A Proposal of Evaluation Method for Blended Cement Based on CO₂ Emissions and Compressive Strength

The cement industry is a major contributor to global warming due to substantial CO₂ emissions, particularly during clinker production, the intermediate step in manufacturing Ordinary Portland Cement (OPC). While blended cements incorporating supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag powder (GGBS, SP) and limestone powder (LSP) have been used to reduce emissions, it remains difficult to directly compare the impact of reduced OPC content on both compressive strength and CO2 reduction. This study proposes a new index, carbon intensity per unit compressive strength (CIt.MPa), which integrates the CO2 emission factor of cement with the 28-day mortar compressive strength. To validate the concept, blended cements composed of OPC, SP, and LSP were produced and tested. Results show that while the CO2 emission factor decreased linearly with increasing SCM content, compressive strength was partially recovered due to the latent hydraulic reactivity of SP. The CIt.MPa index effectively differentiated cements with similar strength but lower carbon emissions, demonstrating its practical potential for concrete users in selecting eco-friendly cement. This approach provides a quantitative tool for balancing mechanical performance and sustainability, contributing to the development of greener concrete.