How long should the concrete to harden
After the concrete has seized, he is solid, but not strong.Put it in water or will continually wet, and the concrete strength will grow! How can this be explained? When wet it will be the chemical processes.They transform the minerals that make up the cement grains in the formation of new stable & ndash;hydrosilicates potassium.This transformation process is very long;it can be accomplished over the years.But many builders can not wait!
Therefore, set the deadline of concrete hardening, after which it can be subjected to design load.For concrete, made in construction and hardening under natural conditions, such period is 28-30 days.
In some cases, you can avoid a longer period of concrete hardening & ndash;during the construction of offshore structures, dams, dikes, embankments, bridges, and t.n.They are built very slowly, and therefore the total load to the poured concrete can be applied over a long time.In these cases, the calculations can take into account the daily 90-strength concrete;it is about 20% above 28-day.
But after the target date set:/ / Beton2006.ru / list / Rastvor-i-beton / "> concrete continues to harden and gain strength, however, significantly slower.This process is slow-curing concrete in the calculation does not take into account.Increase of concrete strength with time, exceeding the set target dates for hardening, as it is to safeguard the reliability of concrete and reinforced concrete structures.
High temperatures (80-90 C) speed up chemical reactions in concrete.For example, if it is steamed, t.e.heated in a humid environment at a temperature, 12-16 hours, you can get a concrete with a strength equal to 65-70% of the 28-day strength of concrete.That is exactly what comes with a factory manufacturing concrete products.And if you raise the temperature even more? Accelerate a hardening? Yes, so much so that at a temperature of 170-180 C for 12-16 hours are the same as the concrete strength increases that exceed the annual level of strength.However, with such a strong heating of the concrete dries very quickly and no longer to harden.This is due to intense evaporation of water contained in concrete.To ";brake ";evaporation of water, it is necessary to provide heating in the chamber (autoclave) high vapor pressure (about 0,8 & ndash;1.2 MPa, or 8 & ndash;12 atm.).This process is called zaparkoy termovlazhnostnoy processing under pressure or autoclaving of concrete.In this cement can be replaced with lime and coarse aggregate & ndash;sand without compromising the quality of products.