The appearance of conventional road surfaces, through which traffic is carried, conceals a complex structure of several layers. Each layer has its own device rules, characteristics and technological purpose. Provided that all layers are of high quality, a safe and durable coating can be obtained. This will be the pavement, which thus forms the basic infrastructure for the movement of cars.
Basic concept of pavement
The basis of roads is most often asphalt concrete and cement concrete. In both cases, the characteristics of the binder components, fractions of crushed stone, sand, and other fillers can vary. Actually, the finished structure of such coatings can be considered as a full-fledged pavement. The definition provides a common set of layers of a given coating, but each layer acts as a separate technological component, for the device of which special requirements are made. To ensure the reliability of the coating, it is necessary to ensure the conditions under which the stress arising in the structural elements from traffic does not have a destructive effect on the structure. This can be achieved by a rational calculation of the structural characteristics that technologists produce before the start of road work.
What is taken into account in the pavement design?
Typical designs are developed as universal coatings for urban roads and for suburban routes. It does not matter if it is a highway or a street. In the development of the project, the level of traffic intensity, properties of the materials used, loads, hydrological and soil conditions, as well as other factors affecting the operation of pavements and foundations are taken into account. On roads with non-rigid coatings, structures with a small volume of stacked layers are provided. In particular, the design of pavements of this type involves the calculation of the permissible deflection of the pavement in unfavorable, from the point of view of external conditions, periods of the year. Reversible deflection is calculated according to one basic characteristic - the elastic modulus.
Also, the resistance of the upper layers of earthen soil, on which the foundation will be laid in the future, is taken into account. For this parameter, technologists introduce the magnitude of the shear stress. If in one of the layers deviations from the equilibrium norm, from the point of view of shear, can lead to residual deformation processes, the design of the pavement may include a change in composition by adding new plasticizers and technical components that increase the rigidity of the base fabric.
Varieties of pavement
All typical designs of pavement are divided into two categories - rigid and non-rigid. Moreover, each technological model of the coating device involves the use of specific indicators of moisture, thickness, size of the sand fraction, gravel and, in general, the properties of the cement-sand base. So, the elastic modulus of the soil base, depending on the design used, can average 300-500 kgf / cm 2 . As an exception, designs that do not involve the construction of a sand layer for drainage can be cited. In this case, the design of non-rigid pavements designed for laying in sandy and sandy soils is carried out. The modulus of elasticity of such a base can reach 1200 kgf / cm 2 . Designs differ in the number of technological layers. This can be a compacted two-layer clothing, and a coating of 5-6 layers. Depending on the external conditions, project developers can add additional layers, for example, with the function of an insulator.
Typical pavement designs
An important component in the improvement of urban infrastructure is the sidewalk. Its coating also refers to varieties of pavement, but, of course, with other technical and operational characteristics designed for pedestrian traffic. The structures of sidewalks in different regions do not differ so much from each other, since climatic conditions have a lesser effect on their surface. Nevertheless, the design takes into account the category of the street, its purpose, the intensity of pedestrian traffic, the characteristics of the soil base, as well as the ratio of the sidewalk to the roadway. In a standard form, the construction of pavement can be implemented in conditions of reinforced soil using asphalt and cement mortars. In some cases, ceramic and asphalt concrete slabs are used, and are also weak based on natural stone. In this case, laying can be performed in several layers, as is the case with ordinary roads.
The basis of pavement
Perhaps this is the most crucial part of the overall design, since it lays the function of the ligament of the top cover with the ground, as well as the distribution of loads. In practice, the application provides a reduction in stress from the effects of the wheels, translating the power potential into the ground. Thus, the base due to the ground cover creates a kind of depreciation effect. But not always pavement has suitable characteristics of the base, from the point of view of protection, from external influences. For example, the lower layer may have optimal working qualities, but under the influence of water will gradually erode. On the contrary, it can demonstrate resistance to climatic influences, but at the same time it is poor to perform load distribution. In order to optimize different characteristics, builders also distinguish functional layers in the base structure. So, the bearing part and auxiliary layers are separately considered. In such a structure, the base coat is responsible for mechanical resistance, and additional coatings counteract the same deposits.
Top part
The outer surface also performs a number of critical functions, the main of which is the direct reception of loads from cars. Direct contact also takes place in relation to climatic precipitation, therefore the protective qualities in the upper part can be called universal. The multifunctionality of the outer coating is achieved due to several layers, as in the case with the base part. So, in order to increase the resistance to cracks in the coating, special layers are used, which may include a geogrid and geotextiles, as well as modified cementitious components. On the surface, pavement has a special treatment, which also protects the coating from moisture and snow. And in addition to protective qualities, reinforcement of the adhesive properties of the surface is also practiced. Special treatments, for example, are also used to increase roughness and improve road and wheel adhesion.
Additional layers
Depending on operating conditions, various negative factors can affect the road surface. Not every typical design can respond to increased loads, in terms of thermal, hydrological and mechanical effects. For example, non-rigid road pavements are highly drainable and do not need additional sand decks, however, their strength properties may require reinforcement. For this, interlayers are created between the bearing part and the upper layers, and technological layers of the polymer film are laid between the substrate and the ground.
Frost-resistant layer
In terms of adverse climatic effects, the most destructive is frost. Protection in case of operation in low temperature conditions involves the use of granular materials, including sand, sand and gravel, slag and crushed stone. A kind of insulation can also be a soil base on which pavement with base layers is formed. However, to prevent freezing, land cover is not enough - it is supplemented with reinforced cementitious elements, as well as hydrophobized embankments and non-porous materials.
Drainage layer
Technological layers of this type are used in areas with subgrade from non-draining soil. Mandatory inclusion of such layers is considered in regions with heavy rainfall. The main function of the drainage layer is to provide a drainage system. In addition, typical designs of road pavements of urban roads, in which the drainage layer is higher in relation to the depth of freezing, should be made only of durable and frost-resistant materials.
Technological defects
Breaks are considered the most dangerous phenomenon that can lead to improper use of pavement device technology. In such cases, there is a risk of complete destruction of the web over the entire thickness with the manifestation of sharp distortions of the structure profile. Less dangerous are the processes of peeling and chipping, which involve surface damage due to the peeling of the binding elements and the loss of individual particles of mineral filling. Common mistakes with which typical designs of pavements are stacked can also cause shifts and the formation of potholes. The formation of open depths also leads to the extrusion of soil to the surface, which makes the coating unsuitable for use.
Conclusion
In recent years, paving technology has changed little. The introduction of new solutions into the industry mainly affects technical support in the form of the appearance of modern machines, tools and equipment for the preparation and laying of different layers. The materials from which pavements of city roads are arranged remain the same. The basis of coatings are also cement filling, sand with gravel and binders. Of course, new modifying components with additives are being introduced more and more often, but they are of a point-like nature of increasing operational properties and do not radically change the characteristics of typical designs.