UCLA

Using alternative cements or binders is an effective strategy to reduce the overall embodied CO2 of concrete. Portland limestone cement (PLC) and limestone calcined clay cement (LC3) are commercially available Portland-based cements with less embodied CO2 than traditional Portland cement. These binders contain lower amounts of Portland cement and include supplementary cementitious materials (SCMs) that can provide additional cementitious properties. Another class of cements known as calcium sulfoaluminate or CSA cements, and more specifically, belite CSA or BCSA cements, are becoming increasingly important because of their high performance and low embodied CO2. One drawback of PLC and LC3 cements is that they lack early-age strengths, i.e., between 1 and 24 hours; however, BCSA cement, due to its unique chemistry and rapid setting behavior, can provide sufficient high early-age strengths necessary for specific applications. The ability of concrete mixes that provide this advantage and offer lower CO2 emissions can also have economic benefits. In this study, low embodied CO2 binders are developed using BCSA and PLC as well as calcined clay to maintain or improve their essential performance characteristics. Cement blends consisting of BCSA, PLC, and calcined clay are prepared, and various properties such as flow, setting time, shrinkage, and compressive strength are measured. The hydration of different phases in these binders and their blends are also evaluated using isothermal calorimetry, TGA/DTG, XRD, and SEM. The results show that replacing only 30% of PLC or LC3 (i.e., a mix proportioned with PLC and calcined clay) with BCSA can significantly improve early-age performance without affecting later-age strength and achieve a low GWP and carbon intensity.