Are there other ways to seal concrete cm e c?

For many years, builders are looking for the best method of laying concrete with a minimum amount of mixing water. In addition to the vibration of concrete, there are other effective methods of compaction. They are called by a mechanical dewatering. These include: pressing, centrifugation and vacuum drying. All of these methods are a general principle: the concrete mixture is kneaded in water in an amount sufficient to ensure that its installation could be conducted without difficulty. And after placing unnecessary for curing water in some way removed from the concrete.

The simplest method of dehydration is pressing. Its mission - to squeeze out the excess water from the concrete before it is laid in the case.To do this, one of the walls of the mold made of a porous, permeable to water and impermeable cement. The porous wall must have high strength. At high pressure in the concrete surface water is pushed through the pores of the concrete wall and compacted. This process is similar to wringing the washing machine. The disadvantage - its duration.

And what is the centrifuge method? Under this method, the concrete mixture is placed a cylindrical tube, rotating at high speed. Centrifugal force throws the placeholder on the wall forms. Water, as the smooth, gets in the center forms, from dripping. Concrete is also located on the inner wall forms a dense layer of uniform thickness with a minimum of water. This method gives a very high strength concretes. With his help produce concrete pipes and poles for power lines.

Rather perfect way to dehydration is a vacuum. Of laid concrete removed excess water through the permeable wall formwork. On the outer surface of the casing to vacuum.

Suppose you want to make a flat horizontal plate to the formwork. At the beginning of a concrete mixture with enough for easy installation of water fill the formwork. At the top of the free surface of fresh concrete formwork set vacuum shield, that is mounted on a frame with her strong bars, wire mesh and cotton filter. The upper bound of the frame hermetically closed sheet metal. Thus formed cavity is attached to a vacuum pump. The shield is made airtight by the line of contact with the surface of the concrete. To control the vacuum to vacuum the wiring at some distance from the input board is connected with a pressure gauge. To discharge pipe connected slop tank which receives water is sucked out of concrete.

Is evacuated from the concrete sucked the excess water. The mixture is compressed and reduced in volume. As a result of rapidly increasing the mechanical strength of concrete - the increment of concrete strength due to evacuation is 50 - 70%.

How much should harden the concrete?

So. Concrete prepared and packed into the form and dehydrated.

Now he has to harden and gain strength. After the concrete has seized, he is solid, but not strong enough.

Put it in the water or will continually wet, and the concrete strength will grow! How can this be explained? When wet it will occur chemical processes. They turn the minerals that make up the cement grains in the new stable education - hydrosilicates potassium. This conversion process is very long, and it can take place over the years. But many builders can not wait!

Therefore the set deadline hardening, after which concrete can be subjected to the design load. For concrete made in construction and hardening under natural conditions, such period is 28-30 days.

In some cases, you can allow a longer period of hardening concrete - in the construction of marine structures, dams, dikes, embankments, bridges, etc. 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 may take into account 90-days strength of concrete, it is about 20% above the 28-day.

But after the target date set concrete continues to harden and gain strength, however, is much slower. This process is slow hardening in the calculations is not considered. Increase the strength of concrete in time, exceeding the established target dates hardening, turns out to be a guarantee of the reliability of concrete and reinforced concrete structures.

High temperatures (80-90 º C) speed up chemical reactions in concrete. For example, if the concrete steamed, ie warm in wet conditions at a temperature 12-16 hours, you can get concrete with a strength equal to 65-70% of the 28-day strength of the concrete. It was well received by the factory manufacturing concrete products. And if you raise the temperature even more? Does accelerated curing of concrete? Yes, so much so that at 170-180є C for 12-16 hours are the same as the concrete strength increases, which will exceed the annual level of strength.However, with such a strong heating of concrete dries quickly and becomes harden. This is explained by intense evaporation of water contained in the concrete. To "slow down" the evaporation of water, it is necessary to provide a heating chamber (autoclave) high vapor pressure (about 0.8 - 1.2 MPa, or 8 - 12 atm.). This process is called Hygrothermal Processing Park the pressure or autoclaving concrete. In this case, you can replace cement lime and coarse aggregate - sand without sacrificing product quality.