Calcined sand-washing slurry-based LC3: hydration, performance, and environmental impact

• Calcined SWS is demonstrated as a viable alternative to metakaolin in LC3 production. • Higher early-stage alumina reactivity of SWS promotes AFt formation, enhancing early-age strength. • The PCE delays C 3 S dissolution, promotes AFt formation, and significantly enhances paste fluidity. • S700 achieves about 34.6% lower GWP than CG per tonne of binder produced. This study investigates the feasibility of using calcined sand washing slurry (SWS) as a sustainable alternative to traditional metakaolin in limestone-calcined clay cement (LC3). Using isothermal calorimetry, XRD, SEM-EDS, and TG-FTIR, the effects of SWS and polycarboxylate superplasticizer (PCE) on hydration, microstructure, and strength development were systematically analyzed. Results show that SWS contains reactive amorphous aluminosilicates that promote AFt formation and enhance early strength. The 750 °C − calcined SWS sample (S750) achieved a 28-day compressive strength of 46.6 MPa − only 3.5 % lower than traditional LC3. PCE significantly improved flowability (175 mm for S750-1) without compromising early strength, and enhanced matrix densification via accelerated AFt generation. Notably, S700 (i.e., 700 °C − calcined SWS sample) exhibited comparable strength and hydration behavior to S750, suggesting that low-temperature calcination is both feasible and energy-efficient. Besides, life cycle analysis shows that compared with CG, the CO 2 emissions of S700 are reduced by approximately 34.6 %. These findings highlight the application potential of SWS in the production of high-performance and low-carbon LC3.