Fire resistance evaluation of clay and concrete masonry units under elevated temperatures using mechanical, chemical, and microstructural characterization techniques

Abstract

Limited studies have directly compared the fire performance of clay and concrete masonry units using integrated mechanical, chemical, and microstructural characterization under identical elevated-temperature conditions. This study addressed this gap by exposing both materials to temperatures ranging from 50 °C to 1000 °C and evaluating their response using compressive and flexural strength testing, FTIR, SEM, BET surface area analysis, ion migration, and moisture retention measurements. Concrete masonry units exhibited significant thermal degradation, with compressive strength decreasing from 25.4 to 16 MPa, flexural strength reducing from 1.42 to 0.03 kN, surface area declining from 14.7 to 1.2 m²/g, and ion migration reaching 2.751 ppm. ANOVA confirmed a statistically significant temperature effect (F = 20.3, p = 8.18 × 10⁻⁷). In contrast, clay masonry units maintained stable compressive strength (18.8–21.07 MPa), showed minimal flexural variation (0.36–0.67 kN), lower ion migration (1.161 ppm), and negligible shrinkage (0.0–0.05%), while exhibiting sintering-induced densification at elevated temperatures. These results demonstrate that clay masonry units possess superior thermal stability and post-fire structural reliability compared to concrete masonry units, providing quantitative evidence to support fire-resilient material selection and sustainable post-fire reuse strategies.