Thermo-mechanical properties and stress-strain curves of ordinary cementitious mortars at elevated temperatures

The mechanical behaviour of three bed-fixing mortars (one reference cement-lime mortar, cube strength 5 MPa and two cement mortars, cube strength 10 and 15 MPa) is investigated in this project in ordinary conditions and after being heated to 200, 400 and 600 °C, and up to 900 °C to evaluate the thermal diffusivity. The objectives of this study are two: (a) to extend the database on the high-temperature behaviour of ordinary cementitious mortars; and (b) to develop stress–strain relationships as a function of the temperature, that may be useful in the formulation of macro finite elements for masonry structures. On the whole, the heat-induced mechanical decay of the cementitious mortars investigated in this study (a) agrees with the experimental results available in the literature and (b) is very similar to that of ordinary concrete, as far as it concerns the compressive strength, tensile strength and elastic modulus. Compared to concrete at high temperatures, however, the mass loss in the mortars is higher, the thermal diffusivity is always smaller and the softening branch of the stress–strain curves indicates a definitely higher ductility. The test results allow calibrating an analytical stress–strain law in compression. The formulation is derived from that provided by Eurocode 2 for concrete at high temperature, but accounting for the smaller elastic modulus, the greater ductility and the gentler softening of the mortars at any temperature.