Freeze–thaw damage evolution of PP- and PVA-fiber-reinforced cementitious composites: mechanical degradation, interfacial deterioration and mesoscale modeling

Freeze–thaw deterioration of fiber-reinforced cementitious composites is controlled by matrix cracking, pore-related defects and fiber–matrix interfacial stability. This study compared polypropylene fiber-reinforced cementitious composite (PP-FRCC), polyvinyl alcohol fiber-reinforced cementitious composite (PVA-FRCC) and fiber-free mortar subjected to 0–150 rapid water-freezing/water-thawing cycles. Mass loss, compressive strength, splitting tensile strength and apparent elastic modulus were measured. Splitting-failure photographs, SEM observations, ImageJ-based local image descriptors and a calibrated three-dimensional mesoscale model were used to interpret damage evolution. After 150 cycles, PP-FRCC and PVA-FRCC retained 82.29% and 84.50% of their initial compressive strength, respectively, whereas mortar retained 66.45%. The apparent elastic modulus decreased by 32.9% and 29.2% for PP-FRCC and PVA-FRCC, respectively, indicating higher sensitivity to freeze–thaw damage than compressive strength. SEM-based image analysis showed increasing visible defect area and fiber–matrix interfacial deterioration with cycling; after 150 cycles, the visible defect area ratio reached 6.8% for PP-FRCC and 5.6% for PVA-FRCC, while the interfacial deterioration ratio reached 21.2% and 17.4%, respectively. A calibration-based three-dimensional mesoscale model reproduced the overall compressive degradation trend and visualized the coalescence of equivalent damage fields during subsequent compression. The statistical and image-based results indicate that fiber reinforcement altered the freeze–thaw degradation pathway relative to mortar, while the differences between PP-FRCC and PVA-FRCC were expressed mainly through mass-loss evolution, apparent stiffness retention and local fiber–matrix interfacial deterioration under the present mixture design and testing regime.