Utilisation of waste material in geo-polymeric concrete

&1 Muhammad Fadhil Nuruddin PhDAssociate Professor, University Tecknology PETRONAS, Tronoh, Perak,Malaysia

&2 Sobia Anwar Qazi MSc<University Teknology PETRONAS, Tronoh, Perak, Malaysia

&3 Andri KusbiantoroPhD student, University Teknology PETRONAS, Tronoh, Perak, Malaysia

&4 Nasir Shafiq PhDAssociate Professor, University Teknology PETRONAS, Tronoh, Perak,Malaysia

Fly ash (FA), silica fume (SF) and rice husks are hazardous waste materials that have no use and in the past have been

landfilled. However, landfilling is becoming expensive and causes contamination to soil and ground water. Utilisation of

waste material in concrete is also very effective in overcoming the problems caused by the production of cement; namely

the emission of carbon dioxide and degradation of the environment due to the quarrying of rawmaterials (limestone and

clay) for the production of cement. This research studywas based on the complete elimination of ordinary Portland cement

(OPC) from concrete that can achieve 28 days target cube strength in the range of 40--50 MPa with the emphasis on the

curing techniques applicable for in situ construction; namely ambient and external exposure curing. Fly ashwas utilised as

a base sourcematerial and silica fume andmicrowave-incinerated rice husk ash (MIRHA)were used as replacements for the

fly ash by 3, 5 and 7%. Alkaline activators, namely sodium hydroxide and sodium silicate solution were used as activators

of silica and aluminium in the source material and sugar was incorporated in themix to increase the hardening time of the

concrete. Compressive strength, flexural strength and scanning electron microscopy (SEM) tests were conducted on the

specimens and the results showed that at 3, 7, 28, 56 and 90 days the fly ash along with silica fume, MIRHA and alkaline

activators could be a good replacement of cement. The compressive strength of external exposure curing for the

geopolymeric concrete reached up to 48.7 MPa at 28 days and this concrete had awell developedmicrostructure shown by

SEM analysis. The flexural strength showed values which were comparable with OPC concrete.=

1. IntroductionMaterial by-products such as fly ash (FA) and silica fume (SF)

which are derived from ever-expanding industrial processes or

waste such as rice husks from agricultural activities are

undesirable materials for the environment if they are not

properly disposed of. These materials may eventually find their

way to landfills, but landfills are becoming scarce and

expensive to maintain (Fytianos et al., 1998). Over time this

may lead to a waste disposal crisis. Fly ash is composed of

smaller particle sizes that contain some toxic elements such as

arsenic, chromium, boron, vanadium and antimony ( Sushil

and Batra, 2006). The toxic elements contained within the fly

ash may be leached from them after being placed in landfills.

Unfortunately, power plants produce millions of tonnes of fly

ash annually, the greater portion of which is mostly wasted in

landfills at a cost of around US$ 1 billion. The global

production of fly ash is expected to rise by 800 million tons

annually in 2010 (Izquierdo et al., 2009). The disposal costs of

fly ash can be saved if, for example, fly ash is used in the

manufacture of concrete; the actual cost of this fly ash is 11--22

cents/kg (Rohatgi et al., 2006).

On the other hand, disposal of rice husk is difficult because of

its low nutritional value; a long time period is required for it to

decompose sufficiently to be used in manure (Zemke and

Woods, 2009). Almost 2.2 million tons of rice husks are

produced per year from agricultural activity in Malaysia,

contributing to an annual production rice of husks of 500--

600 million metric tons worldwide (Bouman et al., 2007).

The utilisation of waste material in concrete as a replacement for

cement can also be useful in overcoming problems caused by the

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:55:31

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro and Shafiq

Proceedings of the Institution of Civil EngineersConstruction Materials 000 Month 2011 Issue CM000

Pages 1–13 doi:

Paper 1000045Received 30/06/2010 Accepted 02/11/2010

Keywords: ???/???/??? ;

ice | proceedings ICE Publishing: All rights reserved

1

production of cement, namely the emission of carbon dioxide

and degradation of the environment due to quarrying of raw

materials (limestone and clay) for the production of cement.

Global concrete production in the world is expected to rise from

about 10 billion tons in 1995 to almost 16 billion tons in 2010

(Odd and Koji, 2000). Cement production also reached a new

record amount of 2?31 billion metric tons with an annual

increase of 5?5%, and that is expected to rise by 4?1% globally to

3?5 billion metric tons in 2013 (World Cement Industry, 2010).

The contribution of the global cement industry to greenhouse

gas emissions that give rise to global warming, is around

1?35 billion tons annually, which is 7% of the total man-made

greenhouse gas emissions in the Earth’s atmosphere (Malhotra,

2002). Apart the issue of carbon dioxide emissions derived

from the production of cement, the quarrying of raw materials

(limestone and clay) for the production of cement is increas-

ingly becoming a source of environmental degradation (Naik

et al., 2005). For example, to produce 1 ton of ordinary

Portland cement (OPC), 1?6 tons of raw materials are needed

and the rate of extraction of raw materials from the Earth is

20% greater than the capacity of the Eearth to replenish itself.

Hence, raw materials consumed in 12 months would take 14?4

months to be replenished (Naik et al., 2005).

In 1979, Davidovits created and applied the term geopolymer

because the process of polymerisation takes place, in which

silica and aluminium, present in the source material [i.e. fly ash

(FA)/ silica fume (SF)/rice husk), reacts with the alkaline liquid

to produce binders. Geopolymeric cements produced in this

manner produce 80 to 90% less carbon dioxide emissions in

comparison with that produced in OPC (Davidovits, 2008).

Such reductions in carbon dioxide emissions ultimately

support decreases in global warming and the depletion of

ozone layer.

For a geopolymer concrete, the polymerisation occurs through

a condensation process in which water and heat is released

during the endothermic chemical reaction. Within the geopo-

lymerisation process, the polycondensation of alumino-silicate

oxides (Si2O5, Al2O2) with alkali polysilicates (sodium or

potassium silicate) takes place producing silica (Si)—oxygen

(O)—aluminium (Al) bonds (Hardjito and Rangan, 2005).

The chemical reaction comprises the following steps (Xu and

Van Deventer, 2000)

(a) Dissolution of silica and aluminium atoms from the

source material through the action of hydroxide ions.

(b) Transport, orientation or condensation of precursor ions

into monomers.

(c) Polymerisation (through the polycondensation process)

and set of monomers into geopolymeric structures.

The hardening of concrete depends upon curing temperature

and curing time. For FA-based concrete, the setting time was

decreased by a factor of six when the temperature was increased

from 6 to 80 C (Brooks, 2002) and according to Wang et al.

(2004), the increased temperature during cure gives rise to

pozzolanic reactions. The reaction of FA is very slow at ambient

temperatures (Puertas et al., 2000) and this delays the initiation

of the setting of concrete (Kirschner and Harmuth, 2004).

Previously, research has been completed on the development of

mixture proportions for FA-based geopolymer concrete

(Hardjito et al., 2004) and for which were determined the

short-term and long-term performance properties of mixes

having low calcium content (Wallah and Rangan, 2006).

Researchers have up to now only found solutions appropriate

for the precast concrete industry such as adapting oven curing

for the production of geopolymeric concrete (Fernandez-

Jimenez et al., 2005; Rangan, 2008) ?. Nonetheless, given the

inherent strength and durability properties of polymer

concrete, there is a dire need to further develop its use for in

situ construction. This is an obvious gap in the previous

research and the information obtained in the present study

may help to provide a useful contribution.

2. Methodology

2.1 Material selection

The materials used in this research study were chosen according

to specifications that met the requirements of the appropriate

British Standards as well as the objectives of this research.

The FA was obtained from Manjung power station, Lumut,

Perak, Malaysia. The densified SF was obtained from Elkem

Materials (Malaysia) having a bulk density of 500—700 kg/m3,

whereas the microwave-incinerated rice husk (MIHRA) was

obtained from the Bernas rice milling plant, Kuala Selangor,

Malaysia. The chemical compositions of FA, SF and MIRHA

are shown in Table 1.

The coarse aggregate used in this experiment was crushed

granite stone having a maximum size of 20 mm (BSI, 1989)

whereas the fine aggregate was a natural Malaysian sand with

a fineness modulus of 2?7, classified in zone 3. Fine aggregate

was also sieved to exclude sizes of less than 5 mm.

Sodium silicate (Na2SiO3; Grade A53) was used in solution and

mixed with 56?31% (wt.) of water, 29?43% (wt.) of silica oxide

(SiO2) and 14?26% (wt.) of sodium oxide (Na2O). Sodium

hydroxide (NaOH) used was in the form of pellets.

The concentration of the sodium hydroxide solution was

8 mol/l and 29?4% (wt.) of pellets were added to the water to

make 1 kg of solution.

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:03

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

2

Sugar was used to increase the setting time of concrete. The

intention in adding refined white sugar to the concrete mix was

to prevent the cement from fully combining with the water and

thus retard the hardening process (McDonnell, 2006? ; Nuruddin

et al., 2009). Sugar is an organic compound which is chemically

named as sucrose or saccharose. Themolecular formula of sugar

used in this study is C12H22O11. Water used in the mix was tap

water in accordance with B.S. 3148:1980 (BSI, 1980).

2.2 Design of mix proportions

The proportions of the different materials used in the mix design

are given in Table 2. The base binder for all mixes was FA (bulk

density of 350 kg/m3). The FA used in the control mix was

replaced by 3, 5 and 7% of 350 kg/m3 of FA by SF andMIRHA.

All other material quantities were kept constant such that the

effects of replacement of FA with SF and MIRHA on the

strength, both in compression and flexure, and the workability

properties of the concrete could be determined. The sodium

silicate to sodium hydroxide weight ratio was 2?5 and coarse to

fine aggregate weight ratio was approximately 1?86.

Sugar was incorporated into the mix in proportions of 3% by

weight of the total binder. Extra water (other than the water

present in the alkaline solutions) was added to the mixture

equal to 10% by weight of the total binder to ensure the

required workability (Table 2).

2.3 Casting and curingCubes of concrete of dimension 100 mm were cast and after 24 h

of casting, the moulds were opened according to EN 12390-1

(CEN, 1996) ?. Specimens were cured under two types of conditions:

ambient and external exposure conditions. For ambient curing

conditions, samples were placed in the shade outside the

laboratory whereas for the curing of samples in external exposure

conditions, samples were placed in a stand covered by a

transparent white plastic sheet and exposed to direct sunlight.

2.4 Test procedureCompressive strength tests were performed on concrete

samples in accordance with BS EN 12390-3:2002 (BSI, 2002)

using a digital compressive testing machine. Three concrete

cubes at ages of 3, 7, 28, 56 and 90 days were tested. During the

test, the concrete cubes were loaded at a constant rate of

6?8 kN/s without any suddenly applied loads.

Flexural strength tests were completed according to BS EN 12390-

5 (BSI, 2000) using a 2000 kN digital compressive and flexural

testing machine. Beams of dimension 100 mm 6 100 mm 6500 mm were cast, cured and tested for each mix after 28 days of

curing.

Scanning electron microscopy (SEM) was performed with a

LEO 1430 VP scanning electron microscope using Inca X-Sight

Oxford Instruments software. Specimens of 0?5 mm diameter

were cored from sample cubes of concrete that had been cured

for 28 days.

3. Results and discussion

3.1 Properties of fresh geopolymeric concreteIn order to find out the fresh properties of geopolymeric

concrete, its workability was measured through a slump test.

Extra water (10%) was added to all the mixes, decided as an

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:03

> Compounds FA: % SF: % MIRHA: %

SO2 51?19 96?36 86?10

Al2O3 24?00 0?20 0?17

Fe2O3 6?60 0?77 2?87

CaO 5?57 0?23 1?03

MgO 2?40 0?52 0?84

SO3 0?88 0?55 0?41

K2O 1?14 1?02 4?65

Na2O 2?12 0?1

Table 1. Chemical composition of FA MIRHA and SF

Type of

curing

Fly ash:

kg/m3

MIRHA/ silica

fume: %

MIRHA/ silica

fume: kg/m3

Coarse agg.:

kg/m3

Fine agg.:

kg/m3

NaOH:

kh/m3

Na2SiO3:

kg/m3

Extra water/

10%: kg/m3

Sugar/3%:

kg/m3

Ambient

curing

350 0 0 1200 645 41 103 35 10?5

339?5 3 10?5

332?5 5 17?5

325?5 7 24?5

External

exposure

curing

350 0 0 1200 645 41 103 35 10?5

339?5 3 10?5

332?5 5 17?5

325?5 7 24?5

Table 2. Mix design proportions

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Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

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appropriate amount after several trial mixes. Slump test results

are shown in Table 3. To improve the workability of

geopolymeric concrete naphthalene-based superplasticiser had

also being investigated (i.e. used by Rangan (2008)) but the

concrete hardened in a short span of time due to the fast setting

time of geopolymeric concrete which made the preparation of

samples harder with prolonged vibrations for compaction. In

the present study, sugar was added to delay the setting time of

the concrete making it easier to produce the samples.

Fly ash particles are spherical in shape with smooth surfaces

(Figure 1) which reduced the water demand in concrete but the

addition of MIRHA to FA-based geopolymeric concrete

increased the water demand in the concrete by reducing the

value of the slump by 5 and 7%, approximately in comparison

with the SF mix and control mix, respectively. With the

increase in percentage of MIRHA, slump was decreased which

showed that as the MIRHA content increased the water

quantity should also be increased in order to maintain the

required consistency of the mix. The decrease in workability

was due to the cellular particles (Figure 2) of MIRHA that

were absorptive in nature. MIRHA is a hygroscopic material

having a specific surface area that is greater than that of

cement due to which it absorbed more water.

On the other hand, in the case of SF addition to the fly ash-

based geopolymeric concrete, there was no change in the slump

value for 3 and 5% replacement but a 5% decrease could be

seen in the 7% replacement of SF. This shows that for the 7%

increment (or more) of SF, the water requirement in the

concrete increased which was due to the increased amount of

silica in the mix. Because of larger surface area and smaller

particle size (Figure 3), SF requires more water when increased

after a certain amount. In comparison with the control mix the

slump value of the SF mix decreased by 1?8%.

3.2 Suitable curing regime for FA-MIRHAgeopolymeric concrete

Figure 4 shows that a 5% (wt.) addition of MIRHA to the

concrete mix provided the highest compressive strength of the

concrete samples cured in ambient conditions, specifically,

28?3 MPa at 90 days. This value was 38?6% greater than that

obtained for the mix having 3% addition, 50?7% greater than

that of the mix with a 7% addition and 19% greater than the

control mix. With respect to the mix having 5% addition of

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:03

Type of mix Slump: mm

FA 230

FA-MIRHA 3% 220

FA-MIRHA 5% 210

FA-MIRHA 7% 200

FA-SF 3% 230

FA-SF 5% 230

FA-SF 7% 230

Table 3. Slump test results for each mix

10 mm EHT = 5.00 kVWD = 7.2 mm

Signal A = SE2Mag = 1.00 KX

Date: 1 Apr 2010Universiti Teknologi

Time: 13:11: 32PETRONAS

Figure 1. FESEM of fly ash

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

4

MIRHA, this quantity was found to be the optimum amount

for FA-based geopolymeric concrete.

External exposure curing conditions (Figure 5) resulted in the

highest compressive strength in comparison with concrete

cured under ambient conditions. Among mixes having

replacements of FA, the 7% replacement by MIRHA gave

the highest compressive strength at 90 days (46 MPa), which

was 48?4% greater than the 5% MIRHA mix and 11?7% less

than the control mix. In the control mix 67% of the 90 day

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:07

10 mm EHT = 1.00 kVWD = 4.9 mm

Signal A = SE2Mag = 1.00 KX

Date: 1 Apr 2010Universiti Teknologi

Time: 13: 20: 49PETRONAS

Figure 2. FESEM image of MIRHA

100 mm EHT = 5.00 kVWD = 7.2 mm

Signal A = SE2Mag = 100 X

Date: 1 Apr 2010Universiti Teknologi

Time: 13: 16:44PETRONAS

Figure 3. FESEM image of silica fume

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

5

strength was developed in the first 3 days which then led to

51?36 MPa at 90 days, the highest strength value of all the

mixes. Whereas between 7 and 28 days, the highest increase in

strength was for the 3%MIRHAmix, for which a 30% strength

increase was obtained in comparison with the control mix. All

results are given in Table 4.

These results explained the importance of heat in the curing of

geopolymeric concrete which was insufficient in ambient curing

conditions to produce the strength increases that were evident

for the concrete cured under external exposure conditions. The

increase in temperature during cure gave rise to a pozzolanic

reaction. When cured in the external exposure conditions the

geopolymeric reaction was enhanced by the heat from sunlight

which helped develop early age strength. It was supposed that

the additional heat helped promote the dissolution of silica and

aluminium atoms from the amorphous portion of the source

material by the action of hydroxide ions and concurrently these

precursor ions converted to monomers that further advanced

the polycondensation process (hardening process) to ultimately

form a geopolymeric structure as described by Davidovits

(2008).

The performance of geopolymeric concrete incorporating

MIRHA depended upon the proper utilisation of its particles

from which the Al and Si content could easily dissolve to form

a supersaturated aluminosilicate solution that further trans-

formed into a gel. This gel consisted of a network of oligomers

which continued to develop g until the maximum volume of

alkaline liquids was used. Following this, the gel started to

harden and the hardening process was enhanced if samples

were cured under the external exposure conditions given the

heat generated from exposure to sunlight.

Figure 6 shows that a 7% (wt.) addition of MIRHA in the mix

provided the highest values for flexural strength for concrete

cured under ambient and external exposure conditions,

attaining 8?38 and 6?52 MPa, respectively. Ambient curing

provided the best in MIRHA geopolymeric concrete.

According to the commentary given in ACI (Neville, 1990)

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:15

Com

pres

sive

stre

ss: M

pa

Age: daysControl mix 3%MIRHA 5%MIRHA 7%MIRHA

1 10 100

60

50

40

30

20

10

0

Figure 4. Compressive strength of FA--MIRHA-based polymeric

concrete with ambient curing

Com

pres

sive

stre

ss: M

pa

Age: daysControl mix 3%MIRHA 5%MIRHA 7%MIRHA

1 10 100

60

50

40

30

20

10

0

Figure 5. Compressive strength of FA--MIRHA-based polymeric

concrete with external exposure curing

Curing type MIRHA: % Compressive strength: MPa

3 days 7 days 28 days 56 days 90 days

Ambient

curing

0 9?50 14?11 19?73 21?92 23?77

3 9?00 11?90 17?92 19?19 20?42

5 9?77 15?89 24?08 27?00 28?30

7 8?55 11?00 16?75 17?03 18?78

External

exposure

curing

0 34?50 42?30 48?70 50?60 51?36

3 18?50 25?98 33?80 37?30 38?50

5 14?98 22?13 27?58 29?80 31?00

7 23?80 31?90 40?70 44?50 46?00

Table 4. Compressive strength of FA-based polymeric concrete

replaced by MIRHA

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

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the tensile strength in flexure should be 10--15% of the

compressive strength which was slightly better for geopoly-

meric concrete. The ratio of flexural to compressive strength

was found to be more than 10--15%, which is perhaps an

indication of good flexural strength for the geopolymeric

concrete as compared with OPC concrete.

3.3 Suitable curing regime for FA--SF geopolymericconcrete strength

Figure 7 shows that 3% (wt.) addition of SF in the FA-based

geopolymeric concrete yielded the highest compressive strength

(32?55 MPa) as compared to the control and othermixes. This value

was 37% greater than the control mix and 5% greater than the SF

sample having a 5% (wt.) addition to the FA-based geopolymeric

concrete which showed the lowest strength amongst all mixes.

This sample gained the most strength within 28 days, after

which no marked difference in strength is evident. Whereas

over a 3 to 7 day period a gain of 106% in strength was

observed for the 5% SF mix.

Figure 8 shows that the control mix provided the highest

compressive strength results, specifically, 32?4% higher than

the 3% SF mix, 56% higher than the 5% SF mix and 10?5%

higher than the 7% SF mix. Among all replacement quantities,

the 7% SF replacement amount provided the highest compres-

sive strength which was comparable with the MIRHA mix

having the same replacement value. The results obtained for

SF as replacement were slightly better than those for MIRHA

because MIRHA absorbed more liquid due to its hygroscopic

characteristic whereas SF needed water after exceeding a

certain amount. This made it possible for the precursor ions to

fully mobilise and thereafter orient themselves into monomers

within the liquid provided. These monomers were then

transformed into oligomers and within the gelation process

were reorganised to form a three-dimensional aluminosilicate

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:16

Fle

xura

l stre

ngth

at 2

8 da

ys: M

pa

Percentage replacement of fly ash with MIRHA3 50 7

9

8

7

6

5

4

3

1

2

0

Figure 6. The 28 day flexural strength of FA--MIRHA-based

polymeric concrete: vertical lines shading, ambient curing;

horizontal lines shading, external exposure curing

Com

pres

sive

stre

ss: M

pa

Age: daysControl mix 3%SF 5%SF 7%SF

1 10 100

60

50

40

30

20

10

0

Figure 7. Compressive strength of FA--SF-based polymeric

concrete with ambient curing

Com

pres

sive

stre

ss: M

pa

Age: daysControl mix 3%SF 5%SF 7%SF

1 10 100

60

50

40

30

20

10

0

Figure 8. Compressive strength of FA--SF-based polymeric

concrete with external exposure curing F

lexu

ral s

treng

th a

t 28

days

: Mpa

Percentage replacement of fly ash with MIRHA3 50 7

9

8

7

6

5

4

3

1

2

0

Figure 9. The 28 day flexural strength of FA--SF-based polymeric

concrete: vertical lines shading, ambient curing; horizontal lines

shading, external exposure curing

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

7

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:17

Curing type SF: % Compressive strength: MPa

3 days 7 days 28 days 56 days 90 days

Ambient

curing

0 7?46 14?11 19?73 21?92 23?77

3 12?07 24?04 30?27 31?75 32?55

5 5?35 11?04 12?97 15?10 16?54

7 11?90 18?39 26?50 28?82 29?98

External

exposure

curing

0 34?50 42?30 48?70 50?60 51?36

3 22?00 28?30 35?00 37?50 38?80

5 19?10 25?10 30?50 32?00 32?90

7 31?90 37?00 42?30 45?10 46?50

Table 5. Compressive strength of FA-based geopolymeric concrete

replaced by SF

1 mm EHT = 15.00 kVWD = 10.4 mm

Signal A = VPSEMag = 5.00 X

Date: 29 Jul 2009Universiti Teknologi

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a

2 mm EHT = 15.00 kVWD = 11.4 mm

Signal A = VPSEMag = 2.00 X

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b

10 mm EHT = 15.00 kVWD = 9.7 mm

Signal A = VPSEMag = 1.00 X

Date: 29 Jul 2009Universiti Teknologi

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c

2 mm EHT = 15.00 kVWD = 10.8 mm

Signal A = VPSEMag = 2.00 X

Date: 29 Jul 2009Universiti Teknologi

Time: 12: 12: 00PETRONAS

d

Figure 10. SEM images of ambient-cured FA-based polymeric

concrete with MIRHA: (a) control mix; (b) 3% MIRHA; (c) 5%

MIRHA; (d) 7% MIRHA

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

8

network. Once the polymerisation process was initiated, it

enhanced the aluminosilicate network that, with the additional

heat from exposure to sunlight, produced a more hardened

matrix which ultimately resulted in higher compressive

strengths. All results are given in Table 5.

Figure 9 shows that in external exposure curing conditions, 7%

inclusion of SF showed the highest values for flexural strength

(7?91 MPa), whereas for ambient curing conditions the best

flexural strength (6?58 MPa) was achieved by the 5% inclusion

of SF.

3.4 Microstructure analysis of geopolymericconcrete

In 3% MIRHA (Figure 10(b)) mix the microstructure was

better hardened in comparison with the control mix

(Figure 10(a)), which was due to the greater amount of silica

oxide present in MIRHA therefore more silica atoms were

expected to dissolve from the source material and participate in

the geopolymeric reaction to produce aluminosilicate gel,

which has a tube-like structure (Figure 11) unlike that of

calcium—silicate--hydrate (C--S--H) gel as found in OPC

concrete (Famy et al., 2003). The composition of aluminosi-

licate gel was examined by energy dispersive X-ray (EDX)

analysis (Figure 12). Fewer micropores were present in the

matrix; this was due to the inclusion of fine MIRHA particles

that filled these pore spaces.

The microstructure of the sample with the addition of 5% (wt.)

MIRHA (Figure 10(c)) was even better than the sample mix

having 3% addition of MIRHA in terms of the extent of

hardening of the gel because the amount of dissolved silica

increased with the increase in the amount of MIRHA.

Although some precipitated particles were present in the

matrix, these were not converted to aluminosilicate gel because

of the reduced temperature during the ambient curing period.

The average temperature was 20--25 C in ambient curing. For

the 7% MIRHA mix (Figure 10(d)) the amount of undissolved

particles were greater in comparison with those evident for the

3 and 5% MIRHA mixes and this showed that additions of

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:25

200 nm EHT = 2000 kVWD = 9.5 mm

Signal A = VPSEMag = 30.00 KX

Date: 31 Mar 2010Universiti Teknologi

Time: 12: 40: 50PETRONAS

Figure 11. FESEM image of polymeric paste showing

aluminosilicate gel

Full Scale 2514 cts Cursor: 0.0001

Ca

Ca

CaK

KK

Fe

Fe Fe

O

AlMg

Si

CaK

Fe

Total

AlMg

Si

Element

O 48.56 64.153.25 2.994.26 3.703.35 2.6224.84 18.701.00 0.5411.583.17

6.11

100.00

1.20

Weight% Atomic%

Na

Na

2 3 4 5 6 7 8 9 10keV

Figure 12. EDX analysis of aluminosilicate gel after 7 days

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Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

9

more than 5% of MIRHA increased the amount of silica in the

mix which was not able to fully react with alkaline liquids. Due

to low heat the polymeric reaction was slow and the time taken

for the alkaline liquids to leach out of the mix before properly

coming into contact with the reactive solid material increased.

As a result, a greater number of unreacted particles were

present in the matrix in comparison with the reactive ones

which consequently provided for a reduction in the compres-

sive strength.

The addition of 3% (wt.) of SF to the geopolymeric concrete

mix (Figure 13(b)) was found to produce a better yield in

comparison with the 5% (Figure 13(c)) and 7% inclusion

(Figure 13(d)) unlike MIRHA because SF contained more

silica content in comparison with MIRHA. This showed that

beyond an addition of 3% of SF, the alkaline liquids were not

sufficient for the mix to dissolve silica from the source material.

Un-reacted particles were still present, given that there was

insufficient heat from the surroundings which in turn

prevented the precipitated particles from converting into a

gel. For those mixtures to which 5 and 7% of SF was added,

un-reacted particles were abundantly present in the matrix

which was also porous because sufficient gel had not formed to

fill these pores.

In comparison with the ambient curing conditions, the curing

of concrete samples in external exposure conditions provided

better microstructural development, which was thought to be

due to the additional heat available during the external

exposure curing period in comparison with that of the ambient

cure. Greater heat helped in greater dissolution of silica from

the pozzolan (FA/MIRHA/SF) and the additional heat

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:29

1 mm EHT = 15.00 kVWD = 10.4 mm

Signal A = VPSEMag = 5.00 X

Date: 29 Jul 2009Universiti Teknologi

Time: 11: 10: 26PETRONAS

a

10 mm EHT = 15.00 kVWD = 7.8 mm

Signal A = VPSEMag = 1.00 KX

Date: 30 Jul 2009Universiti Teknologi

Time: 12: 00: 54PETRONAS

b

10 mm EHT = 15.00 kVWD = 9.8 mm

Signal A = VPSEMag = 1.00 KX

Date: 30 Jul 2009Universiti Teknologi

Time: 12: 36: 28PETRONAS

c

10 mm EHT = 15.00 kVWD = 10.9 mm

Signal A = VPSEMag = 1.00 X

Date: 30 Jul 2009Universiti Teknologi

Time: 12: 46: 37PETRONAS

d

Figure 13. SEM images of ambient-cured FA-based polymeric

concrete with SF: (a) control mix; (b) 3% SF; (c) 5% SF; (d) 7% SF

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

10

Proceedings of the Institution of Civil Engineers tcm1000045.3d 11/7/11 14:56:37

10 mm EHT = 15.00 kVWD = 6.6 mm

Signal A = VPSEMag = 500 X

Date: 30 Jul 2009Universiti Teknologi

Time: 16: 13: 06PETRONAS

Aggregate

Hardened paste

Figure 14. SEM images of external exposure-cured FA-based

polymeric concrete with MIRHA

10 mm EHT = 15.00 kVWD = 8.9 mm

Signal A = VPSEMag = 300 X

Date: 30 Jul 2009Universiti Teknologi

Time: 12: 56: 28PETRONAS

Aggregate

Hardened paste

Figure 15. SEM images of external exposure-cured FA-based

polymeric concrete with SF

Construction MaterialsVolume 000 Issue CM000

Utilisation of waste material ingeopolymeric concreteNuruddin, Qazi, Kusbiantoro andShafiq

11

apparently accelerated the geopolymeric reaction which, in

turn, resulted in the production of aluminosilicate gel that

filled voids at the interfacial transitional zone (ITZ) and within

the matrix.

Unlike the setting times obtained for concrete samples cured

under ambient conditions, the setting time of geopolymeric

concrete cured under external exposure conditions was not

delayed. This is thought to be due to the additional heat

provided by exposure to sunlight which readily promoted

contact of alkaline solutions with the reactive solid material

before being leached from the mix. The average temperature in

external exposure curing was 35—40 C All mixes replaced by

MIRHA (Figure 14) or SF (Figure 15) showed a compact

microstructure with a smaller number of un-reacted particles

which led to a better strength of concrete. The ITZ was

properly developed as no evident interface can be observed

between aggregates and the geopolymeric matrix. Such

microstructural properties were consistent with the 28 day

compressive strength of 48?7 MPa which was as good as OPC

concrete.

On the other hand, in the case of SF addition to the FA-based

geopolymeric concrete, there was no change in the slump value

for replacement values of 3 and 5% whereas a 5% decrease in

slump can be seen for a 7% replacement with SF. This shows

that for the 7% increment (or more) of SF, the water

requirement in the concrete increased which was due to the

increased amount of silica in the mix. It is apparent that given

the smaller particle size and large surface area of SF, SF

requires more water when added to an FA mix beyond

replacement values of 7% (wt.). In comparison with the control

mix, the slump value of the SF mix decreased by 1?8%.

4. Conclusions

(a) Geopolymeric concrete was developed that achieved a

target strength compressive strength at 28 days equal to

that of OPC concrete. The results of a microstructure

study helped verify the cementing potential of geopoly-

meric concrete to be used in the construction industry;

this study was able to show the dense microstructure of

the geopolymeric concrete and the well developed

interfacial transition zone (ITZ) between particles and

cement paste.

(b) External exposure curing conditions were found to be the

best curing regime for geopolymeric concrete given that it

showed the highest value of compressive strength in

comparison with similar concretes cured under ambient

curing in this study.

(c) The compressive strength of the geopolymeric concrete

under external exposure conditions developed up to 28

days however; there was no significant increase in

strength beyond this time.

(d) The flexural strength of geopolymeric concrete was

comparable to OPC concrete.

(e) The best performing geopolymeric concrete mix design,

based on the results of compressive strength tests and a

microstructure study, was the concrete mix cured under

external exposure conditions. This mix comprised

i. fly ash: 350 kg/m3

ii. sodium hydroxide (NaOH): 41 kg/m3

iii. sodium silicate (Na2SiO3): 103 kg/m3

iv. table sugar: 10?5 kg/m3 (3% of FA)

v. extra water: 35 kg/m3 (10% of FA)

vi. fine aggregate: 645 kg/m3

vii. coarse aggregate: 1200 kg/m3 @

AcknowledgementsThe authors would like to acknowledge the University

Technology PETRONAS for providing facilities to complete

this research study.

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