Effects of sintered secondary aluminum ash grinding fine power on the properties of modified magnesium oxysulfate cement-based materials

Abstract

To reduce the production costs of modified magnesium oxysulfate (MMOS) cement-based materials and realize the reutilize of secondary aluminum ash, this study investigated the effects of grinding fine powder derived from sintered secondary aluminum ash (DF) on the workability, mechanical properties, and shrinkage characteristics of MMOS cement-based materials. Various techniques including XRD, SEM, FTIR, TG, ICP, MIP, and hydration heat test were employed to analyze the mechanism. The results indicate that increasing DF content notably enhances the fluidity and reduces shrinkage of MMOS cement-based materials, while mechanical properties generally decrease. However, the decline in mechanical properties becomes negligible when DF content is below 10 %. Enhanced workability and reduced shrinkage deformation were observed at high water-to-binder ratios, whereas superior mechanical properties were evident at low ratios. Microscopic analysis revealed that excessive DF content delays the hydration process, reducing the formation rate of hydration products such as Mg(OH)₂ and 5·1·7 phase, enhances the workability and inhibits the shrinkage deformation of MMOS cement-based materials but is not conducive to early-stage mechanical properties. In the later stages of hydration, residual MgO in MMOS cement forms a dense structure interconnected with 5·1·7 phase crystals, enhancing mechanical properties. The cement shows low levels of heavy metals and harmful substances, all below regulatory limits, while leaching concentrations of heavy metals in untreated raw materials exceed standard requirements. This research supports the environmentally safe treatment and resource utilization of secondary aluminum ash.