toughness testing of ultra high performance fibre reinforced

8/7/2019 Toughness testing of ultra high performance fibre reinforced

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O R I G I N A L A R T I C L E

Toughness testing of ultra high performance fibre reinforced

concreteMarijan Skazlic Dubravka Bjegovic

Received: 8 April 2008 / Accepted: 10 October 2008 / Published online: 22 October 2008

RILEM 2008

Abstract In this paper an investigation is made of

the applicability of the ASTM C 1609 procedure for

testing toughness of ultra high performance fibre

reinforced concretes containing a large amount of

fibre (C2% by volume) and exhibiting deflection

hardening behaviour. All mixtures exhibited deflec-

tion hardening behaviour, and the parameters varied

included (1) the amount of steel fibres, (2) the type of

steel fibres, (3) the size of the longest fibre, (4) the

addition of polypropylene fibres, and (5) the size of

the maximum aggregate grain in the concrete matrix.Based on comparison of the curves obtained from

flexural toughness tests with the evaluation of the test

results obtained according to ASTM C 1609 and with

the statistical analysis, the authors recommended

additional toughness parameters (P100,3.00, P100,4.00,

P100,6.00, T100,3.00, T100,4.00, a n d T100,6.00) for the

evaluation of toughness results. Such additional

toughness parameters are calculated using a similar

procedure as that specified in ASTM C 1609.

Keywords Deflection hardening behaviour Fibre ASTM C 1609 Ultra high performance fibrereinforced concrete Toughness

1 Introduction

One of main advantages gained from fibre reinforce-

ment in concrete is an increase in toughness

properties [13]. The most often used method for

testing toughness of fibre reinforced concrete isflexural toughness testing [3].

The ASTM C 1018 standard has been used for

toughness tests of fibre reinforced concrete for more

than a decade. According to this standard, the

evaluation of toughness test results is made on the

basis of dimensionless parameters of toughness

indexes and residual strength factor [4].

Major complaints from researchers about ASTM C

1018 relate to difficulties in the determination of first

crack and to the problems occurring at accurate

measurement of deflection [3, 57]. It was found outthat, because of errors arising in determination of first

crack, toughness indexes and residual strength factors

are not quite appropriate for the evaluation of the

behaviour of fibre-reinforced concretes with a small

amount of fibres and different fibre volume fraction,

and of those concretes tested on different specimens

[6, 812].

Numerous researches have carried out toughness

tests according to procedures outlined in ASTM C

M. Skazlic (&) D. BjegovicMaterials Department, Faculty of Civil Engineering,

University of Zagreb, Kaciceva 26, Zagreb, Croatia

e-mail: [email protected]

D. Bjegovic

Institute of Civil Engineering Croatia, Rakusina 1,

Zagreb, Croatia

e-mail: [email protected]

Materials and Structures (2009) 42:10251038

DOI 10.1617/s11527-008-9441-3


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1018, but have evaluated the test results according

to the Japanese standard JCI-SF 4 [13, 14]. The

procedure for evaluating toughness test results spec-

ified in JCI-SF 4 has proved to be more reliable than

that laid down in ASTM C 1018 in the case when the

performances of fibre-reinforced concretes with a

small amount of fibres and different fibre volumefractions were to be distinguished [2, 11, 14].

This is because of the disadvantages mentioned

above that in the year 2005 the ASTM C 1018

standard was replaced with a new standard, i.e.

ASTM C 1609 [15]. Thus, any matter contained in

ASTM C 1018 with which the researches often found

faults were excluded from ASTM C 1609. According

to ASTM C 1609, toughness tests are carried out

on concrete beams of 100 9 100 9 400 mm or of

150 9 150 9 600 mm. Flexural load is applied

under constant rate of displacement at one-third oftest specimen spans. The evaluation procedure for

toughness test results is very similar to the evaluation

procedure set down in JCI-SF 4. Specifically, in the

evaluation of the test results, first-peak load, peak

load, residual load, and the areas below the load

deflection curve are calculated (Fig. 1).

Ultra high performance fibre reinforced concrete

(UHPFRC) is a composite construction material with a

cement matrix having a typical compressive strength ofnot less than 150 MPa and to which fibres are added to

improve tensile strength and to ensure deflection

hardening behaviour in flexural tests [16, 17].

Up to today, ASTM C 1609 has been primarily

used for toughness tests of fibre-reinforced concretes

containing small amount of steel fibres (\2% by

volume). In contrast, the applicability of ASTM C

1609 for toughness tests of UHPFRC containing a

large amount of steel fibres (C2% by volume) and

exhibiting deflection hardening behaviour has not

been investigated so far [6].In this paper an analysis is made of the applica-

bility of the ASTM C 1609 procedure for testing

Fig. 1 Definition of

toughness indexes

according to ASTM C 1609

1026 Materials and Structures (2009) 42:10251038


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toughness of UHPFRC containing a large amount of

fibre (C2% by volume) and exhibiting deflection

hardening behaviour. Based on the results obtained,

the authors recommended additional toughness

parameters for the evaluation of toughness behaviour

of UHPFRC. Further research in this area should be

done.

2 Experimental investigation

Flexural toughness and compressive strength tests

were carried out on seven different UHPFRC mix-

tures. Each mixture was prepared three times. All the

mixtures had the same water-binder ratio and fresh

concrete workability. Plain and hybrid steel fibres

were used. Hybrid fibres include steel fibres of

various length and shape, and they are used toachieve synergetic effects in fresh and hardened

concrete [18, 19].

Concrete mix compositions were varied as for the

following factors: (1) the amount of steel fibres (2%,

3% and 5% by volume), (2) the type of steel fibres

(each having 3% by volume of hybrid and ordinary

steel fibres), (3) the size of the longest fibre 30 mm

and 40 mm in the mixture containing 5% by volume

of hybrid steel fibres), (4) the addition of polypro-

pylene fibres (0.8% by volume of polypropylene

fibres to 3% by volume of steel fibres), and (5) thesize of a maximum aggregate grain in the concrete

matrix 0.5 mm and 4 mm. The concrete mix compo-

sitions are given in Table 1.

Considering that the concrete mix compositions

did not include coarse aggregate, they can be also

called ultra high performance fibre reinforced mor-

tars; however, according to the accepted definition

found in the literature, this type of the material is still

termed ultra high performance fibre reinforced con-

cretes (UHPFRC) [6].

2.1 Materials

The concrete components used in this experimental

work had been found suitable for production of

UHPFRC in previous investigations carried out by

the authors [20]. The components used were only

those available in the Croatian market. They included

Portland cement, silica fume, quartz sand, superp-

lasticizer, water, and steel and polypropylene fibres.

Physical and chemical properties of the cement and

silica fume are given in Table 2. The aggregates used

in this study contained quartz sand ranging in size

from 00.5 mm and 04 mm fractions. The specific

gravity and water absorption of the 00.5-mm quartz

sand were 2.68 g/cm3 and 0.76% respectively, and

those of the 04-mm quartz sand were 2.66 g/cm3

and 1.26% respectively. Properties of superplasticizer

are shown in Table 3. Four types of steel fibres (SF 1,

SF 2, SF 3, and SF 4) and one type of fibrillated

polypropylene fibres (PP 1), whose characteristics are

shown in Table 4, were used in this study.

2.2 Specimens

Toughness was tested on 100 9 100 9 400 mm

beams, while compressive strength was tested on

40-mm cubes. Flexural toughness tests were con-ducted on a set of six specimens for each mixture and

compressive strength tests were conducted on a set of

eighteen specimens for each mixture. A total of 42

specimens and 126 specimens for toughness tests and

compressive tests respectively were used. The spec-

imens were prepared in a 70-l laboratory mixer. The

overall duration of the mixing was between 10 and

13 min. In all the mixtures, cement, aggregate and

silica fume were mixed dry for 4 min before the

Table 1 Compositions of concrete mixtures

Mixture

components,

kg/m3

M 1 M 2 M 3 M 4 M 5 M 6 M 7

Cement 1115 1115 1115 1115 1115 1115 1115

Silica fume 169 169 169 169 169 169 169

Quartz sand,

00.5 mm

1073 1073 1073 1073 1073 1073

Quartz sand,

04 mm

1073

Water 204 204 204 204 204 204 204

Superplasticizer 30.8 32.1 34 37.6 37 39 38.5

Steel fibers SF 1 39 156 156

Steel fibers SF 2 1 56 234 234 234 117 156 156

Steel fibers SF 3 78

Steel fibers SF 4 78 78

Polypropylene

fibers PP1

8

Water/binder

ratio

0.16 0.16 0.16 0.16 0.16 0.16 0.16

Materials and Structures (2009) 42:10251038 1027


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addition of water and then, 2 min after water was

introduced, superplasticizer was added. About 1 min

after the addition of the superplasticizer, fibres were

loaded manually. The mixing was completed after a

homogenous concrete mixture was obtained. The

mixing time was the longest in the case of the

mixtures with 5% by volume of steel fibres (M 6 and

M 7). The samples were vibrated on a vibrating table

vibrating at a rate of 150 Hz. The specimens were

demoulded at the age of 14 h. The specimens weretested at the age of 28 days after being cured in water

at the water temperature of 20C. In previous

investigations it was found that the specimens cured

using heat steaming method exhibit higher strength

[6, 16]. Considering that fibre-reinforced concrete

sampleswhich are normally tested using the ASTM

C 1609 procedureare not cured employing heat

steaming method, in this experimental work only

water curing method was applied.

2.3 Items of investigation

Flexural toughness specimens were loaded in a four

point loading configuration with two supports spaced

a distance of 300 mm and two top loading points

spaced at 100 mm according to the ASTM C 1609

standard. The evaluation of toughness test results was

made as specified in ASTM C 1609 as well as by

using the approach recommended by the authors. The

rate of loading during toughness tests was 0.1 mm/

min. The test was conducted on a testing machine

having the flexural capacity of 200 kN. The tough-ness test results were collected at a frequency of

1 Hz.

Table 2 Physical and chemical properties of cement and silica

fume

Physical and

mechanical properties

Ordinary

Portland cement

Silica

fume

Specific gravity (g/cm3) 3.12 2.22

Blaine fineness (cm2/g) 5,030 18,595

Residual material on

the 0.09 mm sieve (%)

3.93

Residual material on

the 0.045 mm sieve (%)

69.8

Chemical properties

SiO2 (%) 19.71 93.02

Al2O3 (%) 5.02 1.37

Fe2O3 (%) 3.00 0.64

CaO (%) 63.51 1.35

Loss by burning (%) 1.22 2.08

SO3 (%) 3.82 0.38

Non-soluble residual in HCl

and Na2O3 (%)

0.33 75.05

MgO (%) 2.17 0.75

Free lime (%) 1.09

Chlorides (%) 0.006 0.027

Na2

O (%) 0.28

K2O (%) 0.75

Denotes not measured items

Table 3 Properties of

superplasticizerMass volume (g/cm

3) pH Solid content (%) Main component

1.07 5.9 24 Polycarboxylate ether

Table 4 Properties of steel

and polypropylene fibersCharacteristics Fiber

SF 1 SF 2 SF 3 SF 4 PP 1

Fiber length (mm) 6 13 30 40 6

Fiber diameter (mm) 0.15 0.15 0.4 0.5 0.015

Fiber aspect ratio 40 87 75 80 400

Density (g/cm3) 7.8 7.8 7.8 7.8 0.9

Tensile strength (MPa) 2,590 2,059 2,193 1,725 256

Elongation at break (%) 3.2 3.3 3.3 3.3 8.3

Modulus of elasticity (GPa) 210 210 210 210 8

Fibre type Straight Straight Hooked ends Hooked ends Fibrillated



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Compressive strength was determined using a press

of 3000 kN capacity with a controlled gain in force.

2.4 Statistical analysis

The statistical method used for evaluating the tough-

ness and compressive strength test results was an

analysis of variance of hierarchy models [2123].

Although the hierarchy model may have an arbitrary

depth, this paper discusses the case when the

specimen consists of several groups, each group

having several sub-groups, and each sub-group

having various numbers of variants. The group means

a certain concrete mixture (M 1 to M 7). Considering

that each mixture was prepared three times, each of

these three tests made a sub-group, and each sub-

group had variants, that is, the test results of a specific

property. Two zero hypotheses (H0) were considered;

the first hypothesis that the groups belong to the same

specimen, and the other hypothesis is that the sub-

groups, within the groups, belong to the same

specimen. The zero hypothesis (H0) about variances

is checked using F-test. The procedure for the

analysis of variance of hierarchy models starts with

calculating experimental F-factors:

Fexp1 s2 between groups

s2 between sub-groups1

Fexp2 s2 between subgroups

s2 within sub-groups2

Table F-factor (Ftabl) is read from the tables for free

variants of the two respective variances with the

selected probability of error of 0.05 [22]. The Fexpand Ftabl are compared and a decision made as to

whether to accept or reject the zero hypotheses. If

Fexp1\Ftabl1, it is concluded that there are no

significant differences between the groups. This

means that, between the mixtures analyzed, there is

no significant difference as for toughness propertiestested. IfFexp1[Ftabl1, a conclusion is made that the

differences between the groups are significant; this

indicates that there are significant differences

between the mixtures investigated with respect to

toughness property tested. If Fexp2\Ftabl2, it is

considered that there are no significant differences

between the sub-groups, or specifically that the test

results are repeatable. When Fexp2[Ftabl2, the test

results are not repeatable.

3 Experimental results and discussion

3.1 Toughness

Table 5 and Fig. 2 present all the mean values of the

results obtained from toughness tests. As the tough-

ness test results were collected at the same frequency,the curves shown in Fig. 2 were obtained by calcu-

lating mean values of the force and deflection in a

specific time interval.

The analysis of the results obtained from the

toughness tests was made using toughness parameters

defined according to ASTM C 1609 (P1, PP, P100,0.50,

P100,2.00, T100,2.00). The authors recommendations to

the evaluation of toughness test results obtained for

UHPFRC specimens described in this paper includes,

besides toughness parameters defined in ASTM C

1069, taking into account additional toughnessparameters, i.e. P100,3.00, P100,4.00, P100,6.00, T100,3.00,

T100,4.00, a n d T100,6.00. These additional toughness

parameters are obtained using the same procedure as

the one specified for the toughness parameters given

in ASTM C 1609. The reason for their inclusion in

the analysis of toughness test results is the fact that

UHPFRC exhibits good behaviour and high tough-

ness also at large deflections. The test results were

statistically analyzed by an analysis of variance of

hierarchy models in order to establish the existence of

a significant difference among the mixtures tested. Inthis process, the toughness parameters defined in

ASTM C 1609 and those from the authors recom-

mendations for toughness evaluation were used.

3.1.1 Amount of steel fibres

In Fig. 3 the curves of the average values obtained

from toughness tests are illustrated. Concrete mix-

tures M 1, M 5 and M 6 differed according to the

amount of fibres. Specifically, the mixtures M 1, M 5

and M 6 contained 2%, 3% and 5% by volume ofsteel fibres respectively.

The analysis of toughness test results using both

the procedure specified in ASTM C 1609 and the

authors recommendations for the evaluation of

toughness test results is illustrated in Figs. 4 and 5.

From the diagrams obtained from both the tests

performed and toughness parameters calculated, it

can be concluded that with an increase in the amount

of steel fibre toughness properties are also increased.



6/14

The results of the statistical analysis of the toughness

test results (Table 6) illustrate that the mixtures M 1,

M 5 and M 6 differ significantly in toughness

parameters obtained using the procedure specified

in ASTM C 1609 (P1, PP, P100,0.50, T100,2.00) and

those toughness parameters obtained using the pro-

cedure proposed by the authors (P100,4.00, P100,6.00,

T100,3.00, T100,4.00, T100,6.00). The obtained resultsproved that the introduction of additional toughness

parameters for the evaluation of toughness behaviour

was justified. In the case when the amounts of steel

fibres are varied, toughness properties change with an

increase in deflection and therefore the behaviour of

these materials should be taken into account also at

the deflection exceeding 2 mm. The toughness

parameters up to the deflection of 2 mm are calcu-

lated according to ASTM C 1609.

3.1.2 Size of the longest fibre

The mixtures M 6 and M 7 contained the same

amount of hybrid steel fibres (5% by volume), but

they differed as for the size of the longest steel fibre

40 mm and 30 mm respectively. The mixture M 6, as

shown in the diagrams in Fig. 3, exhibits better

toughness behaviour than the mixture M 7 does.The results obtained from the calculation of tough-

ness parameters are presented in Figs. 6 and 7. The

statistical analysis of the toughness test results showed

that the mixtures considerably differ only in respect of

the toughness parameter P100,0.50. From Fig. 3 it is

evident that there are no important differences in

toughness tests being carried out either at large or at

small deflections, and it is reasonable that the results

obtained from the toughness parameters specified in

Table 5 Mean values of the results obtained from compressive strength tests and flexural toughness tests

Mixture Compressive

strength tests

Flexural toughness tests

Compressive

strength (MPa)

First-peak

deflection (mm)

First-peak

strength (MPa)

Net deflection at peak

load (mm)

Peak strength

(MPa)

Peak strength/First-peak

strength ratio

M 1 182.9 0.06 11.10 0.91 22.30 2.01

M 2 213.6 0.05 11.41 0.66 21.28 1.87

M 3 197.1 0.07 12.24 0.73 23.09 1.89

M 4 190.0 0.07 13.10 0.84 22.67 1.73

M 5 211.3 0.06 12.62 0.97 22.91 1.82

M 6 223.8 0.13 21.80 0.92 34.21 1.57

M 7 212.0 0.15 19.29 0.88 28.59 1.48

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Deflection (mm)

Load(kN)

M 6

M 7

M 2M 3

M 1

M5

M 4

Fig. 2 The curves of meanvalues obtained from

flexural toughness for all

concrete mixtures



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ASTM C 1609 and from those mentioned in the

authors recommendations correspond.

3.1.3 Type of steel fibre

The mixtures M 2 and M 5 were prepared to containthe same amount of fibres (3% by volume). However,

the difference in their composition was that M 2 had

steel fibres of the same type, while M 5 had hybrid

steel fibres. The curves obtained from toughness tests

are illustrated in Fig. 8, while the evaluations of test

results according to the ASTM C 1609 and authors

recommendations are given in Figs. 9 and 10.

The toughness curves illustrated in Fig. 8 show

that the mixture with hybrid steel fibres, i.e. M 5 has

better behaviour than the mixture M 2. With an

increase in deflection, the mixture M 5 shows far

better behaviour than M 2 because it also contains,

besides short fibres, long steel fibres that are more

effective at large deflections than short fibres. The

statistical analysis of the parameters according toASTM C 1609 showed that there is no significant

difference in behaviour between M 2 and M 5. In

contrast, the statistical analysis of the toughness

parameters recommended by the authors showed an

important difference in these two mixture when the

parameters P100,4.0, P100,6.0 and T100,6.0 are taken into

account. This example illustrates that the evaluation

of toughness behaviour according to ASTM C 1609 is

adequate but incomplete in the case of UHPFRC with

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Deflection (mm)

Load(kN

)

M 6

M 1M 5

M 7

Fig. 3 The curves of mean

values obtained from

flexural toughness tests for

concrete mixtures M 1, M 5,

M 6 and M 7

0.00

20.00

40.00

60.00

80.00

100.00

120.00

P1

PP

P100,0.50

P100,2.00

P100,3.00

P100,4.00

P100,6.00

load(kN)

M 1 M 5 M 6

Fig. 4 Comparison of the

mean values of first-peak

load, peak load and residual

load for concrete mixtures

M 1, M 5 and M 6



8/14

different type of steel fibres when the ratio of a

minimum cross-section size of the specimen to the

fibre length is lower than 5; for this reason, additionaltoughness parameters that more adequately describe

the behaviour at larger deflections should be used.

3.1.4 Addition of polypropylene fibres

The mixtures M 2 and M 4 each contained 3% by

volume of steel fibres except that M 4 also had 0.8% by

volume of polypropylene fibres. The curves obtained

from toughness tests, as presented in Fig. 8, illustrate

that the mixture M 4 exhibits better behaviour up to

deflection of about 2 mm, while M 2 exhibits better

toughness performance beyond this deflection point.

This can be explained by the fact that the addition of

polypropylene fibres owing to their hydrophobic

properties results in reduced adhesion of steel fibres

to cement matrix, and consequently poorer behaviour

at larger deflections.

Figures 11 and 12 show the toughness parameters

calculated for the mixtures M 2 and M 4. The analysisof toughness test results obtained according to ASTM

C 1609 may lead to erroneous interpretation of the

results obtained from testing. ASTM C 1609 takes

into account the behaviour up to the deflection point

of 2 mm, and this is the deflection up to which the

mixture M 4 exhibits better behaviour. In contrast,

the mixture M 2 shows better behaviour beyond this

deflection point. However, if the test results are

analyzed according to the recommendations given by

the authors, toughness parameters at larger deflec-

tions can also be obtained. The statistical analysis ofthe test results shows that the mixture M 2 exhibits

much better behaviour than the mixture M 4 with

respect to the toughness parameters which are not

defined in ASTM C 1609, i.e. P100,4.0 and P100,6.0.

3.1.5 Size of the maximum aggregate grain

The mixtures M 2 and M 3 contained the same

amount of fibres (3% by volume); however, the

0,00

50,00

100,00

150,00

200,00

250,00

300,00

350,00

400,00

450,00

T100,2.00

T100,3.00

T100,4.00

T100,6.00

toughnes

s(Nm)

M 1 M 5 M 6


mean values of toughness

for concrete mixtures M 1,

M 5 and M 6 obtained from

the calculation of the area

under the loaddeflection

curve up to a certain

deflection

Table 6 The statistical analysis of the toughness test results

obtained for the mixtures M 1, M 5 and M 6

Analyzed mixtures M 1, M 5, M 6

Parameters Fexp1 Ftabl1 Fexp2 Ftabl2

P1 62.51 5.14 2.77 3.37

PP 21.79 5.14 2.87 3.37

P100,0.50 69.59 5.14 1.55 3.37

P100,2.00 3.13 5.14 3.15 3.37

P100,3.00 3.24 5.14 2.14 3.37

P100,4.00 5.91 5.14 1.27 3.37

P100,6.00 35.46 5.14 0.34 3.37

T100,2.00 34.84 5.14 0.38 3.37

T100,3.00 7.93 5.14 2.73 3.37

T100,4.00 7.99 5.14 2.29 3.37

T100,6.00 9.05 5.14 1.90 3.37



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mixture M 2 had smaller maximum aggregate grain

(0.5 mm) than the mixture M 3 (4 mm). The

toughness curves (Fig. 13) illustrate that up to the

deflection of about 2 mm better toughness behaviour

is exhibited by the mixture M 3 and beyond this point

by the mixture M 2. This is due to the fact that the

mixture M 2 had a higher ratio of fibre length to amaximum aggregate size than the mixture M 3 (26

and 3.25 respectively), and this parameter is crucial

for mixture behaviour under flexural load at larger

deflections. On the other hand, the results given in

Table 5 illustrate that the mixture with a larger

maximum aggregate size had higher flexural strength

by 9%. This result can be explained by better

distribution of steel fibres in the case of a larger

maximum aggregate size.

The evaluation of toughness tests according to

ASTM C 1609, as shown in Figs. 14 and 15 indicates

that the mixture M 2 shows better behaviour. The

introduction of the additional toughness parameters

illustrated that the mixture M 2 displays better

behaviour at deflection exceeding 2 mm. The statis-

tical analysis of toughness test results showed that M2 has markedly better behaviour than M 3 with

respect to the toughness parameter P100, 6.0 that is not

specified in ASTM C 1609.

3.1.6 Discussion

From the above discussion it is apparent that the

recommendations given by the authors for UHPFRC

toughness tests have some advantages over the

0,00

20,00

40,00

60,00

80,00

100,00

120,00

P1

PP

P100,0.50

P100,2.00

P100,3.00

P100,4.00

P100,6.00

load(kN)

M 6 M 7





M 6 and M 7

0,00

50,00

100,00

150,00

200,00

250,00

300,00

350,00

400,00

450,00

T100,2.00

T100,3.00

T100,4.00

T100,6.00

toughness(Nm)

M 6 M 7



for concrete mixtures M 6

and M 7 obtained from the

calculation of the area under

the loaddeflection curve up

to a certain deflection



10/14

procedure described in ASTM C 1609. The authors

recommendations for the evaluation of toughness test

results, besides toughness parameters defined in

ASTM C 1069, taking into account additional tough-

ness parameters, i.e. P100,3.00, P100,4.00, P100,6.00,T100,3.00, T100,4.00, and T100,6.00. These additional

toughness parameters are obtained using the same

procedure as the one specified for the toughness

parameters given in ASTM C 1609.

In comparison to UHPFRC, conventional FRC has

less quantity of fibres and a lower quality concrete

matrix, which results in poorer bond between the

fibres and the matrix and lower flexural toughness. In

all loaddeflection diagrams obtained from flexural

toughness tests, deflection hardening after first-peak

strength can be noticed. Such deflection hardening

was accompanied by multiple cracks and absorption

of a large amount of energy. The tested fibre-

reinforced concretes behaved in such a way becausethey contained a large amount of fibres exhibiting

good adhesion to the dense and compact matrix.

Owing to their improved properties in comparison

with those of conventional fibre-reinforced concrete,

this concrete type is termed ultra high-performance

fibre-reinforced concrete.

The authors recommend that, when the tests of

UHPFRC containing 2% to 5% in volume of steel

fibers are conducted according to ASTM C 1609,

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7

Deflection (mm)

Load(kN)

M5

M 2M 4

8

M 2 M 4 M 5

Fig. 8 The curves of mean

values obtained from

flexural toughness tests for

concrete mixtures M 2, M 4

and M 5

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

P1

PP

P100,0.50

P100,2.00

P100,3.00

P100,4.00

P100,6.00

load(kN)

M 2 M 5





M 2 and M 5



11/14

additional toughness parameters (P100,3.00, P100,4.00,P100,6.00, T100,3.00, T100,4.00, and T100,6.00) should be

used in any of the following cases:

The ratio between a minimum cross-section size

of the specimen and the fiber length is below 5;

A maximum aggregate size used is larger than or

equal to 4 mm; and

Polypropylene fibers are used in combination

with steel fibers.

3.2 Compressive strength

The results of compressive strength tests are summa-

rized in Table 5. All the mixtures have compressive

strength higher than 180 MPa. By statistical analysis

it was established that the results obtained from

compressive strength tests are repeatable for all

mixtures from M 1 to M 7.

The analysis of the results showed that the

mean values of compressive strength exhibited by

0,00

50,00

100,00

150,00

200,00

250,00

300,00

T100,2.00

T100,3.00

T100,4.00

T100,6.00

toughness

(Nm)

M 2 M 5








0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

P1

PP

P100,0.50

P100,2.00

P100,3.00

P100,4.00

P100,6.00

load(kN)

M 2 M 4





M 2 and M 4



12/14

UHPFRC with 3% and 5% in volume of steel fibres

were higher by 16% and by 17% respectively and by

16% and by 22% respectively compared with

UHPFRC with 2% in volume of fibres. An increase

in the length of steel fibres contained in the concrete

with 5% in volume of fibres caused a 6% increase in

mean compressive strength. The use of hybrid fibres

instead of plain steel fibres in the quantity of 3% involume resulted in a reduction in mean compressive

strength by 1%. The addition of polypropylene fibres

to UHPFRC with 3% in volume of fibres caused a 12%

decrease in mean compressive strength. The increase

of maximum aggregate size from 1 mm to 4 mm in the

case of UHPFRC with 3% volume of fibres resulted in

a decrease in compressive strength by 8%.

Because the compressive strength tests were

carried out on the 40-mm cubes, which are normally

used for testing mortar specimens, comparative

compressive strength testing on 100-mm cubes was

also performed [20]. The obtained test results illus-

trated that mean compressive strength values

obtained from tests on larger cube specimens are

smaller by about 20%.

4 Conclusions

An experimental investigation into toughness and

compressive strength, and a statistical analysis of the

results were carried out on ultra high performance

fibre-reinforced concrete specimens containing a

large amount of fibre (25% by volume) and

exhibiting deflection hardening behaviour. The

parameters varied were the following: (1) the amount

0.00

50.00

100.00

150.00

200.00

250.00

T100,2.00

T100,3.00

T100,4.00

T100,6.00

tou

ghness(Nm)

M 2 M 4








0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7 8

Deflection (mm)

Load(kN)

M 3

M 2

Fig. 13 The curves of

mean values obtained from

flexural toughness tests forconcrete mixtures M 2, and

M 3



13/14

of steel fibres, (2) the type of steel fibres, (3) the size

of the longest steel fibre, (4) the addition of

polypropylene fibres, and (5) the maximum aggregate

size in the concrete matrix. In this investigation,

which was focused on the analysis of the applicability

of the existing toughness test methods specified in

ASTM C 1609 to the UHPFRC specimens, the

following conclusions were made:

The authors recommendations to the analysis

of toughness test results obtained according to

ASTM C 1609 is based on the introduction

of additional toughness parameters (P100,3.00,

P100,4.00, P100,6.00, T100,3.00, T100,4.00, and

T100,6.00)in addition to those given in ASTM

C 1609in order to make this standard fully

applicable for UHPFRC. When testing UHPFRC

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

P1

PP

P100,0.50

P100,2.00

P100,3.00

P100,4.00

P100,6.00

load(k

N)

M 2 M 3





M 2 and M 3

0,00

50,00

100,00

150,00

200,00

250,00

T100,2.00

T100,3.00

T100,4.00

T100,6.00

toughness(Nm)

M 2 M 3










14/14

containing 2% to 5% in volume of steel fibers

according to ASTM C 1609, it is recommended

that additional toughness parameters should be

used in any of the following cases:

The ratio of a minimum cross-section size of the

specimen to the fiber length is lower than 5;

A maximum aggregate size is larger than or equalto 4 mm; and

Polypropylene fibers in combination with steel

fibers are used.

Such additional toughness parameters are calcu-

lated using a similar procedure as that specified in

ASTM C 1609. This is due to the fact that ASTM C

1609 is primarily designedand has been used so

farfor fibre-reinforced concretes with smaller

amount of steel fibres (\2% by volume) and for

fibre-reinforced concretes with matrices of lowerquality than those of UHPFRC and whose behaviour

in toughness tests is much lower than that of UHPFRC.

Further research should be done to verify the

advantage and disadvantage of this standard for

toughness testing of UHPFRC.

Acknowledgements The results presented in this paper

originate from scientific projects (Modern methods for testing

building materials, 082-0822161-2996, Principal researcher

Marijan Skazlic, PhD, Assistant Professor, and The

Development of New Materials and Concrete Structure

Protection Systems, 082-0822161-2159, Principal researcher

Dubravka Bjegovic, PhD, Professor), supported by the Ministry

of Science, Education and Sports of the Republic of Croatia.

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http://dx.doi.org/10.1007/BF02480495http://dx.doi.org/10.1007/BF02473063http://dx.doi.org/10.1016/1065-7355(94)90025-6http://dx.doi.org/10.1617/s11527-006-9103-2http://dx.doi.org/10.1617/s11527-006-9131-yhttp://dx.doi.org/10.1617/s11527-006-9131-yhttp://dx.doi.org/10.1617/s11527-006-9103-2http://dx.doi.org/10.1016/1065-7355(94)90025-6http://dx.doi.org/10.1007/BF02473063http://dx.doi.org/10.1007/BF02480495

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