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Home arrow Engineering arrow Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete: Proceedings of the International RILEM Workshop FRC-CREEP 2016
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Experimental Program

Materials and Concrete Mix

Two series of concrete were produced following the same mixing procedure. The type of fibre, after which the mixes were named, was the main difference between the two series manufactured. SF contained 150 kg/m3 of steel fibres, whereas GF had 44 kg/m3 of glass fibres. These two contents of fibres represent a volume of 1.9 % in SF and 1.6 % in GF with respect to the total concrete volume. Further details about the proportioning of the mixes and the properties of the fibres are presented in Tables 1 and 2, respectively.

The characterization of the material involved the elastic modulus (Ecm), which was determined according with [9] in 4 cylindrical specimens of /150 x 300 mm. The compressive strength (fcm) was tested according with [10] in 4 cubic specimens of 150 x 150 mm and the residual tensile strength (fR1, fR2,fR3and fR4) was assessed by means of the three-point bending test in specimens of 150 x 150 600 mm according with [11]. Table 3 presents the average results of these tests together with the coefficient of variation (CV).

Even though both concrete compositions were similar, a big difference in the compressive strength was detected. This effect might be attributed to higher air content in the GF mix compared with the SF series. Moreover, taking into account the diameter, specific weight and the different contents of fibres, the amount of glass fibres was about 100 times higher than steel fibres. This led to more interfacial transition zones which affected the compressive strength.

Table 1 Mix proportioning of concrete

Material

SF (kg/m3)

GF (kg/m3)

Cement 52, 5R

800

800

Silica sand 0/2

1161

1161

Filler (CaCO3)

200

200

Water

228

236

Nanosilica

40

40

Superplasticizer

30

30

Steel fibres

150

-

Glass fibres

-

44

Table 2 Properties of the fibres

Characteristics

Steel fibres

Glass fibres

Geometry

Straight

Filament

Length (mm)

13

13

Diameter (mm)

0.2

0.018

Tensile strength (MPa)

2300-2500

1400

Elastic modulus (GPa)

210

74

Specific weight (g/cm3)

7.75-8.05

2.7

Table 3 Average mechanical properties of the concrete

Parameters (MPa)

SF

GF

Average

CV (%)

Average

CV (%)

E

cm

34970

3.16

31137

2.72

fcm

102.79

1.54

73.59

3.14

fLOP

7.24

16.59

7.68

11.02

fR1

10.41

9.36

5.03

15.20

fR2

9.79

8.63

1.77

14.41

fR3

8.13

8.88

0.82

13.96

fR4

6.95

11.32

0.46

18.47

a Pouring of the beams and b wrapped beam in moist room

Fig. 3 a Pouring of the beams and b wrapped beam in moist room

To analyse the effect of creep, 12 beams of 40 x 80 x 1200 mm per each dosage were manufactured. The concrete was produced in a vertical axis mixer and directly poured from the skip to the moulds (Fig. 3a). To prevent the loss of superficial water and a consequent early shrinkage a curing layer was sprayed over the free surface of the concrete. All the specimens were demoulded 24 h after the fabrication and were immediately stored in a moist room with a controlled temperature of 20 °C and a relative humidity of 100 % (Fig. 3b). Half of the beams corresponding to each series were wrapped in aluminium tape to analyse the influence of restricting the humidity transfer during the curing.

 
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