Developing and classifying lightweight aggregates from sewage sludge and rice husk ash

In this research, sewage sludge (SS) and rice husk ash (RHA) were used as raw materials instead of clay to produce various lightweight aggregate (LWA) varieties. This solution can help to preserve natural resources and reduce environmental impacts caused by SS and RHA. Previous studies have demonstrated the feasibility of applying SS or RHA to produce LWAs but using both residues together has not yet been tested. The aim is to make a comparative analysis between manufactured and commercially available LWAs and evaluate the effects of the sintering temperature and raw materials on the properties of sustainable LWAs. The raw materials were analysed by laser granulometry, X-ray fluorescence (XRF) and X-ray diffraction (XRD). The developed mixtures were dried and then sintered at temperatures from 1100 to 1250 °C. Replacing clay by SS and RHA residues ranged from 41 to 100 %. Overall, 102 different types of LWAs were produced, of which 45 specimens are available for use in at least 1 of the main commercial LWA application categories. LWAs exhibited a bloating index (BI) from -71.65 to 40.83 %, loss on ignition (LOI) from 5.2–43.6%, particle density (ρd) from 0.63 to 2.01 g/cm³, water absorption (WA24H) from 0.7–105.9% and crush strength (S) up to 17.3 MPa. By and large, the main properties of the aggregates were changed from variations in sintering temperature and raw material proportions. This study demonstrates that it is possible to use SS and RHA to produce LWAs using properties suitable for the main LWA applications in engineering works and services.