Mechanical and microstructural performance of concrete containing household waste ash and silica fume after exposure to 250°C

The increasing demand for sustainable concrete has encouraged the utilization of waste materials. This study investigates the combined effect of household waste ash (HWA) as a partial replacement of fine aggregate (0 to 20%) and silica fume (SF) as a cement replacement (10%). The mechanical, physical, and microstructural properties of concrete were evaluated after exposure to 250 °C for 220 minutes. Concrete workability, density, water absorption, compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV), SEM and EDX analysis were used to determine the influence of HWA. The results indicate that HWA reduced the concrete workability due to the physical properties of HWA (porous and rough texture). However, all mixes maintained acceptable workability (slump greater than 50 mm). Mechanical performance improved at optimum replacement levels. The 10% HWA increased compressive strength from 39.4 MPa to 42.5 MPa (7.8%). The maximum splitting tensile strength of 3.81 MPa (7.6% increase) was achieved at 15% HWA. SEM analysis indicates that 10-15% HWA enhanced mix densification and improved the interfacial transition zone (ITZ) through filler effects. However, excessive replacement (20% HWA) resulted in a less compact microstructure. The findings conclude that 10 to 15% HWA provides an optimum balance and produces concrete with adequate mechanical strength, a refined microstructure, and acceptable thermal stability after exposure to 250 °C.