Recycling cement through thermal treatment – Influence of production process and storage

Abstract

Reactivated cements (RCs) produced from concrete waste offer potential to reduce the demand for new Portland cement. While previous studies mainly focused on the influence of reactivation temperature, this study investigates the effects of production sequence, particle fineness, and storage conditions on the properties of RCs. RCs were manufactured from laboratory produced cement stone by crushing, drying, milling, and thermal treatment at 650 °C. The resulting powders were characterized by Blaine fineness, PSD, and XRD, while workability was assessed through mini spread tests. The results show that milling before reactivation leads to higher milling efficiency and more homogeneous powders with lower specific surface area (SSA) resulting in improved flowability. Increasing particle fineness enhances reactivity and fresh paste density but reduces workability due to higher SSA. Storage conditions were found to have the greatest influence on RC properties. Warm and moist storage promotes pre‐hydration, causing changes in phase composition and doubling the spread diameter of the paste. Overall, the fresh‐state behavior of RCs is primarily governed by SSA and free lime content. The findings provide insights into the parameters that must be controlled for the production of RCs.