High performance CaCO₃-based composites using sodium tripolyphosphate as phase controlling additive: Bamboo fiber driven high strength development

Due to the limited carbonation degree caused by the surface densification of carbonated products, the development of high-strength carbonated composites remains challenging. In this work, bamboo fiber (BFs) is utilized as a reaction reinforcing agent along with sodium tripolyphosphate (STPP) as a CaCO₃ phase controlling additive to prepare high-strength bamboo fiber reinforced carbonated wollastonite composites (BFRCWs). The phase composition and microstructure are systematically investigated by multiscale physicochemical analysis, followed by the determination of macro properties and volume deformation. Results indicate that BF and STPP have a synergistic effect on the microstructural formation and macro performance of BFRCWs. STPP-treated BF (ST-BF) can serve as an internal curing agent and the porous structure of BF provides more channels for ion and CO₂ transport, whereas CaCO₃ phase composition and cementitious behavior is modified by STPP. The addition of ST-BF, particularly for long fibers, accelerates the carbonation reaction, resulting in an increased ratio of poorly crystalline CaCO₃ and a refined pore structure. With increasing ST-BF dosage (0–3 vol%), the cementitious reaction is enhanced, but excessive fibers (3 vol%) incorporation introduces additional porosity, consequently reducing compressive strength. The desired pore structure with the optimal 2 vol% ST-BF (3–6 mm) shows the highest strength of 103.5 MPa at 28 days.