Objective Non-autoclaved aerated concrete (NAAC), as a novel lightweight wall material, holds broad application prospects in the construction sector due to its environmental and energy-saving advantages. However, existing products still have limitations in terms of lightweight properties and thermal insulation performance, restricting their use in buildings with high energy efficiency requirements. To address this issue, this study proposes a solution to enhance NAAC properties by incorporating vitrified microspheres. By leveraging the lightweight properties, low thermal conductivity, and excellent chemical stability of vitrified microspheres, their incorporation into the NAAC matrix optimizes the internal pore structure through particle filling and synergistic effects. This approach not only effectively reduces the dry density of NAAC, further enhancing its lightweight advantage, but also significantly lowers its thermal conductivity. Consequently, the thermal performance of the material is substantially improved, enabling it to better meet the core requirements for wall materials in energy-efficient buildings.
Methods To optimize the synergy between lightweight insulation and mechanical properties in NAAC, this study systematically investigated the influence of vitrified microsphere dosage—set as the core variable in gradient experimental groups—on key physical properties (dry density, moisture content, water absorption rate), mechanical properties (compressive/flexural strength), and thermal performance indicators (thermal conductivity). By quantifying the evolution characteristics and coupling relationships among these parameters, the optimal dosage balancing comprehensive performance was determined. Additionally, microstructural characterization was conducted using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).
Results and Discussion The experimental results clearly demonstrated that the dosage of vitrified microspheres was a key factor in regulating the comprehensive properties of NAAC. Significant correlations were observed between variations in microsphere dosage and multiple performance characteristics of NAAC. As the microsphere dosage increased, the lightweight and porous properties of the material led to a gradual increase in internal porosity and a significant decrease in dry density, achieving the optimization goal of material light weighting. Meanwhile, both moisture content and water absorption exhibited a steady downward trend, enhancing the material's volumetric stability and water resistance. It should be noted that while the mechanical properties, such as compressive and flexural strength of NAAC, experienced a slight decline due to increased porosity, this reduction remained controllable. In contrast, the thermal conductivity continued to decrease with increasing filler content, markedly improving thermal insulation performance and effectively compensating for the original NAAC’s insufficient insulation capabilities. When the vitrified microsphere dosage reached 6%, NAAC achieved an optimal balance of comprehensive properties. The 28-day compressive strength remained at 4.20 MPa, meeting the mechanical requirements for wall materials. Dry density decreased to 638.4 kg/m3, demonstrating significant lightweight advantages. Thermal conductivity dropped to 0.085 1 W/(m·K), substantially enhancing thermal insulation. At this dosage, NAAC successfully achieved synergistic optimization of lightweight properties, mechanical strength, and thermal insulation, providing reliable experimental evidence for its promotion and application in energy-efficient building wall systems.
Conclusion This study indicates that vitrified microspheres, with their lightweight and porous properties, can effectively optimize the internal pore structure of NAAC. This reduces the proportion of interconnected pores while lowering material water absorption and enhancing volume stability. At a vitrified microsphere dosage of 6%, the resulting NAAC precisely balances the core requirements of lightweight and thermal insulation. Key indicators, such as dry density and compressive strength, fully comply with the mechanical properties of Grade A3.5 and density standards of Grade B06 specified in the "Autoclaved Aerated Concrete Blocks" (GB/T 11968—2020) standard. Moreover, its thermal insulation performance significantly outperforms traditional NAAC. This research breakthrough addresses the challenge of synergistically optimizing lightweight properties, thermal insulation, and strength. It provides a solid theoretical foundation and technical support for the industrial-scale production of lightweight insulating NAAC, offering broad engineering application prospects in the field of energy-efficient building wall materials.
Keywords：vitrified microsphere; non-autoclaved aerated concrete; thermal conductivity; microstructure; performance optimization
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