Optimizing calcium efficiency for sustainable cement with GGBFS-fly ash systems.

The global cement industry urgently requires sustainable alternatives to reduce its 2.8 billion tonnes of annual CO₂ emissions. This study investigates maximum feasible cement replacement ratios using regional industrial by-products while maintaining adequate performance characteristics. We systematically evaluated replacement levels from partial to complete substitution using Mae Moh power plant fly ash and Taisei Thailand ground granulated blast furnace slag (GGBFS), employing a novel Calcium Utilization Efficiency (CUE) metric. Four replacement strategies were assessed through comprehensive mechanical testing, microstructural analysis, and CO₂ emission quantification. The optimized 60% replacement system achieved 93.5 MPa strength-exceeding conventional cement by 2.7%-with 72% CO₂ reduction. Most significantly, 100% cement replacement maintained 71% reference strength while achieving 90% emission reduction. The CUE metric increased from 63% (conventional cement) to 94% (complete replacement), demonstrating an 8.6-fold improvement in strength-to-emission ratios. This research establishes maximum feasible replacement boundaries for sustainable cement systems, providing a systematic framework for balancing environmental benefits with performance requirements.