Prestressed compressive strength model of engineered cementitious composite subjected to freeze–thaw damage in cryogenic freezing state

Engineered cementitious composite (ECC) is characterized by excellent strain-hardening properties and strong crack-control abilities. However, in the freezing-thawing environment of some cold regions, the concrete materials, including ECC, are subject to varying degrees of freeze–thaw (FT) damage. This paper investigates the impacts of the cryogenic freezing environment on the evolutionary mechanism of the pore structure and compressive properties of ECC. A nuclear magnetic resonance (NMR) T2 spectrum experiment and uniaxial compression experiment at −18 °C were conducted on ECC with 0 to 300 freeze–thaw cycles (FTs). The results indicated that, as the number of FTs increased, the distribution curves of the NMR T2 spectrum exhibited three peaks. Meanwhile, the drop rate of the compressive stress–strain curves in the freezing state was less than that in the thawing state, and the compressive strength, elastic modulus, and peak strain in the freezing state were higher than those in the thawing state, respectively. Based on the elastic mechanics theory and experimental analysis, the pore frost heave stress equivalence and cryogenic freezing strength equivalence were proposed, and the prestressed compressive strength model of ECC with FT damage in the cryogenic freezing state was developed. It was found that the model prediction results were well consistent with the experimental values.