Incorporating hollow natural fiber (HNF) to enhance CO₂ sequestration and mechanical properties of reactive magnesia cement (RMC)-based composites: Feasibility study

Reactive magnesia cement (RMC) hydrates and carbonates to harden, which can sequestrate CO₂ from ambient air. However, the application of RMC-based composites in construction material is still limited by the inadequate CO₂ diffusion through the dense microstructure of MgO carbonates. This work for the first time investigates and demonstrates the feasibility of utilizing hollow natural fibers (HNFs) to enhance the carbonation and mechanical properties of RMC. In this study, 2 vol.% sisal or PVA microfibers were added RMC-based matrix to make fiber-reinforced composites. The compressive test shows that addition of sisal fibers significantly enhanced the 14-day compressive strength (10 % CO₂ curing) from 20.9 MPa to 39.3 MPa, while PVA fibers only marginally enhanced the strength to 25.0 MPa; the carbonation test of the composites, e.g., phenolphthalein color indication, FTIR, and XPS, shows that the lumens in the natural fibers served as the pathway for CO₂ penetration, which significantly increased the carbonation depeth and degree and thus the material strength. The tensile strength of sisal fibers were tested after conditioning in oversaturated Mg(OH)₂ or Ca(OH)₂ solution, the result shows that the fibers deterioration in RMC-based matrix is minimal, almost neglible compared to that in Portland cement (PC)-based composites. Collectively, these experimental results indicate that RMC and HNF are complementary to each other and can potentially make a new class of sustainable building materials.