Effect of Fibre Type and Quantity on the Short- and Long-Term Behaviour of Polypropylene Fibre Reinforced Concrete Beams

Macro-synthetic fibres are increasingly gaining acceptance as a type of reinforcement for structural applications, particularly in the form of polypropylene fibre-reinforced concrete (PPFRC). However, there is a need for additional understanding of the structural behaviour of PPFRC, particularly in relation to its time-dependent properties such as shrinkage and creep. To address this, an extensive experimental program was conducted on the flexural load-bearing capacity of full-scale PPFRC beams. Beams with spans of 3 m and cross-section sizes of 200 × 250 mm2 were cast from C40/50 concrete with varying amounts of two polypropylene fibre types (0, 3, and 9 kg/m3 and aspect ratios of 56 and 67). Four beams were cast for each of the five types of concrete. After 28 days, two beams from each concrete type were subjected to three-point bending tests until failure. Subsequently, one beam from each concrete was subjected to sustained load for one year in a four-point bending configuration, while another beam from each concrete was left unloaded for one year under the same conditions. After the one-year period, both remaining beams from each concrete were tested until failure in bending. The test results facilitated the assessment of the contribution of fibres to the flexural strength of beams and the impact of sustained load on changes in flexural capacity over a one-year period. These findings were complemented by a comprehensive physical-mechanical characterization of the concretes. The outcomes of this study can offer additional support for the safe and reliable structural use of PPFRC.