Study on Strength Model of Wastewater Concrete with Different Specimen Sizes under Freeze–Thaw Environment

According to wastewater concrete (WWC) specimens of different sizes (L = 40 mm, L = 100 mm, L = 150 mm, L = 200 mm) and different freeze–thaw cycles (FTCs) (N = 0, N = 10, N = 20, N = 30, N = 40, N = 50), the compressive strength (CS) and splitting tensile strength (STS) of specimens with different sizes under different FTCs were tested. After 50 FTCs, the maximum and minimum loss rates of CS of cube specimens were 60.07% and 24.11%, respectively. The maximum and minimum loss rates of STS were 54.76% and 17.42%, respectively. The relationship between the number of FTCs and the size of the specimen on the CS of concrete was obtained, and the damage model of WWC based on damage mechanics theory with the number of FTCs for different specimen sizes was established. Using the fitting method, the strength model of CS and STS for different specimen sizes under FTCs was established. The R2 is 0.9709 and 0.9627, the fitting performance is good, and the freeze–thaw damage (FTD) models can accurately predict the freeze–thaw damage degree of concrete under the coupling effect of FTCs and specimen sizes.