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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

Experimental Program

A conventional fibre reinforced concrete incorporating 40 kg/m3 of hooked-end steel fibres was used. A total of 18 prisms of 150 mm height and 600 mm length and different widths were cast; 6 of 50 mm, 6 of 100 mm and 6 of 150 mm width (the standard size). The specimens were turned on 90° for testing as it is usual. Standard 100 x 200 mm cylinders were also cast to evaluate the compressive strength. All specimens were cured in a moist room and after that they were placed two weeks in a laboratory environment to minimize the variations in strength during long term tests.

To characterize FRC bending behaviour one beam of each width was tested as indicated in the EN 14651 Standard [3] (three-point bending, 500 mm span and

25 mm notch). The crack mouth opening displacement (CMOD) was used as the control signal of a closed-loop servo-hydraulic system, through a clip gage placed 1 mm from the bottom of the beam. The first-peak strength fL) and the residual flexural strengths at 0.5, 1.5, 2.5 and 3.5 mm of CMOD, fR1, fR2, fR3 and fR4, respectively, were calculated.

Four prisms of each width (named b-a to b-d, were “b” indicates the beam width in mm) were pre-cracked up to 0.5 mm, and then were used for creep tests. In these experiments, four-point loading configuration was adopted in order to improve the stability of the test; two beams were loaded together in each frame as shown in Fig. 1. For each pair of beams, the sustained load was calculated in order to apply a bending stress near to 60 % of the stress achieved at the end of the pre-cracking process, which corresponds to fR1 of each specimen.

To evaluate the CMOD during the creep test a mechanical dial gage was placed at the level of the tensile side of the beams (see detail in Fig. 1). The creep tests were conducted in an acclimatized room at 23 ± 2 °C.

The last prisms of each group were also pre-cracked up to 0.5 mm and remain unloaded with the purpose of comparing their mechanical properties with the residual strength properties of the specimens unloaded at the end of the creep tests. At the end of creep tests the content of fibres in the cracked sections were evaluated.

Creep tests

Fig. 1 Creep tests

 
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