EFFECTS OF HIGH TEMPERATURE ON THE RESIDUAL COMPRESSIVE STRENGTH OF HIGH-STRENGTH SILICEOUS CONCRETES

The use of high-strength concretes (f sub c > 60 MPa) in special structures designed to work in a high-temperature environment or to withstand severe thermal accidents requires the mechanical properties of the material to be assessed with regard to high-temperature effects. In this context, the residual mechanical properties of two high-strength concretes (f sub c=72 and 95 MPa), with siliceous aggregates (mostly flint) are studied under uniaxial compression after a single thermal cycle at 105, 250, 400, and 500 deg C. The results show that while concrete toughness increases after a cycle at high temperature, strength and stiffness decrease dramatically, and the recovery of strength in time is either nil or negligible. Furthermore, the stress-strain curves exhibit a rather pronounced softening branch, which has never so far been measured in a high-temperature context and is instrumental in assessing concrete toughness in compression. The knowledge of the residual mechanical properties of a concrete is necessary whenever the thermally damaged structure is required to bear a significant share of the loads even after a severe accident.