Concrete preparation for the foundation: options and their application
Qualitatively executed concrete preparation for the foundation usually precedes the stage of erection of the foundation foundation. Its main task is to exclude the possibility of leakage of cement laitance, which can occur during the pouring of the base with concrete mortar. Concrete preparation is necessary to obtain a reliable foundation with the longest possible service life. Among other things, such a design will allow the best way to redistribute the forces acting at the depth of the soil.
Arrangement of the foundation pit
Under this stage, work is carried out, the main purpose of which is to bring the adjacent soil to the required condition, providing for such a bearing capacity that will be sufficient to withstand the expected load. As a result of the work, the sole of the foundation base should be tightly clasped with soils.
The main stages of preparing the soil for the foundation:
- To begin with, a pit is being equipped;
- The bottom of the formed pit must be cleaned;
- The next step is to compact the bases;
- Next, the soil is dried or moistened, which depends on the process of compaction work.
The trenches under the foundation base are most often equipped manually. This is done before starting the steps aimed at preparing the foundation.
Options for pillow under the foundation: the use of lean concrete
The main purpose of concrete preparation made from this material is to protect against potential cases of subsidence of the soil, as well as to facilitate the progress of construction work. In addition, the tasks of a lean concrete pad include the formation of the best conditions for ensuring the strength characteristics of the structure. If you look at the financial costs, then the use of this material is not always profitable from an economic point of view. Although this method has gained quite a wide popularity and is one of the basic ones.
Materials - Lean Concrete
At its core, lean concrete is a type of cement mix that contains no more than six percent B15 grade cement. As for the filler, gravel or gravel plays its role in this solution. The resulting mixture is poured to the very bottom of the dug pit. It is necessary to place a small layer of such a solution there. It is also worth noting that the thickness of the concrete pour depends on a number of different factors. Here the type of soil, the estimated weight of the building, the possible level of groundwater occurrence, and others take place. All requirements are set out in the collection of building codes and regulations - SNiP. In general, the recommended thickness for pouring is in the range from forty to one hundred millimeters.
With the use of such a design, it becomes possible to avoid the deformation processes of the reinforcing cage, as well as the slab mesh. This is done by the above-described concreting. It makes sense to add various frost-resistant compounds to concrete in cases where the concreting process is carried out in a cold season. It should also be noted that the concrete preparation of the foundation base in winter is much easier, especially compared to crushed stone preparation. This is due to the heating of bitumen, which is very difficult in the process of pouring frozen gravel.
The use of crushed stone preparation
A gravel and crushed stone pillow is relevant in cases where monolithic slabs and pile-support grillages are equipped. In these situations, the plates form a cushion, the layer thickness of which is in the range from one hundred to two hundred millimeters.
What kind of preparation should be used in various cases is not clearly regulated by building codes. There are two types of consideration. For crushed stone preparation, for example, it is recommended to make a thickness of no more than two hundred millimeters. In cases where a monolithic slab or other types of such structures are used as a foundation base, involving reinforcement by means of frame structures, then concrete preparation for the foundation will become relevant for them. It is also worth noting that crushed stone preparation means filling the pillow with hot bitumen. Thus, a film is created and the structure is completely saturated.
Use of profile membranes
Profiled membranes are among the modern technologies for preparing the foundation base. According to the manufacturers of profile membranes, they are able to replace not only crushed stone, but also concrete preparation. The use of such material avoids the so-called "wet" types of work. At the same time, there are significant cost savings. At the same time, the profiles are very easy to install, which contributes to a noticeable acceleration of the preparatory work.
Lean concrete is referred to as grade B7.5. This name was given to it due to the fact that it contains cement in very small quantities. Such a concrete mixture is used only in the process of arranging the foundation for the foundation. If it becomes necessary to carry out other types of construction work, concrete with improved properties is used, in particular with a higher concentration of cement in the solution.
As part of the complex of actions associated with preparing the soil for the foundation, it is first necessary to pour a layer of sand, evenly distributing it along the bottom of the excavated pit. The next layer is poured with cement, which also needs to be leveled using a rake. Next, you need to spray a certain amount of water. The resulting mixture must also be leveled and compacted. After completing all of the above work, lean concrete should be covered with a film of polyethylene, this will protect it from excessive drying.
The sequence of actions for the arrangement of concrete preparation
We will analyze step by step how to make concrete preparation for the foundation. So, you need to act as follows:
- The first step is to mark the construction site;
- The next step is to level the site;
- A ten-meter layer of gravel is poured;
- The pillow is compacted using a vibrating plate;
- The next step will be the arrangement of the formwork. As for its height, it is calculated based on the parameters of the concrete layer. At the same time, the height should not exceed a thirty-centimeter mark;
- This is followed by the installation of the formwork structure;
- As part of the next stage, concrete is poured;
- In order to strengthen the pillow, its reinforcement is performed. For this, rods are used, the cross section of which is not less than eight millimeters;
- By means of a vibrating plate, concrete is rammed;
- The final stage of this work is the installation of reinforcing bars connecting the pillow and the foundation itself. They protrude about 25 centimeters above the concrete surface. A deviation of five centimeters is allowed.
It should be noted that the manufacture of concrete preparation for the foundation makes it possible to obtain a more reliable structure. A concrete pad can be used for almost all types of foundations. It is possible to perform reinforcement in it, but this is not a prerequisite in all cases. In fact, this does not play a special role in the performance of the resulting structure. But there is one feature, which is that an unreinforced pillow is very limited in size.
According to building requirements and standards, the minimum thickness of concrete preparation for the foundation, if reinforcement has not been made, should be at least fifteen centimeters above the soil surface. Reinforcing mesh can be located in the most convenient way. It is performed with rods of eight millimeters in thickness, which are connected to each other by means of a wire. In addition, the welding method can be used for these purposes. Reinforcement, among other things, makes it possible to strengthen the lower part of the concrete preparation, which is a good advantage that characterizes the structure in question.