Performance enhancement and post-fire behavior of concrete incorporating waste fire clay as sustainable solution

Waste fire clay (WFC) was selected for use in this research study as a substitute for fine aggregate (FA) and cement in certain amounts. For this purpose, the amounts of FA and cement in the mixture were replaced with WFC (10%, 20%, 30%, 40% and 50%), while the effect of temperature on strength was also investigated. Regarding the temperature impact, variations of 24oC, 300oC, 600oC, and 900oC were taken into consideration. As a consequence of these alterations, the concrete mixture's flexural strength (FS), splitting tensile strength (STS), and compression strength (CS) were measured and assessed. Consequently, the investigations conducted on the test samples revealed that the CSs rose by up to 30% due to the substitution of WFC in the combination with FA. The rise rates are 11.11%, 16.31%, 19.03%, and 5.79%, respectively. The final mixture ratio of 50% exhibited a consistent reduction of 13.34% relative to the reference sample (34.57 MPa). When cement was added to the mixture in place of WFC, the CSs steadily dropped in comparison to the reference sample (34.57 MPa). The relative decrease rates are 6.74%, 13.65%, 30.14%, 42.26%, and 62.08%. The strength of the combination was shown to decrease with rising temperature values for both FA change and cement change. It was determined that the ultimate strength of concrete was achieved by a 30% substitution of WFC with FA, and a 20% substitution of WFC with cement. Comparative FE-SEM analyses were conducted on concrete that was substituted with FA and cement. FE-SEM analysis showed that increasing chamotte content resulted in denser microstructures with gel-like and acicular crystalline phases formed. The EDX results confirmed the presence of Si, Al and Ca as the main elements, indicating the co-existence of binding phases of the C-S-H and C-A-S-H type.