Preparation of low-carbon cementitious materials based on fly ash from biomass power plant by alkali-salt solid waste synergistic effect: Activator ratio optimization, hydration process and sustainability assessment

Abstract

Promoting the application of biomass power plant fly ash (BPP-FA) in low-carbon cement-based systems, rather than landfill disposal, is an important approach to achieve energy conservation, emission reduction, and resource recycling in the construction industry. Currently, the synergistic activation strategy using various industrial by-products (IBP) as alternative activators shows great potential in raw material availability, production cost, and preparation processes. However, the suitability of different activator types for BPP-FA systems and their specific effects on performance have not been systematically studied. This study investigates the potential of steel slag (SS, 3–15 wt%) and flue gas desulfurization gypsum (FGDG, 5 and 10 wt%) as alkaline and sulfate activators, and systematically examines the effects of activator dosage on setting time, hydration behavior, ion leaching, and mechanical performance. Multiple characterization techniques, including XRD, FTIR, TG-DTG, and SEM-EDS, were employed to elucidate mineral phase evolution and microstructural development. In addition, a life cycle assessment (LCA) was conducted to evaluate the economic and environmental benefits of different mix designs, with further consideration of potential engineering applications. The results show that the setting time of the sample is affected by the chemical dissolution and hydration reaction process. The presence of sufficient sulfate is the basic premise to drive the dissolution-precipitation reaction forward. With increasing SS content, the average pH value of pore solution in G5/G10 group increased from 10.81, 10.72–11.02, 10.90, respectively. This alkalinity change effectively promoted the dissolution and reactivity of BPP-FA particles. In addition, the gel products exhibited improved crystal structure (higher Ca/Si ratio, greater degree of polymerization, and refined morphology), while the matrix developed a denser pore structure. For the optimal group BS6-G10, its GWP is only 44.14 kg CO₂-eq/t, and EE is 714.95 MJ-eq/t, which are about 95.3 % and 87.6 % lower than OPC, respectively. At the same time, its economic index EI is 4.60 CNY/t·MPa, and the sustainability index SI is 2.35 kg CO₂-eq/t·MPa. The results of this study not only expand the high-value application path of IBP such as BPP-FA, but also provide a scientific basis and theoretical basis for its application in low-carbon cementitious materials, which is conducive to the green and sustainable development of building materials.