How CO2 Curing Can Turn Alum Sludge Into Construction Material

Abstract

Alum sludge is produced as a by-product of drinking water treatment processes when aluminium sulfate is used as a coagulant. For the last decade, sludge production has increased significantly with increasing demand for drinking water due to population growth, and a green and economic management strategy is needed for this sludge. Based on our recent studies, alum sludge is a feasible substitute to replace either sand or cement in concrete blocks, which could be an efficient way to dispose of and reuse the sludge as raw material for this concrete product. For sand replacement, oven-dried sludge may deteriorate the mechanical and durability performance of concrete blocks due to its organic content hindering the cement hydration. An advanced technology, named CO2 curing, can improve the performance of sludge-derived concrete, e.g., compressive strength and resistance to sulfate attack. Also, the CO2 curing method has benefits for recycling of the abundant CO2 in the ambient environment. For cement replacement, grinding and calcining procedures have to be applied to eliminate the organic content and activate the pozzolanic activity of sludge. The obtained results show that a maximum of 10% cement can be replaced by alum sludge ash without compromising the mechanical performance of concrete blocks. This paper gives a summary of the latest alum sludge application studied by our research team.