Temperature impact on the mechanical properties of high-strength concrete

This paper investigates the impact of moderately high temperatures, up to 85 °C, on the properties of high-strength concrete, including compressive strength, flexural tensile strength, and dynamic modulus of elasticity, with the focus on the evolution and potential decay of these properties. An experimental campaign was conducted with concrete specimens cured for three different durations: 7, 28, and 90 days. These tests were supplemented with chemically bound water and pore structure analysis to relate these with the mechanical properties. Results indicate that earlier exposure to elevated temperatures accelerates the decay of mechanical properties. The specimens cured for 90 days and then exposed to 85 °C for up to 180 days exhibited a slight decrease in compressive strength, flexural strength, and dynamic modulus of elasticity by 3.0%, 6.5%, and 3.0%, respectively, compared to those maintained at 23 °C. In contrast, specimens cured for only 7 days before exposure to 85 °C showed a more pronounced decrease in these properties, with compressive strength, dynamic modulus of elasticity, and flexural strength decreasing by 10.0%, 8.1%, and 12.4%, respectively. Furthermore, this study confirms that compressive strength is positively correlated with chemically bound water, but negatively correlated with the water-accessible porosity.