Preparation, Property Control, and Microstructural Mechanisms of Red Mud–metakaolin Composite Cement-based Foamed Materials

To promote the efficient utilization of red mud solid waste and the development of low-carbon, energy-efficient building materials, cement-based foamed materials were prepared using red mud, metakaolin, and cement as a composite cementitious system, with solid hydrogen peroxide as the foaming agent. A two-variable experimental design, considering the presence or absence of a superplasticizer, was employed to investigate the effects of foaming agent dosage on mechanical properties, pore structure, and thermal performance through compressive strength testing, scanning electron microscopy (SEM), and thermal conductivity measurements. The results indicate that compressive strength increased significantly with curing age and exhibited an initial increase followed by a decrease with increasing foaming agent dosage, with an optimal dosage of 0.5%, at which the 28-day compressive strength reached 31.6 MPa for specimens containing a superplasticizer. Microstructural analysis revealed that this optimal dosage promoted the formation of a uniform and fine closed-cell pore structure, while secondary hydration reactions involving red mud and metakaolin generated gel phases that effectively filled pores and enhanced matrix compactness. The incorporation of a superplasticizer further improved particle dispersion and hydration efficiency, resulting in increased densification and strength. Overall, this study provides a feasible approach for producing high-performance cement-based foamed materials with high red mud content and offers mechanistic insights into the performance regulation of low-carbon, energy-efficient building materials.