Revealing the connection between carbonation regimes and early pozzolanic reactivity of recycled concrete powder: Impact of composition and microstructure

This study aims to establish relationship between carbonation regimes and the early pozzolanic reactivity of carbonated recycled concrete powder (CRCP) by comparing the composition, structure and surface properties of the carbonation products. The surface of dry CRCP was characterized by a silica-rich layer and contains low-polymerized silica phases along with over 18 % of unstable calcium carbonate (Cc). Wet CRCP exhibits a silica-rich surface with the highest degree of silica polymerization and stable calcite in its composition. Semi-dry CRCP has a calcium-rich surface also contains high silica polymerization and over 29 % unstable calcium carbonate, and the highest specific surface area, leading to the fastest silicon dissolution and calcium consumption during pozzolanic reactions. The early pozzolanic reaction kinetics in semi-dry and wet carbonation are limited by the dissolution of carbonation products, whereas dry carbonation does not exhibit this limitation. Understanding this connection is crucial for selecting optimal carbonation techniques to enhance waste concrete utilization.