Fracture damage and softening constitutive relationship of polyethylene fiber-reinforced composite concrete under freeze–thaw cycles

To explore the effects of freeze–thaw cycles on polyethylene fiber (PF)-reinforced concrete (PFRC), five sets of specimens with varying PF volume percentages (0%, 0.1%, 0.2%, 0.3%, and 0.4%) were tested. Results indicated that up to 0.3% PF volume, increasing PF content improved crack initiation toughness, unstable toughness, and fracture energy. Beyond 0.3%, these properties slightly decreased. Freeze–thaw damage reduced concrete toughness and energy, but PF mitigated this effect. Higher PF content led to smaller losses in fracture toughness and energy during freeze–thaw cycles. A calculation model for PFRC's freeze–thaw damage was developed from experimental data, and a bilinear softening constitutive relationship curve for PFRC under freeze–thaw conditions was derived based on Petersson's concrete model.