Assessing the influence of void and thermal interactions on the mechanical performance of self-compacting concrete under elevated temperature

The article aims to evaluate the post-high temperature exposure residual response of self-compacting concrete (SCC) in the presence of continuous internal voids. The influence of high temperatures on the mechanical behavior, especially compressive strength, have been reported in literature, while its interaction with the influence of void content, geometry, and distribution has not been rigorously characterized. This study presents an experimental program that investigates the absolute compressive strength response of SCC containing voids of varying dimensions across multiple mix grades (M30, M40, and M50) subjected to progressive heating levels of 100, 200, 300, 400, and 600 °C. In addition to solid reference specimens, three groups of specimens incorporated distinct void geometries VD1, VD2, and VD3 with dimensions of 50 × 50 × 150 mm, 75 × 75 × 150 mm, and 100 × 100 × 150 mm were selected to represent three levels of void ratios and to evaluate their impact on the absolute response of the specimens. The test results showed that for solid SCC specimens, compressive strength exhibited a temperature-dependent evolution, increasing with thermal exposure up to 300 °C, where the M50 grade attained 78.72 MPa, approximately 17.23% higher than its ambient value. Beyond this threshold, strength declined markedly, with reductions of 20–40% observed at 600 °C across all mix grades (M30-M50), reflecting thermally induced microstructural degradation. The presence of voids exerted a pronounced effect on absolute performance at elevated temperatures: at 600 °C, M50 specimens exhibited absolute strengths of 38.07 MPa (VD1), 18.41 MPa (VD2), and 10.84 MPa (VD3), representing an overall loss exceeding 80% relative to the room-temperature solid specimen.