How does a frost on concrete
For fresh concrete frost danger.Concrete is very sensitive to cold.And it affects primarily on setting time and curing speed.When the temperature drops from 20 to 5 with setting slowed down to 2 & ndash;5 times.But it appears particularly sharp slowdown in the further decrease in temperature & ndash;to 0 C.However, if you restore a normal temperature curing, the curing rate of re-taking the usual.
In that case, if the temperature of concrete falls to 0 C, at a temperature hardening stops completely.This is primarily due to the fact that the freezing of the concrete contained in it is the free water freezes and slows the formation of cement stone.From this it follows that the cease and hardening of concrete.Freezing in the concrete, water increases in volume by 9%.As a result, the pores of the concrete begins to develop a lot of pressure.This is what causes the destruction of the structure has not yet hardened concrete.Accumulated on the surface of grains of coarse aggregate during the freezing water forms a thin film of ice that separates the surface of the aggregate from contact with cement paste.Subsequently, many times getting worse monolithic. In that case, if the freeze:/ / Beton2006.ru / list / Rastvor-i-beton / Beton-BSG-M.html "> concrete at an early age, the ice crystals would destroy many of the cement glue.If mixing the concrete was carried out before freezing, and hardening of concrete has not yet begun, it will not start and after freezing.But if the hardening began, it shall be suspended until the free water in concrete will be in the form of ice.
When thawing frozen concrete free water into a liquid, and curing resumed.In it occur the same process as before freezing, but with the changing structure.These changes in the structure of concrete reduces its strength and adhesion to the reinforcement.The ultimate strength is the lower than before the concrete was subjected to freezing.
The most dangerous period in the freezing concrete of cement.Concrete is also detrimental and repeated freezing and thawing it in the initial period of hardening (thaw and freeze).