Durability evaluation of engineered cementitious composite subjected to salt freeze-thaw cycles

This study aimed to investigate the evolution mechanisms of durability and mechanical properties of engineered cementitious composites (ECC) under the salt freeze-thaw cycle. A multi-scale experimental program was then carried out to evaluate the time-dependent variations in surface damage, microstructural characteristics, and compressive performance of ECC. The test results revealed that the macroscopic damage of ECC exhibited distinct spatial evolution-initiating at the surface (slurry spalling) and advancing inward (fiber-matrix bond layer exposure) as the cycle number climbed, with 100 cycles identified as a critical threshold. The salt freeze-thaw effect promoted the transformation of transition pores within ECC into macropores, and a dynamic evolution mechanism was analyzed. Notably, the physical phase changes of the salt solution dominated the pore expansion at a high cycle number. After 200 cycles, the uniaxial compressive strength and elastic modulus of ECC decreased by approximately 29.34 % and 36.70 %, respectively. The degradation of fiber-matrix interfacial bonding strength shifted the compressive toughness of ECC from strength-controlled to deformation-controlled behavior, primarily due to the transition from bond-slip to friction-slip response at the interface. Finally, a degradation model was developed using an elastoplastic three-phase sphere model, which could be used to predict the residual compressive strength of ECC at varying porosity levels well. The findings of this study can provide valuable technical insights and theoretical foundations for the maintenance and strengthening of concrete structures in cold and saline regions.