Valorisation of alum sludge to produce green and durable mortar

Abstract

Alum sludge is a typical by-product of drinking water treatment processes. Most sludge is disposed of at landfill sites, and such a disposal method may cause significant environmental concern due to its vast amount. This paper assessed the feasibility of reusing sludge as a supplementary cementitious material, which could efficiently exhaust stockpiled sludge. Specifically, the pozzolanic reactivity of sludge at different temperatures, the reaction mechanism of the sludge–cement binder, and the resistance of sludge-derived mortar to microbially induced corrosion were investigated. The obtained results indicated that 800 °C was the optimal calcination temperature for sludge. Mortar containing sludge up to 30% by weight showed comparable physical properties at a curing age of 90 days. Mortar with 10% cement replaced by sludge can significantly improve the resistance to biogenic corrosion due to the formation of Al-bearing phases with high resistance to acidic media, e.g., Ca4Al2O7·xH2O and strätlingite. Graphical abstract: [Figure not available: see fulltext.].