Low-carbon alkali-activated concrete production using multi-waste materials

This study introduces a novel multi-waste binder design approach for high-strength alkali-activated concrete (HSAAC), in which ground granulated blast furnace slag (GGBFS) content was reduced to only 20%. Ten mixtures were prepared by replacing up to 80% of GGBFS with various waste materials, including waste charcoal ash (WCA), silica fume (SF), metakaolin (MK), waste ceramic powder (WCP), waste basalt powder (WBP), quartz powder (QP), and coal powder (CP). The influence of different curing regimes, including water, heat, and steam-water curing, was evaluated based on compressive strength development, while the physical, mechanical, durability, and environmental performances of the mixtures were assessed under water curing conditions. The results show that the steam-water treatment system produced higher compressive strengths for all mixtures after 28 days compared to the other curing systems. The WCA20 mixture showed a 3.5% improvement in workability. The control, MK40, and WCP20 mixtures achieved high-strength concrete requirements, with compressive strengths of 87, 75, and 70 MPa, respectively. The QP20 and WBP20 mixtures exhibited enhanced flexural strength, with increases of up to 44% and 25%, respectively, and achieved tensile strengths of 7.16 MPa and 6.21 MPa, respectively. MK20 and QP20 exhibited superior resistance to both sodium sulfate (Na₂SO₄) and magnesium sulfate (MgSO₄) attack. Microstructural analysis further confirmed the strength enhancement observed after sodium sulfate exposure. The SEM–EDS results revealed denser reaction matrices and increased Ca/Si ratios of 0.31 and 0.27 for MK20 and QP20, respectively, suggesting the formation of additional Ca-bearing reaction products and continued matrix densification. Environmental assessment revealed improved sustainability across all mixtures, with WCP and WBP showing the highest environmental performance among the multi-waste blends.