Mechanical and thermal conductivity properties of alkali-resistant glass fiber shale ceramsite lightweight concrete based on microstructure

In view of the difficulty for existing lightweight concrete to synergistically meet the multiple requirements of lightweight phase change energy storage concrete (LPCESC) substrates for lightweight properties, resistance to phase change material (PCM)-induced deterioration, and thermal conductivity efficiency, this study developed a new type of alkali-resistant glass fiber shale ceramsite lightweight concrete (AGFSCLC) as the LPCESC substrate. Through macroscopic performance tests, the variation laws of its dry apparent density ( ρ ), compressive strength ( f cu ), splitting tensile strength ( f ts ), and thermal conductivity were investigated. A modified model considering fiber agglomeration effect and interface failure was proposed. Scanning electron microscopy and nuclear magnetic resonance were used to analyze the microstructure, and the correlation mechanism between pore fractal dimension and macroscopic properties was revealed. The results show that when the volume content of alkali-resistant glass fiber ( V r ) is ≤ 1 %, the ρ of AGFSCLC is controlled within 1177–1459 kg/m³ , meeting the lightweight requirement of LPCESC substrates. Compared with V r = 0 %, when V r = 1 %, the f cu increases by 8.18 %-15.89 %, the specific strength increases by 2.92 %-10.36 %, and the f ts significantly increases by 36.40 %-52.87 %, indicating that the material has the ability to resist strength deterioration caused by PCM incorporation. The thermal conductivity increases by 14.05 %-14.74 %, achieving a balance between heat storage and release efficiency and thermal insulation performance. Further microscopic analysis shows that the fractal dimension of mesopores (2–50μm) and macropores (>50μm) has a linear positive correlation with the 28-day f cu (R²>0.90), confirming that the complexity of mesopore/macropore structures can be used as a key microscopic indicator to characterize macroscopic strength. This study promotes the functional upgrading of lightweight concrete from a single partition wall material to an energy storage-structure integrated material. It not only has the ability to resist strength deterioration caused by PCM, prolonging the service life of prefabricated buildings, but also meets the needs of building energy conservation under the “dual carbon” goals.