Effective reutilization of textile sludge from common effluent treatment plant with mineral admixture as a partial replacement for cement in mortar mixes

Abstract

Treatment of textile industry effluents produces hazardous sludge. The improper disposal of sludge causes secondary pollution due to the leaching of heavy metals from it. Therefore, the prerequisite for the disposal of such hazardous sludge is its stabilization and solidification. The utilization of sludge as a resource for building materials is one of the sustainable solutions. The present study evaluates the feasibility of partially substituting cement with the textile common effluent treatment plant (TCETP) sludge and mineral admixture such as sugarcane bagasse ash (SBA) in cement mortar mixes. The 13 mortar mixes are prepared consisting of a control mix, four binary mixes with sludge (2.5, 5, 7.5, and 10%) and eight tertiary mixes with sludge (2.5, 5, 7.5, and 10%) and SBA (5, 10%) replacing cement by volume. Few binary and tertiary blended cement mortar mixes have demonstrated comparable strength, permeation, durability, and leaching properties that are on par with the control mix. The modified mortar mixes 2.5T, 5T, 2.5T5S, 5T5S, and 7.5T5S have improved strength compared to 7.5T, 10T, 10T5S, 2.5T10S, 5T10S, 7.5T10S, and 10T10S. Increased strength in mortar mixes is mainly attributable to the filler effect of sludge and SBA and the development of secondary CSH gel. The mortar mixes 7.5T, 10T, 10T5S, 2.5T10S, 5T10S, 7.5T10S, and 10T10S have increased sorptivity indices showing the presence of large-size pores. Durability results suggest a loss in strength due to sulfate attack. Carbonation is not observed in the mixes, and all the mixes are alkaline. However, the leaching study shows the presence of heavy metals in leachate solution above the permissible limit, mainly with mixes having 10% sludge and is within the permissible limit for all other mixes. The SEM image and XRD fingerprint analysis revealed the formation of porous structure and a reduction in CSH gel formation at higher replacement by sludge and SBA.