Utilizing silica-rich waste material for enhancing the properties of concrete and its environmental assessment

Some of the industrial solid waste materials, despite having sizeable quantities of silica and alumina, do not meet the requirements of a supplementary cementitious material (SCM) as per ASTM C618. Conversely, these materials may well be classified as alternative supplementary cementitious materials (ASCM) in accordance with ASTM C1709. Even though they have the potential of enhancing the properties of concrete and promoting sustainability, these materials are often underutilized in construction. In an asphalt batching drum plant, large quantities of waste silica-rich ASCM (SR-ASCM) are collected during the crushing and heating of limestone aggregates. Hence, the primary aim of this study was to find the feasibility of using SR-ASCM as a partial replacement of ordinary Portland cement (OPC) for developing structurally viable and durable concrete towards a sustainable future. The raw SR-ASCM obtained from the plant was characterized to determine its mineralogical and morphological properties. Subsequently, the engineering properties and durability of concrete synthesized by partially replacing OPC with SR-ASCM were thoroughly investigated. Based on the characterization results, SR-ASCM failed to qualify as an SCM; however, due to its sizable pozzolanic activity, it could be classified as an ASCM. Concrete with 15% OPC replacement achieved a compressive strength of 51.9 MPa after 90 days, comparable to the control mix (51.0 MPa). There was remarkable resistance to chloride penetration in SR-ASCM-based concrete when the curing was extended from 7 to 90 days, with a 36% reduction in the chloride migration coefficient. These outcomes show that the mechanical properties and durability of SR-ASCM concrete were either equal to or better than those of conventional concrete. This was probably due to the SR-ASCM's pozzolanic reactivity and physical influence on the microstructure. A substantial reduction in CO₂ emissions in the range of 14 to 33% was achieved across different replacement levels of OPC by SR-ASCM. Promoting the integration of such materials in concrete will have significant socio-economic and environmental advantages.