Preparation strategy and performance development mechanism of river sediment based non-sintered lightweight aggregate

The production of artificial lightweight aggregate (LWA) from river sediment (RS) has been identified as a feasible disposal method for this solid waste material. However, the traditional high-temperature sintering process is associated with significant CO₂ emissions. To tackle this issue, this study investigated the use of RS combined with fly ash (FA) and slag as geopolymer precursors for the production of non-sintered ceramsite (NSC), and coated with sulphoaluminate cement (SAC) on its surface for preparing coated non-sintered ceramsite (CNSC) to improve its mechanical properties and waterproofing capabilities. The study found that when the content of FA and slag is 15 wt% and 10 wt%, respectively, and the ratio of SAC is 0.4, this combination represents the optimal mix proportion. The developed CNSC achieved a maximum compressive strength of 6.4 MPa. Its minimum 1-hour water absorption was 5.3 %, and the bulk density ranged from 834.4 kg/m³ to 1125.9 kg/m³. Based on 3D X-ray computed tomography, the structural characteristics of CNSC were clarified as having a loose and porous interior with a dense outer shell, and a quantitative relationship between SAC ratio and mechanical properties was established. The combination of coated non-sintered ceramsite (CNSC) and alkali-activated foamed concrete (AAFC) was also attempted for the first time, and the resulting CNSC-based AAFC panels achieved a compressive strength of 6.2 MPa, a surface density of 89.5 kg/m² and a heat transfer coefficient of 0.29 W/(m²·K), which provides a replicable and scalable approach for the sustainable utilization of river sediment and the development of green wall materials.