Water treatment sludge and rice husk ash to sustainable geopolymer production

Water Treatment Sludge (WTS) comes from a basic sanitation service and has increased generation. In Brazil, WTS is widely discarded into watercourses, or when it is treated to increase the solids content, the residue is landfilled. The objective of this research was to produce geopolymer using non-calcined WTS as partial replacement of metakaolin (MK). The alkali source was an alternative sodium silicate solution made from the mixture of NaOH and rice husk ash (RHA). MK was partially replaced by WTS in the proportions of 0%, 15%, 30%, and 60% in mass. Additional RHA was used in the geopolymer mixtures to keep SiO2/Al2O3 molar ratio constant. Geopolymer mortars were cured at room temperature. Mechanical properties and durability characteristics were investigated. WTS replacement decreased the flow, flexural and compressive strengths, and increased porosity and permeability of geopolymer mortar. The replacement of 15% of MK by WTS had 25 MPa of compressive strength at 28 days, which is a good result to make concrete or building components. The results show that the use of non-calcined WTS and sodium silicate solution from RHA in geopolymer is technically feasible, resulting in a sustainable and environmentally friendly alternative for WTS and RHA disposal.