Effect of sugar cane bagasse ash on properties and hydration mechanism in silica fume-based MgO-SiO2-K2HPO4 system

This study investigates the influence of sugar cane bagasse ash (SCBA) as a supplementary cementitious material on the properties and hydration mechanisms in silica fume-based MgO-SiO2-K2HPO4 system. SCBA was incorporated at varying dosages (0–25 %) to evaluate its influence on fluidity, setting time, mechanical strength, microstructure, and hydration products. Results indicate that SCBA effectively prolongs the setting time and enhances the fluidity of the paste without requiring a retarder, with the optimum performance observed at 15 % SCBA content. Although compressive strength slightly decreased with higher SCBA content, flexural strength significantly improved, reaching 23.2 MPa at 56 days with 15 % SCBA, highlighting a strategic trade-off that prioritizes bonding capacity and toughness, which are critical for applications such as concrete repair. Microstructural analyses revealed that SCBA contributes to physical filling and participates in chemical reactions, promoting the formation of magnesium silicate hydrate (M-S-H) and amorphous phosphate phases that refine the pore structure and reduce the proportion of harmful pores. The incorporation of SCBA also delays MgO dissolution and K-struvite formation through competitive water adsorption and ion interactions, thereby improving reaction kinetics and workability. These findings demonstrate the dual role of SCBA as both a physical filler and a chemical participant, which provides a sustainable and performance-tailoring strategy for magnesium potassium phosphate cement, enabling its optimization for critical applications like concrete repair where workability, setting time, and interfacial bonding are paramount.