This article was downloaded by: [139.57.125.60]On: 26 September 2014, At: 00:07Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

The IES Journal Part A: Civil & Structural EngineeringPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tiea20

Comparative experimental study of mechanicalproperties of concrete prepared by different fibresHui-ge Xinga, Fu-gang Xub & Jia-wen Zhoubc

a College of Architecture and Environment, Sichuan University, Chengdu, Sichuan 610065,PR Chinab State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University,Chengdu, Sichuan 610065, PR Chinac College of Water Resources and Hydropower, Sichuan University, Chengdu, Sichuan 610065,PR ChinaPublished online: 07 May 2014.

To cite this article: Hui-ge Xing, Fu-gang Xu & Jia-wen Zhou (2014) Comparative experimental study of mechanicalproperties of concrete prepared by different fibres, The IES Journal Part A: Civil & Structural Engineering, 7:3, 151-162, DOI:10.1080/19373260.2014.911972

To link to this article: http://dx.doi.org/10.1080/19373260.2014.911972

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

TECHNICAL PAPER

Comparative experimental study of mechanical properties of concrete prepared

by different fibres

Hui-ge Xinga, Fu-gang Xub and Jia-wen Zhoub,c*

aCollege of Architecture and Environment, Sichuan University, Chengdu, Sichuan 610065, PR China; bState Key Laboratory ofHydraulics and Mountain River Engineering, Sichuan University, Chengdu, Sichuan 610065, PR China; cCollege of Water Resources

and Hydropower, Sichuan University, Chengdu, Sichuan 610065, PR China

(Received 21 February 2014; accepted 2 April 2014)

This paper reports a comparative experimental study on the mechanical properties of concrete containing different types offibres: polyvinyl alcohol (PVA), polypropylene (PP) and steel fibres. Compression and three-point bending tests areperformed on both plain concrete and each type of fibre-reinforced concrete (FRC). The experimental results show that thepresence of fibres has less of an effect on the FRC’s compressive strength. The tensile strength is commonly increased bythe addition of fibres, but an appropriate fibre content of PVA or PP fibres should be selected. PVA and PP fibres decreasethe concrete’s elastic modulus, but steel fibres increase the modulus due to the steel’s higher Young’s modulus. The FRCcontaining PVA shows brittle characteristics, but the FRC containing steel or PP fibres have load-deflection curves withflattened descending paths. Flexural behaviour of the concrete is improved by addition of steel or PP fibres, but not byPVA fibres, and the concrete’s fracture toughness is increased by the addition of steel fibres.

Keywords: concrete; fibre reinforcement; mechanical properties; experimental testing

1. Introduction

Concrete is one of the most commonly used construction

materials due to its high strength and workability. The

material’s brittle nature causes collapse to occur shortly

after the formation of initial cracks. However, the addition

of fibres can convert concrete’s brittle characteristics to

become more ductile (Feleko�glu, Tosun, and Baradan

2009). Fibre-reinforced concrete (FRC) has been used

with increasing frequency in various applications, includ-

ing in the construction of a hydropower station, and is cur-

rently always used in tunnel linings, rock slope

stabilisation and dam construction. Adding fibres has

been found to enhance the compressive, tensile and shear

strength and the flexural toughness and durability of con-

crete (Debs, Montedor, and Hanai 2006). The mechanical

properties of FRC depend on the type and content of the

added fibres and the concrete mix proportions.

Fibres regularly added to concrete include steel,

organic, and inorganic fibres, and can be grouped into two

categories: those with low and high elastic moduli. Syn-

thetic fibres, such as polypropylene (PP) and polyethylene,

belong to the first category, whereas steel, glass and carbon

fibres belong to the second (Sun et al. 2001). PP fibre is a

synthetic fibre commonly used in the concrete and has a

low Young’s modulus (Kakooei et al. 2012). However, due

to PP’s ductility, fineness, and dispersion and the large

quantity of fibres used in concrete, PP fibres can be

appropriately distributed around coarse aggregate particles

so that plastic cracks are restrained. Researchers have

reported that PP fibres can improve the flexural ductility,

toughness, split tensile strength, and long-term durability

of concrete (Song and Hwang 2004; Hsie, Tu, and Song

2008). On the other hand, polyvinyl alcohol (PVA) fibres

perform very differently in concrete due to their surface

formation and high strength. The Young’s modulus of

PVA fibre is also close to that of concrete (Corinaldesi and

Moriconi 2011). At early ages, the PVA fibres have been

found to control crack propagation and improve concrete’s

toughness and resistance to impact (Schwartzentruber, Phil-

ippe, and Marchese 2004; Kou and Poon 2010).

Steel fibres are considerably longer and have a higher

Young’s modulus than synthetic fibres (Ding and Kusterle

2000; Altun, Haktanir, and Ari 2007; Haktanir et al.

2007). The tensile strength, ductility, toughness, and dura-

bility of concrete are significantly improved by the addi-

tion of steel fibres due to their high elastic modulus and

stiffness (Holschemacher, Mueller, and Ribakov 2010;

Shafigh, Mahmud, and Jumaat 2011). These qualities give

the steel a greater potential for crack control. However,

they also increase the weight of the concrete and lower its

workability (Giner et al. 2012). The cost of steel fibre is

usually greater than that of synthetic fibre, although the

mechanical performance of steel fibre-reinforced concrete

(SFRC) is better than that of synthetic fibre-reinforced

*Corresponding author. Email: jwzhou@scu.edu.cn

� 2014 The Institution of Engineers, Singapore

The IES Journal Part A: Civil & Structural Engineering, 2014

Vol. 7, No. 3, 151�162, http://dx.doi.org/10.1080/19373260.2014.911972

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

concrete (Olivito and Zuccarello 2010; Akcay and

Tasdemir 2012).

The goal of this study is to evaluate the mechanical

properties of concrete containing different fibres and iden-

tical mix proportions, comparative experiments to deter-

mine the effect of dosage of PVA, PP, and steel fibres

(hooked-end) on strength and fracture properties of concrete

are performed. Two densities of 20 kg/m3 and 30 kg/m3 are

considered for the steel fibres, while densities of 0.9 kg/m3

and 1.8 kg/m3 are considered for the PVA fibres and only

one density of 3.5 kg/m3 is considered for the PP fibres.

Compression and three-point bending tests are performed

on the various FRCs, and their mechanical performances

are compared.

2. Experimental study

2.1. Materials

Cement: The cement used in this study is ordinary Port-

land cement (CEM I 42.5R), the chemical, physical and

mechanical properties of which are listed in Table 1. The

material’s density is 3.22 g/cm3 and the compressive

strength of standard mortar at 28 days is 48.1 MPa.

Fly ash: Mingchuan fly ash, which is a type II fly ash

according to DL/T 5055-2007 is provided by the Guizhou

fly ash corporation. The physical properties of the fly ash

are determined according to the DL/T 5055-2007 proce-

dure. Its density is 2.32 g/cm3 and its strength activity index

at 28 days is 89%. Twenty per cent of Portland cement is

substituted with fly ash in all concrete specimen mixes.

Aggregates: The aggregates used in the specimens are

all man-made from crushed limestone. Crushed limestone

with continuous grading (0�5 mm) and a maximum size

of 5 mm is used for the sand component, and crushed lime-

stone with continuous grading (5�40 mm) and a maximum

size of 40 mm is used for the gravel component of the

aggregate. The sand density is 2.68 g/cm3 (0�5 mm) and

the gravel densities for the different grades are 2.72 g/cm3

(5�20 mm) and 2.74 g/cm3 (20�40 mm), respectively.

Superplasticiser: A high-range water-reducing admix-

ture (superplasticiser) was employed during mixing to

improve the workability of the concrete. The JG-2H super-

plasticiser used in this study is produced by the Being spe-

cialty materials corporation with a density of 1.08 g/cm3

and a dry extract of 75%. The material’s pH value is 5.18

and the surface tensile strength is 80.6 mN/m.

Steel fibre: The steel fibres (Figure 1(a)) used in this

study are Dramix RC-65/35-BN type with hooked ends.

This variety is cylindrical, with a length of 35.5 mm, a

diameter of 55 mm and an aspect ratio of 65. The tensile

strength of steel fibres is 1100 MPa and their modulus of

elasticity is 210 GPa, which is larger than that of concrete.

Polyvinyl alcohol (PVA) fibre: High elasticity PVA

fibres (Figure 1(b)) are used in the specimens. These fibres

are cylindrical, with a length of 12.0 mm, a nominal diam-

eter of 160 mm and an aspect ratio of 750. Their tensile

strength is 1200 MPa and modulus of elasticity is 32 GPa,

which is close to that of concrete.

Polypropylene (PP) fibre: The PP fibres (Figure 1(c))

used in this study are fine PP monofilaments, which are

cylindrical, with a length of 55.0 mm, a nominal diameter

of 910 mm and an aspect ratio of 60. Their tensile strength

is 420 MPa and modulus of elasticity is 3�10 GPa, which

is less than that of concrete.

Table 2 shows the main characteristics of the various

fibres used in this study.

2.2. Mix proportions and specimen preparation

Six concrete mixes are studied: one group of plain concrete

without any fibres (plain), two groups containing 0.9 kg/m3

(PVA-0.9) and 1.8 kg/m3 (PVA-1.8) of PVA fibres, two

groups containing 20 kg/m3 (SF-20) and 30 kg/m3 (SF-30)

of steel fibres, and one group containing 3.5 kg/m3

(PP-3.5) of PP fibres. All of the concrete mixes are

prepared with a water�cement ratio of 0.53 and constant

volumes of cement (316 kg/m3) and fly ash (79 kg/m3).

Table 3 summarises the compositions of the concrete mixes

under study.

The constituent materials are initially mixed without

any fibres. The fibres are then added in small amounts to

avoid balling and produce concrete with uniform material

Table 1. Chemical, physical and mechanical properties of CEM I 42.5R type Portland cement.

Oxide composition (wt.%) Mixed compounds (Bogue%)

SiO2 20.43 C3S 59.68 C3A 1.62

Fe2O3 5.08 C2S 14.92 C4AF 15.44

Al2O3 3.86 Compressive strength (MPa)

CaO 60.82 At 3 days 20.2 At 28 days 48.1

MgO 4.27 At 7 days 28.2

SO3 2.26 Physical properties

Free CaO 0.17 Density (g/cm3) 3.22 Initial setting time (min) 207

Loss on ignition 0.87 Blaine SSA (m2/kg) 311 Final setting time (min) 260

Insoluble residue 0.33

152 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

consistency and good workability. The slump of the plain

concrete is approximately 160�180 mm (average value is

172 mm), with air content of approximately 5%. The aver-

age value of slumps for PVA-0.9, PVA-1.8, PP-3.5, SF-20

and SF-30 are 160 mm, 151 mm, 134 mm, 116 mm and

98 mm, respectively. The addition of fibres will result in

the decreasing of workability for concrete, especially for

the steel fibres. Larger amount addition of fibres means

lower workability of concrete. The specimens are

unmolded after 24 h of curing in a controlled laboratory

environment, after which they are cured in a water curing

tank at 21� until they reach an age of 28 days.Figure 2 shows the distribution characteristics of dif-

ferent fibres in concrete. Fibres can be uniformly dis-

persed in the mixtures, because of the good mobility of

plain concrete. For the PVA fibres in the concrete, they

are hard to see because of their small size. However, the

PP fibres and steel fibres can be seen clearly in the con-

crete. The distribution of fibres in concrete will be influ-

enced by the mixing ratio.

The freshly mixed concrete samples are placed into

a cubic mould in three equal layers to cast a standard

150 � 150 � 150 mm cubical concrete specimen for a

compression test, and into a 150 � 150 � 500 mm

beam mould for a three-point bending test (Figure 3).

Three cubic concrete specimens are subjected to uniax-

ial compression tests, for each group of concrete, while

three plain concrete beam samples and six beam sam-

ples from each group of FRC are subjected to three-

point bending tests.

Table 2. Main characteristics of the fibres used in concrete mixes.

Fibre type Length (mm) Equivalent diameter (mm) Aspect ratio Tensile strength (MPa) Young’s modulus (GPa)

PVA 12.0 16 750 1200 32

Steel 35.5 550 65 1100 210

PP 55.0 910 60 420 3-10

Figure 1. Steel (a), polyvinyl alcohol (b) and polypropylene (c) fibres used in this study.

Table 3. Concrete mix proportions.

Proportion (kg/m3)

Mix Water Cement Fly ashSand

(0/5 mm)Gravel

(5/20 mm)Gravel

(20/40 mm) SuperplasticiserPVAfibre

Steelfibre

PPfibre

Plain 166 316 79 832 591 394 3.16 � � �PVA-0.9 166 316 79 832 591 394 3.16 0.9 � �PVA-1.8 166 316 79 832 591 394 3.16 1.8 � �SF-20 166 316 79 832 591 394 3.16 � 20 �SF-30 166 316 79 832 591 394 3.16 � 30 �PP-3.5 166 316 79 832 591 394 3.16 � � 3.5

The IES Journal Part A: Civil & Structural Engineering 153

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

2.3. Test methods

The test methods employed to determine the mechanical

properties of FRC, the three-point bending and uniaxial

compression tests are widely applied to ordinary concrete.

Among these, the bending test is the most commonly

adopted test method owing to its simplicity, while the uni-

axial compression test offers the advantage of directly

determining the compressive strength of a concrete sam-

ple. The compression tests are performed with a strain

rate of 0.10 mm/min.

Three-point bending tests are carried out according to

EN 14651 with Zwick Toni equipment (Figure 4(c)). The

deflection is measured using a linear variable displace-

ment transducer (LVDT), as shown in Figure 4(a). The

specimens have a sawcut (notch) of 25 mm in the middle

of the beam on its bottom surface. The test is deflection

controlled by the speed of the LVDT measurement

device: (a) deflection from 0 to 0.1 mm is performed at

0.05 mm/min and (b) deflection from 0.1 to 3.5 mm is per-

formed at 0.2 mm/min, and the test stops at a deflection of

3.5 mm. Figure 4(b) shows a beam specimen during the

testing process.

2.4. Calculation of mechanical parameters

The compressive strengths of the specimens are directly

determined by a uniaxial compressive test, which meas-

ures the maximum strength during the test process on the

FRC samples. The modulus of elasticity is indirectly com-

puted based on the stress-strain curve and the linear elastic

section is used for the computation.

Figure 5 shows the load-deflection curves from the

three-point bending tests along with typical defection

points. PL is the maximum load between deflections of 0

and 0.05 mm, and the corresponding flexural strength is

computed as follows (Olivito and Zuccarello 2010):

sL ¼ 3PLl

2bðh� a0Þ2ð1Þ

In most cases, PL is the maximum load over the

entire load-deflection curve. As shown in Figure (5),

sR,1 is the residual flexural strength at a crack mouth

opening displacement (CMOD) of 0.5 mm or a deflec-

tion of 0.47 mm, sR,2 is the residual flexural strength at

a CMOD of 1.5 mm or a deflection of 1.32 mm, sR,3 is

the residual flexural strength at a CMOD of 2.5 mm or

a deflection of 2.17 mm, and sR,4 is the residual flexural

strength at a CMOD of 3.5 mm or a deflection of

3.02 mm. These four residual flexural strengths can be

computed with Equation (1).

The flexural strength, tensile strength, fracture tough-

ness, equivalent energy absorption and flexural toughness

ratio are computed based on the load-deflection curves

Figure 2. Distribution characteristics of fibres in concrete: (a)PVA fibres, (b) PP fibres and (c) steel fibres.

154 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

from the three-point bending tests. The flexural strength

(sf) of each FRC sample is determined as follows (Olivito

and Zuccarello 2010):

sf ¼ 3Pmaxl

2bðh� a0Þ2ð2Þ

where Pmax is the maximum load, b and h are the beam

thickness and height, respectively, a0 is the notch depth

and l is the span length.

And the tensile strength (st) of each FRC sample

(Olivito and Zuccarello 2010) is obtained as follows:

st ¼ 3Pmaxl

2bh2ð3Þ

The fracture toughness KIC of each sample can be

computed as follows (Qian and Piet 2005):

KIC ¼ Pmaxl

bh3=2f

a0

h

� �ð4Þ

where f() is a function of a0/h based on the American

Society for Testing and Materials (ASTM) standard, and

can be computed as follows (Holschemacher, Mueller,

and Ribakov 2010):

fa0

h

� �¼ 2:9

a0

h

� �1=2

� 4:6a0

h

� �3=2�

þ21:8a0

h

� �5=2

� 37:6a0

h

� �7=2

þ 38:7a0

h

� �9=2�

ð5Þ

The equivalent flexural strength (se) is obtained as

follows:

se ¼ Vkl

bh2dkð6Þ

where dk is the deflection value of l/150, Vk is the equiva-

lent energy absorption at a deflection of dk, and the equiv-

alent energy absorption per unit volume is determined as

the area under the load (P)-deflection (d) curve (Figure 5),

the value of which can be calculated as follows (Khaloo

and Afshari 2005):

Vk ¼Z dk

0

Pdd ð7Þ

Next, the flexural toughness ratio (Kang et al. 2010) of

each FRC sample can be obtained as follows:

Re ¼ se

sfc;crað8Þ

where sfc;cra is the flexural strength at the crack initiation,

the value of which can be calculated using the following

equation:

sfc;cra ¼ Pcra � l

bh2ð9Þ

where Pcra is the load when at the crack initiation.

A flexural toughness index (Kang et al. 2010) was

used to estimate the energy absorbed during the deflection

of a beam, here is introduced to describe the improvement

of concrete by the addition of fibres, the value of which

can be calculated using the following equation:

I ¼ se=splain ð10Þ

where splain is the equivalent flexural strength of plain

concrete.

Figure 3. Concrete specimens for experimental study: (a) cubical and (b) concrete in beam mould.

The IES Journal Part A: Civil & Structural Engineering 155

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

3. Results and discussions

3.1. Compressive and tensile strength

Table 4 shows the compressive strengths of the plain con-

crete and FRC varieties. The experimental results show

that the compressive strength of FRC is not greatly

affected by the presence of fibres, which has been reported

by other researchers. After a series of concrete slab tests,

Khaloo and Afshari (2005) have found small changes in

the compressive strength of concrete due to the addition

of fibres. Concrete’s compressive strength is influenced

by its composition and the quantity of fibres added, and

there is usually a small decrease in compressive strength

when fibres are added, although the compressive strength

occasionally increases slightly.

The experimental results show that the average com-

pressive strength of plain concrete is 41.23 MPa, while

the compressive strength of PVA and PP FRC is smaller

and greater quantities of PVA fibres result in decreased

compressive strength. When the volume of PVA fibres

Figure 4. Three-point bending test: (a) transducer position scheme, (b) beam specimen and (c) experimental equipment.

156 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

measures 0.9 kg/m3, the compressive strength is 40.97

MPa, but this strength decreases to 39.97 MPa when the

volume is increased to 1.8 kg/m3. In terms of the SFRC, a

volume of 20 kg/m3 produces a compressive strength of

40.14 MPa, which increases to 42.62 MPa when the vol-

ume is 30 kg/m3, indicating higher compressive strength

with increased quantities of steel fibres. However, the fail-

ure mode of concrete changes considerably from brittle to

ductile with the addition of these fibres. Due to bridging

effect of the fibres, the cubic specimens are not crushed,

but rather maintain their integrity until the end of the test.

Table 5 shows the elastic modulus and tensile/com-

pressive ratio of different concrete mixes. The tensile

strength of plain concrete is 2.66 MPa, and the addition of

steel fibres increases the concrete’s tensile strength. This

phenomenon has been reported by many other experi-

ments (Sun and Wu 2005), and crack resistance can

improve the tensile strength of concrete. The tensile

strength of SFRC increases to 2.84 MPa when the volume

of steel fibres measures 20 kg/m3, and the concrete’s ten-

sile strength increases with the increasing volume of steel

fibres. However, there is little increase in the tensile

strength of PP FRC (2.69 MPa), and the tensile strengths

of the PVA FRC are 2.83 MPa and 2.52 MPa when the

volumes of PVA measure 0.9 kg/m3 and 1.8 kg/m3,

respectively. The tensile strength is influenced by the vol-

ume of PVA fibres due to the additional voids formed by

these mixes’ somewhat poor workability. As shown in

Table 5, the tensile/compressive ratio of plain concrete is

approximately 6.5%, which changes slightly with the

addition of PVA or PP fibre to range between 6.3% and

6.8%. However, the increased tensile/compressive ratio

in SFRC is more obvious � the ratios of the SF-20 and

SF-30 samples are both 7.1%.

Figure 6 shows the strength effectiveness of concrete

when different fibres are added. The addition of PVA or

PP fibres usually results in a small decrease in the con-

crete’s compressive strength, while the addition of steel

fibres results in a small increase in compressive strength.

However, if the volume of steel fibres measures less than

a critical value, the concrete shows a small decrease in

compressive strength instead. The tensile strength of FRC

increases with the addition of fibres due to their crack

resistance effect, but an appropriate fibre content should

be selected because larger volumes of PVA or PP fibres

do not improve the tensile strength of concrete.

Figure 5. Load-deflection curve from the three-point bendingtest with typical deflection points.

Table 4. Compressive strengths of plain and fibre-reinforced concretes.

Steel fibre (MPa) PVA fibre (MPa) PP fibre (MPa)

No. Plain (MPa) 20 kg/m3 30 kg/m3 1.8 kg/m3 0.9 kg/m3 3.5 kg/m3

1 42.69 39.52 42.6 42.24 42.51 42.29

2 42.82 42.41 43.84 42.76 38.02 39.06

3 38.18 38.49 41.43 37.91 39.39 36.76

Average 41.23 40.14 42.62 40.97 39.97 39.37

Table 5. Elastic modulus and tensile/compressive ratios of the concrete mixes.

MixElastic modulus

(GPa)Compressivestrength (MPa)

Tensile strength(MPa)

Tensile/compressiveratio (%)

Plain 33.49 41.23 2.66 6.5

PVA-0.9 31.03 40.97 2.83 6.9

PVA-1.8 29.40 39.97 2.52 6.3

PP-3.5 29.97 39.37 2.69 6.8

SF-20 34.68 40.14 2.84 7.1

SF-30 36.86 42.62 3.04 7.1

The IES Journal Part A: Civil & Structural Engineering 157

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

3.2. Modulus of elasticity

The modulus of elasticity is obtained by the tangent at the

origin using the average of the measured deformations.

As shown in Table 5, the modulus of elasticity of plain

concrete is 33.49 GPa. PVA and PP fibres not only

decrease the concrete’s modulus of elasticity but also

decrease its compressive and tensile strength. The modu-

lus of elasticity of concrete with PVA fibres decreases

gradually with the increase in fibre content, with values of

31.03 GPa and 29.40 GPa for PVA contents of 0.9 kg/m3

and 1.8 kg/m3, respectively. However, the modulus of

elasticity of concrete with steel fibres increases gradually

with an increase in fibre content, with values of 34.68

GPa and 36.86 GPa for steel fibre contents of 20 kg/m3

and 30 kg/m3, respectively.

Figure 7 shows the modulus effectiveness of concrete

with the addition of different fibres. Compared to plain

concrete, the PVA-0.9, PVA-1.8 and PP-3.5 FRCs are

weakened by 7.33%, 12.19% and 10.51%, respectively,

while the SFRCs are strengthened by 3.55% and 10.06%

when fibre contents are 20 kg/m3 and 30 kg/m3, respec-

tively. As shown in Table 2, the Young’s modulus of steel

fibre is 210 GPa, but that of PP fibre is 3-10 GPa and that

of PVA fibre is 32 GPa. The different Young’s moduli of

the fibres appear to affect the static elastic moduli of

concretes in which they are used according to the appro-

priate content of fibre used in this experiment. The static

elastic modulus of concrete increases as the Young’s mod-

ulus of the fibre being used increases.

3.3. Load-deflection curves

Table 6 summarises the flexural and fracture properties of

different concrete samples, and the load-deflection behav-

iour of each mix is illustrated in Figure 8. Experimental

results show that, the plain concrete and PVA FRC exhibit

extremely brittle behaviour (Figure 8(a), 8(c) and 8(d)).

The initial cracking load and maximum load are approxi-

mately equal and the corresponding deflection values are

very low (30�45 mm). Plain concrete demonstrates its

brittleness, and the load decreases rapidly with the

increase in deflection after the peak load. When steel

fibres are introduced into the concrete, the shape of the

load-deflection curve is changed. Concrete containing

steel fibres shows a flattened descending path in its load-

deflection curves and an increase in deflection at the peak

load (Figure 8(b), 8(e) and 8(f)). After the drop in load,

PP and steel fibres bridge the initial crack and regain load

by stretching and resisting cracks. The maximum loads

increase and the corresponding deflection value increases

at the same time (45�65 mm). The PP FRC’s load-deflec-

tion curve shows a small increase in the peak load, but the

corresponding deflection increases. A comparison of the

load-deflection curves for the different concrete samples

is shown in Figure 8(g) and 8(h).

Table 7 shows the experimental results for peak load

and corresponding deflection in each concrete type. The

average peak load of plain concrete is 11.97 kN and the

corresponding deflection is 42 mm. These values increase

slightly with the addition of PVA fibres (0.9 kg/m3),

although the peak load decreases with an increase in the

fibre content (1.8 kg/m3). The corresponding deflection of

the PVA FRC decreases at larger values, deflecting

36 mm and 34 mm in PVA-0.9 and PVA-1.8, respectively.

When steel fibres are introduced into the concrete, the

Figure 6. Strength effectiveness of concrete with the additionof different fibres.

Figure 7. Modulus effectiveness of concrete with the additionof different fibres.

Table 6. Flexural and fracture properties of different concretesamples.

Mix No.

Flexuralstrength(MPa)

Toughnessindex

Fracturetoughness(N�mm1/2)

Plain 1799�1801 3.83 1.00 21.79

PVA-0.9 1775�1780 4.08 2.46 22.91

PVA-1.8 1781�1786 3.62 1.52 20.43

PP-3.5 1802�1807 3.87 4.30 21.52

SF-20 1787�1792 4.09 6.51 24.44

SF-30 1793�1798 4.39 8.82 26.05

158 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

Figure 8. Load-deflection curves for the concrete mixes subjected to three-point bending tests: (a) plain concrete, (b) PP-reinforcedconcrete, (c) PVA-reinforced concrete, 0.9 kg/m3, (d) PVA-reinforced concrete, 1.8 kg/m3, (e) steel-reinforced concrete, 20 kg/m3, (f)steel-reinforced concrete, 30 kg/m3, (g) comparison of different concretes and (h) partial enlargement of (g).

The IES Journal Part A: Civil & Structural Engineering 159

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

peak load is increased with the fibre content and reaches

12.77 and 13.72 for SFRC-20 and SFRC-30, respectively.

The corresponding deflection increases at the same time.

The average value of peak load in Table 7 is used to com-

pute the tensile strength and flexural strength of each con-

crete type.

3.4. Flexural strength and toughness

Figure 9 shows the flexural effectiveness of concrete with

the addition of different fibres. The flexural strengths

(MPa) are 3.83, 4.08, 3.62, 3.87, 4.09 and 4.39 for plain,

PVA-0.9, PVA-1.8, PP-3.5, SF-20 and SF-30 concretes,

respectively. These results highlight the effectiveness of

steel fibres at improving the flexural behaviour of con-

crete, with an increase in flexural strength of greater than

6%�15% that increases with increasing fibre content.

However, the effectiveness of PP fibres at improving the

flexural behaviour of concrete with a little increasing ratio

is about 0.18%. On the other hand, most of the concrete

mixes prepared with PVA fibres show reduced flexural

performance compared to the reference mixture without

fibres. The strength reduction is �6.14% for a PVA fibre

content of 1.8 kg/m3.

Figure 10 shows the residual flexural strength of the

different concrete samples. This residual flexural strength

is calculated based on Figure 5 and Equation (1). As

shown in Figure 10, the residual flexural strength of con-

crete decreases with the increasing deflection after the

peak load. The residual flexural strength of plain concrete

is only 0.21 MPa when the deflection is 0.47 mm. After

the peak load, this strength decreases sharply over a short

time period. The residual flexural strength of PVA FRC is

only 0.31-0.42 MPa when the deflection is 0.47 mm, and

the beam fails and loses its load capacity when the deflec-

tion approaches 1.32 mm. However, concrete containing

PP or steel fibres has residual flexural strengths greater

than 0.5 MPa when the deflection is 3.50 mm. The resid-

ual flexural strengths (MPa) of SFRC-20 are 1.35, 1.16,

1.01 and 0.93 when the deflections (mm) are 0.47, 1.32,

2.16 and 3.02, respectively, decreasing slowly with

increasing deflection. The residual flexural strength of

concrete containing steel fibres also increases with

increasing fibre content.

Figure 11 shows the energy absorption of the different

concrete samples and indicates that the concrete’s energy

absorption increases with increasing deflection. As shown

in Figure 10, the maximum deflection for plain concrete is

Table 7. Experimental results for peak load and corresponding deflection of the samples.

Mix Plain PVA-0.9 PVA-1.8 PP-3.5 SF-20 SF-30

Peak Range 11.80�12.14 12.31�13.67 10.08�12.73 11.53�12.99 12.10�14.04 13.20�14.51

load (kN) Average 11.97 12.77 11.32 12.10 12.77 13.72

Corresponding Range 41�43 33�39 31�38 45�56 44�53 54�65

deflection (mm) Average 42 36 34 51 49 59

Figure 9. Flexural effectiveness of concrete with the additionof different fibres.

Figure 10. Residual flexural strength of the different concretetypes.

Figure 11. Energy absorption of the different concrete types.

160 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

approximately 0.81 mm, and the PVA FRC concrete

shows an increase of approximately 1.10�1.35 mm. The

deflection of PP and SFRCs is greater than 3.50 mm. The

experimental results show that the concrete’s energy

absorption is less affected by the PVA fibres, but the addi-

tion of steel or PP fibres causes clear increase in the

energy absorption, especially for the steel fibres and with

increasing fibre content.

The toughness index is used to measure the energy

absorbed during the deflection of a beam by a specified

amount and is represented by the area under the load-

deflection curve during a three-point bending test (Kang

et al., 2010). Experimental results indicate that the flex-

ural toughness index of concrete is increased by the addi-

tion of different fibres (Table 6). Since the flexural

strength is less drastically improved by the addition of

PVA fibres, the flexural toughness index increases only

slightly and decreases with increasing fibre content. The

flexural toughness index of concrete containing steel

fibres increases significantly, and increases further with

increasing fibre content. The flexural toughness indices are

6.51 and 8.82 when the fibre content measures 20 kg/m3

and 30 kg/m3, respectively.

3.5. Fracture toughness and characteristics

The plain concrete and PVA FRC fail at deflections of less

than 1.5 mm. However, the PP FRC and SFRC withstand

external loading at deflections greater than 3.5 mm. The

open mouth of the fracture position indicates that the frac-

tures are very straight and the crack propagation repre-

sents typical tensile failure. The crack propagation is

resisted by the added fibres, especially the steel fibres, and

is influenced by the fibre lengths. The tensile stress of

steel fibres impacts the concrete during the crack propaga-

tion process and results in greater deformation of the steel

fibres at the open mouth.

As shown in Table 6, the fracture toughness of the

plain concrete is 21.79 N mm1/2. There is a small increase

in fracture toughness with the use of 0.9 kg/m3 PVA fibres,

which produce a value of 22.91 N mm1/2, and the increase

in toughness compared to plain concrete is approximately

5.1%. The fracture toughness of the PVA FRC decreases

with increasing fibre content. At a PVA fibre content of

1.8 kg/m3, the fracture toughness measures 20.43 N mm1/2.

Finally, the concrete’s fracture toughness increases with the

addition of steel fibres, and an increase in the volume of

fibres resulted in a larger fracture toughness.

4. Conclusions

This study performs compression tests and three-point

bending tests on FRC to compare the mechanical perfor-

mance of concretes prepared with different fibres. The

addition of steel fibres (hooked-end), PVA fibres and PP

fibres is considered, and the results of the comparative

experimental study lead to the following conclusions:

(1) The experimental results show that the compres-

sive strength of FRC is minimally affected by the

presence of fibres. The tensile strength of the con-

crete samples increases with the addition of fibres

due to the crack resistance effect, but appropriate

fibre content should be selected because greater

quantities of PVA and PP fibres do not improve

the concrete’s tensile strength.

(2) Larger volumes of PVA or PP fibres decrease the

concrete’s modulus of elasticity. The modulus of

elasticity of concrete containing PVA fibres

decreases gradually with the increase in fibre con-

tent, and the static elastic modulus of concrete

increases with the addition of steel fibres, which

have a higher Young’s modulus.

(3) The loading on the concrete samples decreases

rapidly with the increase in deflection after the

peak load in plain concrete and PVA FRC. Con-

crete containing steel fibres exhibits a flattened

descending path in its load-deflection curve and

an increase in deflection at the peak load.

(4) The experimental results for flexural strength

illustrate the effectiveness of steel and PP fibres in

improving the flexural behaviour of concrete. On

the other hand, most of the concrete mixes pre-

pared with PVA fibres display reduced flexural

strength. The improved energy absorption of con-

crete containing steel or PP fibres is obvious,

especially for the steel fibres, and this energy

absorption increases with increasing fibre content.

(5) The crack propagation of FRC is influenced by the

length of the fibres. The fracture toughness of the

concrete is increased with the addition of steel

fibres, and an increase in fibre content further

increases fracture toughness.

These conclusions are drawn for concrete samples

containing identical water/cement ratios and mix propor-

tions. In the future, further studies will be necessary to

better understand the mechanical properties of concrete

improved by the addition of fibres.

Acknowledgements

Thanks for the help of Xiang-yu Chen and Wen-xiao Xu in theexperimental tests.

Funding

The support of the National Natural Science Foundation ofChina [grant number 51209156], [grant number 41102194] isgratefully acknowledged.

The IES Journal Part A: Civil & Structural Engineering 161

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014

References

Akcay, B., and M.A. Tasdemir. 2012. “Mechanical Behaviourand Fibre Dispersion of Hybrid Steel Fibre Reinforced Self-compacting Concrete.” Construction and Building Materials28: 287�293.

Altun, F., T. Haktanir, and K. Ari. 2007. “Effects of Steel FiberAddition on Mechanical Properties of Concrete and RCBeams.” Construction and Building Materials 21: 654�661.

Corinaldesi, V., and G. Moriconi. 2011. “Characterization ofSelf-compacting Concretes Prepared with Different Fibersand Mineral Additions.” Cement and Concrete Composites33: 596�601.

Debs, M.K., L.C. Montedor, and J.B. Hanai. 2006.“Compression Tests of Cement-Composite Bearing Pads forPrecast Concrete Connections.” Cement and Concrete Com-posites 2: 621�629.

DL/T 5055-2007. 2007. Chinese Standard. Technical Specifica-tion of Fly Ash for Use in Hydraulic Concrete. [In Chinese.]Beijing: China Architecture & Building Press.

Ding, Y.N., and W. Kusterle. 2000. “Compressive Stress�StrainRelationship of Steel Fibre-Reinforced Concrete at EarlyAge.” Cement and Concrete Research 30: 1573�1579.

EN 14651. 2005. European Standard. Test Method for MetallicFibered Concrete � Measuring the Flexural Tensile Strength(Limit of Proportionality (LOP), Residual). Brussels: AustrianStandards Institute.

Feleko�glu, B., K. Tosun, and B. Baradan. 2009. “Effects of FibreType and Matrix Structure on the Mechanical Performanceof Self-compacting Micro-Concrete Composites.” Cementand Concrete Research 39: 1023�1032.

Giner, V.T., F.J. Baeza, S. Ivorra, E. Zornoza, and �O. Galao.2012. “Effect of Steel and Carbon Fiber Additions on theDynamic Properties of Concrete Containing Silica Fume.”Materials Design 34: 332�339.

Haktanir, T., K. Ari, F. Altun, and O. Karahan. 2007. “A Com-parative Experimental Investigation of Concrete Rein-forced-Concrete and Steel-Fibre Concrete Pipes UnderThree-Edge-Bearing Test.” Construction and BuildingMaterials 21: 1702�1708.

Holschemacher, K., T. Mueller, and Y. Ribakov. 2010. “Effectof Steel Fibres on Mechanical Properties of High-StrengthConcrete.”Materials Design 31: 2604�2615.

Hsie, M., C.J. Tu, and P.S. Song. 2008. “Mechanical Propertiesof Polypropylene Hybrid FiberReinforced Concrete.” Mate-rials Science and Engineering: A 494: 153�157.

Kakooei, S., H.M. Akil, M. Jamshidi, and J. Rouli. 2012. “TheEffects of Polypropylene Fibers on the Properties of Rein-forced Concrete Structures.” Construction and BuildingMaterials 27: 73�77.

Kang, S.T., Y. Lee, Y.D. Park, and J.K. Kim. 2010. “TensileFracture Properties of an Ultra High Performance FiberReinforced Concrete (UHPFRC) with Steel Fiber.” Compo-sites Structures 92: 61�71.

Khaloo, A.R., and M. Afshari. 2005. “Flexural Behaviour ofSmall Steel Fibre Reinforced Concrete Slabs.” Cement andConcrete Composites 27: 141�149.

Kou, S.C., and C.S. Poon. 2010. “Properties of Concrete Pre-pared with PVA-Impregnated Recycled ConcreteAggregates.” Cement and Concrete Composites 32:649�654.

Olivito, R.S., and F.A. Zuccarello. 2010. “An ExperimentalStudy on the Tensile Strength of Steel Fiber ReinforcedConcrete.” Composites Part B: Engineering 41: 246�255.

Qian, C.X., and S. Piet. 2005. Fracture Properties of ConcreteReinforced with Steel-Polypropylene Hybrid Fibres. Cementand Concrete Composites 22: 343�351.

Schwartzentruber, A., M. Philippe, and G. Marchese. 2004.“Effect of PVA, Glass and Metallic Fibers, and of an Expan-sive Admixture on the Cracking Tendency of UltrahighStrength Mortar.” Cement and Concrete Composites 26:573�580

Shafigh, P., H. Mahmud, and M.Z. Jumaat. 2011. “Effect of SteelFiber on the Mechanical Properties of Oil Palm Shell Light-weight Concrete.”Materials Design 32: 3926�3932.

Song, P.S., and S. Hwang. 2004. “Mechanical Properties ofHigh-Strength Steel Fiber-Reinforced Concrete.” Construc-tion and Building Materials 18: 669�673.

Sun, P.J., and H.C. Wu. 2005. “Transition from Brittle to DuctileBehavior of Fly Ash Using PVA Fibers.” Cement and Con-crete Composites 30: 29�36

Sun, W., H.S. Chen, X. Luo, and H.P. Qian. 2001. “The Effect ofHybrid Fibers and Expansive Agent on the Shrinkage andPermeability of High-Performance Concrete.” Cement andConcrete Research 31: 595�601.

162 H.-g. Xing et al.

Dow

nloa

ded

by [

] at

00:

07 2

6 Se

ptem

ber

2014