Towards standardisation of zinc slag as a sustainable fine aggregate substitute in concrete

In the construction industry, a huge demand for alternative construction materials has driven interest in industrial by-products as substitutes for natural aggregates. The present study evaluates zinc slag (ZS) as a partial to full replacement for natural sand in normal and high strength concrete. Zinc slag was characterised for physical, chemical, particle size distribution, density, water absorption, hazardous element content and leaching potential. Furthermore, comprehensive experimental evaluation of fresh properties, compressive strength, dry shrinkage and carbonation resistance was conducted for concrete mixes with 0-100% ZS replacement of fine aggregates in accordance with relevant standards. The results demonstrated that zinc slag exhibits favourable properties with reduced water demand of 9 to 16 kg/m3. Compressive strength increased by up to 8% (from 31.2 MPa reference normal strength concrete) and 6% (from 52.4 MPa reference high strength concrete) at 28 days across 0-100% ZS replacement levels. Dry shrinkage found to be less than − 600 µɛ for all ZS replacement irrespective of concrete grade and in the range of control mixes. Carbonation depth and air content remained within acceptable limits, and alkali silica reactivity was negligible. These findings indicate that zinc slag can be a sustainable and effective alternative to fine aggregate in wide range of applications in the construction industry. The study contributes critical data needed for the potential inclusion of ZS as a fine aggregate in the upcoming revision of construction material standards.