Multilayer complexation engineering in reed-MOC composites: SHMP-induced dual-phase protection for water-resistant lightweight construction materials

Lightweight foams fabricated from shredded reeds bonded with magnesium oxychloride cement (MOC) offer a sustainable solution to mitigate reed resource waste, environmental pollution, and reliance on non-renewable building materials. However, the poor water resistance of MOC limits its broader application. To address this limitation, a novel multilayered “reed scraps-complex-cement particles” structure was developed using reed scraps as aggregate, MOC as the binder, and sodium hexametaphosphate (SHMP) as a modifier. PO 4 3 − from SHMP reacted with Mg 2+ in MOC to form a complex that encapsulated cement particles as a protective “outer layer,” which in turn shielded 5-phase crystals from water erosion. Moreover, SHMP dispersed cement particles uniformly onto reed surfaces to form an “inner layer.” The synergistic integration of these layers significantly enhanced water resistance and ultimately achieved a 215 % improvement after 3-day immersion, while strengthening interfacial compatibility between reed scraps and MOC. The composite exhibited ultralight density (0.2 g·cm −3 ) and high compressive strength (1.7 MPa). With its exceptional water stability, eco-friendly composition, and lightweight properties, this material demonstrated significant potential for advancing sustainable construction practices, particularly in moisture-prone environments and energy-efficient building systems. • Innovative multi-layer integrated structure is proposed to enhance water resistance of MOC. • Interfacial compatibility between reed scraps and MOC is enhanced by interweaving layers. • This material excels in light weight, water resistance and eco-friendliness.