Special concreting methods: detailed description of possible

During the construction of various objects, sometimes there are certain conditions under which conventional methods of construction are either unavailable or inefficient and in such cases special concreting methods are used.

These methods include:

• туркретирование;
• vacuuming;
• as well as an underwater method of concreting objects, which is successfully used in civil and industrial construction.

Below this will be discussed in more detail, and in addition, you can watch the video on this topic in this article as an addition to the material.

Description

Brief description of special methods

• If there is a need to arrange any storage, reservoir, or construction occurs in the zone of intensive influx of groundwater, then in such cases an increased density of concrete structure is required.. This is achieved by separate concreting by vibration: the vibration, gravitational, and vibratory pressure method. Here, cement-sand mortar is injected between large aggregates that were previously laid in the formwork, in addition, when vibrating the pressure, additional vibration is used, which more condenses the mortar.
• In those situations when there is a need to perform work under water, at a depth of up to 50 m, concreting is used by the VPT method (vertical movement of the pipe). The essence of this technique is as follows: concrete is supplied to pre-established forms through pipes with a diameter of 200 to 300 mm, and they are lowered to the very foundation. When you want to increase the thickness of the layer, the pipe is raised, that is, reduce the number of sections.
• When the depth does not exceed 20 m, in such cases the method of BP (ascending solution) is used, which can be either pressure or non-pressure. To do this, they fence off a certain area and throw stones there, where steel pipes with a diameter from 37 to 100 mm are installed at a certain interval. For these pipes, under pressure or without it (by gravity), cement-sand mortar is poured in, which fills the voids between the previously thrown stones.
• Also, if it is necessary to fill to a depth of no more than 20 m and at the same time the class of concrete will not exceed B20, then a concreting technology is used, called bunker laying.. In such cases, concrete floors or slabs are placed on the bottom of the reservoir as a base, and the solution is poured onto them with a grab. In this case, between the drop-down box and the base, the minimum distance is kept that allows such work to be performed.
• At a depth of 1.5 m, when the construction area is large enough and the grade of concrete does not exceed the class B25, ramming is performed. This is done on small fenced-off areas, since the area is large, the solution is delivered to the site using a pipe or a grab, while respecting the minimum distance to the base. The tamper is made evenly so as not to disturb the process of setting the previously laid section, and the instruction requires that the distance to the water mirror does not exceed 25-30 cm.

• При нанесении тоннельной отделки, нанесении защитного слоя для предварительно напряжённых резервуаров, использовании пневмоопалубок, усилении и ремонте ЖБК и тому подобное, применяется «мокрое» и «сухое» торкретирование поверхности. «Мокрый» способ или пневматическое бетонирование подразумевает нанесение раствора на поверхность под давлением - сжатый воздух подаёт смесь в сопло, где так переходит во взвешенное состояние, после чего попадает на обрабатываемый участок. «Сухой» метод похож, только здесь в насадку подаётся сухая смесь, которая там размешивается водой, затворённой в сопле, после чего попадает на поверхность в виде раствора.

• For interfloor ceilings, floors, arches, shells, spatial and vertical structures (diaphragms, columns, walls, partitions, etc.) use the method of vacuuming. Its essence is to remove from the compacted solution up to 10% -25% of the water that has been closed using vacuum shields.

Underwater concreting

Note. Underwater method is the laying of the solution under a layer of water, when drainage work is not performed. The most common and productive is considered to be HWP.

In this case, underwater concreting - the technology of vertical movement of the pipe implies work at a depth of 1.5 m to 50 m in the pit, which is fenced from running water.

For arranging such fencing, you can use special spatial formwork made of wood, concrete products, reinforced concrete structures or metal, as well as any larger shells - piles, knitting, grooves, and so on. In this case, such a structure must be impermeable to the cement-sand mortar.

To transport the mixture to the destination, seamless steel pipes from 200 mm to 300 mm in diameter are used, and the line is not solid, but is assembled from links of 1-3 m in length.

The assembled pipeline is fixed to the faucet or winches that are behind the pitted fencing, with a funnel mounted at the top to receive the mixture, and below, to prevent water from entering, install a valve that can be opened while on the scaffold. One such pipeline can serve the site up to 12 m in diameter.

After the pipes are lowered to the base and the lower valves are closed, they are filled to the top with concrete. After the dispatcher opens the valve, the concrete spreads over the formwork, rising above the edges of the lower link - this happens under the columnar forced pressure of the mixture until the level in the pipe and formwork level off. The solution can be fed through the channel with a pneumatic blower or directly from the concrete mixer.

Depending on the thickness of the area to be cast, the end of the pipe must be constantly immersed in the solution, as required by the concreting technological regulations: at a depth of 10 m - by 0.8 m, and at a depth of up to 20 m - by 1.5 m. as a mounted platform, it is filled with a solution, the pipeline is lifted upwards, gradually separating from it one by one link, but at the same time it is important to ensure that water does not get inside.

After the required thickness of the site is reached, the pipe is completely removed from the installation site.

When the solution according to the method of vertical displacement of the pipe is stacked with vibration, it needs mobility, which is possible to measure by sinking of a cone by 6-12 cm, but if this happens without vibration, then 16-20 cm of shrinkage will be needed. The mixture is made of gravel, or add 2-3 parts of crushed stone to it, while using a plasticizer without fail.

In order to avoid force majeure circumstances when installing arrays with a volume of more than 200 m³ method of vertical movement, to begin with flooded test structures under water. These are experimental blocks with a volume of 3 m.³, on which there is a possibility of modes of operation and the quality of concrete, since the cost of such testing contributes to the fact that the final price is lower.

The method of the ascending solution or BP is shown in the upper schematic diagram: the solution is pumped into stone fill (crushed stone, gravel) through pre-installed steel seamless pipes from 37 mm to 100 mm in diameter. Such a mixture can be cement, cement-sand, or cement with various additives.

The mortar fills the voids between the stones, rising from the bottom up - this displaces water and forms a concrete monolith - this is also called the injection injection molding method.

In those cases, when BP is produced in enclosing mines, then vertical spaces of the mine, which are made of rolled metal - rail, channel, tavr, etc., are mounted in the formwork space. After that, a large stone is poured, and then everything happens in the same way - the solution displaces water, turning the structure into a monolith.

At a depth of 1.5 m for concreting objects with a large area, where the grade of concrete is not higher than 300, the method of tamping or vibration is used. In this case, the sediment of the cone should be about 5-7 cm - the solution is fed through a pipe. Pay attention to the picture - it can be seen that the tamper begins with an underwater slope, with an angle to the horizontal of 35? -45 ?.

Торкетирование

Примечание. Торкетированием бетона называется технология струйного нанесения раствора на поверхность при помощи сжатого воздуха. При этом цементно-песочная смесь или торкрет могут укладываться, как в один, так и в несколько слоёв.

This method is usually used to strengthen the surfaces of structures that are not strong enough (thin) walls - these can be one-sided formwork, tanks, domes and vaults. In addition, gunning serves as protection against the penetration of moisture in underground structures (basements, warehouses), for embedding (sealing) of seams and during repair and restoration work to eliminate defects.

The cement-sand mixture is prepared separately here and with the help of a compressor under pressure (compressed air) through the hose it is fed to the nozzle, where water from the tank simultaneously flows - also under pressure.

Получается, что увлажнённые частицы смеси вырываются из насадки со скоростью 100 м в секунду, ударяется о поверхность и прилипает к ней. При этом неизбежно возникают потери, так как не все частицы остаются на обрабатываемой поверхности - некоторые отскакивают и оседают на пол - их называют «отскоком».

It is noteworthy that the ceilings and walls are shotcrete gradually, in several layers, while the floor can be applied to the mixture to full thickness. The time interval between the application of gunning is set by the laboratory and it is determined by the rate of hardening of the solution, that is, each new layer should not destroy the previous one.

But in order for adhesion to be optimal, the gap should not exceed the time of full setting, otherwise the percentage of rebound will increase.

Vacuuming

Примечание. Vacuumingм называется процесс удаления свободной воды и воздуха из раствора, который только что уложили. Осуществляется это с помощью понижения давления, то есть, образованием вакуума для внешних и внутренних слоёв конструкции.

In order for the process of cement hydration to occur, it is enough that it contains only 20% of water from its total mass - all the remaining mixing water is used to impart certain technological properties, such as elasticity and mobility of the mass.

The problem is that water occupies a certain space in the solution, forming pores, therefore, after its evaporation, empty spaces remain there, which lowers the density of the material. Therefore, a special method is used to remove shuttered water and air at construction sites - this is the mechanical removal of these elements from the freshly laid solution.

To this end, between the mortar and concrete formwork, a thin cavity is equipped with a woven and woven mesh, from which air is pumped out by a pump. There, due to uneven pressure, mixing water begins to flow along with the air from the concrete, which is constantly pumped out, as shown in the upper schematic figure.

Conclusion

In conclusion, I would like to draw your attention to those who are looking for concreting by the method of freezing - this method does not exist! There is a laying of concrete in the cold, in which electric heating is used, using for this purpose heating formwork, infrared radiation, electromatics, as well as anode or wire (PNSV) heating by a step-down transformer.