Thermal Performance and Sustainability Assessment of Nano-Silica Modified Slag Based Recycled Aggregate Concrete

The aggregate constitutes 60-70% of the total volume of materials used in concrete production. Replacing natural aggregates with construction and demolition waste is both a compelling and challenging task in the creation of new concrete. The present study was conducted on natural aggregates replaced with recycled aggregates at 0%, 30%, 45%, and 60% and Portland slag cement as a binder with M-Sand instead of river sand. Recycled aggregates concrete was exposed to high temperatures at 200℃, 400℃ and 600℃ at intervals of 1hr, 2hr, 3hr and 4hr durations after 28 days and also compared results with control concrete (0% recycled aggregates). Portland slag cement (PSC) + 1.5% of Nano silica were used. By an addition of 1.5% of Nano silica (NS) to binder material, it gives additional properties to concrete to reduce void ratio and still becomes denser and shows better performance under temperature. In this study, natural aggregates were replaced by recycled aggregates at 30%, 45% and 60%. Concrete containing recycled aggregate up to roughly 45% is appropriate for applications where temperatures must not exceed 400℃. Beyond 600℃, deterioration was substantially more severe and temperature has a significant impact on the mechanical characteristics of concrete. The compressive strength and durability studies of concrete showed better results with Nano silica at 45% replacement of recycled aggregates. Additionally, the properties of the inter facial transition zone (ITZ) between hydrated paste and recycled aggregates were examined using scanning electron microscope (SEM) analysis. Sustainability index of a recycled aggregate concrete is evaluated by considering embodied energy, global warming potential and global temperature potential. Despite the rise in porosity with increasing replacement, the inter facial bond remained stronger with recycled aggregates at replacement levels of up to 45%.