The appearance of ordinary road surfaces on which traffic is carried out hides 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 asph alt concrete and cement concrete. In both cases, the characteristics of the binder components, fractions of crushed stone, sand, and other fillers may vary. Actually, the finished structure of such coatings can be considered as a full-fledged pavement. The definition provides for a common complex of layers of a given coating, but each layer acts as a separate technological component, for the device of which special requirements are imposed. To ensure the reliability of the coating, it is necessary to provide conditions under which the stress arising in the structural elements from traffic does not have a devastating effect onstructure. This can be achieved by a rational calculation of the characteristics of the structure, which is carried out by technologists before the start of road work.
What is considered in the pavement design?
Typical designs are developed as universal coatings for both city roads and country roads. It doesn't matter if it's a highway or a street. In the development of the project, the level of traffic intensity, the properties of the materials used, the loads, hydrological and soil conditions, as well as other factors that affect the operation of road surfaces and foundations, are taken into account. In roads with non-rigid pavements, structures with a small volume of laid layers are provided. In particular, the design of pavements of this type involves the calculation of the allowable deflection of the pavement in unfavorable, from the point of view of external conditions, periods of the year. Reversible deflection is calculated from one basic characteristic - the modulus of elasticity.
The resistance of the upper layers of earthen soil, on which the base will be laid in the future, is also taken into account. For this parameter, technologists enter the magnitude of the shear stress. If in one of the layers deviations from the norm of equilibrium, in terms of shear, can lead to residual deformation processes, then the design of the pavement may include changing the composition by adding new plasticizers and technical components that increase the rigidity of the base sheet.
Varieties of pavement
All standard designspavements are divided into two categories - rigid and non-rigid. At the same time, each technological model of the coating device provides for the use of specific indicators of moisture, thickness, size of the sand fraction, crushed stone and, in general, the properties of the cement-sand base. So, the modulus of elasticity of the soil base, depending on the design used, can average 300-500 kgf/cm2. As an exception, constructions that do not involve the construction of a sand layer for drainage can be cited. In this case, the design of non-rigid pavement is carried out, designed for laying in sandy and sandy soils. The modulus of elasticity of such a base can reach 1200 kgf/cm2. The designs also differ in the number of technological layers. It can be both compacted two-layer clothing, and a coating of 5-6 layers. Depending on external conditions, project developers can add additional layers, for example, with an isolator function.
Typical sidewalk designs
An important component in the improvement of urban infrastructure is the sidewalk. Its surface also belongs to the types of pavement, but, of course, with other technical and operational characteristics designed for pedestrian traffic. Pavement structures in different regions do not differ so much from each other, since climatic conditions have less impact on their pavements. Nevertheless, the design takes into account the category of the street, its purpose, intensitypedestrian traffic, the characteristics of the soil base, as well as the ratio of the sidewalk to the carriageway. In the standard form, the pavement design can be implemented in the conditions of reinforced soil using asph alt and cement mortars. In some cases, ceramic and asph alt concrete slabs are used, as well as weak ones based on natural stone. In this case, laying can be carried out in several layers, as is the case with conventional roads.
Basic pavement
Perhaps, this is the most critical part of the overall design, since it is responsible for the function of bonding the top coating with the ground, as well as the distribution of loads. In practice, the base provides a reduction in stress from the impact of the wheels, transferring the power potential to the ground. Thus, the base due to the earth cover creates a kind of depreciation effect. But pavement does not always have suitable characteristics of the base, in terms of protection from external influences. For example, the lower layer may have optimal working qualities, but under the action of water it will gradually erode. Conversely, it can show resistance to climatic influences, but at the same time perform poorly in load distribution. In order to optimize various characteristics, builders also distinguish functional layers in the base structure. Thus, the carrier part and auxiliary layers are considered separately. In such a structure, the base coat is responsible for mechanical resistance, and additional coatingscounteract the same precipitation.
Top
The outer surface also performs a number of critical functions, the main of which is the direct acceptance of loads from cars. Direct contact also takes place in relation to climatic precipitation, so the protective qualities in the upper part can be called universal. The multifunctionality of the outer coating is achieved due to several layers, as is the case with the base part. So, in order to increase the resistance to cracks in the coating, special interlayers are used, which may include a geogrid and geotextile, as well as modified binder components. On the surface, pavement has a special treatment that also protects the coating from moisture and snow. And besides the protective qualities, the strengthening of the adhesive properties of the surface is also practiced. Special treatments, for example, are also used to increase roughness and improve road grip with wheels.
Additional layers
Depending on the operating conditions, various negative factors can affect the road surface. Not every typical design can meet increased loads in terms of thermal, hydrological and mechanical effects. For example, non-rigid pavements are highly drainable and do not need additional sand decks, but their strength properties may need to be reinforced. To do this, layers are created between the bearing part and the upper layers, and technologicallayers of polymer film between the base and primer.
Frost-resistant layer
Frost is the most damaging climate impact. Protection in case of operation in conditions of negative temperatures involves the use of granular materials, including sand, sand and gravel mixtures, 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, the ground cover is not enough - it is supplemented with reinforced binders, as well as hydrophobized embankments and non-porous materials.
Drainage layer
Technological layers of this type are used in areas with subgrades made of non-draining soil. Mandatory inclusion of such layers is considered in regions with abundant precipitation. The main function of the drainage layer is to provide drainage. In addition, standard pavement structures for urban roads, in which the drainage layer is higher in relation to the freezing depth, should be made only from durable and frost-resistant materials.
Technological defects
Breaks are considered the most dangerous phenomenon that can lead to improper use of pavement technology. In such cases, there is a risk of complete destruction of the web throughout its thickness with the manifestation of sharp distortions of the structure profile. The processes of peeling and chipping are less dangerous,which suggest surface damage as a result of flaking of binders and the loss of individual particles of mineral filling. Common mistakes made with typical pavement designs can also cause slips and potholes. The formation of open abysses also pushes the soil to the surface, making the pavement unusable.
Conclusion
In recent years, pavement technology has changed little. The introduction of new solutions in 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 the pavements of urban roads are made remain the same. The coatings are also based on cement fillings, 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 nature to increase operational properties and do not radically change the characteristics of standard structures.
