Thermophysical and thermomechanical properties of basalt-phenolic FRP rebars under high temperature

An experimental investigation was conducted on the thermophysical and thermomechanical properties of phenolic-basalt fiber-reinforced polymer (P-BFRP) rebars subjected to high temperature. As a comparison, vinylBFRP (V-BFRP) and epoxy-BFRP (E-BFRP) rebars were also investigated within the same program. The mass variation of all BFRP rebar types was similar in air atmosphere while P-BFRP rebars decomposed more slowly in nitrogen atmosphere. All BFRP rebar types were found to have a similar specific heat and thermal conductivity up to 350 degrees C. P-BFRP rebars exhibited a much higher glass transition temperature compared with the other two types of BFRP rebars. Three failure modes could be differentiated for all BFRP rebar types according to three temperature ranges, the latter were shifted to higher values for P-BFRP rebars. No reduction in tensile strength occurred in P-BFRP rebars up to 300 degrees C, while V-BFRP and E-BFRP rebars experienced a significant degradation of tensile strength at around 100 degrees C already. This advantage of P-BFRP rebars was mainly caused by the much higher Tg which delayed the initiation of interfacial bonding failure up to 300 degrees C. The elastic modulus of all BFRP rebar types exhibited a similar degradation, which was caused by progressive fiber and fiber bundle failure due to non-uniform stress distributions.