Influence of internal autoclave effect and thermal shock on the residual capacity of fire-exposed self-compacting concrete

Purpose This study aims to clarify the influence of the internal autoclave effect and cooling-induced thermal shock on the residual mechanical capacity and constitutive behavior of fire-exposed self-compacting concrete (SCC). Design/methodology/approach C35 SCC specimens were exposed to different target temperatures ranging from 20 °C to 700 °C and then subjected to two cooling regimes: natural cooling and water cooling. Residual compressive strength, failure morphology, surface damage characteristics and uniaxial stress-strain behavior were investigated. A Modified Popovics-based constitutive model was further calibrated to describe the post-fire mechanical response of SCC under different cooling regimes. Findings The results show that the dense matrix of SCC promotes moisture entrapment and hydrothermal reactions at intermediate temperatures, leading to a strength rebound of approximately 8.1%–9.9% at 300 °C in the naturally cooled specimens. Water cooling induces severe thermal shock, resulting in surface cracking, corner spalling and greater residual strength loss at high temperatures. The proposed constitutive model captures the degradation of peak stress, peak strain and curve shape with good accuracy. Originality/value This study provides experimental evidence for the coupled hydrothermal-mechanical response of SCC after fire exposure and proposes a calibrated constitutive model for post-fire residual capacity assessment of SCC structures subjected to different cooling conditions.