Fine fractions of recycled aggregates: Integrated characterisation of physical and chemical properties, life cycle impacts and performance in cementitious mixtures

Abstract

This study presents an exploratory investigation into the properties of fine recycled aggregates, with a particular focus on particles smaller than 250 micrometres (fines), obtained from construction and demolition waste sources in Belgium. Such materials are often neglected and discarded due to their perceived low quality. Concrete-based recycled fines and mixed waste-based recycled fines were separated into three distinct size ranges and characterised through a range of physical, chemical and mineralogical tests. Additionally, an environmental impact evaluation was carried out to compare the production of these recycled fine aggregates to that of natural siliceous sand. The study also includes a practical performance assessment by partially replacing cement in mortar mixtures with the finest fraction of recycled materials. Physical characterisation has revealed the direct relationship between particle size and bulk density, the inverse relationship between size and specific surface area and the high variability in particle shape. Chemical and mineralogical analysis demonstrated some compositional differences related to calcium and silicon ratio in concrete-based and mixed waste-based recycled fines, and pointed to their limited reactivity. While the fresh properties and strength performance of mortars with recycled fines was slightly reduced compared to reference materials, recycled fines performed similarly to other common fillers, such as quartz and limestone. Environmental impacts of recycled aggregates were found to be lower in most categories compared to natural siliceous sand. The outcomes of this study underline the importance of proper characterisation of recycled fines and provide a basis for their practical and environmentally conscious use in cementitious materials.