Effect of sustained load on the flexural bearing capacity of polypropylene fibre and minimum steel-bar reinforced concrete beams
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Abstract
Macro-synthetic fibres are becoming increasingly attractive as concrete reinforcement in structural applications, polypropylene fibre reinforced concrete, and macro-synthetic fibre reinforced concrete (MSFRC) in general, being an example of this tendency. Nonetheless, further knowledge needs to be gathered in relation with the time-dependant properties (i.e., creep) of the MSFRCs when its use is oriented to design-for-cracking structural elements. For this purpose, an extensive experimental programme was carried out on the flexural load bearing capacity of full-scale MSFRC beams (with mini-mum conventional steel reinforcement). Namely, beams with spans of 3 m and cross-section size of 200×250 mm were produced from a C40/50 concrete with 0 (reference), 3 and 9 kg/m3 of polypropylene fibres. Four beams were cast from each concrete type. After 28 days, two beams from each concrete type were tested until failure in three-point bending configuration. Then, one beam from each concrete was placed under sustained load for one year in a four-point bending configuration, whereas another beam from each concrete was left unloaded for one year under the same environmental conditions. After one year, both remaining beams from each concrete were tested until failure in bending. The results of the tests allowed assessing the effects of the sustained load on the remaining bearing capacity of the beams and confirming that the inclusion of a minimum steel-bar reinforcement was sufficient to prevent the beams from uncontrolled deformations triggered by tertiary tensile creep. The results were accompanied by full physical-mechanical characterization of the concretes. The preliminary results presented herein allow confirming that using MSFRC in cracking-allowed structural applications -with at least minimum mechanical (as per codes) steel-bar reinforcement amount- is reliable from the structural standpoint.

