Recovering hydrated cement from recycled concrete for improving technological properties of engineering bricks

Abstract

In Europe, around 500 million tons of construction and demolition waste (C&DW) are generated annually, a third of which is concrete. Recycling mainly focuses on coarse aggregates, but 20-30 % v/v of the output includes fine particles and hydrated cement powder (HCP). As HCP can be partially reactivated at 450-650 degrees C, its reuse in clinker production is under study, though high energy demands hinder its viability. This research investigates an alternative: substituting clay with up to 30 % HCP in fired clay bricks, leveraging the high-temperature process already involved. Bricks were fired at three temperatures and characterised in terms of mechanical, mineralogical, chemical, and thermal behaviour. A life cycle impact assessment evaluated environmental feasibility. Results show that HCP enhances brick properties, especially at higher firing temperatures. However, despite improvements such as reduced thermal conductivity, global warming potential and water consumption impacts are higher, posing a trade-off between material performance and environmental cost.