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Concrete exposure to high temperatures produces changes in its internal structure, for instance loss of its strength and deformation capacity, in extreme cases risking the service life of the structure. The damage level will depend on the temperature reached, exposure time, cooling velocity and type, size of the structural element and the material's own characteristics. In this paper results of conventional concretes (CC) made with a natural coarse aggregate and different water/cement (w/c) ratios exposed to high temperature are compared with those obtained with recycled concretes (RCs) of similar characteristics produced by employing 75% by volume of recycled coarse aggregate (crushed waste concretes). The concretes were evaluated by ultrasound and resonance frequency, and further determination of the static modulus of elasticity and compressive strength was possible. In all cases the parameters evaluated in concretes exposed to high temperatures are lower than in others with the same characteristics and without any type of processing. For exposure to 5008C for 1 h, the RC with a low w/c ratio performs better than the CC.

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