Compressive Strength and Microstructure of Alkali-Activated Blast Furnace Slag/Sewage Sludge Ash (GGBS/SSA) Blends Cured at Room Temperature

Abstract

In the present work, ground granulated blast furnace slag (GGBS) and sewage sludge ash (SSA) blends were assessed for the production of alkali-activated pastes and mortars. Percentages of SSA to substitute GGBS ranged from 0 to 30 wt% and sodium concentrations of 6–10 mol kg−1 were used for the activating solutions. Pastes and mortars were cured at 20 °C for up to 90 days. Raw materials were characterised by granulometric analysis, XRF, XRD, FTIR and SEM techniques. The replacement percentage of GGBS by SSA and the sodium hydroxide concentration of the alkaline activator were optimised to produce mortar with compressive strengths close to 30 MPa after 28 curing days at room temperature. Best results were obtained in samples blended with 20 wt% SSA activated with 6 mol kg−1 NaOH solutions which, according to the XRD, FTIR and microscopic results, contained higher amounts of (N,C)–A–S–H gel. The potential use of SSA for the development of alternative cementitious materials at room temperature has been demonstrated.