Abstract: During the winter construction of concrete in northern areas, the newly poured concrete often suffers damage due to sudden temperature drop. In order to study the effect of early freezing on the mechanical properties of concrete under uniaxial compression,the uniaxial compression tests of concrete under the curing conditions of different freezing temperatures (-5 ℃, -10 ℃) and different freezing moments (1.0 h, 3.5 h, 8.0 h, 24.0 h) were carried out, the full stress-strain curve under uniaxial compression was obtained, and the constitutive equation suitable for uniaxial compression of early frozen concrete was obtained by fitting. The results show that the change trend of the stress-strain curve of concrete after early freezing is basically similar to that of normal cured concrete, but in the descending section, the early frozen concrete is steeper, and the ductility and plastic deformation ability are reduced. The freezing temperature has no obvious effect on the peak stress and peak strain. With the delay of the freezing time, the peak stress first drops and then rises, and the peak strain first rises and then drops. The mechanical properties of frozen concrete after the initial setting and before the final setting are the most severely damaged. The stress-strain curve equation of early frozen concrete based on the fitting of Professor Guo Zhenhai’s model is in good agreement with the experimental curve. The most unfavorable freezing point for the peak stress, peak strain, ductility and plastic deformation ability of the early frozen concrete is around 4 h after curing.

Key words: early freezing, freezing moment, freezing temperature, full stress-strain curve, constitutive model, concrete damage