Effect of additives on properties and microstructure of lightweight aggregates produced from MSWI bottom ash sludge

In order to solve problems of land occupation and environment damage resulted from massive municipal solid waste incineration bottom ash sludge (MSWI-BAS), sintered lightweight aggregates (LWA) were prepared from MSWI-BAS. Additives are of great significance for the preparation of high-performance LWA and the utilization of MSWI-BAS resources, so their effect on properties of LWA was investigated. The results showed that when the content of water glass was 20%, compressive strength of LWA reached a maximum of 8.4 MPa, and 1-hr water absorption reached a minimum of 5%. The reason was that the addition of water glass brought a lot of Na⁺ and Si(OH)₄, and the internal crystals of water glass were converted into rod-shaped zeolite crystals, thereby forming a high-density structure. The addition of coal powder led to the formation of gas in LWA, thus reducing the density of LWA. At the same time, it was also conducive to earlier generation of liquid phase in LWA, making its internal structure dense. When the content of coal powder was 5%, 15%, and 20%, the modification effect was better, and compressive strength of LWA was larger, about 4 MPa. Additives are of great significance for the preparation of high-performance LWA and the utilization of MSWI-BAS resources.Implications: In this study, we have prepared LWA with MSWI-BAS. At the same time of X-ray diffractometer (XRD) and FT-IR analysis of raw materials, we also investigated effect of water glass and coal powder on characteristics (particle density, 1-hr water absorption, and compressive strength) of lightweight aggregates, and good results were obtained. For explanations, several characterizations were carried out, such as XRD and SEM. The sludge disposal problem is reduced. It opens up a new way for the utilization of solid waste resources. In addition, it meets with the concept of green development of building materials and makes the production of LWA have a broader development prospect.