Influence of Oil Shale Residue on the Frost Resistance of Fly-Ash-Based Autoclaved Aerated Concrete

To promote the high-value utilization of industrial solid waste and enhance the durability of construction materials in cold regions, this study investigates an autoclaved aerated concrete (AAC) system prepared primarily with fly ash and oil shale residue, with a particular focus on its frost resistance. The physical and chemical properties of the raw materials were characterized using X-ray fluorescence (XRF) and X-ray diffraction (XRD) to optimize the pore structure and mineral composition. A systematic evaluation of 15 continuous freeze-thaw cycles was conducted, comprehensively analyzing the compressive strength retention, mass loss rate, and thermal conductivity. The experimental results indicate that a 50% replacement of fly ash with oil shale residue, combined with an optimized water-to-binder ratio (0.66), significantly improves the pore uniformity and skeleton stability of the AAC. The optimized mixture (YYY50W) achieved a compressive strength of 5.2 MPa and a low thermal conductivity of 0.1654 W/(m·K). After 15 freeze-thaw cycles, the mass loss was minimal (<3 g), and the compressive strength retention rate ($R$) reached 90.0%, demonstrating superior frost resistance. This study elucidates the microstructural mechanism by which oil shale residue promotes the formation of low-crystallinity tobermorite and C-S-H gels, providing potential experimental evidence for the utilization of industrial by-products in building materials for cold environments.