Effects of sodium salt additive to produce ultra lightweight aggregates from industrial sludge-marine clay mix: Laboratory trials

The production of lightweight aggregates from waste is regarded as an environmentally benign means of recycling waste into materials for green building construction, supporting the circular economies of modern societies. In this investigation, aggregates are synthesized from industrial sludge-marine clay mixes using thermal sintering at 1000‒1300 °C with or without the addition of two sodium salts. The sludge-clay 50/50 mix that is fired at 1200 °C and the 0/100 to 50/50 mixes that are fired at 1300 °C yield aggregates with a specific gravity of less than unity (lightweight aggregates). The addition of two sodium salts at 1.5% w/w facilitated the formation of lightweight aggregates. This study reports the first time the production of ultra-lightweight aggregates with a specific gravity of less than 0.35 g/cm³ and sufficiently low water adsorption ratios from a 50/50 mixture with added NaCl and from a 20/80 mix with added Na₂CO₃ for construction material use. The sodium salt is posited to change the melt properties at the firing temperature used, causing the molten layers to retain their integrity when subjected to gas blasting with the formation of large internal pores and sufficient surface sealing.