Thermal strain behavior and strength degradation of ultra-high-strength-concrete

With the increasing application of high-strength-concrete (HSC) in high-rise-buildings for which structural safety performance is needed. However, the thermal mechanical behavior of HSC exposed to fire differs from that of normal-strength concrete (NSC). HSC is known to show different thermal strain behavior and strength degradation from NSC. It is needed to consider the thermal strain of HSC at elevated temperature under loading condition. In this study, the thermal strain behavior and strength degradation of HSC when exposed to elevated temperatures under loading conditions were examined experimentally. The compressive strength, thermal expansion, total strain, and hightemperature-creep at elevated temperatures were evaluated. To evaluate the thermal expansion of HSC at elevated temperatures, HSC with compressive strengths of 80,130, and 180 MPa concrete were heated to 700 °C at a rate of 1 °C/min. The total strain and high-temperature-creep were measured under the loading condition of 25 % of the compressive strength at room temperature. The experimental results clearly showed that the strength degradation of HSC increased with the higher compressive strength at elevated temperature. Thermal expansion occurred consistently regardless of the strength level without loading. However, 180 MPa concrete failed while being heated to around 300 °C. The transient creep had a large influence on the high temperature-creep as the HSC was heated at elevated temperature while under a load. It is considered that the reduced amount of aggregate and increased binder content make extremely density matrix in HSC, and it is particularly evident as the compressive strength increased.