Lightweight and high-strength foam concrete based on low-grade magnesite: Proportion optimization and performance characterization

• Main hydration products of FBMSC: brucite, periclase, and 5·1·7 phase. • The 5·1·7 phase does not decompose after carbonation. • FBMSC exhibits excellent carbonation resistance. To promote the sustainable development of foam concrete (FC) and enhance the resource utilization of low-grade magnesite (LGM), this study investigates the preparation and performance characterization of foam basic magnesium sulfate concrete (FBMSC) using LGM. A series of single-factor experiments were conducted to optimize the mix ratios and assess the impact of variables such as water-to-binder (W/S) ratio, citric acid (CA) content, calcium stearate (CS) content, and hydrogen peroxide (H 2 O 2 ) content on the workability, foaming behavior, and mechanical properties of FBMSC. The results revealed that the optimal conditions for FBMSC were (W/S 0.40; CA 0.25 %; CS 0.3 %; H 2 O 2 1.5 %), which resulted in a dry density of 602.34 kg/m 3 , a compressive strength of 6.16 MPa, and a specific strength of 10227 N·m/kg after accelerated carbonation, demonstrating excellent lightweight and high-strength characteristics. Microstructural analysis further revealed that FBMSC possesses outstanding carbonation resistance. The 5 Mg(OH) 2 ·MgSO 4 ·7H 2 O (5·1·7 phase) remains stable without decomposition before and after accelerated carbonation, and there are no significant changes in the phase composition or microstructure of the samples. The 5·1·7 phase interlocks with brucite to form a rigid skeletal structure, which imparts excellent mechanical properties to the samples. These findings underscore the potential of FBMSC as a sustainable and high-performance material for construction applications.