Impact of elevated temperatures on the mechanical properties and microstructure of waste rubber powder modified polypropylene fiber reinforced concrete

To investigate the impact of elevated temperature on the residual mechanical properties and microstructure of waste rubber powder modified polypropylene fiber concrete (RPFC). A total of 20 mix proportions were designed, considering the effects of waste rubber powder (WPR) dosage, polypropylene fiber (PP fiber) dosage and different ambient temperatures on the mechanical properties and microstructure of RPFC. Surface color change, weight loss, residual compressive strength of RPFC were evaluated after exposure to 100C, 200C, 400C and 600C. Meanwhile, the digital image correlation (DIC) technique was adopted to monitor the surface crack development of prism specimens at different loading stages. By X-ray diffraction (X-RD) analysis and scanning electron microscope (SEM) observation, the chemical and physical changes of RPFC were explored comprehensively. The results showed that the weight loss of RPFC increased after high temperature and the microcracks on the surface of the specimen increased significantly with the WRP content increase at 600 degrees C. Below 200 degrees C, the strength loss rate of RPFC is lower than that of PP fiber concrete; it is significantly higher in 400C than that of PP fiber concrete. RPFC exhibits lower intensity in the X-RD curve than that of PP fiber concrete. The needle-like channels and pores formed thanks to fibers and WRP melting helps to release the vapor pressure and improve the concrete resistance to bursting. Finally, the relationship between ambient temperature and compressive strength was established.