Mechanical and thermal properties of concrete with partial replacement of fine aggregates by glass and rubber wastes

Purpose The purpose of this study is to evaluate the mechanical and thermal performance of concrete containing waste glass fine aggregate (GFA) and rubber fine aggregate (RFA) as partial replacements for natural sand. The main goal is to explore how combined glass and rubber contents affect the strength, weight loss and post-fire residual properties of concrete exposed to elevated temperatures up to 600°C, thereby contributing to sustainable construction practices through the reuse of non-biodegradable waste materials. Design/methodology/approach Experimental investigations were carried out by replacing fine aggregate with glass and rubber wastes at different proportions. Waste glass (0.85–2 mm) replaced sand by 5%, 10% and 15% by weight, while rubber (3–5 mm) replaced sand by 5% and 10% by volume. The fresh and hardened properties were evaluated through slump, density, compressive and tensile strength tests before and after heating to 600°C. Microstructural analyses were performed using scanning electron microscopy (SEM) to study the internal morphology of the mixes. Findings The results revealed that all specimens experienced strength reductions after exposure to elevated temperature. Higher rubber content caused greater losses due to combustion and micro-void formation, while moderate glass content slightly improved compressive strength before heating. The mixture containing 5% rubber and 5% glass exhibited the most balanced performance in terms of mechanical strength and post-fire resistance. SEM observations confirmed that an optimal hybrid mix minimized voids and improved the interfacial transition zone. Originality/value This research provides new insights into the combined use of glass and rubber waste as fine aggregate replacements in concrete exposed to elevated temperatures, which has not been extensively investigated before. The study’s originality lies in evaluating both mechanical and microstructural behavior under thermal conditions, highlighting the optimal hybrid ratio of 5% glass and 5% rubber. The results present a novel contribution to the development of fire-resistant and sustainable concrete materials. Figure 19 SEM images of G10–R10 ambient temperature A scanning electron microscope image of a textured surface at 200x magnification. A scanning electron microscope image displays a textured surface with various depressions and ridges. The image is taken at a magnification of 200 times, with a working distance of 24.64 millimeters and a high voltage of 15.0 kilovolts. The field of view is 722 micrometers, and the scale bar indicates 200 micrometers. The surface appears rough with multiple circular and elongated depressions, some of which have smaller features within them. The image is labeled with technical details including the date of capture, November 5, 2022, and the equipment used, a MIRA3 TESCAN electron microscope.