State of the art review on supplementary cementitious materials in India – II: Characteristics of SCMs, effect on concrete and environmental impact

A large number of wastes and naturally occurring resources have been recognized as Supplementary cementitious materials (SCM) for their role in clinker substitution and the resulting low carbon cement. While helpful for optimum utilization, existing literature fails to help stakeholders in selecting a suitable SCM. To address this challenge, the manuscript reviews over 20 different SCMs investigated in India for their availability, characteristics (physical, chemical, mineral and morphological), effect on the properties of concrete (workability, strength and durability) and environmental impact. The study shows that over 380 Mtpa of SCMs are generated in India, more than the estimated need of 105 Mtpa. The asymmetrical distribution of SCM availability call for alternative SCMs in some regions (12.22 Mtpa shortage) and high-volume utilization in other regions (131.88 Mtpa excess). The review uses a characteristics-based classification to identify SCMs with similar traits and understand their effects on concrete. Results show that SCMs having particle sizes similar to cement and spherical morphology improve the workability of concrete. Similarly, SCMs with very-fine particle size (specific surface area greater than 1200 m2/kg) and high Ca content (more than 10% Ca in chemical composition) improve concrete's compressive, flexural, and split tensile strength. The addition of SCM also improves durability against chloride ion penetration and wetting and drying cycles. Recommendations have also been made to guide stakeholders towards the suitable application of different SCMs. Multi-blended cement and long-term environmental impact have also been discussed to help stakeholders select a sustainable SCM.