Development and Life Cycle Assessment of High-Volume Biomass Ash-Based Hybrid Alkaline Cements for Low-Carbon Green Cement

The cement industry accounts for about 8% of global CO2 emissions, and alkali-activated materials with high solid waste content can help achieve decarbonization of the cement industry and sustainable development, offering promising technical pathways for the development of low-carbon green cement. Biomass ash, as a promising raw material for solid-waste valorization, is limited due to its low substitution rate and poor early strength. This study determined the optimal pretreatment method for high-content (≥70%) biomass-ash-based blended cement and prepared biomass-ash-based hybrid alkaline cements (BHACs) with the aid of chemical additives. The 28 d compressive strength of the ground-ash-based blended cement reached 34.59 MPa. Single-component sodium sulfate achieved the highest 2 d strength (38.4 MPa), whereas sodium citrate reduced early strength. The synergistic effect of binary mixtures was limited, whereas sodium sulfate–sodium citrate combinations have the potential to achieve a balance between strength and flowability. Life cycle assessment (LCA) shows that, compared with CEM I 52.5R, all citrate-free BHAC groups reduce global warming potential (GWP) by over 59.42% and cumulative energy demand (CED) by over 45.67%. Based on early compressive strength and a “cradle to gate” life cycle assessment, BHACs are considered to have the potential to balance mechanical and environmental performance, promoting the industrial-scale solid-waste valorization of biomass ash for green low-carbon construction materials.