In recent times, with rapid development in the construction sector, the use of enormous amounts of materials is required for the production of concrete. Fire penetrates concrete, leading to chemical contamination, small cracks, and lightening. These effects can significantly change the properties of concrete’s structure, reduce its strength and durability, and also change the behavior of the structure and lead to effects on the environment. An attempt was made to study the effects of elevated temperature on the mechanical characteristics of self-compacting concrete (SCC) with by-products including fly ash as a partial replacement for cement and waste copper slag as a partial replacement for fine aggregate at 0%, 10%, 20%, 30%, 40%, 50%, 60%, and 70%. The SCC specimens were subjected to elevated temperatures ranging from 200, 400, 600, and 800 °C, respectively, for a steady-state of two hours in a digital muffle furnace. The residual compressive strength, mass loss, ultrasonic pulse velocity, and residual density along with a visual inspection of cracks and color changes were observed. In this study, with over 400 °C temperatures, surface fractures appeared. The residual compressive strength (R-CMS) of all the individual temperatures of the SCC-WCS% mixes exhibited a gain in strength range from 31 to 34 MPa at 400 °C, 26 to 35 MPa at 600 °C, and 22.5 MPa to 33.5 MPa at 800 °C, respectively. Microstructural analysis of SCC-WCS% mixtures subjected to elevated ambient temperatures is carried out with a scanning electron microscope (SEM) and X-ray diffraction (XRD).

Conventional coarse aggregates, extracted from natural sources, pose environmental challenges such as habitat destruction, resource depletion, and high energy consumption. To mitigate these effects, this study prepared geopolymer aggregates (G.A.) using fly ash–GGBFS and an alkali ac- tivator solution through pelletization. Furthermore, two aggregate drying methods, oven drying, and ambient air drying, are adopted to evaluate their optimal performance through physical and mechanical tests. The results Indicated that oven-dried geopolymer aggregates exhibited optimal behavior in all experimental aspects compared to ambient air-dried aggregates. Specifically, the 80% fly ash–20% GGBFS mixed aggregates demonstrated lower crushing value (20.80%), impact value (24.7%), water absorption (13.67%), and abrasion values (7.01%) than other mixes. No considerable difference was observed in the density and specific gravity of aggregates between the two drying methods. Subsequently, these aggregates were used as a 100% replacement for conventional coarse aggregates in concrete, and the concrete's mechanical properties, such as compressive, split tensile, and flexural strengths, were investigated. Please update the following sentence in place of the highlighted sentence. The mix M3 (i.e., 80% fly ash–20% GGBFS mixed aggregates incorporated concrete) showed superior performance and are considered the opti- mum mix. Specifically, in the compressive strength results, the mix M3 showed a 26.31% and 14.28% strength increase compared to the 100% fly ash aggregates incorporated concrete mix in oven-dried aggregates and ambient-dried aggregates incorporated concrete, respectively. The lin- ear regression equation derived from the experimental results was used to predict the split tensile and flexural strength, showing a good correlation between the experimental and expected results.