Microstructure and mechanical properties of sustainable cementitious materials with ultra-high substitution level of calcined clay and limestone powder

Abstract Supplementary cementitious materials have been widely used to partially replace ordinary Portland cement. An increasing level of the substitution is a highly effective way to reduce carbon dioxide emission and energy consumption of cementitious materials. However, the availability of traditional supplementary cementitious materials (e.g., fly ash and slag) cannot meet the needs from the cement industry in the near future, particularly for the underdeveloped countries because they have limited industries with such by-products. In this study, calcined clay and limestone powder as supplementary cementitious materials are adopted to replace cement at ultra-high substitution levels for the production of sustainable cementitious materials. The influence of ultra-high substitution of calcined clay and limestone powder (i.e., from 50% to 80%) on the microstructure and mechanical properties of cementitious materials are investigated. The results show that the addition of calcined clay and limestone powder together with 50%-70% substitution of cement is beneficial for improving the toughness, densifying the microstructure, and refining the pore structure of cementitious materials even though the compressive strength is not obviously improved. This study reveals that the key factor to affact the substitution level is the availability of portlandite in the mixture, which controls the amount of calcined clay participating in the pozzolanic reaction.