Recovery of residual anhydrous clinker in finely ground recycled concrete

The costs of construction waste handling, a scarcity of landfill sites, and requirements for sustainable construction have placed recycling of concrete the most abundant construction material in the world under scrutiny. Unlike recycling of aggregates, utilization of sub-sieve fractions from recycled concrete has not yet been adopted in the construction industry. In this study, we investigate the possibility of recovering residual anhydrous clinker embedded in grains of stripped mortar within these fines. Different samples of waste concrete were finely ground and studied using microscopy and chemical analyses to assess the amount of residual clinker. Its contribution to hydration processes was measured by calorimetry, and the impact of recycled concrete fines on mechanical properties of cement pastes was tested. The results indicate that residual anhydrous clinker is present in waste concrete and can be recovered by grinding. Replacing Portland cement with the recycled material in pastes led to a significant increase of tensile strength, while deterioration of compressive strength was negligible when the concrete fines contained higher amounts of residual clinker and when the amount of fines did not exceed 30% of Portland cement weight