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Construction and Building Materials 22 (2008) 1963–1971

and Building

MATERIALS

Performance of self-compacting concrete containing fly ash

J.M. Khatib *

School of Engineering and the Built Environment, University of Wolverhampton, Wulfruna street, Wolverhampton, WV1 1SB, UK

Received 19 June 2006; accepted 12 July 2007Available online 24 September 2007

Abstract

The influence of including fly ash (FA) on the properties of self-compacting concrete (SCC) is investigated. Portland cement (PC) waspartially replaced with 0–80% FA. The water to binder ratio was maintained at 0.36 for all mixes. Properties included workability, com-pressive strength, ultrasonic pulse velocity (V), absorption and shrinkage. The results indicate that high volume FA can be used in SCCto produce high strength and low shrinkage. Replacing 40% of PC with FA resulted in a strength of more than 65 N/mm2at 56 days.High absorption values are obtained with increasing amount of FA, however, all FA concrete exhibits absorption of less than 2%. Thereis a systematic reduction in shrinkage as the FA content increases and at 80% FA content, the shrinkage at 56 days reduced by two thirdcompared with the control. A linear relationship exists between the 56 day shrinkage and FA content. Increasing the admixture contentbeyond a certain level leads to a reduction in strength and increase in absorption. The correlation between strength and absorption indi-cates that there is sharp decrease in strength as absorption increases from 1 to 2%. After 2% absorption, the strength reduces at a muchslower rate.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Absorption; Fly ash; Self-compacting concrete; Shrinkage; Strength

1. Introduction

There has been an increase in using self-compacting con-crete (SCC) in recent years and a number of papers havebeen published [1–6]. SCC was first developed in Japan inthe late nineteen eighties to be used in the construction ofskyscrapers [1]. The introduction of SCC represents majortechnological advances, which leads to a better quality con-crete and an efficient construction process [7]. SCC allowsthe construction of more slender building elements andmore complicated and interesting shapes [8]. The produc-tion of SCC allows the pumping of concrete to a greatheight and the flow through congested reinforcing barswithout the use of compaction other than the concreteself-weight. As a result, the use of SCC can lead to a reduc-tion in construction time, labour cost and noise level on theconstruction site [7,9].

0950-0618/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2007.07.011

* Tel.: +44 1902 32 2282; fax: +44 1902 32 2743.E-mail address: [email protected].

The use of chemical admixtures is always necessarywhen producing SCC in order to increase the workabilityand reduce segregation. The content of coarse aggregateand the water to binder ratio in SCC are lower than thoseof normal concrete. Therefore SCC contains large amountsof fine particles such as, blast-furnace slag, fly ash and limepowder in order to avoid gravity segregation of larger par-ticles in the fresh mix [10–12].

The strength and drying shrinkage of SCC is similar tothose of conventional concrete at the same water to cementratio [12]. Compared with traditional concrete, SCC showsa lower permeability and absorption by capillary action,which might be attributed to the less porous zone andrefinement of pore structure [13].

It is well established that the use of fly ash (FA) in con-crete increases the workability and contributes towardslong-term strength. The incorporation of FA reduces theneed of superplasticiser necessary to obtain a similar slumpflow compared with the concrete containing only cement asbinder [14]. The strength and shrinkage of SCC containing

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Table 2Details of mixes

Mix No. Proportions(% by mass ofbinder)

Content (kg/m3)

PC FA PC FA Water Faga Cagb ADc (%)

M1 100 0 500 0 180 876 876 0.6M2 100 0 500 0 180 876 876 0.7M3 100 0 500 0 180 876 876 1.0M4 80 20 400 20 180 845 876 0.7M5 60 40 300 40 180 813 876 0.7M6 40 60 200 60 180 782 876 0.7M7 20 80 100 80 180 751 876 0.7

a fine aggregate.b coarse aggregate.c admixture, % by mass of binder.

1964 J.M. Khatib / Construction and Building Materials 22 (2008) 1963–1971

high volume FA were found to be similar to that of normalconcrete. Also the shrinkage was not noticeably differentfrom that of traditional concrete. The results were basedat varying water to binder ratios [6,9].

The present work investigates selected properties of SCCcontaining FA at constant water to binder (PC+FA) ratioof 0.36. The properties comprised workability, density,compressive strength, absorption, ultrasonic pulse velocityand drying shrinkage. The dosage of chemical admixtureswas maintained constant for all FA mixes.

2. Experimental

2.1. Materials

The constituents of mixes were Portland cement (PC),fly ash (FA), water, fine aggregate and coarse aggregate.The PC and FA complied with EN 197-1 and EN 450,respectively. The fine aggregate used conformed to classM of BS 882: 1992, and 10 mm nominal size crushed andwashed was used as coarse aggregate. The only admixture(AD) used to produce self-compacting concrete was aliquid based on a modified synthetic carboxylated polymer.The AD conformed to Types A and F Admixtures of BS5075 Parts 1 & 3 and EN 934-2:2000 with a relative densityof 1.08. Composition of PC and FA are given in Table 1.

2.2. Mix proportions

A total of 8 mixes that were employed to examine theproperties of self-compacting concrete (SCC) with andwithout fly ash (FA). Properties investigated were, work-ability using the flow table, density, compressive strength,absorption, ultrasonic pulse velocity and length change.Details of mixes are given in Table 2. The control mixesM1–M3 had a proportion of 1 (PC): 1.75 (fine aggregate):1.75 (coarse aggregate) without the inclusion of FA. Three

Table 1Composition and properties of bindera

PCb FAc

SiO2 (%) 20.2 50.5Al2O3 (%) 4.2 24.7Fe2O3 (%) 2 7.4CaO (%) 63.9 2.6MgO (%) 2.1 1.5SO3 (%) 3 0.8Na2O (%) 0.14 0.8K2O (%) 0.68 3.0Insoluble residue (%) 0.37 –Loss on ignition (%) 2.81 –Free lime (%) 2.37 –Specific surface area (m2/kg) 368 356Residue retained on 45 lm sieve (%) 15.16 –Initial set (min) 115.0 –

a PC+FA.b Portland cement.c fly ash.

different dosages of admixtures (AD) were used for thesecontrol mixes. The dosages of AD were 0.6%, 0.7% and1.0% (by mass of PC) for mixes M1, M2 and M3, respec-tively. In mixes M4-M7, PC was partially replaced with20%, 40%, 60% and 80% FA (% by mass of binder), respec-tively. The binder (b) consists of PC and FA. The dosage ofAD for these mixes was 0.7% (by mass of binder). Thewater to binder (w/b) ratio for all mixes was maintainedconstant at 0.36 and no adjustment to the water contentwas made for mixes containing FA.

2.3. Casting, curing and testing

Cubes of 100 mm in size and prisms of dimensions75 mm · 75 mm · 300 mm were used for the determinationof density, compressive strength, absorption, ultrasonicpulse velocity (V) and length change. For each mix, 18cubes and 2 prisms were prepared. Before casting, theworkability test using the flow table was conducted accord-ing to BS 1881, Part 105: 1984. The table had dimensions of700 mm · 700 mm and these are the minimum recom-mended dimensions [15,16]. Specimens (cubes and prisms)were then cast in steel moulds and were not subjected toany compaction other than their own self-weights. Thespecimens were kept covered in a controlled chamber at20 ± 2 �C for 24 h until demoulding. Thereafter, cubeswere placed in water at 20 �C. The prisms, however, wereleft to air cure in a controlled chamber at 20 �C and 60%RH. The cubes were used to determine the density, com-pressive strength and absorption while the determinationof V and length change were conducted on the prisms.Testing was determined at 1 day, 7, 28 and 56 days. Also,length change was determined at additional testing dates.The method for determining the density, compressivestrength, V, and length change was according to BS1881,Part 114:1983, Part 116: 1983, Part 217: 1983 and Part206: 1990, respectively.

For the determination of water absorption, cubes weretaken from the curing tank at the desired curing age andplaced in an oven at 100 �C until a constant mass was

J.M. Khatib / Construction and Building Materials 22 (2008) 1963–1971 1965

achieved. This took about 3 days. The cubes were left tocool in an air-tight container. The dry mass of specimenswas determined before they were immersed in water forhalf an hour. The absorption was then calculated as theratio of water mass absorbed to that of dry mass of sampleand expressed as a percentage.

3. Results and discussion

3.1. Workability

All mixes exhibited high workability, in that the flowspread (i.e. diameter) for all mixes is in excess of 700 mmexcept for the control mix M1 where a spread of 635 mmis obtained where a relatively low dosage of AD is added(Table 2). These values are higher than those indicatingelsewhere [6,9]. Slump flow of 650 ± 50 mm is requiredfor SCC [15], and all the mixes under investigation fall inthis category. Visual examination of mixes containing FAsuggest that there is further increase in workability, as dem-onstrated by the ease of flow in the moulds, compared withthe control at the same dosage of admixtures (i.e. 0.7%). Itis well established that the use of FA in concrete reducesthe water demand for a given workability. Therefore, con-crete containing FA will cause an increase in workability atconstant water to binder ratio.

Table 3Density of mixes (kg/m3)

Mix % FA % AD Density (kg/m3)

M1 0 0.6 2272M2 0 0.7 2423M3 0 1.0 2432M4 20 0.7 2416M5 40 0.7 2380M6 60 0.7 2365M7 80 0.7 2307

0

0.5

1

1.5

2

2.5

3

0.5 0.6 0.7 0

% Ad

Ab

sorp

tio

n (

% b

y d

ry m

ass)

Fig. 1. Influence of admixtur

3.2. Density

Table 3 presents the density values for all mixes at differ-ent curing times. each density values represents the averagedensity at the various curing times. For the control mixes(M1–M3), an increase in AD content resulted in anincrease in density. This can be attributed to the bettercompaction and reduction in voids in concrete containinghigh AD content due to the higher flow obtained. At thesame AD content, the incorporation of increasing amountsof FA in concrete causes a systematic reduction in density,mainly resulting from the lower density of FA comparedwith PC. Although the mix proportions of SCC are differ-ent than those of traditional concrete, it is worth notingthat the density values of SCC are similar to those of tradi-tional vibrated concrete [17], indicating the good compac-tion of SCC.

3.3. Absorption

The influence of varying AD content on absorption isshown in Fig. 1 (mixes M1–M3). There is a decrease inabsorption with the increase in curing period and thisdecrease is substantial between 1 day and 28 days. As canbe expected the prolonged curing period (56 days) led tolower absorption compared with that obtained at 28 daysof curing. Using an optimum dosage of AD (e.g. 0.7%)causes a decrease in absorption compared with a relativelylow (0.6%) or high (1.0%) dosage of AD. The use of lowdosage of AD may cause an increase in void if compactionwas not used, and at high AD content segregation mightlead to an increase in absorption.

Fig. 2 shows the influence of incorporating FA in con-crete on absorption at a constant AD content of 0.7%.There is substantial decrease in absorption between 1 daycuring and the other curing times (28 & 56 days). Theincrease in curing time from 28 to 56 days, results in further

.8 0.9 1 1.1

mixture

1day

28 days

56 days

e dosage on absorption.

0

1

2

3

4

5

6

0 20 40 60 80

% FA

Ab

sorp

tio

n (

% b

y d

ry m

ass)

1 day

28 days

56 days

Fig. 2. Influence of FA content on absorption (AD = 0.7%).


reduction but at a much slower rate compared with thoseobtained between 1 day and 28 days of curing. There is sys-tematic increase in absorption with increasing FA contenthowever, at 56 days all FA mixes including the 80% FAmix exhibited absorption values of less than or equal to2%, which is considered to be a low water absorption[18]. The low absorption is an indication of good compac-tion achieved by the concrete self-weight. The compactionis expected to be better especially in the presence of FA dueto the increased workability. Generally, the absorption val-ues for all mixes are lower than those reported in anotherinvestigation [19].

3.4. Compressive strength

The effect of different dosages of AD on concretestrength for the control mixes (M1–M3) is shown inFig. 3. Using either a relatively low or high dosage of

0

10

20

30

40

50

60

70

80

90

0.5 0.6 0.7

% Admixture (by

Str

eng

th (

N/m

m2 )

Fig. 3. Influence of admixt

AD reduces the strength, whereas using an optimum doseof AD (e.g. 0.7%) causes an increase in strength. As sug-gested earlier, low dosage might lead to the creation of poreif concrete is to be compacted under its own self-weightonly, whereas high dosage might lead to segregation. Thiscan justify the relatively high strength obtained when amedium dose of AD (0.7%) is added to the concrete.

Fig. 4 shows the influence of FA incorporation on con-crete strength at a constant addition of AD (0.7%). Con-crete containing 40% FA shows higher 56 days strengththan the other FA mixes including the 20% FA mix, wherea high strength of approximately 70 N/mm2 at 56 days isobtained. Generally and at the same water to binder ratio,there is strength reduction for concretes containing FAcompared with that of the control. However, and even athigh FA content (60%), a long-term high strength of about40 N/mm2 is achieved at the same water to binder ratio.Higher strength would be expected in the FA mixes if the

0.8 0.9 1 1.1

mass of binder)

1 day

7 days

28 days

56 days

'

ure dosage on strength.

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80

% FA

Str

eng

th (

N/m

m2 )

1day

7 days

28 days

56 days

Fig. 4. Influence of FA content on strength (AD = 0.7%).

Table 4Ultrasonic pulse velocity for all mixes (m/s)

Mix % FA % AD 1 day 7 days 28 days 56 days

M1 0 0.6 4219 4525 4566 4518M2 0 0.7 4392 4608 4710 4724M3 0 1.0 4298 4539 4623 4546M4 20 0.7 3958 4367 4367 4412M5 40 0.7 4011 4464 4601 4525M6 60 0.7 3517 4071 4184 4167M7 80 0.7 2126 3641 3750 3755


w/b ratio was lowered to achieve similar workability tothat of the control. The trend is similar to results obtainedelsewhere on SCC containing FA [20].

Correlation between strength and water absorption forall mixes (M1–M7) is shown in Fig. 5. As can be expected,an increase in strength is associated with a decrease inwater absorption. There is sharp decrease in strength asthe absorption increases from 1% to 2%. For absorptionbeyond 2%, there is a much slower reduction in strengthwith the increase in absorption.

3.5. Ultrasonic pulse velocity (V)

Table 4 presents the V values for all mixes at differentcuring times. The trend in V is similar to that of compres-sive strength. Using medium dosage of AD causes anincrease in V as compared with low and high dosage ofAD. Also the 40% FA mix show the largest value of V

compared with the 20% FA mix and the other FA mixes

0

10

20

30

40

50

60

70

80

90

0 1 2

Abso

Str

eng

th (

N/m

m2 )

Fig. 5. Relationship between

for the same AD addition. Generally there is decrease instrength with the increase in FA content.

The strength versus V values are plotted in Fig. 6. Anexponential relationship exists between strength (y) and V

(x). That is: y = 0.003e0.00217x with an R2 of 0.97 indicatinga strong correlation. This agrees with correlations obtainedelsewhere [21]. The relationship seems to be independent ofthe FA content.

3 4 5 6

rption (%)

M1M2M3M4M5M6M7

strength and absorption.

0

10

20

30

40

50

60

70

80

90

2000 2500 3000 3500 4000 4500 5000

V (m/s)

Str

eng

th (

N/m

m2 )

M1M2M3M4M5M6M7Best Fit

y=0.003e0.00217x

R2=0.97

Fig. 6. Relationship between strength and V.


3.6. Length change

The effect of using different amount of AD on shrinkageis shown in Fig. 7. The results suggest that low AD dosageincreases shrinkage, whereas a decrease in shrinkage occursat high AD content. A substantial increase in shrinkage

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

0 10 20

Time

Len

gth

Ch

ang

e (m

icro

stra

in)

Fig. 7. Influence of admixtu

takes place during the first 28 days of hydration, afterwhich period there is little change in shrinkage.

Fig. 8 displays the shrinkage profiles for the control mixM2 and for mixes containing FA (M4–M7). As for theresults in Fig. 7, most of the shrinkage occurs during thefirst 28 days. After that, there is little change in shrinkage

30 40 50 60

(days)

0.6%AD

0.7%AD

1.0%AD

re dosage on shrinkage.

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

0 2010 30 40 50 60

Time (days)

Len

gth

Ch

ang

e (m

icro

stra

in)

0% FA-control

20% FA

40% FA

60% FA

80% FA

Fig. 8. Influence of FA on shrinkage (AD = 0.7%).


up to at least 56 days. Increasing the amounts of FA resultsin a systematic reduction in shrinkage. At high FA content(60%) the 56 days shrinkage is reduced to half and withvery high FA content (80%) the shrinkage is about onethird compared with that of the control. This is better illus-trated in Fig. 9, where the 56 days shrinkage data are plot-ted against FA content. There is a linear relationshipbetween FA content and shrinkage. If a straight line is fit-

y = 3.5

R2

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

00 20

%

Sh

rin

kag

e (m

icro

stra

in)

Fig. 9. Shrinkage versus FA c

ted to the data an equation in the form of y = 3.5x � 425 isobtained with an R2 = 0.98 indicating a strong correlation.The trend in shrinkage is similar to those reported else-where, however, and despite of the high binder content inthe present investigation the shrinkage values are muchlower for comparable aggregate contents [6]. This couldbe attributed to the high CaO (13.4%) content of FA usedin the other investigation [6], as opposed to 2.4% CaO used

003x - 425.42

= 0.9803

40 60 80

FA

ontent at 56 days curing.

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

00 10 20 30 40 50 60 70 80

28-day Strength (N/mm2)

56-d

ay S

hri

nka

ge

(mic

rost

rain

)M1

M2M3

M4

M5

M6

M7

Trend Liney=-4.47x-105.8R2=0.66

Fig. 10. Relationship between shrinkage and strength at 56 days curing.

Table 5Estimation of shrinkage of SCC concrete

Mix Mix ID e* = �bt /[a+t]

a b Correlation coefficient (R2)

M1 0% FA 7.99 525 0.99M2 0% FA 4.06 483 0.99M3 0% FA 7.17 444 0.99M4 20% FA 12.10 467 0.99M5 40% FA 13.87 350 0.99M6 60% FA 5.70 214 0.99M7 80% FA 8.53 188 0.99

* e is shrinkage in microstrain.


in the present work. The shrinkage values obtained forSCC are higher than those obtained for traditional vibratedconcrete [6,17]. Fig. 10 correlates the 56 day shrinkage with28 strength data. An increase in strength is associated withan increase in shrinkage. Persson [9] reported a parabolicrelationship between the 28 day strength and long-termshrinkage with an R2 of 0.58 where there is an increase inshrinkage as the strength increases up to a certain pointbefore it start decreasing. In this work, it is found that alinear correlation gives y = �4.47x�105.8 with an R2 of0.66 (Fig. 10), whereas a parabolic correlations givesy = 0.009x2 � 5.19x � 94.9 with an R2 of 0.66.

The change in shrinkage with time can be described bythe following equation [17]: e ¼ �bt

aþt ; where e is the shrink-age value in microstrain at time t in days, a is a constantrelated to the initial slope and b is another constant relatedto ultimate shrinkage values and other factors includingenvironmental conditions, specimens size and strength. Fit-ting the above equation to the experimental data, values ofa and b were obtained for each of the mixes. These valuesare presented in Table 5 with their correlation coefficients(R2). R2 for all mixes is 0.99 indicating a strong correlation.The values of b are higher than those reported elsewhere[17], partly due to the relatively high cement content for

the control. The a values increase as FA content increasesup to 40% before it starts to decrease beyond FA contentsof 40%. However, the b values decreases with the increasein FA content.

4. Conclusions and recommendations

The following conclusions are based on the results of thepresent investigation:

1. High percentage of FA can be used to produce SCCwith an adequate strength. Using of up to 60% FA asPC replacement can produce SCC with a strength ashigh as 40 N/mm2.

2. Although the absorption increases with increasing FAcontent, the absorption values of SCC containing highvolume (80%) of FA is below 2% at 56 days of curing.

3. Incorporating increasing amounts of FA in SCC reducesthe drying shrinkage. and there is linear change inshrinkage with the increase in FA content. Replacingcement with 80% FA can reduce the shrinkage by twothird.

Acknowledgements

The authors would like to thank Mr Creed for conduct-ing the experimental programme and the concrete labora-tory technical staff Mr Skelton and Mr Harwood fortheir assistance.

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