Alkali-activated cement: the influence of partial replacement of sewage sludge from Wastewater Treatment Plant for metakaolin

Wastewater Treatment Plant sludge has shown to be a potential input for the production of alkali-activated cement, mainly due to its chemical composition with high contents of silica and alumina. Moreover, sewage sludge use in developing alkali-activated cement represents an environmentally appropriate solution by including it in the production chain of alkali-activated cement and reducing CO₂ emissions compared with Portland cement. In this sense, the objective of this study is to evaluate the influence of the partial replacement of water treatment plant sludge by metakaolin on the properties of alkali-activated cement. To this end, as a function of setting time and compressive strength, three dosages of alkali-activated cement were analyzed with partial replacement in the mass of calcined sludge from a Wastewater Treatment Plant in the city of Porto Velho (Brazil) by metakaolin in the proportions of 20%, 35%, and 50%. The results show that alkali-activated cement has fast setting times since they are less than 30 minutes and two dosages (35% and 50%) showed strength higher than 25 MPa, which makes the alkali-activated cement suitable for application in civil construction. Statistical analysis revealed that the partial replacement of 30% of Water Treatment Plant sludge by metakaolin significantly affects the compressive strength property. (author)