When fresh concrete is exposed to extremely low temperature, the free water in the concrete is cooled below its freezing point and transforms into ice, which causes decrease in compressive strength of concrete. When freezing takes place after a proper precuring time, the decrease in compressive strength does not occur. Of the many influencing factors, the age of concrete at the beginning of freezing, water-cement ratio, and cement-type are significantly important on the loss of compressive strength.
In this study, tests were performed to examine how these factors affect the compressive strength of concrete frozen at early ages and investigate the source of frost damage in fresh concrete. The results from the tests showed that the loss of compressive strength decreases as the beginning of freezing was delayed and water-cement ratio was lower. In addition, the test result showed that concrete made with type III cement was less susceptible to frost damage than concrete made with ordinary portland cement and freezing damage occurred through the formation of ice lenses. Growth of ice lenses requires a steady supply of free water. In other words, the frost damage of fresh concrete is dependent on the amount of the free water in the concrete before freezing. The freezable water exist in capillary pores so that the frost resistance of fresh concrete can be determined by means of the saturation degree of the capillary pores. The saturation degree of capillary pores can be expressed as a function of hydration degree and water-cement ratio. And hydration degree of fresh concrete can be acquired from adiabatic temperature rise curve which is expressed as a function of time. The time when saturation degree of the capillary pores is reached the critical saturation degree which is about 97% is the precuring time required to prevent frost damage.
Based on the concept of critical saturation degree of the capillary pores, a method to predict the precuring time required to prevent damage of concrete frozen at early ages was suggested.
