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Combined effect of polypropylene fiberand silica fume on mechanical propertiesof concrete composite containing fly ash

Peng Zhang, Qingfu Li and Haiyang Zhang

Abstract

A parametric experimental study has been conducted to investigate the combined effect of polypropylene fiber and silica

fume on the mechanical properties (compressive strength, splitting tensile strength, and compressive modulus of elas-

ticity) of concrete composite containing fly ash. Five different fiber volume fractions, four contents of fly ash, and four

silica fume contents were used. The results indicate that the contribution of silica fume on the growth of compressive

strength and splitting tensile strength is performed at the early curing period, and the contribution of fly ash on the

growth of compressive strength and splitting tensile strength is performed at the later curing period, when the fly ash

content is not beyond 20% and the silica fume content exceeding 3%. The addition of fly ash and silica fume greatly

increases the compressive modulus of elasticity at 28 days curing. Though the addition of polypropylene fiber decreases

the compressive strength of the concrete with fly ash and silica fume, the splitting tensile strength is improved and

compressive modulus of elasticity is decreased effectively, which can decrease the rigidity and increase the ductility of the

concrete composite containing fly ash and silica fume to protect the concrete from damages for large deformation.

Keywords

concrete composite, polypropylene fiber, silica fume, fly ash, mechanical property

Introduction

As a by-product from thermal power stations, fly ashhas been used in blended cements,1,2 and it has beenused successfully to replace Portland cement up to30% by mass, without adversely affecting the strengthand durability of concrete composite.3,4 Because flyash causes environmental pollution and the cost ofstorage of fly ash is quite high, the utilization of flyash in concrete technology, both in regard to environ-mental pollution and the positive effect on a country’seconomy, are beyond dispute. The fly ash concretesystem offers a holistic approach that can help us toachieve the goals of meeting the rising demands forconcrete, enhancement of concrete durability withlittle or no increase in cost (in some instances reducedcost), and ecological disposal of large quantities of thesolid waste products from coal-fired power plants.5

Several laboratory and field investigations involvingconcrete containing fly ash had reported to exhibitexcellent mechanical and durability properties.6,7

Despite the benefits of fly ash, practical problemsremain in field application. At early stages of aging,the strength of concrete containing a high volume offly ash as a partial cement replacement is much lowerthan that of control concrete, due to the slow processof the pozzolanic reaction of fly ash, and its contribu-tion toward the strength development occurs only atlater ages.8 Different approaches have been used toaccelerate the pozzolanic reaction of fly ash and,thereby, to increase the early strength of concretecontaining fly ash. The activators have been used toimprove the unsatisfactory early properties of

School of Water Conservancy and Environment Engineering, Zhengzhou

University, Zhengzhou 450001, P R China.

Corresponding author:

Peng Zhang, School of Water Conservancy and Environment Engineering,

Zhengzhou University, Zhengzhou 450001, P R China

Email: [email protected]

Journal of Reinforced Plastics

and Composites

30(16) 1349–1358

! The Author(s) 2011

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DOI: 10.1177/0731684411425974

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Portland cement paste with fly ash added as a cementreplacement.9

Today, silica fume is known as a by-product of sil-icon metal and ferrosilicon alloy industry instead of awaste product and its utilization in composite technol-ogy has increased recently.10 The first utilization ofsilica fume in concrete was reported in 1952 by aNorwegian researcher. It was only in the late 1970sthat silica fume started to be used as a supplementarycementitious material in concrete in Scandinavia. It wasnot until the early 1980s that it began to be used in thisway in North America.11 Because of significantimprovements attained on interfacial zone of cementpaste-aggregate, silica fume is known to produce ahigh-strength concrete and is used in two differentways: as a cement replacement, in order to reduce thecement content (usually for economic reasons), and asan additive to improve concrete properties (in bothfresh and hardened states).3

Therefore, to increase the early strength of con-crete containing fly ash, the application of silica fumetogether with fly ash provides an interesting alternative,and many researchers have recently conducted investi-gations using a combination of the two by-products.12

However, a lot of research achievements indicate thatsilica fume can cause the concrete to have a more brittlestructure, and ductility improvement is an importantgoal in concrete science and must be taken into accountby researchers.13,14 Short fibers have been known andused for centuries to reinforced brittle materials likecement or masonry bricks. Now, there are numerousfiber types available for commercial use, the basictypes being steel, glass, synthetic materials, and somenatural fibers.15–19 Because polypropylene fiber is akind of man-made synthetic fiber with the propertiesof low modulus of elasticity, high strength, excellentductility, excellent durability, and low price, manyexperimental works related to the use of polypropylenefibers in cement matrix composites have beenpublished.20,21

However, little information is presently knownregarding the combined effect of polypropylene fiberand silica fume on the mechanical properties of con-crete composite containing fly ash. Therefore, the pre-sent work investigates ternary blends of fly ash, silicafume, and polypropylene fiber using an extensive rangeof mixes: fly ash (by mass) from 10 to 25%, silica fume(by mass) from 3 to 12%, and polypropylene fiber

(by volume) from 0.04 to 0.12%. The volume fractionswere chosen referring to the common volume fractionsof polypropylene fiber used in concrete. Fly ash andsilica fume were mixed in concrete composite by repla-cing the same quantity of cement, and polypropylenefiber was mixed in concrete with the dosage of cemen-titious materials unchanged.

Materials and experimental methods

Raw materials

Ordinary Portland cement (Class 42.5R) produced byTongli Factory, Grade I fly ash and silica fume, a by-product of the silicon and ferrosilicon were used in thiswork. The cement, fly ash, and silica fume propertiesare given in Table 1. The polypropylene fiber used inthis investigation was single short fiber, which was pro-duced by Danyang Synthetic Fiber Plant in the JiangsuProvince of China. This fiber was manufactured bymixing modified polypropylene short fiber with differ-ent lengths and section shapes together in proportionin special production techniques. There are two dif-ferent section shapes, which are ‘Y’ shaped (50%) and‘X’ shaped (50%). The proportion of the fibers with thelength of 10–15mm is about 60%, and the other 40%of the fibers have the length of 15–20mm. The basicphysical properties of polypropylene fiber in this studyare shown in Table 2. The water to be mixed was local

Table 1. Properties of cement, fly ash, and silica fume

Composition (%) Cement Fly ash Silica fume

Chemical compositions

SiO2 20.17 51.50 93.72

Al2O3 5.58 18.46 0.82

Fe2O3 2.86 6.71 0.48

CaO 63.51 8.58 0.34

MgO 3.15 3.93 1.44

Na2O 0.12 2.52 0.40

K2O 0.57 1.85 1.22

SO3 2.56 0.21 0.47

Physical properties

Specific gravity 3.05 2.16 2.30

Specific surface (cm2/g) 3295 2470 —

Table 2. Physical properties of polypropylene fiber

Density (g/cm3) Linear density (dtex) Fiber length (mm) Tensile strength (MPa) Elastic modulus (MPa) Melting point (�C)

0.91 10–20 10–20 �450 �4100 160–170

1350 Journal of Reinforced Plastics and Composites 30(16)



tap water. Coarse aggregate with a maximum size of20mm and fine aggregate with a 2.82 fineness moduluswere used in this experiment. The specific gravity andsilt content of the coarse and fine aggregates were 2.75and 0.5%, and 2.62 and 0.9%, respectively. A high-range water reducer agent with a commercial name ofpolycarboxylate HJSX-A was used to adjust the work-ability of the concrete mixture.

Mix proportions

In all, 18 mixture proportions were made, and the firstone was control mix (without fly ash, silica fume, andpolypropylene fiber). There are four proportions withfly ash replacing the same quantity of cement by massranged from 10 to 25%, and four proportions withsilica fume replacing the same quantity of cement bymass ranged from 3 to 12%. Another four proportionswere arranged with silica fume replacing the samequantity of cement by mass ranged from 3 to 12%,and 15% cement replaced by fly ash. The rest five pro-portions were arranged with polypropylene fiber mixedin concrete by volume ranged from 0.04 to 0.12% withthe dosage of cementitious materials unchanged, and15% cement replaced by fly ash and 6% cementreplaced by silica fume. Mix proportions are given inTable 3.

Preparation of specimens

The 150mm concrete cubes were cast for compressivestrength and splitting tensile strength, 150� 300mmquadruple prisms for compressive modulus of elasticity.All the mixes were mixed in the mixing plant. In orderto distribute the fibers uniformly, a forced mixingmachine was adopted. The forced machine has anaxis with several vanes, which is different from theself-loading concrete mixer. When the axis is turning,the axis drives the vanes to turning and the mixture canbe well mixed. Fibers were dispersed by hand in themixture to achieve a uniform distribution throughoutthe mixture. The mixing procedure, which was designedby trial and error, was chosen as follows: before waterwas added into the mixes, the coarse aggregate and fineaggregate were mixed initially for 1min, and the binderand polypropylene fiber were mixed for another 1min.Finally, the high-range water reducer agent and waterwere added and mixed for 3min. The fiber distributionhas great effect on the working performance of the mix-ture and the mechanical properties. If the fibers are notdistributed well, the fibers will be assembled altogether.As a result, the reinforcement of fibers on the compos-ite material will be decreased, and the fibers cannoteffectively bridge microcracks. From the working per-formance of the mixture, and the fracture section of thespecimen, it can be seen that the fibers of this study

Table 3. Mix proportions of the concrete mixtures

Mix

no.

Cement

(kg/m3)

Fly ash

(%)

Flyash

(kg/m3)

Silica

fume (%)

Silica

fume

(kg/m3)

Fiber

volume

fraction (%)

Fine

aggregate

(kg/m3)

Coarse

aggregate

(kg/m3)

Water

(kg/m3)

water

reducer

agent (kg/m3)

1 494.0 — — — — — 647 1151 158 4.94

2 444.6 10 49.4 — — — 647 1151 158 4.94

3 419.9 15 74.1 — — — 647 1151 158 4.94

4 395.2 20 98.8 — — — 647 1151 158 4.94

5 370.5 25 123.5 — — — 647 1151 158 4.94

6 479.2 — — 3 14.8 — 647 1151 158 4.94

7 464.4 — — 6 29.6 — 647 1151 158 4.94

8 449.5 — — 9 44.5 — 647 1151 158 4.94

9 434.7 — — 12 59.3 — 647 1151 158 4.94

10 405.1 15 74.1 3 14.8 — 647 1151 158 4.94

11 390.3 15 74.1 6 29.6 — 647 1151 158 4.94

12 375.4 15 74.1 9 44.5 — 647 1151 158 4.94

13 360.6 15 74.1 12 59.3 — 647 1151 158 4.94

14 390.3 15 74.1 6 29.6 0.04 647 1151 158 4.94

15 390.3 15 74.1 6 29.6 0.06 647 1151 158 4.94

16 390.3 15 74.1 6 29.6 0.08 647 1151 158 4.94

17 390.3 15 74.1 6 29.6 0.10 647 1151 158 4.94

18 390.3 15 74.1 6 29.6 0.12 647 1151 158 4.94

Zhang et al. 1351



were distributed well. After casting, all the specimenswere finished with a steel towel. Immediately after fin-ishing, the specimens were covered with plastic sheets tominimize the moisture loss from them. All the speci-mens were stored at temperature of about 23�C in cast-ing room. They were demolded after 24 h, and thencured at 100% relative humidity and controlled temper-ature (21� 2�C) before testing.

Compressive strength and splitting tensilestrength tests

The tests of compressive strength and splitting tensilestrength were carried out by hydraulic pressure uni-versal testing machine according to the ChineseStandard.22 Before testing, the specimen was put ontothe pad of the elevating platform of the test machine.The loading rate of compressive strength test wascontrolled between 0.5MPa/s and 0.8MPa/s. For split-ting tensile strength test, because the type and width ofthe splitting pad have great effect of tensile strength ofconcrete, the same splitting pad was applied throughoutthe testing process of all the specimens. The loadingrate of tensile strength test was controlled between0.05MPa/s and 0.08MPa/s. Compressive strength andsplitting tensile strength can be computed as follows:

fcu ¼F

Að1Þ

fts ¼2F

�A¼ 0:637

F

Að2Þ

where, fcu, compressive strength, MPa; fts, splitting ten-sile strength, MPa; F, the maximum pressure at failure,N; A, area of the cross section of the specimen, mm2.Each set includes three specimens, and the averagevalue of the three data was computed as the final result.

Compressive modulus of elasticity test

Compressive modulus of elasticity test was also carriedout by hydraulic pressure universal testing machineaccording to the Chinese Standard.22 During thecourse of loading and unloading, the deformation ofthe specimen was measured using 2 micrometers withdial indicators, which were supported by dial holderson the two symmetrical sides of the specimen, respec-tively. The 2 micrometers with dial indicators were fixedin the two symmetrical sides of a rectangular steelholder, which encircled the specimen. The other twosymmetrical sides of the rectangular steel holder werestuck to the other two symmetrical sides of the speci-men. In order to make the top-loading board touch theupper surface of the specimen closely, two times of

preloading of ‘loading–unloading’ was carried out,and the preload was one third of the maximum pressureat failure. To keep the deformation changing equably,the loading rate of compressive modulus of elasticitytest was controlled between 0.2MPa/s and 1MPa/s.The elastic deformation of each grade of pressure canbe computed as the difference of the numerical readingsof the micrometer with dial indicator, when the speci-men was being loaded and after the specimen wasunloaded. Compressive modulus of elasticity can becomputed as follows:

Ec ¼Fa � F0

A�

L

�nð3Þ

where, Ec, compressive modulus of elasticity, MPa; Fa,final pressure (one third of the maximum pressure atfailure), N; F0, initial pressure (the pressure of0.5MPa), N; L, scale distance for deformation mea-surement, mm; A, load-carrying area of the specimen,mm2; �n, average value of the deformation differenceof both sides under the pressure of Fa and F0, when thespecimen was loaded for the last time, mm. The initialpressure F0 and the final pressure Fa were determinedaccording to the reference of JTJ E30-200522 and thecompressive strength of HPC. Each set includes threespecimens, and the average value of the three data wascomputed as the final result.

Experimental results and discussion

Compressive strength

Compressive strengths of concrete mixes were deter-mined at 3, 7, 28, and 90 days of curing. The test resultsare given in Figures 1–4. Figure 1 shows the variation

0 5 10 15 20 25 30 3540

50

60

70

80

Com

pres

sive

str

engt

h (M

Pa)

Fly ash (%)

3 d 7 d 28 d 90 d

Figure 1. Compressive strength vs. fly ash content.




of compressive strength with fly ash percentages at dif-ferent ages. From the results, it can be seen that thecompressive strength of concrete with fly ash is increas-ing gradually with the increase of curing period understandard maintenance condition. Because the additionof fly ash reduces the cement content and the initialhydration rate of cement is considerably little, all flyash concrete mixes were found to have lower strengthsthan the control mix, and the compressive strengthdecreases with the increase of the fly ash percentageat the age of 3 days. At the age of 7 days, comparedto 3 days, the increase of compressive strength of con-crete with fly ash is larger than that of the control mix,and the decrease of compressive strength with theincrease of the fly ash percentage is less than that of 3days. Nevertheless, the mixes with 10% and 15% fly

ash content were found to attain greater strengthsthan the control mix (61.5MPa) at 28 days of curing,reaching 62.6MPa and 64MPa, respectively. At 90days of curing, the compressive strength of fly ash con-crete mixes with 10%, 15%, 20%, and 25% cementreplacement with fly ash, were higher than the controlmix (68.4MPa), and the mix with 15% fly ash contentattained the maximum compressive strength(79.5MPa), which increased by 16% than the controlmix. At all ages, the compressive strength beginsdecrease after the fly ash percentage exceeds 15%.

Figure 2 shows the variation of compressive strengthof silica fume concrete mixes with 3%, 6%, 9%, and12% cement replacement with silica fume at differentages. As can be seen, the compressive strength increaseswith the increase of silica fume content, and thestrengths of different silica fume contents are lowerthan that of the control mix at 3 days curing. Afterthe age of 3 days, the compressive strength is increasedby different silica fume content, and the compressivestrength increases gradually with the increase of silicafume content. Especially at 90 days, the contribution ofsilica fume on the growth of compressive strength ismore significant, for example, compared with the con-trol mix, the compressive strength increases from68.4MPa to 81.2MPa, and increases by 19% with12% cement replacement with silica fume.

From Figure 3, it can be seen that the variation ofcompressive strength of fly ash concrete with 15% flyash is not evident with the increase of silica fume con-tent, however, the strengths are all lower than the mixwith 15% fly ash and without silica fume. The growthrules of compressive strength at 7 days and 28 days withthe increase of silica fume content are similar with thoseof the mixes without fly ash. At the age of 90 days, the

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.1630

40

50

60

70

80

Com

pres

sive

str

engt

h (M

Pa)

Fiber volume fraction (%)

3 d 7 d 28 d 90 d

Figure 4. Effect of fiber volume fraction on compressive

strength.

0 3 6 9 12 15 1830

40

50

60

70

80

90

Com

pres

sive

str

engt

h (M

Pa)

Silica fume (%)

3 d 7 d 28 d 90 d

Figure 3. Compressive strength vs. silica fume (with 15% fly

ash).

0 3 6 9 12 15 1840

50

60

70

80

Com

pres

sive

str

engt

h (M

Pa)

Silica fume (%)

3 d 7 d 28 d 90 d

Figure 2. Compressive strength vs. silica fume (without

fly ash).

Zhang et al. 1353



compressive strength has the trend to increase with theincrease of silica fume content, while the strength ofsmall silica fume content is lower than the mix withthe same silica fume content and without fly ash.From Figures 2 and 3, it can be seen that the contribu-tion of silica fume on the growth of compressivestrength is performed at the early curing period, andthe contribution of fly ash on the growth of compres-sive strength is performed at the later curing period.Silica fume acts as a filler due to its smaller particlesize, and the pozzolanic reaction of the silica fume pro-duces additional C-S-H gel, which grows into the cap-illary spaces that remain after the hydration of thecement in mortar mixes.23 Therefore, it would appearthat silica fume acts both physically (as filler) andchemically (reacting with Ca(OH)2 to form C-S-H) toaid in the strength improvement of fly ash mixes.

Figure 4 shows the varying rule of the compressivestrength with 15% fly ash and 6% silica fume at differ-ent ages with the increase of polypropylene fibervolume fraction. As can be seen from the figure, ingeneral, the addition of polypropylene fiber decreasesthe compressive strength of concrete with 15% fly ashand 6% silica fume, however, the effect of polypropyl-ene fiber on the compressive strength of 3 days curing isnot obvious. With the increase of fiber volume dosage,the compressive strength of 7, 28, and 90 days stages isdecreasing gradually, and the decrease is so great afterthe fiber volume dosage exceeds 0.1%. At 90 dayscuring period, compared with the control mix, thedecrease of compressive strength were determined as2.5%, 5.0%, 5.1%, 6.2%, and 11.5% for 0.04%,0.06%, 0.08%, 0.1%, and 0.12% fiber volume dosagefor compressive strength, respectively.

Splitting tensile strength

Splitting tensile strengths of concrete mixes were deter-mined at 3, 7, 28, and 90 days of curing. The test resultsare given in Figures 5–8. The variations of splittingtensile strength with fly ash percentages at differentages are illustrated in Figure 5. A considerable increasefor the splitting tensile strength was observed byincreasing the curing period. For each curing period,there is an increase trend in splitting tensile strengthwith the increase of fly ash content within fly ash con-tent of 20%, and the increase at 90 days curing is espe-cially considerable. However, the splitting tensilestrength begins to decrease after fly ash content isincreased continuously. With the increase of fly ashcontent, there is no obvious variation on splitting ten-sile strength at 3 days curing.

The relation curves between the splitting tensilestrength and silica fume content of 3, 7, 28, and 90days curing are given in Figure 6. Increasing silica

fume content, a considerable increase in the splittingtensile strength of the mixes without fly ash wasobtained at each curing period, for example, comparedwith themix without silica fume, the increase were deter-mined as 5%, 9%, 15%, and 20% for silica fume contentof 3%, 6%, 9%, and 12% at 28 days curing period,respectively. At 90 days curing, the increase in splittingtensile strength is slight with the increase of silica fumecontent. The results indicate that the contribution ofsilica fume toward the splitting tensile strength develop-ment occurs only at early ages, especially with the highercontent of silica fume.

Figure 7 shows the varying rule of the splitting ten-sile strength of silica fume concrete with 15% fly ash atdifferent curing ages with the increase of silica fume

0 5 10 15 20 25 30 353

4

5

6

7

Spl

ittin

g te

nsile

str

engt

h (M

Pa)

Fly ash (%)

3 d 7 d 28 d 90 d

Figure 5. Splitting tensile strength vs. fly ash content.

0 3 6 9 12 15 183

4

5

6

7S

plitt

ing

tens

ile s

tren

gth

(MP

a)

Silica fume (%)

3 d 7 d 28 d 90 d

Figure 6. Splitting tensile strength vs. silica fume (without fly

ash).




content. As can be seen, with the increase of silica fumecontent, the splitting tensile strength decreases gradu-ally when silica fume content is small, however, thesplitting tensile strength increases gradually whensilica fume content is larger because the existence offly ash, which restrain the contribution of silica fumetoward the splitting tensile strength development, whensilica fume content is small. Compared the concreteonly mixed with different contents of silica fume, incor-porating fly ash and silica fume lowers the splitting ten-sile strength of early stages, but improves the splittingtensile strength of later stages.

The variations of the splitting tensile strength of con-crete with 15% fly ash and 6% silica fume vs. polypro-pylene fiber volume fraction are given in Figure 8.

It can be generally seen that, as the fiber volume frac-tion increase from 0.04 to 0.1%, the splitting tensilestrength decreases gradually at 3 days curing period,and remain almost unchanged at 7 days curingperiod, while increases slightly at 28 days and 90 dayscuring period, for example, at 90 days curing period,compared with the control mix, the splitting tensilestrength increases from 6.12 to 6.58MPa, and increasesby 7.5% with 0.1% fiber volume dosage. After the fibervolume fraction exceeds 0.1%, the splitting tensilestrength begins to decrease with the increase of thefiber volume fraction.

Compressive modulus of elasticity

Figure 9 shows the variation of compressive modulus ofelasticity of concrete mixes with 10%, 15%, 20%, and25% cement replacement with fly ash at 28 days curing.As can be seen from the figure, the content of fly ashhas a significant effect on compressive modulus of elas-ticity. Within the fly ash content of 20%, the compres-sive modulus of elasticity increases gradually with theincrease of fly ash content. Compared with the controlmix, the increase were determined as 0.7GPa, 2.1GPa,and 2.4GPa for 10%, 15%, and 20% cement replace-ment with fly ash, respectively. However, as the fly ashcontent increases continuously, great decrease in com-pressive modulus of elasticity was obtained. The addi-tion of fly ash in concrete increases the brittleness ofconcrete.

The variations of compressive modulus of elasticityof silica fume concrete mixes with 3%, 6%, 9%, and12% cement replacement with silica fume at 28 dayscuring are illustrated in Figure 10. From the results, itcan be seen that the compressive modulus of elasticity

0 3 6 9 12 15 183

4

5

6

7S

plitt

ing

tens

ile s

tren

gth

(MP

a)

Silica fume (%)

3 d 7 d 28 d 90 d

Figure 7. Splitting tensile strength vs. silica fume (with 15%

fly ash).

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.163

4

5

6

7

Spl

ittin

g te

nsile

str

engt

h (M

Pa)


3 d 7 d 28 d 90 d

Figure 8. Effect of fiber volume fraction on splitting tensile

strength.

0 5 10 15 20 2541

42

43

44

45

Mod

ulus

of e

last

icity

(G

Pa)

Fly ash (%)

28 d

Figure 9. Modulus of elasticity vs. fly ash content.

Zhang et al. 1355



of silica fume concrete with different percentagescement replacement was higher than the control mix,and a considerable increase for compressive modulusof elasticity was observed by increasing the contentof silica fume. The results indicate that the additionof silica fume makes the concrete more brittle.

Figure 11 shows the varying rule of compressivemodulus of elasticity of fly ash concrete with 15% flyash at 28 days curing age with the increase of silicafume content. As can be seen, the compressive modulusof elasticity of fly ash concrete was slightly reduced by3% silica fume content, while 6%, 9%, and 12% silicafume content greatly increase the compressive modulusof elasticity of fly ash concrete, for example, comparedwith the concrete only mixed with 15% fly ash, theincrease were determined as 1GPa, 2.1GPa, and

3GPa for silica fume content of 6%, 9%, and 12% at28 days curing period, respectively.

Figure 12 indicates the contrast relationship betweencompressive modulus of elasticity of non-fibrous con-crete (15% fly ash and 6% silica fume) and polypropyl-ene fiber-reinforced concrete (15% fly ash and 6% silicafume) with different fiber dosage. From the figure, itcan be seen that the addition of polypropylene fibercan decrease compressive modulus of elasticity effec-tively, which is benefit to improve the anticrackingperformance of concrete containing fly ash and silicafume. As the polypropylene fiber volume fractionincreases, the compressive modulus of elasticity willgradually decrease, for example, at 28 days curingperiod, compared with the control mix, the compressivemodulus of elasticity decreases from 44.8GPa to41.9GPa, and decreases by 6.5% with 0.12% fibervolume dosage. The main reason why polypropylenefiber decreases the compressive modulus of elasticity ofconcrete containing fly ash and silica fume is that itendures much larger compressive and tensile deforma-tion than concrete, and its addition makes the compositematerial stressed as a whole.24 Namely, after polypro-pylene fiber with low modulus of elasticity is added intoconcrete, the rigidity of the composite material decreasesand the ductility increases, which protects concrete fromdamages for large deformation.

Conclusions

This article reported experimental results of compres-sive strength, splitting tensile strength, and compressivemodulus of elasticity studies conducted on fly ash andsilica fume concrete composite reinforced with

0.00 0.02 0.04 0.06 0.08 0.10 0.1241

42

43

44

45

Mod

ulus

of e

last

icity

(G

Pa)


28 d

Figure 12. Effect of fiber volume fraction on modulus of

elasticity.

0 3 6 9 1243

44

45

46

47

48

Mod

ulus

of e

last

icity

(G

Pa)

Silica fume (%)

28 d

Figure 11. Modulus of elasticity vs. silica fume (with 15%

fly ash).

0 3 6 9 1241

42

43

44

45

46

47

Mod

ulus

of e

last

icity

(G

Pa)

Silica fume (%)

28 d

Figure 10. Modulus of elasticity vs. silica fume (without fly ash).




polypropylene fiber. The following conclusions can bedraw from the results presented in this article:

1. With the content of fly ash from 10 to 20%, fly ashhas great improvement on the compressive strengthand splitting tensile strength of concrete at latercuring periods, and the compressive strength andsplitting tensile strength increase gradually with theincrease of fly ash content. The compressive modulusof elasticity increases gradually with the increase offly ash content, when the fly ash content is notbeyond 20%. The compressive strength, splittingtensile strength, and compressive modulus of elastic-ity begin to decrease after the fly ash content beyond20%.

2. Silica fume has great improvement on the compres-sive strength and splitting tensile strength of concreteat early curing periods, and the compressive strengthand splitting tensile strength increase gradually withthe increase of silica fume content. With the increaseof silica fume content, the compressive modulus ofelasticity has a trend to increase at 28 days curingperiod.

3. With the existence of 15% fly ash, compared to thecontrol mix, the compressive strength and splittingtensile strength of concrete with different contents ofsilica fume are improved greatly both at early curingperiods and later curing periods. The compressivemodulus of elasticity with 15% fly ash is higherthan that of the concrete without fly ash and withthe same silica fume content. However, to obtain thebetter combined effect of silica fume and fly ash, thesilica fume had better exceed 3%.

4. Though the addition of polypropylene fiberdecreases the compressive strength of the concretewith 15% fly ash and 6% silica fume, the splittingtensile strength is improved and compressive modu-lus of elasticity is decreased effectively, which candecrease the rigidity and increase the ductility ofthe concrete containing fly ash and silica fume toprotect the concrete from damages for largedeformation.

Funding

The authors would like to acknowledge financial support

received from China Postdoctoral Science Foundation(grant no. 20110491007), and the key scientific and techno-logical project of Henan Province (China) (grant no.

112102310479).

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