From waste to value: Upcycling residual cementitious fines via flash calcination

The concrete industry contributes ∼8% of global CO 2 emissions, mainly from clinker production. Recycling concrete yields residual cementitious fines (RCF), enabling clinker substitution. This study investigates flash calcination as a thermal activation route to restore RCF reactivity. RCF were flash calcined (fRCF) and compared with untreated RCF and limestone powder. Chemical, mineralogical and physical analyses were performed. Flash calcination dehydrated portlandite and ettringite, reduced particle size, increased density and enhanced reactivity. Mortars with 25-100% clinker replacement by fRCF were tested in CEM I and CEM III/B at 1, 7, and 28 days. At 100% replacement, fRCF reached 16.3 MPa at 28 days. In CEM III/B, fRCF retained 99.4-101.4% of reference strength at 25-75% replacement, versus 36.9-78.7% in CEM I. Flash calcination thus increases RCF reactivity, enabling high clinker substitution, particularly in slag-containing systems. EU demolition waste can supply 75% clinker replacement in CEM III/B or 46% of total demand.