Synergistic effects of supplementary cementitious materials in limestone and calcined clay-replaced slag cement

The replacement of slag cement with limestone and calcined clay (LC2) is beneficial to expand the sources of SCMs and reduce CO2 emissions in the global cement industry. In this paper, the synergistic interactions between slag cement and LC2 are studied using multi-technique characterization including TGA, XRD and SEM. The results indicate that the addition of LC2 enhanced both compressive and flexural strength of slag cement mortars. Characterization of the microstructures show LC2 can optimize the phase assemblages of slag cement by stabilizing ettringite whilst promoting the formation of hemicarboaluminate and monocarboaluminate. It is concluded that faster reaction of calcined clay and nucleation effect of limestone compensate for the slow early hydration of slag cement whilst slag contributes to the later performance. The synergistic hydration effects of slag and LC2 offers unique opportunities to reduce CO2 footprint without compromising early and long-term performances.