The mechanical strength of road surfaces allows them to be rationally used in house construction as the main element of the foundation for buildings, garages and agricultural buildings.
What advantages and disadvantages does this material have for the base, what type of soil can the slabs be used on, as well as calculations and a detailed description of the laying technology in the current article.
Scope and calculation of foundations made of road slabs
Road slabs are used as a foundation for construction in areas with soil that has low bearing capacity or is highly moist. Such a foundation is also suitable when there is significant freezing of the soil, or when there is a possibility of horizontal movement.
Road slabs
Ready-made road slabs are high-strength reinforced concrete products that are resistant to a variety of external destructive influences. They are used as a foundation for light structures:
- low-rise houses, dachas and cottages (up to 2 floors);
- garages;
- courtyard buildings (sheds, summer kitchens);
- baths
When they are used, pressure from the structure to the ground is transmitted evenly over the entire supporting area.
Before starting construction, it is necessary to determine the thickness of the base. It is determined by the magnitude of the future load on the supporting structure. So, for a garage or shed, a foundation with a height of up to 0.2 m is sufficient, but for a house this parameter should be more than 0.25 m.
When calculating the base parameters, take into account:
- the weight of the future building with all equipment, furniture and other items;
- snow load;
- soil properties;
- climatic features of the region.
Due to the large support area, the base of road slabs has a high load-bearing capacity. The individual elements are connected to each other using reinforcement, which ensures good structural rigidity.
The heavier the building, the more massive the foundation for it should be. The thickness of the supporting structure determines the stability of the structure being built. Road slabs produce a solid base that can withstand fairly large loads.
Preparatory work
When choosing the thickness of the slabs, it is important to focus on the lightness of the structure. For baths and summer kitchens, 100 mm products are quite suitable. If you plan to build a large house, you will have to choose slabs from 200-250 mm.
To begin, mark the area. This is done based on the parameters of the design documentation. First, they place the first point on the site. From it you need to measure a line equal to the length of the house. Based on it, a line is marked that will determine the width of the foundation. Based on these lines, the entire area for future construction is marked out. Be sure to drive pegs into each corner of the resulting rectangle. They will help determine the accuracy of the site geometry. A cord is pulled onto the pegs - diagonally and along the edges of the future foundation. If the diagonal segments are equal, the marking is done correctly.
Then you need to dig a pit. It is prohibited to install road slabs directly on the ground. The height of the pit should be 20-25 cm greater than the depth of groundwater rise. It differs in different regions. The value taken as a conventional value is 1.5 m - this parameter should be guided by.
The bottom of the pit must be level. To do this, it is leveled and compacted. The walls should also not have recesses. After compaction is completed, a sand cushion is applied. The bottom of the pit is covered with a 15-20 cm layer of sand. Then the sand is moistened and compacted. The readiness of the sand cushion can be determined by the footprints left by the boots. If they are not there, you can proceed to the next stage.
Pros and cons of the foundation
Road slab foundations have both advantages and disadvantages. They are presented in the table below.
| № | Advantages | Flaws |
| 1 | simplicity and relative speed of construction | It is necessary to use lifting equipment during construction |
| 2 | high degree of strength of the erected supporting structure | it is problematic to determine the quality of used building materials |
| 3 | lower cost compared to a monolithic reinforced concrete base | limited weight of the structure being built |
| 4 | small amount of excavation work | the construction of a basement is often not provided for |
The popularity of the material is due to its relative cheapness and ease of installation. It is better to use new products with established quality for the house, and used building materials are suitable for outbuildings.
Laying slabs
Classification
The production of road reinforced concrete slabs is carried out in accordance with the regulatory requirements of the GOST 21924.0-84 standard, according to which the products are graded into three main categories:
- RDP are the most popular and widespread reinforced concrete slabs of a universal type, which are used when it is necessary to construct permanent and temporary roads with an average load level of no more than 6 tons per wheel. The products can be reused after dismantling. Their load capacity is 10 - 30 tons and depends on the brand of concrete used in the manufacture. Precast concrete products are designed for operation in severe frost conditions – down to – 50 °C;
- PDN – products made on the basis of reinforced concrete with a prestressed reinforcement structure. Having increased load characteristics, the dimensions of the reinforced concrete products are 6000 mm in length and 2000 mm in width with a weight of 4200 kg. Due to the strength of the body due to the rigidity of the reinforcement frame, the products are recommended for use in heaving and soft types of soil;
- PAG is the most durable type of airfield slabs. The average weight of a product unit is 5 tons. Precast concrete products are focused on the construction of roads for heavy types of transport, as well as the construction of runways for aviation (PAG-18, as well as PAG-14). Structurally, the elements can have a smooth or corrugated surface, providing different grip on vehicle wheels. In the production of products, concrete mortar with grades from M350 to M400 is used. The maximum load reaches 75 tons. The products can be used at temperatures down to -35 °C.
Construction technology
The technology involves carrying out work in several stages. Initially, you need to stock up on the following required tools and devices:
- grinder;
- level (laser, water or construction);
- bayonet and shovel shovels;
- mason's trowel;
- crowbar;
- tamping;
- cord (rope), pegs;
- roulette.
The technology for constructing a supporting structure for a building from a road slab is similar to creating a monolithic slab. The pre-built area is cleared of debris, stones and vegetation.
Carrying out excavation work, waterproofing slabs and insulation
Construction work begins with marking the construction site. According to the plan, stakes and rope mark the perimeter of the foundation. In this case, the diagonals of the resulting contour must be equal to each other, and the angles must correspond to 90 °.
Laying insulation
After marking, they dig a pit with shovels or an excavator of the required depth. Then the following work is carried out:
- cover the leveled bottom of the resulting excavation with a sand cushion 0.2-0.25 m thick, which is carefully compacted, regularly moistening it;
- the sand is covered with a waterproofing coating on top;
- thermal insulation is laid on it to minimize heat loss through the concrete floor;
Roofing felt and other rolled products are often used as waterproofing materials. The strips are laid with an overlap of 10-15 cm, and the seams are sealed with a burner. At the same time, the sides also extend onto the walls of the pit. This ensures a high degree of tightness.
The insulation can be polystyrene foam or extruded polystyrene foam. The ends of the slabs are also thermally insulated.
The sand cushion, and accordingly the soil underneath it, should be well compacted to reduce the likelihood of subsidence during further operation of the building.
Waterproofing will protect concrete from the destructive effects of moisture and eliminate the penetration of dampness into the house. Insulation helps reduce heat loss through the concrete floor of a building.
Installation of slabs and concreting
After laying the sand cushion, waterproofing and insulation, the installation of the slabs begins. For this, different lifting equipment is used, since these reinforced concrete products are heavy.
Installation of slabs on a waterproofing coating
During installation, the elements of the supporting structure are placed tightly to each other. When all the foundation has been laid out, then do the following:
- install the formwork, fixing it with stops;
- prepare concrete solution;
- seal all the seams with it;
- make a screed layer of about 3 cm, leveling the solution using a rule and a trowel;
- periodically moisten the concrete (so that it sets evenly) and cover it with plastic film;
- After the screed has gained the required strength, the shields are dismantled.
- For formwork, lumber 2.5 cm thick is suitable. The boards in the panels are connected using self-tapping screws or nails.
A small gap is left between the formwork and the foundation structure for filling with mortar.
During work, check the level of the subfloor to ensure it is level.
The concrete will fully set in about a month (the time depends on the climatic characteristics of the region). Only after this they begin to build the building.
High quality material
You can prepare the working solution yourself or buy it ready-made. In the first case, you will need cement, sand and small crushed stone. The components are mixed in a ratio of 1:3:2, respectively. Stir the solution until a homogeneous mass is obtained.
You can lay a reinforcing mesh on top of the slabs, and make a screed on top of it. This will further strengthen the structure.
Insulation and waterproofing
After the cushion is completed, formwork is performed. It is best to make it from boards 25 mm thick. They need to be connected with screws and nails. To make the formwork stand more firmly, it is fixed with stops.
Then bricks are laid at the bottom of the pit. They should be placed over the entire area of the base. Waterproofing is laid on the brick layer. Roofing felt is used for this purpose. It must be laid over the entire area of the base and overlapped at the edges by 15 cm. The seams are sealed using a gas burner.
Then a layer of thermal insulation is laid out. It is made of polystyrene foam or extruded polystyrene foam. It is important to pay attention to the insulation of the ends of the slabs. To do this, waterproofing is attached to the inside of the formwork.
Construction guidelines
To get a high-quality, reliable foundation from road slabs, you need to follow some simple recommendations. Their practical implementation will also provide the base with a longer service life.
The main advice from professionals is as follows:
- it is necessary to use high-quality materials for construction;
- for formwork it is advisable to use smooth boards of the same thickness;
- sealing of seams and screed should be done with concrete of at least grade M300, which will provide greater strength to the supporting structure and improve the adhesion of its elements;
- it is necessary to lay the road slab completely under the entire building in order to minimize the pressure on the ground;
- costs can be reduced if bitumen is used instead of roll waterproofing;
- a sand cushion is mandatory on loose or clay soils.
If you follow the technology and the recommendations outlined, then the use of ready-made reinforced concrete products allows you to obtain a durable, strong foundation.
The process of laying road slabs is shown in the video below.
For a house no more than 2 stories high or outbuildings, a base made of road slabs is a reliable support on various types of soil. In terms of strength, such a foundation is inferior to a slab monolithic one, so it is suitable only for relatively light structures. But economically it will cost less, and its construction will also take less time. You must first correctly calculate the future load in order to determine the required slab thickness. This will help, together with compliance with construction technology, to avoid deformation and destruction of the created supporting structure.
Laying slabs
The slabs are laid on the created base. The distance between them should not be more than three centimeters. The exit points of the rings are connected with wire. It is useless to weld them - if there is serious movement of the ground, the joints will still be broken. A reinforcement frame of the required height is placed on top of the slabs. Afterwards, concrete is poured over the entire area of the future foundation.
It is worth preparing a concrete mixture from cement (1 part), crushed stone (2 parts) and sand (3 parts). Each component is introduced gradually, with the addition of water. The result should be a homogeneous mixture, not too thick and not too thin. It is necessary to fill all the resulting voids with the solution, including those that appear between the slabs and the formwork. This will not take as much mortar as would be needed to create a monolithic foundation without the use of slabs.
This technology for laying road slabs under the foundation of a residential building will ensure the greatest strength of the foundation. If you are laying a recessed strip foundation, you should use two slabs as blocks, located 10 cm from each other. They are buried in the ground on their edges. Concrete mortar is poured between the slabs.
In order for the foundation of the house to serve for many years, it is worth correctly calculating the load on the foundation. Only light wooden or frame houses can be built on road slabs. This foundation is suitable for all types of soil, which is a significant advantage over other types of foundations.
