Mechanism for activity variation of landfilled coal ash: Deterioration in landfilling and improvement in pretreatment

Landfilled coal ash (LA) may serve as an alternative to fly coal ash (FA) as a stable and abundant supplementary cementitious material (SCM), particularly given the gradual phasing out of coal-fired power plants in many developed regions. This study investigates the physicochemical properties of fresh FA, original LA (OLA), mechanochemically activated LA (GLA), and negative-pressure sieved LA (SLA). Additionally, it evaluates the potential activity of LA and the fundamental properties of LA-based blended cements produced with different pretreatment methods. The results show that long-term landfilling significantly reduces LA activity. The primary causes of this deterioration are macroscopic impurity contamination and microscopic partial reactions. Both mechanochemical activation and negative-pressure sieving pretreatments can improve LA activity and optimize the fundamental properties of LA-based blended cements through particle modification and particle selection, respectively. Owing to their distinct mechanisms for improving activity, blended mortars prepared with GLA exhibit improved water demand and strength performance compared to those made with SLA. This study contributes to the theoretical foundation for the resource utilization of landfilled coal ash, and provides potential option for pozzolanic materials in thermal coal plant closing areas.