Application of water treatment sludge in the manufacturing of lightweight aggregate

This study assesses the possible use of water treatment sludge for the production of lightweight aggregate (LWA), and focuses on the engineering properties of concrete made from this LWA. The experiments in this study involve 10 sludges from ten water treatment plants in Taiwan. All sludges can be used to manufacture LWAs in the laboratory, and exhibit a particle density (ρa) of 0.65–2.05 g/cm3 and water absorption of 0.5–15%. Five sludges are suitable for manufacturing both structural LWA (ρa = 1.2–1.8 g/cm3) and non-structural LWA (ρa < 1.0 g/cm3), and the other five sludges are only suitable for manufacturing structural LWA. The sludge collected from the Hsing-Zu plant was successfully used to produce both structural and non-structural LWA on a large scale using a commercial rotary kiln. The resulting aggregates possessed a particle density of 1.35 g/cm3 or 0.98 g/cm3 and a bulk density of 726 kg/m3 or 518 kg/m3 for the structural LWA and non-structural LWA, respectively. The structural LWA meets the ASTM C330 requirements, with a bulk density less than 880 kg/m3 for light coarse aggregate, and is a suitable LWA for structural concrete. The engineering properties of the concrete made from the structural LWA comply with the requirements of structural lightweight concrete.