On Concrete Properties during Heating and Cooling

The use of parametric/natural fires in the design of reinforced concrete structures in fire conditions requires an accurate definition of the temperature-induced evolution of the thermal and mechanical properties. Within this context, the characterization of four normal-strength concretes (f(c)(20) = 4200 to 6800 psi [29 to 47 MPa]), with siliceous and carbonate aggregates, are studied herein concerning the thermal diffusivity D (between 68 and 1652 degrees F [20 and 900 degrees C]) and under uniaxial compression after different thermal cycles, with reference maximum temperatures of 392, 752, and 1112 degrees F (200, 400, and 600 degrees C). The results show that thermal diffusivity exhibits mostly irreversible behavior after exposure to temperatures over 1382 degrees F (750 degrees C). Concerning the compressive strength, the hot and residual values (when Ttest = 68 degrees F [20 degrees C]) are, overall, in line with the most common standard provisions. Quite interestingly, the tests carried out at intermediate temperatures (with T-test not equal T-max and T-test > 68 degrees F [20 degrees C]) highlighted a strength decay, which is not simply an interpolation between hot and residual values.