Design and characterization of sustainable mortars incorporating industrial waste–derived materials

Environmental pressures necessitate finding alternatives to Portland cement using alkali-activated aluminosilicate materials. Mortars containing different types of class F fly ash (Romania and Canada), furnace slag, silica fume and sand, activated with 5.1 M potassium hydroxide solution and 40% sodium silicate solution. Three mixes were tested (Mix 1 - fly ash Romania, Mix 2 - fly ash Canada and Mix 3 - fly ash Canada and slag). The activators were chosen to develop materials with high mechanical strength. The activation process occurred at controlled laboratory conditions (20 ± 2℃ and 65% relative humidity). Mix 3 showed the highest strength values of 43.8 MPa and a flexural strength of 7.4 MPa after 28 days. Mix 2 had a compressive strength of 26.0 MPa, in contrast to 8.3 MPa for Mix 1. The addition of blast furnace slag (Mix 3 vs. Mix 2) nearly doubled the compressive strength values. Proposed mixes are an effective alternative to cement mortar that reduce waste, through valorization of industrial by-products and diminish carbon dioxide emissions by 30%. Microstructural analyses (SEM and XRD) confirmed the formation of reaction products consistent with the observed mechanical strength. The developed mixes show promising mechanical performance and contribute to reducing CO₂ emissions in construction materials.