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

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 °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. • The recycling of concrete aggregates produces a powder rich in hydrated cement and fine aggregates • This powder may successfully replace natural clay for manufacturing extruded bricks up to 30% • Hydrated cement is dehydrated and reacts with the clay minerals during firing stage • Despite porosity is increased, ultimate compression strength is barely reduced • By increasing firing temperature from 900 to 1100 ºC, the effect of replacing ratio is enlarged