Substitution of sewage sludge ash for sand in concrete containing sintered coarse aggregate: A lightweight concrete with fully solid waste aggregate

The preparation of lightweight concrete by coarse aggregates of sintered sewage sludge ash (SSA) provides a new direction for the disposal of SSA. To further improve the disposal efficiency of SSA, this study explores the feasibility of replacing fine aggregates with SSA in lightweight concrete. The achievement of this objective provides a theoretical basis for the efficient utilization of SSA and conservation of natural building materials, thus promoting low-carbon, environmentally friendly, and sustainable development. Six substitution ratios of 0%, 15%, 30%, 45%, 60%, and 100% are designed to investigate the physical and mechanical properties, microstructural characteristics, pore features, chemical compositions, and heavy metal ion leaching rate of the concrete. Results indicate that with increasing SSA substitution ratios, the density, compressive strength, flexural strength, and freeze-thaw resistance of SSA sintered aggregate concrete gradually decrease, while the water absorption and long-term drying shrinkage increase. The porosity first decreases and then increases. In particular, the oven-dried density, water absorption, and compressive strength of the fully SSA aggregate concrete are 1483 kg/m3, 21.50%, and 19.29 MPa, respectively, meeting the density and strength requirements for structural lightweight concrete. To meet the strength grade of the concrete formulated (LC30), the replacement rate of SSA should not exceed 45%. The packing effect of SSA enhances the compactness of the concrete, reducing the heavy metal ion leaching rate and ensuring environmental safety. However, the porous and small-particle nature of SSA reduces the bonding of mortar and increases the water absorption of the concrete, leading to a decrease in concrete strength.