Fracture behavior of carbon fiber reinforced coral aggregate seawater concrete

Coral aggregate concrete (CAC) — produced from dead coral fragments recovered from marine environments — can reduce transportation and time costs in construction. However, CAC is characterized by pronounced brittleness and elevated chloride-ion content, motivating the incorporation of carbon fibres (CFs) to improve its mechanical performance. To elucidate the fracture behaviour of carbon fibers reinforced coral concrete (CFRCC), three-point bending tests were carried out to examine the influence of CFs on fracture properties and crack propagation. The experimental factors included concrete grade (C20, C30, C40), initial crack-depth ratios ( a 0 /h = 0.3, 0.4, 0.5, 0.6) and carbon-fibre contents ( ρ s = 0 %, 0.5 %, 1.0 %, 1.5 %, 2.0 % by weight of cement). Initial fracture toughness ( K IC ini ) and unstable fracture toughness ( K IC un ) were obtained using the double-K fracture criterion (DKFC), which partitions the beam fracture process into crack initiation stage, stable crack propagation stage, and unstable crack propagation stage, while introducing the fracture energy ( G F ), stable fracture energy ( G FS ), and unstable fracture energy ( G FU ) to comprehensively characterize the evolution of fracture energy throughout the entire process. The results revealed that an increase in concrete strength enhanced both the fracture resistance and energy dissipation capacity of the beams. Conversely, while variations in initial crack-depth exerted minimal impact on fracture resistance, the energy dissipation capacity declined as the initial crack-depth ratio increased. The optimum CFs content was determined to be 1.5 %. The incorporation of CFs notably improved the macroscopic fracture resistance and energy dissipation capacity of CFRCC beams during the stable crack propagation stage and unstable crack propagation stage; however, the effect on K IC ini was minimal, implying that CFs primarily exert a crack arresting effect at the macroscopic level. In light of the initial damage, the evolution characteristics of the D - CMOD and P - CMOD curves of the beams were further examined, culminating in the development of damage models for the P - CMOD curves of both CASC and CFRCC. Utilizing the fracture parameters and the established damage models, the fracture arrest mechanism of CFs in CFRCC beams was systematically analyzed. Considering the strong correlation between splitting tensile strength and fracture performance, an empirical formula that accounts for splitting tensile strength, initial crack-depth, and CFs content was proposed, which is applicable for calculating the fracture parameters of CFRCC.