Feasibility of sludge generated in water-based paint industries as cement replacement material

An estimated 2100 tonnes of solid sludge is generated per annum from the water-based paint industries of Bangladesh. This paint sludge (PS) is usually incinerated, consuming energy and generating greenhouse gases and other pollutants. Through chemical analysis and standardized tests, it was shown that PS contains a similar array of oxides as Ordinary Portland Cement (OPC) and has pozzolanic characteristics. Considering these, PS was examined as a cement replacement material to create an alternative and economically beneficial way of disposing of this waste. Cement paste and mortar samples were prepared by replacing 5%, 10%, 15%, 20% and 30% of OPC with PS. To assess mechanical and durability properties of PS-incorporated samples, different tests were carried out that included consistency, setting time, compressive strength, soundness, sulfate attack, alkali silicate reactivity and chloride diffusion. Both initial and final setting times of PS-incorporated cement increased with an increase in PS fraction but remained within the standard limit. Compressive strength increased for 5% PS replacement but decreased with further increase in PS replacement compared to 100% OPC mortar. A slightly higher rate of compressive strength gain was observed at later ages for PS-incorporated cement than 100% OPC, which confirmed the pozzolanic characteristic of PS. The addition of PS was found to reduce the expansion of mortar bars in both soundness and ASR tests. It also inhibited ettringite crystal formation in the mortar matrix for sulfate exposure. Initially, chloride permeability increased in the early days for PS-incorporated mortar but was found to decrease rapidly at later ages. Altogether, it may be concluded that a 15% replacement of OPC with PS would comply with the necessary strength and durability standards.