Impact of Limestone–Metakaolin Ratio on the Performance and Hydration of Ternary Blended Cement

Abstract

Once sulfates become limited, the interaction of limestone with metakaolin (MK) is initiated, resulting in the formation of carboaluminates in a blended cement system. In this study, two different types of MKs (sourced from coal mining residue and soft clay) were adopted to examine limestone–MK ratios of 1:8, 1:4, 1:2, 1:1, and 2:1, by fixing the cement and MK content at 55% and 15%, respectively. The optimal limestone–MK ratio of 1:4 was found (equal to limestone content of 3.8%) to achieve the highest compressive strength of 60 MPa due to the formation of more carboaluminate content in both MK blended cement systems. This finding was corroborated with the thermodynamic modeling that the highest hydrates volume was achieved at the optimal limestone–MK ratio of 1:4. An overdosage of limestone reduces its reaction degree, reflecting the fact that excessive limestone content could only acts as filler in the system.