Synergistic effects of boiler ash and polypropylene fibers on the mechanical and durability properties of fly ash-based geopolymer foam concrete

Abstract

This study investigates the mechanical, thermal, and durability performance of one-part geopolymer foam concrete (GFC) incorporating boiler ash (BA) as a partial replacement for fly ash (FA) and polypropylene fibers (PPF). Nine distinct mixtures were prepared with varying BA replacement levels (0%, 10%, and 20%) and PPF contents (0%, 0.5%, and 1%). Comprehensive testing was conducted to evaluate compressive and flexural strength, thermal conductivity, porosity, water absorption, sorptivity, freeze-thaw resistance, and high-temperature durability. The experimental results indicate that replacing FA with BA enhances the geopolymer matrix’s mechanical and durability properties through improved gel formation and matrix densification. The optimal mixture, containing 20% BA and 0.5% PPF, achieved a 41.52% increase in compressive strength compared to the reference mixture (0% BA, 0% PPF). This mixture also exhibited the lowest porosity (23.82%), water absorption (16.76%), and sorptivity (8.28%), along with the highest thermal conductivity (0.619 W/mK). However, mixtures with higher BA and PPF contents experienced reduced high-temperature resistance, with strength losses of 16.2% and 27.1% observed at 400 °C and 900 °C, respectively. Durability assessments revealed significant improvements in freeze-thaw performance. The optimized mixture demonstrated minimal weight loss and significant compressive strength gains after 15 freeze-thaw cycles. Microstructural analysis confirmed the synergistic effects of BA and PPF in enhancing the matrix’s densification, reducing pore connectivity, and bridging micro cracks. Additionally, BA’s high calcium content contributed to the formation of dense C-S-H and C-A-S-H gels, which played a crucial role in enhancing strength and reducing permeability. This study underscores the potential of BA as a sustainable alternative to FA in GFC production, highlighting its role in waste valorization and environmental sustainability. The findings provide valuable insights for optimizing BA and PPF content in GFC formulations, promoting their application in eco-friendly and high-performance construction materials.