The hygrothermal assessment of cement-ash-based mortar

Cement is the second most consumed substance by weight in the world, after water. The growing demand for reduced emissions of CO2 urges the cement industry to find materials with a low CO2 footprint, which calls for cement substitution. An assumption of the study has been that sewage sludge ash (SSA), an industrial by-product, can be applied as a potential cement substitute in cement-based materials without compromising material performance. The study investigated the effect of partial replacement of cement by SSA in mortar on hygrothermal properties of mortar. Two sewage sludge ashes originated from wastewater treatment plants located in the Greater Copenhagen area, Denmark. SSAs consisted of larger particles compared to cement particles; thus cement-ash-based mortar resulted in more porous structures compared to cement-based mortar. The higher porosity was responsible for a decrease of the thermal conductivity of the mortar. Significant differences were recognized in sorption isotherms of individual components, i.e. cement and ashes. However, their effect on the sorption isotherms of the mortars was minor.