Investigation on interface fracture properties and nonlinear fracture model between ECC and concrete subjected to salt freeze-thaw cycles

The work aims at investigating on interface fracture properties and nonlinear fracture model between ECC and concrete under salt freeze-thaw cycles. Based on the interface nonlinear fracture mechanism, a three-parameter nonlinear fracture model was proposed to comprehensive and accurately reflect the degradation law of interface fracture properties under salt freeze-thaw cycles. The experimental results showed that the salt freeze-thaw erosion had a very negative effect on interface fracture properties. Moreover, the occurrence of interface fracture under salt freeze-thaw cycles was affected remarkably by ECC strength grade, and the higher ECC strength always leads to later occurrences of interface fracture. Regardless of cycles, the fracture propagation process of all specimens included three phases: initial crack, stable crack propagation, and instability failure. Moreover, the three phases all occurred at the interface, and the crack did not extend to ECC or concrete substrate. Meanwhile, the fibers bridging effect was very significant at the phases of crack stable propagation and instability failure. Only one kind of wedge-splitting load-crack mouth opening displacement (CMOD) curve was observed. As number of cycles increased, slope of rising section curve and ultimate wedge-splitting loads all gradually decreased, while the CMOD corresponding to ultimate splitting load had little change. The salt freeze-thaw erosion had a very negative effect on three fracture parameters. Moreover, the three fracture parameters all decreased continuously with the increasing number of cycles. (C) 2020 Elsevier Ltd. All rights reserved.