Layers of the road during construction: device and norms

The immediate quality and durability of the highway are determined by the accuracy of compliance with the laying sequence. roadwear. Errors in choosing the thickness of the gravel pillow or ignoring the requirements for soil compaction lead to rapid destruction of the asphalt cloth, the appearance of tracks and cracks after one operating season. A properly formed multilayer structure distributes the load from the wheels of the vehicle, transferring it to the ground base without critical deformations.

Modern building regulations, such as SNIP 3.06.03-85 and updated versions SP 34.13330There are strict requirements for each level of the pie. Engineers are obliged to take into account not only the intensity of traffic, but also the climatic features of the region, the level of groundwater and the frost resistance of materials. Violation of technology at the stage of formation of the lower layers hidden from the eyes, will inevitably affect the upper finishing surface, making useless any expensive repairs.

The fundamental principle of construction is the gradual decrease in the strength of materials from the bottom up and increase their frost resistance. Foundation ground It takes on primary pressure, so its load-bearing capacity should be maximum. If the natural soil does not meet the requirements, it is replaced or strengthened with special additives such as cement or lime, which allows you to create a stable platform for further work.

Preparation of earthbed and geotextiles

The first step in creating a reliable road is the formation of a ground-clothIt is the foundation of the entire structure. Engineers excavate the soil or, conversely, build a mound, carefully sealing each layer until a density coefficient of at least 0.95-0.98 is reached. The quality of this stage is critically important, as any subsidence of the soil will lead to fractures of the overlying layers of asphalt and concrete.

It is widely used to separate dissimilar materials and prevent their mixing. geotextile. This synthetic material has high tensile strength and excellent filtering properties, which allows water to escape from the structure without washing out small particles of the soil. The laying of geotextiles is especially relevant on weak and hollow soils, where the risk of deformation is high even with the observance of other technologies.

⚠️ Warning: Laying geotextiles on an uneven base with sharp stones or debris can cause them to rupture and lose functionality. Before rolling the material, the surface must be carefully aligned.

An important aspect is the provision of drainage from the surface of the earth. Water stagnating at the base of the road expands when it freezes and causes swelling, and when it melts, the structure is blurred. Therefore, the formation of transverse slopes and the device of drainage systems at this stage are mandatory procedures to ensure durability.

Underlayer and pillow arrangement

The prepared earthen cloth is laid down sublayerIt is often called a pillow. The main materials here are sand and crushed stone, which can be used both separately and in combination. The sand cushion serves to level the surface and prevent capillary moisture from rising to the upper layers of the road.

The gravel layer, laid on top of the sand or directly on the ground, takes on the main load for the distribution of pressure from transport. The fraction of crushed stone is selected depending on the calculated load: for highways with heavy cargo traffic, large fractions of 40-70 mm are used, which are propped with smaller crushed stone to create a monolithic structure.

The process of compacting the cushion is a key point determining the bearing capacity of the structure. Use of the vibrating allows you to achieve the necessary density at which the crushed stone ceases to move under load. Insufficient sealing will lead to a shrinkage of the road during operation and the appearance of longitudinal waves on the asphalt.

The stainless and the stainless stainless

Above the underlayer are located load-bearing bases that are often made from processed materials. It can be crushed stone, reinforced with cement or bitumen, or gravel mixtures. Such materials have high strength and frost resistance, which allows them to work effectively in harsh climates.

In the case of cement-base It is important to observe the temperature regime and hardening times of the mixture. Cement binds the particles of rubble, creating an artificial stone that is practically free of shear deformations. This is especially important for public transport stops and areas with heavy truck braking.

The thickness of the load-bearing layers is calculated individually for each project, taking into account the expected flow of transport. Errors in the calculations can lead to the fact that the road will not withstand the design load, and the process of destruction will begin, which cannot be stopped by cosmetic repair of the coating.

Asphalt concrete covering: lower and upper layers

The final stage of construction is laying pavementIt is usually made up of two layers: the lower (binding) and the upper (wearing). The lower layer is made of coarse-grained asphalt concrete, which provides a strong bond with the base and distributes loads.

The upper layer is made of fine-grained or porous mixtures with a high bitumen content and special additives that improve the grip of the wheels with the road. It is this layer that is directly exposed to tires, water and ultraviolet light, so the requirements for its quality are imposed.

⚠️ Attention: The temperature of the asphalt mixture when rolling should not fall below 80-90 degrees Celsius. Laying the cooled mixture will lead to poor sealing and rapid painting of the material.

To ensure the monolithic structure between the layers must be made spilling bitumen-emulsion. This creates an adhesive film that prevents the “pie” of the road from being bundled under the action of horizontal braking and acceleration forces of vehicles. Without a high-quality bonding, the layers will work independently, which will accelerate wear.

Concrete roads and combined structures

Unlike flexible asphalt coatings, concrete-road They have a fundamentally different structure of layers. Here the main load is a cement concrete plate, which is laid on a carefully prepared base. Concrete roads have a long service life, but require a complex device of deformation seams.

Combined designs combine the advantages of both types of coatings. For example, the lower layers can be made of rubble treated with cement, and the upper layers can be made of asphalt concrete. Such solutions allow optimizing the cost of construction, while maintaining high performance characteristics of the track.

Particular attention is paid to reinforcement during the construction of concrete roads. Metal grids or fibre fibers are added to concrete to prevent cracking when stretched. The laying technology requires a continuous process and strict control over the vibration of concrete to remove air bubbles.

Quality control and modern technologies

Modern road construction is not complete without strict laboratory-monitoring at all stages. Core selection, density testing by the cutting ring method, testing of samples for compression and stretching - all this allows to guarantee the compliance of the built road with the design indicators. The use of geodetic instruments allows you to control the levelness of the surface with an accuracy of millimeters.

New technologies, such as adding modifiers to bitumen (polymers, rubber crumbs), can significantly increase the elasticity of the coating. This is especially true in regions with large temperature changes, where ordinary asphalt cracks quickly. Modified bitumens They retain their properties both in heat and in severe frost.

Automation of the installation and sealing processes is also taking a new level. Intelligent sealing systems installed on the rollers transmit data on the degree of compaction of the layer in real time, excluding the human factor. This allows for the construction of roads that last for decades without major repairs.