Preparation of artificial lightweight aggregate using alkali-activated incinerator bottom ash from urban sewage sludge

The preparation of lightweight aggregates (LWAs) using sewage sludge ash (SSA) by cold bonding technology can reduce the negative impact of SSA on the environment, it is an efficient solution to dispose of SSA. In this study, the granulated blast furnace slag (GBFS) was mixed with SSA to improve the performance of the prepared LWAs, with a dosage of 15% (SSA-G15) and 30% (SSA-G30) SSA by weight. Moreover, the 15% cement and 15% GBFS (SSA-G15C15) were added to the SSA as the third batch for comparison. The physical and mechanical characteristics of the LWAs were investigated, including particle size distribution, density, water absorption, compressive strength, and freeze-thaw resistance. Besides, the mineral composition, bonding type, microstructure, porosity, and heavy metal leaching behavior of the LWAs were evaluated by XRD, FTIR, SEM, MIP, and ICP, respectively. Results showed that all LWAs exhibited a uniform particle size distribution, a bulk density below 700 kg/(3), and an acceptable leaching value of harmful metals as recommended by NEN-EN 6966, 2005. The SSAG15C15 aggregates had higher cylinder compressive strength (1.8 MPa) and lower mass-loss rate (62.06%) under freeze-thaw cycles due to the dense microstructure compared to other batches. The water absorption value of SSA-G15C15 was 24.58%, within the acceptable limits as recommended by ACI-213R. It can be concluded that the application of SSA to produce LWAs is feasible, with a promising potential in sustainable lightweight concrete.