Effect of freeze-thaw cycles and chloride salt erosion coupling conditions on fatigue properties of PE-ECC

Engineered cementitious composites (ECC), which are a kind of novel composite building material with high ductility and high toughness, can be utilized in areas susceptible to salt-freezing damage, such as that caused by snowmelt agents, seawater, and saline soils. In this paper, engineered cementitious composites reinforced with polyethylene fibers (PE) are analyzed to study the changes in the flexural static load properties, and flexural fatigue life of PE-ECC specimens after four different freeze-thaw cycles (0, 50, 100 and 150) in fresh water and a 3.5% mass fraction NaCl solution. The results show that upon reaching 150 freeze-thaw cycles, there was a notable disparity in the relative equivalent flexural strength between specimens subjected to chloride salt freeze-thaw and freshwater freeze-thaw environments, with the former exhibiting a 1.07-fold increase in damage compared to the latter specimens. Using the relative dynamic elastic modulus as the damage variable, a relationship model was made between the relative equivalent flexural strength and the freeze-thaw damage degree of PE-ECC in two freeze-thaw environments. The flexural fatigue life of PE-ECC after freeze-thaw obeyed a two-parameter Weibull distribution, and the P-S-N curves at various reliability probabilities correlated well with the test results. The safety coefficient of PE-ECC varied with changes in freeze-thaw conditions, necessitating an increase in the safety coefficient to assure structural safety in locations with more severe freeze-thaw damage. The results of this study can serve as a reference for the development of freeze-thaw-resistant designs for PE-ECC structures in future applications.