concrete.[2]

G. Hemanaag & SRK Prasad (2014)

conducted a study on Geo-polymer concrete

using Metakaolin, Fly ash replacing cement.

In this study, experiments are conducted on

fly ash and metakaolin based GPC with

various molarities of alkaline liquids. The

compressive strengths are compared for

different proportions. It is observed that

metakaolin based GPC attained higher

strengths compared to fly ash based GPC.

Also observed that molarity is directly

proportional to compressive strength i.e.

increase in molarity resulted in increase of

compressive strength.[3]

M.Muthuanand, Dr.G.Dhanalakshmi (2015) on their study on metakaolin based geopolymer concrete, came to conclusion

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that the compressive capacity of concrete cubes gradually increases with the addition of 10% of metakaolin. Due to a good alkaline reaction between fly ash and metakaolin, mix with 70% fly-ash and 30% metakaolin shows good compressive strength. Also, the increase in metakaolin proportion results good compressive strength.[7]

Chunchu Bala Rama Krishna and M.Rama Krishna investigated compressive and flexural strengths for various combinations of fly ash and metakaolin with different molarities like 8M, 10M & 12M considering M30 grade concrete. Air dry curing is adopted. The results showed that there is a significant increase in strength when the molarity has increased. It is also found that the type of metakaolin used affected the strength of geopolymer concrete. Buff colored(Pink) Metakaolin has given higher strength, unlike white metakaolin.[4]

P.K.Jamdade & U.R.Kawde investigated the behavior of fly ash based geopolymer concrete at elevated temperature curing in an oven. The cubes cast are subjected to different curing temperatures i.e. 600C, 900C & 1200C. The observed results revealed that as curing temperature increases, compressive strength increases. But cubes cured at 600C attained greater compressive strength and cubes cured at 900C & 1200C has not shown a significant increase in the compressive strength.[5]

III. Materials

A. Coarse Aggregate

Coarse aggregates used in the study are crushed

stones of 20mm and 10mm size obtained from nearby

quarry site. As per IS 10262:2009,20mm aggregates

are taken 60% of total aggregate content and 10mm

aggregates are taken 40% of total content. The

specific gravity of coarse aggregate obtained is 2.69.

Figure No.1 Coarse Aggregates

B. Fine Aggregate

The fine aggregate adopted in the present study is

robosand. Robo sand or M-Sand is used as a

replacement of river sand. Robo sand is a purified

form of quarry dust and washed to remove the fine

rock dust to enhance the quality as per IS: 2386-

1975.It has proper gradation with particle size ranging

from 0-4.75mm. It is free from deleterious substances

which are likely to be present in the normal sand. It

makes the concrete cohesive with a low number of

voids due to perfect gradation. The specific gravity of

this robo sand obtained is 2.65 and fineness modulus

is 3.5

Figure No.2 Robo Sand

C. Flyash

It is a residue that is obtained from the combustion

of coal. They are in rich in silicates and alumina

which react with the alkaline activators to produce a

gel that can bind the constituents resulting in the geo

polymerization process. Fly ash is acquired from the

Thermal power plant, Vijayawada. The present is

carried out by using Class-F Fly ash. The fineness of

fly ash is 15%. The specific gravity of fly ash

obtained is 2.13.Bulk density of fly ash is 965 kg/m3

Figure No.3 Fly ash

D. Metakaolin

Metakaolin is obtained from the clay mineral

kaolin through calcination at 650-7500 c in an

externally fired rotatory kiln. It is a highly reactive

compound and pozzolanic in nature. It is available in

different forms such as white and buff colored. In the

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present study light, buff colored metakaolin is used. It

is acquired from Surat, Gujarat by Navapad Sales.

The specific gravity of metakaolin is 2.41

Figure No.4 Metakaolin

E. Alkaline Activators

Alkaline activator adopted in the present study is a

composite mix of Sodium Hydroxide (NaOH) and

Sodium Silicate (Na2SiO3). Sodium hydroxide, also

known as caustic soda is locally available in the form

of flakes and pellets. Sodium Silicate is available in

liquid form. Sodium Hydroxide dissolves in water to

form NaOH solution. These are the most important

components in the geopolymer mix as they enhance

several reactions with aluminosilicates that are

available in fly ash and metakaolin.

Table No.1 Chemical Composition of Fly Ash

IV. METHODOLOGY

A. Alkaline Solution Preparation

The alkaline solutions are to be prepared

24hours prior to use in concrete. Sodium hydroxide

and Sodium silicate are used in preparing alkali

solution. Sodium hydroxide is present in the form of

flakes which are to be dissolved in water to make

Sodium Hydroxide solution. In the present study 12M

(12 Molarity) is considered. So, for making a 12Molar

solution 480grams of sodium hydroxide flakes are to

be dissolved in water to make a one-litre solution.

Heat is evolved when both solutions are mixed. So,

they are mixed in concrete separately.

Molarity=moles of solute/litre of solution

12M=12 molarity

=2 x molecular weight

=12 x40

=480 gm

B. Mix Design

As there are no confined codal practices for an

optimum geopolymer mix, quantities of constituents

are calculated by trail method and assuming the

density of concrete as 2400 kg/m3 and rest of the

calculation is carried out by considering the density of

concrete.

Benny Joseph and George Mathew has proved

that total volume occupied by fine & coarse aggregate

is taken as 70% which resulted in appreciable

strengths [8]. Then the occupancy of geopolymer

binders i.e., fly-ash, metakaolin& alkaline activators

is obtained as 30% of volume. The alkaline liquid to

powder content (FA & MK) ratio is adopted as 0.45.

The ratio of Na2SiO3 to NaOH is taken as 2.5.

In order to verify the feasibility of robo sand over

river sand in strength point of view, a sample mix is

done and the test results are observed

Table No.2 Mix Proportions for GPC with

Robo Sand

Table No.3 Mix Proportion for GPC with

River Sand

Oxides Percentage %

SiO2 60.53

Al2O3 26.21

Fe2O3 5.8

CaO 1.94

MgO 0.39

K2O+Na2O 1.01

SO3 0.28

Loss on Ignition 2.0

Mix No Mix Proportion

GPC 1 100%+0%MK

GPC 2 80%+20%MK

GPC 3 60%FA+40%MK

GPC 4 50%FA+50%MK

Mix No Mix Proportion

GPC 5 50%FA+50%MK

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Table No.4 Quantities of Materials

V. Test Procedure

A. Mixing and Casting

Mixing and casting of geopolymer based

concrete are similar to normal concrete.

Firstly a dry mix is prepared consisting of

coarse aggregate, robo sand, powder

content i.e., fly ash and metakaolin as per

different proportions in required

quantities. Then sodium hydroxide and

sodium silicate are added to the dry mix

separately. Proper mixing is done for 5-7

min to attain good bond between the

constituents. Then the mix is filled into

150*150*150mm moulds and to attain

uniform filling of concrete, compaction is

done at the rate of 25blows for 3 layers.

As the setting time is very slow, the cubes

are allowed to rest in the mould for 1 or 2

days. Then the cubes are removed from

the moulds for curing.

B. Curing

Curing is carried out in 2 stages. In the

first stage, the cubes are kept in the oven

for 24-48 hrs at 600c. In the second stage,

the cubes are allowed to be cured in open

atmosphere i.e., AMBIENT CURING.

C. Testing

The cubes are tested for 7 & 28 days after

curing. The compressive strength value

can be obtained by subjecting the cubes

after desirable curing period to gradual

loading under a compressive testing

machine which has a capacity of

subjecting 1000KN load.

Figure No.5 Compressive testing machine

VI. Results and Discussion

For the mix proportion 100% fly-ash and 0%

metakaolin with robosand, compressive

strength at 7days is 4.416 N/mm2 and 28

days compressive strength is 6.84 N/mm2.

For the mix proportion 80% fly-ash and 20%

metakaolin with robosand, the compressive

strength at 7days is 5.5 N/mm2 and 28 days

compressive strength is 8.36 N/mm2.

For the mix consisting 60% fly-ash and 40%

metakaolin with robosand, the compressive

strength at 7days is 6.85 N/mm2 and 28 days

compressive strength is 10.53 N/mm2.

Mix Mass Of Materials in Kg/m3

Coarse

Aggregates

Fine Aggregates Fly-ash Metakaolin NaOH Na2SiO3

20

MM

10

MM

River

Sand

Robo

Sand

GPC 1 705.6 470.4 - 504 496.551

- 63.84 159.6

GPC 2 705.6 470.4 - 504 397.2 99.351 63.84 159.6

GPC 3 705.6 470.4 - 504 297.93 198.62 63.84 159.6

GPC 4 705.6 470.4 - 504 248.27 248.27 63.84 159.6

GPC 5 705.6 470.4 504 - 248.27 248.27 63.84 159.6

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For the mix proportion 50% fly-ash and 50%

metakaolin with robosand, the compressive

strength at 7days is 8.52 N/mm2 and 28 days

compressive strength is 12.75 N/mm2.

For the mix proportion 50% fly-ash and 50%

metakaolin with river sand, the compressive

strength at 7days is 3.48 N/mm2 and 28 days

compressive strength is 5.125 N/mm2.

Table No.5 Compressive Strengths for

Different Mix Proportions

Table No.6 Compressive Strength comparison for

river and robo sand

Figure No.6 Compressive Strength At 7

days

Figure No.7 Compressive Strength At 28

days

Mix

No

Mix Proportion Compressive

Strength in N/mm2

7 Days 28 Days

GPC 1 100%FA+0%MK 4.416 6.84

GPC 2 80%FA+20%MK 5.52 8.36

GPC 3 60%FA+40%MK 6.85 10.53

GPC 4 50%FA+50%MK 8.52 12.75

Type

Of

Sand

Mix Proportion Compressive

Strength in N/mm2

7

Days

28 Days

River

Sand

50%FA+50%MK 3.485 5.125

Robo

Sand

50%FA+50%MK 8.52 12.75

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Figure No.8 Compressive Strengths at 7&28 days

Figure No.9 Compressive Strengths at 7&28 days for

river sand and robo sand

VII. CONCLUSIONS

The compressive strength of geopolymer

concrete specimens at 7 days has achieved

65% of its final strength at 28days.

For every 20% addition of metakaolin, there is an

increase of 25% in compressive strength.

For proportion containing 50%Flyash and

50%Metakaolin with robo-sand, there is an

increase of 44-48% in compressive strength

compared to that of river-sand.

There is an increase in compressive strength

as metakaolin content increases.

Low compressive strength values are resulted

due to the use of light buff colored

metakaolin and fly ash used which brought a

drastic decrease in the compressive strength.

So, metakaolin being a material that can

attain higher strengths can regulate the

strength to get lowered which is dependent

on many conditions including the color of

metakaolin used, type of curing and weather

conditions as it requires high temperatures to

get processed to result in desired strength.

The variation of strength can be observed as

a linear variation representing the peak

strength for GPC 4

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VIII. References

[1] J.Davidovits "Geopolymers Inorganic Polymeric

New Materials" 1991 Journal of Thermal Analysis 37;

1633-1656

[2] RukmangadharaRao.S et al. Int. Journal of

Engineering Research and Applications IJERA ISSN:

2248-9622, Vol No. 5, Issue 12, (Part - II) Dec 2015,

PP.84-88

[3]G.Hemanaag, S.R.K Prasad, “Geopolymer

Concrete Using Metakaolin, Fly ash and their

comparison", IJERT, Volume.3, Issue No 8, Aug

2014

[4] Chunchu Bala Rama Krishna & M.Rama Krishna

2015,”An Experimental Study on Geopolymer

Concrete with fly ash and metakaolin as source

materials", IJMETMR, Vol.2, Issue No:12

[5] P.K.Jamdade, U.R Kawade, “Evaluate Strength of

Geopolymer Concrete by Using Oven Curing” IOSR

Journal of Civil Engineering, Volume No. 11, Issue 6,

PP: 63-66, e-ISSN: 2278-1684/p-ISSN: 2320-3340,

November-December 2014.

[6] Hardjito et al., 2005 Fly Ash Based Geopolymer

Concrete, Australian Journal of Structural

Engineering, 2005. 6: pp 1-9.

[7] M.Muthuanand, G.dhanalakshmi 2016

“Metakaolin Based Geopolymer Concrete, ICCEET

2016, IJARMATE, VOLUME NO.2, Special Issue 2