LAUSR

The elevated temperature behavior of low-strength concrete specimens has been presented in this article. Concrete cylinders of 17 MPa (designated as M17) and 21 MPa (designated as M21) were employed. The temperature progression in the core of the cylinders showed some differences for the M17 and M21 specimens. Discoloration of the concrete started at 300°C, whereas hairline cracks appeared at 400°C on the surface of cylinders. Explosive spalling took place in few specimens at 400°C–600°C of furnace temperature due to the pore pressure generated by steam. The loss of compressive strength of the concrete was similar for both M17 and M21 specimens, both at 7 and 28 days, which reached 60 % after heating at 700°C. The ductility and residual Poisson’s ratio of concrete increased with the increase in heating temperatures. The elastic modulus decreased sharply after heating at 300°C, and the concrete lost more than 80 % stiffness after 600°C exposure. The residual tensile strength of the concrete decreased rapidly after heating at 400°C and became less than 10 % at 900°C. The comparison of observed data to the theoretical predictions based on the analytical models suggested by some of the international codes indicated differences between the predicted and observed data.