Experimental evaluation and reliability analysis of void configuration effect on the compressive strength of self-compacting concrete exposed to elevated temperatures

Assessing the structural reliability of concrete at elevated temperatures is essential for fire-sensitive applications, as thermal exposure progressively deteriorates its mechanical properties. Self-compacting concrete (SCC), renowned for its superior flowability and compaction, remains insufficiently characterised under such conditions when internal voids are present. These voids, whether intentional or accidental, can disrupt heat transfer pathways and generate stress concentrations, thereby intensifying thermal damage and diminishing post-fire strength. This study systematically examined the compressive strength behaviour of SCC specimens containing voids when subjected to elevated temperatures of 100 °C, 200 °C, 300 °C, 400 °C, and 600 °C. Cube specimens were cast with voids of varying dimensions (50 ×50 ×100 mm, 75 ×75 ×100 mm, and 100 ×100 ×100 mm) strategically positioned at central, top-central, bottom-central, top-corner, and bottom-corner locations. Reliability of compressive strength across all thermal exposures was assessed through Weibull statistical analysis. Results demonstrated that under ambient conditions, central voids produced the most severe strength reductions, up to 66 %, while corner voids caused losses of 14–40 % depending on their size and placement. At 600 °C, large central voids precipitated strength declines approaching 80 %, with M50 SCC decreasing from 46 MPa (small void) to below 10 MPa (large void). Notably, both M40 and M50 mixes exhibited transient strength gains of 17 % and 14 %, respectively, at 300 °C. However, voids located at lower specimen regions induced catastrophic damage modes such as base crushing and spalling, underscoring the critical influence of void geometry and location on SCC’s fire resilience.