Exploring low-grade clay minerals diving into limestone calcined clay cement (LC3): Characterization − Hydration − Performance

Abstract

The physicochemical properties of calcined kaolinite clay have an impact on the hydration kinetics of limestone calcined clay cements (LC3). Therefore, this study compares the effects of two types of common clays, namely low-grade kaolinite (LGK) and mixed minerals (MIX), on the characterization, heat of hydration, setting times, and strength development mechanisms in LC3. The characterization of calcined clays is initially conducted. After conducting heat of hydration, TGA, and XRD analyses, the phase assemblage of both LC3 and ordinary Portland cement (OPC) systems is investigated. This is followed by quantifying the amounts of AFt/AFm, portlandite, and calcite. The more amorphous nature of the LGK compared to the MIX results in the formation of Stratlingite, which contributes to gaining strength at an early age. Hemi-carbonates and mono-carbonates are useful for achieving adequate compressive strength. The LC3 exhibits a lower heat of hydration compared to the OPC, which is advantageous in reducing the likelihood of thermal cracking in concrete structures. However, the LC3-MIX exhibits a higher heat of hydration after 36 h due to an excess of alkali content in the clay mixture. Moreover, the compressive strength of the LC3 exhibited a striking similarity to that of the OPC.