Effect of heating–cooling regimes on the compressive strength of alfa fibre concrete

In the first part of this research study, concretes with different dosages of alfa fibre were formulated. At ambient temperature, the results showed that the incorporation of 1% per volume of concrete of untreated alfa fibre (UAF) yielded the highest mechanical values among the alfa fibre concretes. The addition of alfa fibres produced an increase in ductility, compared with the no-fibre concrete. In the second part, specimens of ordinary concrete (OC) and concretes with polypropylene fibres, treated alfa fibre (TAF) and UAF were heated to various temperatures up to 800°C, with an average heating rate of 7–8°C/min, in steps of 100°C, maintained for 3 h. At the end of these heating rates, two cooling regimes were applied: air cooling or water cooling. The impact of these heating–cooling regimes was assessed through a study of the residual compressive strength. For both regimes and for all types of fibre concretes, the compressive strength drastically reduced up to 800°C with linear tendencies. More damage was observed in the fibre concretes quenched in water. For both cooling regimes, the use of alfa fibres led to an improvement in the residual compressive strength compared with OC, more particularly in the temperature range 500–800°C.