Research on the Correlation between Microstructure and Macroscopic Properties of Magnesium Oxysulfide Foamed Lightweight Blocks Based on Proportion Optimization

Abstract

To address the high carbon emissions and resource consumption of traditional Portland cement, this study prepared lightweight and high-strength magnesium oxysulfide foamed blocks based on magnesium oxysulfide cement by optimizing the raw material ratio, adding composite modifiers and compounding mineral admixtures. The effects of oxygen-sulfur ratio, water-sulfur ratio, citric acid-potassium aluminum sulfate composite modifier, silica-fly ash double admixture system and glass fiber reinforcement on the mechanical properties, water resistance and volume stability of the material were systematically investigated. The intrinsic correlation between macroscopic properties and microscopic structures (hydration product morphology, pore distribution, fiber-matrix interface) was revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the optimal raw material ratio was MgO: MgSO₄:H₂O = 8:1:20, and the compound modifier (citric acid 1.2wt% + potassium aluminium sulfate 2.0wt%) significantly increased the softening coefficient from 0.41 to 0.91; The double addition of silica fume and fly ash (total dosage 30%, mass ratio 1:2) simultaneously increased compressive strength (66.2 MPa) and flexural strength (13.35 MPa), and significantly improved volume stability (28-day drying shrinkage strain reduced to 2304 µm/m). The lightweight block (with a bulk density of 800 kg/m³) prepared by physical foaming process has a compressive strength of 12.2 MPa and a 28-day volume shrinkage rate of only 1.11%; An addition of 0.6wt% of glass fibre can further enhance early strength and crack resistance. Microscopic analysis indicates that the increased generation of 5·1·7 phase (5 mg (OH)₂·MgSO₄·7H₂O) after modification, optimized crystal morphology, and densification of structure are the keys to the macroscopic performance improvement. The wall mechanics test confirmed that the compressive, shear and flexural strengths of the masonry met the requirements of the code. This study provides theoretical and experimental evidence for the industrial production and application of magnesium oxysulfide foamed lightweight blocks.