Thermal Treatment of Recycled Concrete Fines for Sustainable Cement: Linking Physicochemical Transformations, Reactivity, and Life Cycle Assessment

Recycled concrete fines (RCF), generated during the demolition and recycling of concrete structures, are a promising secondary raw material for cementitious systems, yet their low reactivity has limited large-scale use. In this study, RCFs were subjected to controlled thermal treatments at 400, 600, and 800 °C to systematically investigate their physicochemical transformations and subsequent influence on the blended cement performance. Characterization revealed temperature-dependent modifications in particle size, surface property, phase assemblage, and morphology, which were directly correlated to hydration kinetics, rheology, and mechanical strength. Among the tested conditions, thermal treatment at 600 °C optimally enhanced the RCF reactivity by decomposing weak hydrates while preserving carbonate phases, leading to improved hydration, workable rheology, and higher compressive strength. A cradle-to-gate life cycle assessment further quantified the environmental trade-offs, showing that moderate activation conditions can balance property enhancement with reduced carbon emissions. This integrated analysis highlights thermal treatment as a practical pathway for valorizing recycled concrete fines in sustainable cementitious systems, advancing circular economy practices and low-carbon construction materials.