Sustainable enhancement of alkali-activated foam concrete using vegetable waste ash and fly ash: Improving mechanical, thermal, and durability properties

Abstract

This study evaluated the effectiveness of using vegetable waste ash (VA) and fly ash (FA) as sustainable partial replacements for ground blast furnace slag (GBFS) in alkali-activated foam concrete (AAFC) to improve mechanical properties, thermal insulation, and durability. VA, sourced from incinerated vegetable processing waste, and FA were used both individually and in combination to replace GBFS at 5 %, 10 %, and 15 % by weight. The AAFC mixtures were prepared with a fixed binder content of 500 kg/m3 and a water-to-binder ratio of 0.45, using pumice as the lightweight aggregate. The mechanical, fresh, and durability properties of AAFC mixtures were evaluated using sodium metasilicate as an activator, with curing at 80 °C for 24 h followed by ambient exposure. Compressive and flexural strengths were tested at 7, 28, and 91 days. Results indicated that VA significantly enhanced compressive and flexural strengths, with optimal performance at a 10 % VA replacement. Ternary mixtures containing 2.5 % and 5 % of both FA and VA demonstrated superior mechanical properties compared to the reference mixture. The thermal conductivity of the AAFC mixtures ranged from 0.164 to 0.204 W/mK. These values fall within the range typically considered favorable for thermal insulation applications, indicating that the AAFC mixtures possess excellent insulating properties. After exposure to 800 °C, the reference mixture with 100 % GBFS exhibited the highest strength loss of 31.08 %, while the mixture with 10 % VA (10 % VA and 90 % GBFS) showed the lowest strength loss of 12.34 %. All binary and ternary mixtures incorporating VA, FA, or their combinations demonstrated significantly reduced strength loss compared to the reference mixture. All VA-incorporated mixtures exhibited enhanced freeze-thaw resistance, with 5 % and 10 % FA mixtures also outperforming the reference. Ternary mixtures with 2.5 % VA + 2.5 % FA and 5 % VA + 5 % FA further demonstrated superior freeze-thaw resistance compared to the reference, highlighting their improved durability.