Road surfaces experience heavy loads, the sources of which are not only cars, but also natural phenomena with negative factors of economic operation. To provide the canvas with a sufficient set of protective qualities, a wide range of materials are used that form its structure. The choice of certain road-building materials in each case is individual and is made on the basis of a comprehensive study of a particular operation site.
Mechanical properties of materials
These are the most significant operational qualities of materials that determine the resistance of a coating to vehicle loads. There is a whole range of mechanical properties that make it possible to evaluate the sensitivity of the web to loads. In particular, tests of road building materials are carried out according to the following qualities:
- Strength. The ability of a material to take on the action of external forces without being destroyed.
- Crushability. Also an indirect indicator of strength, which is determined by the compression of the material in the capacitive cylinder.
- Abrasion. The ability of road material to change mass under the influence of abrasive forces.
- Fragility. The ability of road building material to collapse under external influences without permanent deformations.
- Elasticity. This quality determines the ability of a material to restore its original shape with parameters after external forces have ceased mechanical action.
- Plastic. A property that shows how much the material is able to deform irreversibly. In the process of testing road-building materials for plasticity, in particular, the dynamics of changes in the shape and volume of the studied structure under external load is determined. The peak moment is also recorded, after which the destruction process begins.
Physical properties of materials
Thanks to the study of this category of properties, technologists determine how much this or that material is able to withstand atmospheric phenomena and is generally suitable for application conditions. Such properties include moisture resistance, heat resistance, resistance to frost, density, porosity, etc. For example, the density indicator is determined using a pycnometer - this is a calibration flask, which is filled with crushed material. Next, the tank is filled with water, boiling and insisting on a sand bath. At the end of the test, the powder is weighed and the density and porosity coefficient is determined by comparing the primary indicators with the test results. For some groups of road building material, the voidness indicator is also important. The degree of filling of the defective areas with loose bulk material depends on it.
Chemical properties of materials
These properties determine how the material will chemically interact with the environment. In this part, the following qualities can be distinguished:
- Weather resistant. The ability of the structure of materials to maintain integrity under the influence of solar radiation, temperature, precipitation, gases, microorganisms, etc.
- Corrosion protection. A property that determines resistance to acidic environments, alkalis, flowing and marine fluids. For example, bitumen is sensitive to alkaline environments, and concrete is destroyed by the action of sea salts.
- Solubility. Determines the ability of materials to form new substances and solutions when interacting with water.
- Hardening. This property of road-building materials indicates their ability to transfer in their structure from a plastic state to a solid state.
Also, from the point of view of installation and operating conditions, technological qualities are also important. These are universal properties due to which the structure compaction, its degree of delamination, viscosity and other characteristics are evaluated.
Classification of natural materials
Despite technological development in the manufacturing sector, the category of natural building materials for laying roads is the main one. As a rule, these are products of mining enterprises, which, in turn, is divided into igneous, sedimentary, and metamorphic materials. They should be considered separately:
- Igneous rocks. This is a group of primary materials that formed during the cooling of magma. Their basis is formed by mineral components concentrated under the action of high temperatures and pressure.
- Sedimentary. These are rocks of the secondary group, which differ in that they formed on the surface of the earth at low temperatures under medium pressure. There is also a classification of road-building materials within this category, which distinguishes chemical, debris and organogenic rocks based on a genetic basis. In each case, its own set of characteristic properties and operational features.
- Metamorphic. These are rocks of magmatic structures that formed at high temperatures, but had undergone complete or partial transformation by the time of development.
Classification of Artificial Materials
Unlike natural materials for laying roads, artificial ones are, to one degree or another, a production product. The basis is made up of materials that were obtained by special manufacturing - usually under industrial conditions. Moreover, as a raw material for production, mainly natural rocks are used, and less often - technical. The category of so-called local road-building materials, which are used only in special cases, is also highlighted. As a rule, these are secondary resources left after production processes - for example, swamp ore, slag, ash, shell, etc. Industrial waste can be used, but also in some cases, when this is allowed by the requirements for road clothes. In general, local materials and waste are economically beneficial, but in terms of technical and physical characteristics they lose to the main natural and specially made products.
Types of stone materials
Mostly, raw materials from debris and rock are used, which undergo the main processing and can be used in different structures of the roadbed. The rocks are most durable, so they are laid in critical technological layers. Clastic rocks are characterized by a loose structure and are more often used as the basis for cement-concrete and asphalt-concrete mixtures. The main road-building materials of the stone group include crushed stone, cobblestone, saber, seeding, paving stones, etc. There are also classifications according to the degree of processing and composition. In accordance with the first sign, the materials are divided into chipped, piece and sawn, and by composition - into simple (homogeneous) and complex (agglomerates).
The most technologically advanced material of this kind is considered to be cement stone, formed as a result of crystallization of hydration and hydrolysis products. Thanks to the crystalline processes that diverge throughout the structure of the stone, high strength is achieved as with reinforcement. The rate of hardness gain is determined by the reactions of the material with clinker elements and the mineralogical composition of cement. In factory processing conditions, plasticizers can be added to give the product additional properties.
Loose materials and their classification
This is an extensive group of road materials that were formed during the weathering of hard rocks. As a result of erosion and leaching, small elements of different fractions are formed, which are also characterized by the inclusion of various impurities and other foreign bodies. The following classification of road building materials is used to sort the loose weathering products by origin:
- Glacial or fluvioglacial.
- Alluvial or river.
- Aeolian or wind.
- Sea and lake.
Distinguish such materials by fraction:
- Boulders Roughly rolled rock fragments of mainly round shape with a fraction of 150 mm or more.
- Pebbles. For roads, small river pebbles of 5-20 mm in size are mainly used.
- Gravel. It covers a wide size range from 3 to 70 mm, but mainly loose clusters of fragments up to 40 mm in diameter belong to this group.
- Sand. Granular elements of weathered rocks, the fraction of which varies from 0.15 to 3 mm.
Soil materials
These are heterogeneous bulk materials, which are mainly formed by several types of mineral particles - for example, sand, clay and dusty inclusions. A kind of power framework of the soil is formed by grain solid elements that touch each other (about 75-80% of the total composition), and the gaps are filled with a dusty mass (15-20%). Clay elements account for 5-10%. There are technological standards that determine the optimal content of soil components, as well as the types of elements. Soil road building material can be both natural and technical. The optimal compositions are mainly of artificial origin, and in the conditions of production, technologists can also add sandy loam, loam and other additives to optimize the characteristics of the road construction composition.
Portland cement as a cement base for roads
This material is included in the group of hydraulic binders, the curing of which occurs in air or water. The basis of Portland cement is clinker grinding with gypsum additives in the amount of 3-5%. Clinker itself is obtained in the process of firing a finely dispersed mixture of clay and limestone. Mixtures of marl, blast furnace slag, flask, nepheline waste, etc. can also be added as modifying additives. This road-building material can be produced in different versions, which have their own marking of 300,400, 550, etc. This figure indicates an indicator of activity, that is, the value of bending strength. In road construction, the practice of using almost all brands of Portland cement is practiced, each of which is selected for reasons of expediency of use in specific conditions, taking into account the requirements.
Construction lime
Another variety of binders used in the device of road cloths. Lime is obtained by calcining carbonate rocks, which also contain clay impurities in the amount of 6-7%. An increase in the proportion of impurities is achieved by preserving ferrites, aluminates, and silicates, the combined content of which increases the hydraulic properties of the material. Based on lime, various road-building materials and products are produced in the form of powder mixtures. Again, these are mainly binding components, but the integrated use of air lime with other elements is also practiced in order to strengthen the bearing soils. This is a function of the active additive used in combination with bitumen, cement and mineral waste. As a full-fledged technological component, lime is used in the creation of tar emulsions.
Production of road building materials
The main production processes take place at mining enterprises, where processing operations are carried out. In particular, the following work is carried out to prepare raw materials for further use in road construction:
- Separation of monoliths from the main breed.
- Crushing, grinding and crushing.
- Grinding in mills and special electrical equipment.
- Filtering through a sieve.
- Sorting of medium- and small-fraction materials in order to obtain agglomerates.
After the mechanical preparation of the raw materials, the processes of thermal, chemical and biological treatment are carried out. These can be firing, drying, impregnation, protective coatings, etc. At the final stage, control of road-building materials is carried out according to several parameters. In particular, the fraction, physical and chemical qualities, technological and operational properties are evaluated. For checking, special devices with in-line scanning can be used.
The use of materials for laying roads
In pavement clothes, several technological layers are used, each of which performs its own tasks. There are also intermediate functions - for example, in binders, sealing and modifying materials. The most common use of road-building materials for universal use, which can be laid in the base of the canvas, but also be used to perform auxiliary tasks. For example, gravel is added to the composition of cement concrete and tar concrete mixtures as a filler on the one hand, and on the other hand, it is used to arrange drainage structures and embankments in separate sections of roads. Also, sand can be used as a filler for binder solutions, and for the device of underlying formations. It is widely used as a repair material when you need to align a separate area or fill a hole.
Of course, the use of these materials is not complete without special equipment. This is an extensive segment of vehicles involved in the maintenance of road building materials. Both machines and auxiliary technical equipment are required for laying, compacting, tamping, leveling, concrete mortar preparation, etc. Concrete mixers, asphalt pavers, crushers, sorting cars, rollers and vibratory hammers can be attributed to this technique. And this applies only to immediate work activities related to the formation of roadbed, but also complex construction rarely does without transportation machines, brush cutters, forklifts and cranes.
Quality control of road building materials
There is a set of test methods by which the compliance of the material with technical parameters and operational properties is checked. One of the most common controls is a sieve. Safety and control sieves are used to assess the quality of the material, its degree of granularity and friability.
Using power hydraulic and electromechanical units, indicators such as elasticity, tendency to deformation, density, etc. are checked. There are special regulatory modules with indicators and ratios for each group of building materials. For road construction using gravel, for example, the method of crushing the probe in a cylindrical container is used. Further sieving of the crushed material through a sieve allows you to set the coefficient of loss in mass under load.
Separate control standards are also applied in relation to cement-concrete mixes. The samples taken are checked for strength, mobility during transportation and other quality indicators. At the outlet, the manufacturer labels each batch indicating the date of production, volume and basic technical and physical parameters.
Conclusion
In addition to an extensive assortment of standardized materials for road laying, there is a significant segment of secondary and auxiliary products and industrial wastes that are also used in this field. These include water glass, gypsum binders, fiberboard and even wood products. Of course, the quality of road-building materials of this category is not so high in comparison with concrete mixtures or the main bulk products of mining processing, but they can also be useful in solving certain problems. After all, do not forget that the roadway is a complex device in structure, which includes natural components that are not subjected to technical processing at all.
In most cases, the quality of ready-made road pavements is determined not so much by the direct characteristics of the materials used as by the chosen laying technology. In each case, a project is developed with a specific recipe for the device of each layer. Next, a construction schedule is developed, according to which already responsible contractors select materials and implement work activities.