The freeze-thaw damage of concrete is caused by the volume expansion of water in concrete after freezing. When the expansion force exceeds its tensile strength, it will cause micro-cracks in concrete, and the cracks will continue to expand after repeated freezing and thawing, leading to the decrease of concrete strength until it is destroyed.
Expression method of frost resistance: it is expressed by frost resistance label, and it is expressed by the maximum number of freeze-thaw cycles that the 28-day-old stone can withstand when its compressive strength decreases by no more than 25% and its weight loss does not exceed 5% after being saturated with water at-15 ~ 200 C.
Extended data:
Methods of improving frost resistance:
1. Choosing suitable cement is an important means to improve the frost resistance of concrete. The test results show that early strength portland cement should be used. Cement has high hydration heat and the highest early-release strength. Generally speaking, the three-day compressive strength of cement is equivalent to the seven-day compressive strength of ordinary portland cement, and the effect is obvious.
2. Try to reduce the water-cement ratio and slightly increase the dosage of cement to increase the hydration heat and shorten the time to reach the age strength.
3. Mixed air entraining agent. Under the condition of keeping the concrete mixture ratio unchanged, air entraining agent can increase the volume of cement paste, improve the fluidity of mixture, improve its cohesiveness and water retention, buffer the water pressure caused by concrete freezing and improve foam. Resistance of concrete.
4. Adding early strength agent can shorten the setting time of concrete and improve the early strength of concrete. Sodium sulfate (2% of cement dosage) and ms-f composite early strength agent (5% of cement dosage) are widely used.
5. Choose aggregate with high hardness and few cracks to make its thermal expansion coefficient close to that of surrounding mortar.
Baidu encyclopedia-antifreeze