Strains under transient hygro-thermal states in concrete loaded in multiaxial compression and heated to 250 °C

Previous experimental research has shown that the compactive strains in concrete subjected to a load-then-heat regime exceed those measured in heat-then-load tests under compression. This excess in strain is known as transient thermal creep or load-induced thermal strain (LITS). All previous experimental research on LITS in mature concrete has been conducted in unsealed conditions, mainly under uniaxial compression (with a few biaxial compression tests, but no multiaxial tests) on specimens subjected to monotonic heating to high temperatures (> 500 °C). This paper presents the findings from a novel laboratory investigation of LITS under uniaxial, biaxial and hydrostatic compression in partially sealed conditions, at transient temperatures of up to 250 °C. The results from 49 experiments show that LITS in the sub-250 °C range is highly dependent on the moisture flux conditions and, consequently, on the relationship between heating and drying rates.