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Comparison of engineering and durabilityproperties of fly ash blended cement concrete

made in UK and MalaysiaN. Shafiq*, M. F. Nuruddin and I. Kamaruddin

Annual global production of fly ash is y66108 ton out of which only 20 to 25% is utilised in the

construction industry. Largely it is used as a partial replacement of cement for producing

concrete. Properties of such concrete depend on the chemical composition of fly ash, source and

method of burning of coal in power stations, etc. The present paper presents a comparative study

on the properties on concrete containing fly ash obtained from two different sources, Drax Power

Station, UK and Manjung Power Station, Malaysia. Fly ash obtained from Malaysia contained

11?47%CaO and its particles were coarser than the fly ash obtained from Drax, UK, whichcontained less calcium oxide (2?55%). Malaysian fly ash concrete required more water to achieve

the targeted slump of 55¡5 mm of fresh concrete, such concrete showed 4 to 7% high porosity

and 27 to 36% low compressive strength as compared with the porosity and compressive

strength of the concrete made with Drax, UK fly ash.

Keywords: Fly Ash, Slump, Total porosity, Compressive strength, Porosity–strength relationship

Introduction

Fly ash is a byproduct obtained from combustion of

pulverised coal in thermal power plants. Its physical,

chemical, and mineralogical properties are dependent on

the type and source of coal, type of combustion system,

combustion temperature, type of pollution control

system used, etc. World annual utilisation of coal for

generating electricity in power stations is y486109 ton,

which produces y66108 ton of fly ash.1

The pozzolanic and cementitious properties of fly ash

make it a useful cement replacement material for

producing high performance concrete. Its major con-

stituents are SiO2, Al2O3, Fe2O3, and CaO; their relative

percentages mainly depend on the type of coal burned at

the power plant. Fly ash obtained from burning of

bituminous coals like anthracite contains relatively low

amounts of calcium oxide, CaO and is known as lowcalcium fly ash. Burning of sub-bituminous coals like

lignite results in ash with higher CaO content and may

be called high calcium fly ash. ASTM classifies low

calcium fly ash as class F and the high calcium fly ash as

class C.2 Low calcium fly ash with proper composition

possesses pozzolanic properties, where as high calcium

fly ash has hydraulic properties. In the last decade, fly

ash has increasingly been used as a major cement

replacement material. Despite this, .80% is disposed of

as waste material.3

At present y28% of electricity in Malaysia isgenerated by pulverised coal firing, which consumesy86106 ton of coal annually and 65% generated by

natural gas. In order to reduce the dependency onnatural gas as a main fuel for electricity generation, in2004 the government of Malaysia decided that by 2010the share of coal in the fuel mix for electricity generationwould rise to y40%. Increased use of coal burning inthermal power plants will increase the production of flyash to an estimated 2?56106 to 36106 ton per annum.

The purpose of the present study was to establishresearch data on properties of concrete incorporating flyash as obtained from Malaysian sources and to comparethis with the properties of concrete containing fly ashfrom UK sources. Research on fly ash in concrete in UKand Europe is very well established and included asstandard in code documents of the new British–Euro

standards, BS EN 450 (Ref. 4) and establishing compar-ison to the present work may help the concrete manu-facturer in Malaysia to appropriately use the Malaysianfly ash in concrete production. For this purpose, a set of laboratory tests were conducted at the University of Leeds UK (UL) and a contemporary set of laboratory

tests were conducted at the University TechnologyPETRONAS (UTP) in Malaysia. Identical concretemix proportions were used and a constant value of

55¡5 mm of slump was maintained in both labs.

Experimental

Material properties and mix proportionSix different concrete mixes were prepared with binder(OPC and fly ash), sand and gravel in the ratio by weight

Department of Civil Engineering, University Technology PETRONAS,31750, Tronoh, Perak, Malaysia

*Corresponding author, email [email protected]

ß 2007 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute

Received 25 April 2005; accepted 30 July 200731 4 Advances in Applied Ceramics 2007 VOL 106 NO 6 DOI 10.1179/174367607X228089

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of 1: 2?3 3 : 3?5 were chosen based on achieving maximumpacking of aggregates and minimum porosity. Three of the mixes denoted by UK0, UK30 and UK40 wereprepared at UL and the other three MY0, MY30 andMY40 were made at UTP; 0, 30 and 40 in the above mixdesignation indicates the percentage of partial replace-

ment of cement by fly ash in concrete. The OPC usedcomplied with the requirements of BS EN 197-1.5

Ordinary Portland cement, OPC from Castle CementUK was used for concrete mixes produced in UK whereOPC from Malayan Cement Malaysia was used forconcrete mixes made in Malaysia. Sand and the gravelsconforming to BS 882 (Ref. 6) were used as fine andcoarse aggregates respectively. For concrete mixesproduced at the University of Leeds, UK fly ash fromDrax power station was used; it was ASTM Class F flyash, for concrete mixes prepared at the UTP, Malaysia flyash was obtained from Manjung power station at Lumut,Perak. Chemical composition and physical properties of fly ash as obtained from two different sources are given inTable 1, the data of Malaysian fly ash was furnished bythe material supplier and results were certified by the

SIRIM Berhad Malaysia; the Malaysian standardsinstitute. Table 2 shows the details of concrete mixes,their proportions and targeted slump values.

In order to compare the properties of the two sets of

concrete mixes prepared in UK and Malaysia; work-ability of all concrete mixes in terms of slump wastargeted to 55¡5 mm. For all concrete mixes various

trials of water/binder (w/b) ratio were chosen until thetargeted slump value was achieved, chosen w/b ratio forall concrete mixes is given in Table 2. The slump waskept constant to reflect Malaysian site practice.

Casting, preparation and curing of specimensConcrete samples were cast and cured to providesamples for determining the compressive strength, total

porosity and oxygen permeability at 3, 7, 28, 90 and 180days. For each of the tests, compressive strength, totalporosity and oxygen permeability three samples weretested. Concrete cubes of dimension 15061506150 mm

were cast in standard steel moulds for compressivestrength test, according to British Standards BS 8110,1997. For total porosity test 50 mm diameter 40 mmthick cylindrical discs were cored from concrete planks

of dimensions 4006200640 mm. Oven dried cylindricaldiscs those were used for the total porosity test werepreserved in air/water tight bags for onwards use for the

oxygen permeability test. Twenty four hours aftercasting, all specimens’ cubes and planks were strippedfrom the moulds and samples were placed in water bathfor curing until the designated ages for testing.

Testing of specimenCompressive strength

Concrete cubes at the defined ages were tested in

accordance with British Standards, BS 1881, Part 116;7

a universal hydraulic testing machine with a maximumcapacity of 500 kN was used to test the specimens.

Total porosity

Total porosity of concrete was determined by a vacuum

saturation method developed by RILEM CP 113(Ref. 8) and explained by Shafiq and Cabrera.9 At thedefined ages for testing, three 50 mm diameter discswere cored out from concrete planks. Total Porosity

of the samples was determined using equation asbelow

P %ð Þ~W s{W d

W s{W w|100 (1)

where P is the total porosity in percentage, W s is themass of saturated samples measured in the air W d is themass of oven dried samples measured in the air, and W wmass of saturated samples measured in water, all massmeasurements are in g.

Measurement of oxygen permeability

Oxygen permeability of cylindrical concrete samples of 50 mm diameter and 40 mm thick was determined usingrecently installed permeability testing rigs in theConcrete Technology Laboratory at UTP. The perme-ability rigs at UTP were fabricated according to thedesign of the permeability rigs installed at UL.Cylindrical concrete samples that were previously usedfor determination of total porosity were preserved in air/

water tight bags for onwards use for measurement of oxygen permeability. The coefficient of oxygen perme-ability was calculated by modified Darcy’s equation (2)as follows9

Table 1 Chemical composition of fly ash obtained fromdifferent sources

Oxide composition

Percentage, %

Drax, UK Manjung, Malaysia

SiO2 50.20 56.39Al2O3 28.59 17.57Fe2O3 13.17 9.07

CaO 2.55 11.47MgO 1.28 0.98SO3 0.57 0.55K2O 2.39 1.98Na2O 0.98 1.91Specific gravity 2.40 2.37fineness, m2 kg21 306 243

Table 2 Details of concrete mixes

Mix type

Cement, OPC Fly ash, FA Sand Gravel Slump

w/c*kg m23 Source kg m23 Source kg m23 kg m23 mm

UK0 325 Castle cement 0 Drax, UK 757 1137 55¡5 0.550UK30 227.5 97.5 757 1137 55¡5 0.490UK40 195 130 757 1137 55¡5 0.480MY0 325 Malayan cement 0 Manjung, MY 757 1137 55¡5 0.560MY30 227.5 97.5 757 1137 55¡5 0.525MY40 195 130 757 1137 55¡5 0.515

*Water cement ratio.

Shafiq et al. Comparison of engineering and durability properties of cement concrete

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K ~2m poutQL

A p2in{ p2

out

À Á (2)

where K is the intrinsic permeability of concrete in m2, m

is dynamic viscosity of flowing fluid (for oxygen at 20uC,dynamic viscosity is 2?02610216 N s m22) pout is the

outlet pressure, that is equal to 1 bar at standardtemperature and pressure, and pin is the inlet pressure,which was kept between 1 to 4 bar,9 q is the gas flow ratein m3 s21, L is the thickness in mm and A is the

crossectional area of c in m2 of cylindrical disc.

Results and discussion

Fly ash from Drax UK versus from Manjung MalaysiaChemical analysis of fly ashes obtained from twosources is given in Table 1, it was observed that the flyash obtained from Drax, UK contained very lowcalcium oxide as 2?55% and the fly ash obtained fromManjung, Malaysia contained 11?47%CaO. The silicacontent was determined as 50 and 56% respectively inUK and Malaysian ashes. There are huge differencesbetween the UK and the Malaysian fly ash. Not only arethe Si contents different, but so are the Al contents, andthe Si/Al ratios are 2 and 3 for the UK and Malaysian flyash respectively. Fineness modulus of the two ashesshows that the ash obtained from Malaysia was coarserthan the ash obtained from Drax UK. In general basedon the chemical analysis results, it would be expected

that the UK fly ash possess better pozzolanic propertiesthan that of Malaysian ash.

Properties of fresh concreteThe target value of slump of 55¡5 mm was keptconstant for all concrete mixes. It was observed(Table 2) that the fly ash reduced the water demand.Comparing the w/(cz f ) ratio it was noted that the UKfly ashes reduced the w/(cz f ) ratio to ,0?5 whileachieving the target slump. Therefore, concrete mixesincorporating Drax, UK fly ash would be more work-able with less water demand; hence higher durability can

be achieved.

Total porosity of concreteFigure 1 shows the values of total porosity of differentconcrete samples. It was observed that the total porosity

of concrete mixes made with 100% cement was 5–14%higher than the total porosity of the concrete containingfly ash at all ages of testing.

Comparing the effects of fly ash obtained from Drax,UK and Manjung, Malaysia on total porosity of concrete, it was noted that concrete containing DraxUK fly ash yielded 4–7% lower porosity that the totalporosity of concrete containing Malaysian fly ash. It isdue to the fact that the fly ash obtained from Drax isfiner than the Malaysian fly ash as shown in Table 1.The total porosity of concrete is an important char-acteristic that controls its compressive strength anddurability.

Concrete compressive strengthFigure 2 illustrates the compressive strength test resultsof different concrete mixes. It was noted that at earlyages up to 14 days fly ash concrete exhibited 35–48%lower compressive strength as compared to the com-pressive strength of concrete containing no fly ash. Flyash is a pozzolanic material and its effect on strengthstarts after 28 days when the pozzolanic reaction starts.It was observed that after 28 days, concrete containing

fly ash continued to gain compressive strength, whereasconcrete without fly ash gained ,5% further strengthafter 28 days.

After 90 days and 180 days UK fly ash concreteexhibited about 42% and 77–80% increment in strengthrespectively as compared to the 28 days strength.

Similarly, with concrete mixes containing Malaysianfly ash, increments of 50–52% and 65–75% wereobserved. From the preceding discussion, it can be

noted that there was almost similar trend in post 28 daysstrength development for concrete containing UK andMalaysian fly ash. At 180 days, about 3–7% higher

compressive strength of UK fly ash concrete wasobserved as compared to no fly ash concrete, whereasslightly lowered strength was observed with concretecontained Malaysian fly ash.

Compressive strength of concrete containingMalaysian fly was observed 27–46% lower than thecorresponding concrete mixes containing UK fly ash. Itis due to facts that the UK fly ash is finer and possessedlow calcium oxide as compared to the Malaysian fly ash,which caused the higher pozzolanic reaction in UK flyash concrete than the Malaysian fly ash concrete.

Total porosity–strength relationshipIn Fig. 3 compressive strength of both mixes are plottedagainst their respective values of the total porosity. The

correlation between porosity and strength was non-linear,10 with a power function as the best fitted curve. Itis observed that there is a wider gap between two fitted

1 Total porosity P of different concrete with ¡1 standard

deviation, %

2 Compressive strength f cu of different concrete with ¡1

standard deviation, MPa


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curves at higher porosity as 11%; such gap tends to

become closer at lower porosity as 8%, the probablereason would be differences in laboratory conditions,material properties and ambient environmental condi-tions between UK and Malaysia.

Oxygen permeabilityTable 3 shows the measured coefficients of oxygen

permeability of different concrete mixes; their corre-sponding logarithmic values are plotted in Fig. 4.Coefficient of oxygen permeability followed the same

trend as observed in porosity and compressive strength.In general, Malaysian mixes showed higher permeabilityas compared to their corresponding UK mixes. Effects

of age were also observed to be very significant onlowering the permeability of the same mix. For examplefor concrete mix UK0, coefficient of permeability, K at

the age of three days was measured 21 times higher thanthe coefficient of permeability measured at the age of 90

days. Similarly, for concrete mix, MY0 the coefficient of permeability at the age of 3 days was obtained as24 times higher than the coefficient of permeability

measured at the age of 90 days. In case of UK concretemixes containing fly ash, the coefficient of permeabilityat the age of 3 days was measured 42–47 times more

than the coefficient of permeability measured at the ageof 90 days, similarly for Malaysian fly ash mixescoefficient of oxygen permeability at the age of three

days was measured 35–38 times greater than thatmeasured at the age of 90 days. More significantreduction in fly ash mixes at later age is due to faster

pozzolanic reaction took place after the age of 28 days.

In general coefficient of oxygen permeability of concrete mixes containing no fly ash was measured four

to five times higher than the coefficient of permeability

of the corresponding concrete mix containing fly ash.

Lower coefficient of oxygen permeability of fly ash

containing concrete can enhance the durability of

concrete than the concrete containing no fly ash.

Relationship between porosity, compressivestrength and permeability

All three parameters porosity, compressive strengthand permeability control the durability of concrete

and to some extent all these parameters are inter-

related. Cabrera (1989),11 presented two models; one

for OPC concrete and the other for fly ash concrete

of the relationship between porosity, compressive

strength and oxygen permeability, the models are

well accepted by researches and referred in many

publications.

Cabrera (1989) model for OPC mixes

log K ~{15:54z1:11logP

f cu

R2~0:

71

(3)

Cabrera (1989) model for OPC/PFA mixes


f cu

R2~0:85

(4)

Similarly for the present research study porosity,

permeability and compressive strength results for con-

crete containing no fly ash and concrete containing fly

ash were plotted in Fig. 5, the following statistical

correlations were obtained.

Porosity, compressive strength and permeability

relationship for no fly ash concrete


f cu

R2~0:81

(5)

Porosity, compressive strength and permeability rela-

tionship for fly ash concrete


f cu

R2~0:95

(6)

When compared the correlations obtained in the present

study for with that presented by Cabrera (1989) there

were some difference found in the coefficient of log P f cu

,

Table 3 Coefficient of oxygen permeability K of differentconcrete mixes, m2

Mix type

Coefficient of oxygen permeability K , m2

Age at testing, day

3 7 28 90

UK0 7.16E-17 4.23E-17 1.01E-17 3.36E-18UK30 3.22E-17 9.73E-18 1.92E-18 7.06E-19UK40 3.51E-17 1.08E-17 2.25E-18 7.27E-19

MY0 1.42E-16 7

.66E-17 1

.94E-17 5

.81E-18

MY30 1.20E-16 4.90E-17 1.30E-17 3.14E-18MY40 1.18E-16 5.24E-17 1.47E-17 2.98E-18

4 Coefficient of oxygen permeability log K of different

concrete with ¡1 standard deviation, m2

3 Total porosity P and compressive strength f cu relation-

ship with ¡1 standard deviation


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however values of constant are quite comparable, the

difference between coefficients of log P f cu

would be due

to wide range of data included in Cabrera (1989) model.

ConclusionsBased on the above results and discussions followingconclusions are made.

1. There are differences between the UK and the

Malaysian fly ash. Not only are the Si contents different,but also are the Al contents, and the Si/Al ratios are 2and 3 for the UK and Malaysian fly ash respectively.

Malaysian fly ash is much coarser than the UK fly ashand that the Ca contents are also different.

2. Workability, compressive strength and total por-osity of concrete were affected by both source andamount of fly ash.

3. Fly ash obtained from Manjung Power Station,

Malaysia was coarse and contained a higher content of calcium oxide as compared to the fly ash obtained fromDrax Power Station, UK.

4. Concrete containing Manjung, Malaysia fly ashrequired more water to achieve the targeted slump of 55¡5 mm; thus exhibited lower strength and higher porosity ascompared with the concrete made of Drax, UK fly ash.

5. At early age up to 14 days compressive strength infly ash concrete was developed to a very low level ascompared to the strength developed in control mix.

6. At the age of 180 days fly ash concrete showedbetter strength than control concrete.

7. Effects of age on the coefficient of oxygen

permeability were more significant on fly ash concrete

than the OPC concrete.8. Coefficient of permeability of fly ash concrete was

reduced to y20% of the coefficient of permeability of

OPC concrete.

9. While there appeared to be differences between the

UK and Malaysian systems, the errors in the measure-

ments mean that such differences should be treated withcaution.

AcknowledgementsThe authors would like to acknowledge students and

technicians Mr Lau, Mr Fong and Mr Johan for

producing test data at Concrete TechnologyLaboratory at UTP, Tronoh, Malaysia. The authors

would like to extend the acknowledgement to the

department of civil engineering at University of Leeds

for providing data on UK concrete.

References

1. International energy outlook, Report of Energy Information

Administration, USA, 2007.

2. American Standards for Testing of Materials, ASTM C618–80,1980.

3. P. K. Mehta: Proc. 3rd Int. Conf. on ‘Fly ash, slag, silica fume and

natural pozzolans in concrete’, Trondheim, Norway, June 1989,

ACI-CANMAT, 1–43.

4. ‘Fly ash for concrete: definitions, requirements and conformity

criteria’, BS EN 450-1, BSI, 2005.

5. BS EN 197-1, Specifications for Portland cement, BSI, London,

2002.

6. ‘Specifications for aggregates from natural sources for concrete’,

BS 882, BSI, London, 1992.

7. ‘Method for determination of compressive strength of concrete’, BS

1881, Part 116, BSI, London, 1983.

8. RILEM: Mater. Struct., 1984, 17, (101), 393–394.

9. N. Shafiq and J. G. Cabrera: Cement Concr. Compos., 2004, 26,

381–387.

10. K. Wesche: ‘Fly ash in concrete: properties and performance’;1991, London, RILEM.

11. J. G. Cabrera, A. R. Cusens and C. J. Lynsdale: Proc. IABSE

Symp. on ‘Durability of structures’, Vol. 57/1, 249–254; 1989,

Lisbon, IABSE.

5 Relationship between porosity to compressive strength ratio log (P / f cu) and coefficient of oxygen permeability, log K

with ¡1 standard deviation


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