Phases assemblage of the hydration products of trial blends of OPC, limestone and calcined clay cement

Conventional use of binary blended cement has been fast changing towards a composite cementitious system which enables the use of two or more substitute materials in conjunction. Limestone and calcined clay cement (LC3) is one such promising blend of composite cement. This ternary combination can significantly improve the substitution level of clinker with good mechanical characteristics. This is owing to the fact that limestone in the presence of calcined clay results in the new chemistry with the formation of additional hydrates. This paper discusses the phase assemblage at different hydration stages in the LC3 cementitious system up to 28 days. The X-ray diffraction technique was used to study the phases in the Ordinary Portland cement, Portland Pozzolana cement and LC3 to understand the phases and their evolution in the different systems. XRD confirmed the formation of a carboaluminate phase at an early age. This phase seemed to remain stable up to 28 days. A semi-quantitative estimate suggests an increase in the amount of ettringite (AFt) phase due to stabilization of this phase in the presence of limestone. The amount of bound water was also evaluated for the different hydrated systems. Further, faster depletion of portlandite was observed in the system due to calcined clay's high reactivity and synergistic hydration kinetics in the LC3 blend.