Residual fracture energy of high-performance and normal concrete subject to high temperatures

Test data on the residual fracture energy of two significantly different concrete types are presented. About 80 beams of high performance basalt concrete and ordinary gravel concrete have been tested in accordance with the RILEM work of fracture method. The beams are heated at 1degreesC per minute up to a certain maximum temperature and kept at this temperature for 8 hours before cooling them back to room temperature and testing in three-point bending. The tests show that the two concretes behave almost identical when the fracture energy G(F) is considered as a function of maximum temperature. It is found that the damage introduced by a maximum temperature of 300 to 400degreesC increases the fracture energy by 50 % compared with the reference tests at room temperature. A more tortuous crack surface is one plausible explanation for the significant increase in G(F). The article also presents temperature and weight loss recordings from the heating scenarios and finally, the characteristic length and the cohesive tensile softening curve are shown to depend on the maximum temperature. Basically it is demonstrated that the temperature exposure makes the concrete significantly more ductile.