Balancing mechanical strength and thermal insulation in basalt fiber-reinforced ceramsite concrete (BFRCC): Microscopic mechanism analysis and multi-objective optimization

In the global effort to advance low-carbon construction, ceramsite concrete has emerged as a promising sustainable material due to its excellent thermal insulation properties. However, achieving an optimal balance between mechanical strength and thermal performance in ceramsite concrete remains a critical challenge for energy-efficient building applications. This study examines the effects of water-cement (w/c) ratios, basalt fiber (BF) length, and BF content on the mechanical-thermal properties of basalt fiber-reinforced ceramsite concrete (BFRCC) by single-factor experiments and response surface methodology (RSM). Results indicate that increasing the w/c ratio to 0.4 and incorporating 12 mm BF at 0.4 vol% reduces BFRCC's thermal conductivity to 0.519 W/(m·K) while maintaining LC30 strength at 34.65 MPa. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were combined to elucidate the underlying mechanisms governing multiscale structural-thermal relationships. Microstructural characterization analysis indicates that a robust three-dimensional interlocking framework composed of "fiber-ceramsite-cement matrix" effectively distributes stress within the matrix, slows crack propagation, and refines pore structures to impede heat transfer pathways. Additionally, RSM optimization identified optimal parameters: w/c ratio = 0.3997, BF length = 12 mm, and BF content = 0.512 vol%. Experimental validation confirmed the model’s high predictive accuracy (relative error <5 %). These findings offer practical guidance for designing structurally and thermally integrated ceramsite concrete mixes to advance sustainable construction.