Performance and hydration of ternary cements based on Portland clinker, carbonated recycled concrete paste (cRCP) and calcined clay

Abstract

This study explored composite cements consisting of Portland clinker, two pozzolans (alumina-silica gel in carbonated Recycled Concrete Paste (cRCP) and metakaolin), and calcium carbonate. The rapid reactivity of alumina-silica gel resulted in full reaction within 28 days, while metakaolin exhibited slower reactivity. cRCP played a significant role in strength development between 1 and 7 days, with metakaolin becoming prominent thereafter. The combination of materials preserved their distinct characteristics. Early hydration was mainly influenced by clinker and cRCP, leading to high early compressive strength. After alumina-silica gel dissolved, metakaolin forms a microstructure, reducing porosity and allowing for continued strength improvement over time. The pozzolans did not hinder their respective reactions, and calcium carbonate from cRCP stabilized ettringite content, similar to limestone-calcined clay systems. This study’s findings offer insights for developing multi-component cement with cRCP and calcined clays, resulting in higher strength and reduced CO2 footprint compared to calcined clay-limestone cements.