Comparative study on the compressive performance of NSC and HSC with preload under 24-hour high temperatures

Abstract

This study explores the compressive performance of normal strength concrete (NSC) and high strength concrete (HSC) with preload under 24-hours sustained high temperature (SHT). A unique test setup was designed to accomplish the compressive tests of concrete under high temperatures. The effects of temperature, concrete strength and preloading are given attention. Besides, microscopic tests were carried out to reveal the variation mechanism of concrete performance. The results show that the degradation of the compressive strength of concrete under SHT is significantly more severe than under short-term high temperatures. At the same temperature and initial load level, HSC shows greater strength degradation than NSC. Pre-loaded concrete generates considerable creep under SHT, and its effect on the peak strain of concrete cannot be ignored. The peak strain of NSC and HSC is most significantly affected by the initial load level and temperature, respectively. At temperatures not higher than 350 °C, the deterioration of the compressive performance of concrete is mainly attributed to the dehydration decomposition of calcium silicate hydrate and the cracking of interface transition zone. Preloading can inhibit these reactions and improve the compressive performance of concrete under SHT. Further, a general model for the compressive stress-strain relationship of concrete under SHT considering concrete strength and preloading was developed, which can be used for the design and analysis of concrete structures serving at high-temperature environments.