The composition of road concrete and the basic requirements for laying the pavement. From the history of the invention of concrete

Concrete roads are widely used abroad. In Russia, this technology is not yet so popular. This is due to the fact that laying asphalt is much cheaper than a concrete highway. But over the years, the prices for these two types of roadway are gradually equalized. Concreting is used for the construction of highways, airfields, bridges and much more. The material is laid with the help of special machines, because it is difficult and time-consuming to do it with your own hands.

Advantages and disadvantages of concrete roads

Concreting has both advantages and disadvantages. It is superior to asphalting in many respects. The advantages of such roads:

• Sturdy enough and do not need to be repaired. Concrete pavement lasts more than forty years and does not need frequent repairs, while asphalt can last a maximum of ten years, and it needs to be repaired every year.
• Transport consumes less fuel. This advantage is due to the fact that when moving cars with a large load, the concrete road is not deformed, and vehicles need twenty percent less fuel to move.
• Resistant to extreme weather conditions. They are not affected heavy rains or very high (low) air temperatures.
• Preservation of ecology. Since transport spends less fuel for movement, the environment is polluted less.
• Economical use of natural resources. Concrete is made from limestone, while asphalt is made from petroleum.

Disadvantages:

• Price. The price of concrete pavements is much higher than the use of asphalt.
• Problematic repair. If the base becomes unusable, then you need to change the whole plate.
• Travel insecurity. When periods of rain and heavy snowfall come, slipping of vehicles on such roads is quite common.

Pavement structure

The structure has three layers of coating:

1. An additional layer is the earth, as the basis for the future roadbed.
2. The underlying layer is the base for the future laying of concrete, the formwork is being made.
3. The concrete pavement itself, which may have one or more layers.

They can also additionally build tunnels, roadsides, bridges and supports for them, etc.

How does the terrain affect construction?

For a concrete road, a variety of technologies are used. If a concrete route is built in a mountainous area, then it repeats the relief. When highways are built, the terrain is leveled, filling in numerous depressions, cutting off the interfering hills. Quite often they build bridges and carry out tunnels. In order to allow vehicles to move at normal speed, sharp turns and descents are avoided during construction to avoid emergencies.

Technological process of filling the road

The laying of a concrete road consists of a number of stages:

1. Ground layer preparation. First of all, the soil must have a dense structure. If the soil layer is of insufficient density, the concreted part will collapse. The ground coating should be rolled, while gradually adding it so that the rolling is layered. The soil should be used when wet. If there is insufficient moisture, use water. If the humidity level is above normal, the soil base should be dried using loosening, adding sand or slag.
2. Water withdrawal. Similar work is carried out both in urban areas and rural areas. Removal of precipitation helps to increase the operating time and secure the ride. Water is a danger on the road for moving vehicles. Due to water splashes, the driver’s visibility deteriorates, and when the temperature drops, ice appears on the surface. To avoid this, the roadbed is tilted, it is possible to use drainage layers. Possible places of accumulation of water are leveled with soil. Outside the city, water accumulates in ditches (one to two and a half meters wide), which drain water into ditches, reservoirs, and riverbeds. In populated areas, water goes into the city sewer. Devices that conduct water are constantly cleaned so that they do not lose their throughput. If water has seeped into the soil balls, this is a direct danger to the roads, because the pavement may eventually collapse.
3. Underlayment layer. It implies a structure, the thickness of which ranges from twenty to forty centimeters. It prevents moisture from escaping and also improves drainage. The litter layer prevents the appearance of cavities and cracks. If the area is dominated by clay, peat soils that accumulate water, then they are cut off, adding large stones and gravel. That is, it all depends on the soil type and the climatic zone in which the work is carried out. Also important is the geotextile lining between the layers. Stone materials must be strengthened with binders. These include cement, slag mixed with quicklime, ash. The layers are carefully rolled so that the lower layers are dense.
4. Formwork collection. It is made from lumber, taking into account the height of the fill (approximately 100 - 150 millimeters). When choosing a height, take into account the fact that ribs are needed at the edges, which increase strength. Boards should be no less than fifty millimeters thick. They are covered with a special solution, which will then facilitate detachment from concrete. In the case of heavy compaction machines, formwork is made of steel, which does not deform and will last longer. At its base, it has a sole that increases the level of stability.

The formwork sections are set in line and well secured so that they do not fall apart when the concrete is vibrated by heavy paving machines.

The technology of using plates in the construction of the road

Road concrete slabs.

Manufacturing has a certain sequence:

1. Temperature seams. Sections for pouring are separated. To fill the seams, a material is used that absorbs energy. It can be either soft wood or insulating cardboard. At a depth of about forty to fifty millimeters, it is necessary to make waterproofing with a sealed substance in order to prevent debris or stones from entering. If this moment is missed, then later during the expansion of the slabs due to the stones of the upper layer of the seam. In a normal climate, the distance between the seams should be somewhere between 20-30 meters. The level of reliability for long plates is about 50%, for short ones - about 85%. Strength is characterized by the level of resistance to cracking between periods of repair work. Special steel rods are “threaded” through the side faces using a special mechanism. The width of the two road lanes varies between 6 and 9 meters. Also, between the strips, a shrinkage is made - a temperature seam that prevents the appearance of cracks.
2. Bedding layer. It is covered with waterproofing, sometimes moistened. Concrete is poured in one go, quickly (because of its short pot life). Dilution with water is prohibited because the properties of the material are lost. Concrete is brought to the construction site directly from the factory, where it is kneaded. When the mixture is unloaded, special machines with blades drive up to level the area. All this happens in small areas, where each layer is worked out well in turn, so that the density level is the same everywhere. In the case of reinforcement, to begin with, a layer of about 40 mm is poured. A grid goes on top of it, and then the formwork is filled.
3. The stage of compaction of the concrete layer. A special vibrating machine is used, which has a leveling and vibrating bar in front. The level of plasticity of the coating is determined by such a characteristic as, not quite a liquid state. When the concrete has hardened slightly, it is sprinkled with a little water to prevent cracks. Next comes the covering with sand, burlap and other materials to avoid evaporation.

Concrete mixes need to be given enough attention, as their poor quality can result in constant repairs, which are very expensive.

In the construction of monolithic cement-concrete pavements, a set of machines is used, which makes it possible to mechanize all production processes and organize the construction of the road by the in-line method. When organizing the construction of cement-concrete pavements by the in-line method, the scope of work is divided into separate sections, based on the convenience of the machines included in the kit. The dimensions of the sections (captures) depend on the nature of the mutual linking of the machines with each other in work, which determines the entire system of organizing the construction of the coating as a whole.
As mentioned earlier, monolithic cement-concrete coatings can be one- and two-layer. On city highways and high-speed roads, such coatings are laid on foundations made of soils reinforced binders, as well as on gravel and crushed stone bases. On streets with low traffic intensity, intra-block passages, it is allowed to arrange cement-concrete pavements on sandy bases. In the case of the use of sandy bases, as well as frost-protective and drainage layers of sand, the work is carried out in the following sequence. Sand is brought in by dump trucks and distributed by a bulldozer or motor grader to the required vertical mark. After leveling, the sand is compacted by rollers on pneumatic tires.
The preliminary leveling of the sand layer is carried out by an autotrader, and the final leveling and compaction is carried out by a base profiler after the installation of the rail forms. The base or underlying layer should be compacted at the optimum moisture content of the sand, therefore, if necessary, before the passage of the profiling mechanisms, the sand is moistened with a watering machine.
The technological process of building crushed stone and gravel bases consists of the removal of materials by dump trucks, leveling with bulldozers or motor graders and compaction by rolling. It is advisable to use crushed stone laying machines in this case. When constructing foundations from soils reinforced with binders, manufacturing process can be carried out by the method of mixing in installations or by the method of mixing on the road. The technological sequence of operations is determined in this case in accordance with. the current "Guidelines for the use in road and airfield construction of soils reinforced with binders".
The technological process of setting up a cement-concrete pavement on a finished base with a set of concrete-laying machines includes the following operations: preparation of the base for rail-forms and installation of rail-forms; final layout and compaction of the base; surface treatment of the base (if it is made of a cement-sand mixture) with bitumen emulsion: installation of gaskets, pins of expansion joints, blocks for water intake wells; distribution of concrete mix; when installing two-layer coatings, after spreading the lower layer of the coating, a reinforcing mesh is laid, and then the concrete mixture of the upper layer is distributed; compaction of the concrete mixture and surface finish of the coating; arrangement of expansion joints; removal of rail molds; curing; filling expansion joints.

On fig. 105 shows a technological flow diagram for the installation of monolithic cement-concrete pavements of urban roads with a set of concrete-laying machines moving along rail forms. Rail molds can be installed on widened pavement bases. If such a base does not provide a non-sag position of the rail forms under the load from the machines of the concrete paving set, then a reinforced base must be arranged under the rail forms. Rail-forms must have strength and rigidity to ensure the passage of machines used for coating without deformation on them.
Before installation, check the condition of the rail forms and the correctness of the geometric dimensions. Curvature of the rail molds in the vertical plane should not exceed 2 mm, in the horizontal plane 5 mm. The difference in the height of the rail-form links at the joints should not exceed 2 mm. The rail molds must be cleared of old concrete. Deformed and faulty rail molds are rejected and not allowed for use.
Rail-forms are transported to the place of laying by cars or tractor carts. The rail-forms are installed in the design position by truck cranes with the expectation of a two-shift operation of the concrete paving machine. The breakdown of the rail-form installation line in the plan is carried out on one side of the coating using a theodolite, on the other side - according to a template. Installation of rail-forms in height is carried out according to design marks using a level.
The correctness of the installation of the rail forms is checked with geodetic tools, and the parallelism is checked with a template. The links of the rail-forms are connected with bolts, fastened to the base with metal pins.
Before the start of laying the concrete mix, the rail-forms must be run in, for which a concrete distributor with a bunker filled with sand is passed through them at least twice. All detected drawdowns are eliminated. The difference in height marks of two adjacent rail forms should not exceed 2 mm.
The mechanization of processes for the final compaction of sandy bases, frost-protective, draining and leveling layers is carried out by profilers DS-502A (B). The DS-502A profiler is manufactured in four modifications: for a flat profile device with a width of 3.5; 5 and 7 mm and for the installation of a gable profile with a width of 7 m. The DS-502B machine is designed for a strip width of a flat profile of 7.5 and 3.75 m, a gable profile of 7.5 m. Technical specifications base profilers are given in Table. 70.
When the profiler moves, the blade of the machine cuts off the unevenness of the base and accumulates a prism of material in front of it, filling up the depressions and giving the surface evenness and the necessary transverse slopes. The base is compacted with the help of a vibrating beam made in the form of a box-section beam, on the top panel of which vibrators with circular vibrations are mounted.

To reduce the coefficient of friction of the coating on the base, a leveling layer of sand treated with bitumen or cement is arranged. The work on profiling and compaction of this layer is also carried out by the DS-502A (B) machine.
After completing the final finishing of the base, gaskets with pins for expansion joints and structural elements of compression joints are installed. The normal operation of the joints between the plates depends not only on the design of the pin joints, but also on the thoroughness of the work performed during the construction process. If the seams are arranged in compliance with all technical rules, then for many years of operation of the road there will be no difficulties and only routine maintenance of the seams will be required. Improper work can lead to the rapid appearance of deformations, the correction of which will be costly.
In the practice of building main roads with cement concrete pavements in our country, for fastening gaskets and pins, supporting basket frames made of reinforcing steel with a diameter of at least 6 mm are used. In this case, the groove above the wooden spacer can be created in both freshly laid and hardened concrete.
In addition to these methods, when installing plank pads in the seams of concrete pavements, the method of fixing the pads with pins driven into the base on both sides of the board is used. After concreting, the pins must be removed, since the remaining pins anchor the concrete pavement to the base and, as a result, additional stresses appear in the concrete.
Simultaneously with the installation of the elements of the seams on the pavement of the roadway in the places provided for by the project, the structures of the manhole blocks of the water intake wells are installed. Blocks of wells are installed by truck cranes.
During the construction of reinforced concrete pavements, an additional operation is the laying out of reinforcing meshes or a frame. Reinforcement is prepared centrally at manufacturing enterprises urban road construction. Reinforcing meshes and frames are delivered to the place of laying on cars and installed in the design position by a crane on a car.
Before starting the laying of the concrete mix, the following is checked: a) the correct installation of the rail forms (their correct position in plan and longitudinal profile, the reliability of fastening the butt joints of individual links), the thoroughness of the lubrication of the side walls of the forms; b) reliable fastening of gaskets and pins in expansion joints; c) the sufficiency of wetting the leveling layer of untreated sand or sandy base.
The concrete mixture is transported to the place of laying in dump trucks with special bodies (with side unloading), which ensure convenient and quick unloading of the mixture into the distributor. The bodies of dump trucks must be waterproof, have serviceable closures and a smooth surface, devices for sheltering the mixture from drying out or moistening. After each trip, the bodies of dump trucks must be washed with water.
The duration of transportation of the concrete mixture on Portland cement with the onset of setting of at least 2 hours should not exceed: 30 minutes at an air temperature during concrete laying from +20° to + 30°C; 60 min - at air temperature below +20°. At air temperature from +30 to +35°С, relative air humidity less than 50% and concrete mixture temperature not more than 30°С, the duration of concrete mixture transportation should not exceed 30 minutes. The mobility (rigidity) of the concrete mixture should be assigned taking into account the time of its transportation to the place of laying and the air temperature. To maximize the use of a set of concrete placing machines and obtain concrete of a homogeneous composition, the concrete mixture must flow evenly and continuously during work shift.
In Russia, a series of ZIL-MMZ-553 concrete trucks has been produced, designed to transport concrete mix in hot climates. This machine, made on the basis of the ZIL-164A car, differs from the dump truck in the body structure, which has the shape of a gondola with a steeply inclined rear wall. The angle of inclination of the bottom to the horizon reaches 80°, and the rear wall - 48°. The bottom of the oval shape and the side walls of the body have air gaps 80 mm thick. The body has a protective cover, which opens at the time of loading.
Reception of the concrete mixture from vehicles (dump trucks) and its distribution over the base of the coating are carried out by the hopper of the concrete mixture distributor DC-503A (B). Table 71.

Concrete mixture from dump trucks is unloaded into a distribution hopper, which distributes it over the base, moving across the roadway. By adjusting the height of the hopper under the base, it is possible to change the thickness of the laid concrete layer. The required increase in the thickness of the uncompacted layer of the concrete mixture against the design thickness of the coating is determined empirically, depending on the speed and plasticity of the mixture. With a cone draft of 1-2 cm, this increase is 2-3 cm.
A more efficient distribution of the concrete mix is ​​achieved by using concrete mix screw distributors. The DS-507 auger distributor, created in Russia, is designed for distribution and preliminary compaction of the concrete mixture over a strip 7.0-7.5 m wide. The main working body of the DS-507 machine - a reversible auger - consists of two halves, each of which has an independent drive. There are two blades in front of the auger, which cut off excess mixture and contribute to its uniform distribution. Both the auger and blades can be set to the desired height using the lift cylinders. The second working body of the DS-507 concrete distributor is a vibrating beam, which performs preliminary compaction of the distributed concrete mixture. The vibrobeam is made in the form of a welded beam, on which six mechanical vibrators are installed.
When constructing a two-layer coating, first lay the concrete of the lower layer with a thickness of 2/3 of the total thickness of the coating, then lay the prefabricated welded reinforcing mesh and the second layer of concrete. In this case, it is recommended to use two distributors for separate placement of the concrete mixture in the lower and upper layers of the pavement.
The organization of work on the construction of a two-layer pavement should ensure the rhythmic laying of the mixture with the expectation of obtaining a homogeneous monolithic and dense concrete throughout the entire thickness of the pavement. In this regard, the gap in time between laying the lower and upper layers at an air temperature of 5 to 20 ° C should be no more than 1 hour; at a temperature of 20-25 ° C - no more than 40 minutes and at a temperature of 25-30 ° C - no more than 30 minutes. It is necessary to complete work on the construction of a two-layer coating section with the calculation of laying the upper and lower layers at the same time.
After the passage of concrete-laying machines, leveling, compaction and finishing of the coating is performed by a concrete finishing machine DS-504A (B). The technical characteristics of concrete finishing machines DS-504A and DS-504B are given in Table. 72.

Recently, a new rail concrete finishing machine DS-508 has been created, which, together with a concrete mix distributor DS-507, is designed for laying road concrete in a pavement 7 and 7.5 m wide, mainly on stabilized soil foundations.
Concrete finishing machine DS-504A(B) moves along the rail-forms behind the distributor and performs work with three working bodies - a compacting paddle shaft, a vibrating beam and a screed.
The paddle shaft is located at the front (in the direction of travel) of the concrete finishing machine. When the shaft rotates, the blades evenly distribute the concrete mixture over the width of the strip being laid and partially compact it. Behind the shaft there is a vibrating bar, which, making oscillating movements, finally compacts the laid concrete mixture.
The screed of the machine consists of two screeds - the front vibration and the rear screed. Both beams perform swinging movements across the roadbed, sliding on the surface of the laid concrete. Thanks to the rocking movements of the beam, the surface of the concrete is finally leveled and smoothed out. The coating is finished in 1-2 passes in one place when the machine moves forward. On the reverse run, the machine rises to the transport position, leaning on the running wheels. For good compaction and surface finish of laid concrete, correct installation working parts of the machine. A self-propelled concrete finishing machine is operated by one driver.
During the construction of monolithic coatings with a set of wheeled vehicles, the rail-forms are removed by a crane no earlier than 24 hours after the concrete has been laid, after the concrete has gained the required strength, which is established empirically. The removed rail-forms are transported to the beginning of the stream, where they are installed in a new section by the same crane.
The most efficient machines for paving road concrete are trackless machines that move along the roadbed under construction on caterpillar tracks. Precise observance of the design arrangement of the concrete pavement in plan and profile is achieved in this case with the help of automatic tracking systems. The trackless paver differs from the rail machines also in that it has a single pass and is equipped with working elements for spreading, compacting and finishing concrete.
The main advantage of trackless pavers, or slipform pavers as they are called, is their high productivity achieved by single pass, as well as the fact that their use eliminates the extremely laborious, inefficient work of installing and dismantling rail forms.
Sliding forms are mounted between the tracks of the stacker. The distribution of concrete unloaded in front of the machine by dump trucks is carried out by auger or paddle working body. The frame with paddles can be lowered and raised by a hydraulic cylinder, moved on a cross tube carriage and thus evenly distributes the mixture across the entire width between the sliding forms.
For profiling the coating, a transverse beam is used - a slab with a pallet about 2 m wide. In front of this slab, the concrete mixture is compacted by rod electric vibrators immersed in concrete up to half the thickness of the coating. Upper layer concrete is additionally compacted with a vibrating tube mounted directly in front of the profile beam. The surface of the coating is leveled with a transverse slab with a pallet width of 0.7 m. Finally, the surface of the coating is smoothed out by a floating transverse beam with a pallet width of 0.4 m.
The paver may have a mechanism for making a longitudinal seam by inserting an elastic spacer into the freshly laid concrete. The control of the concrete paver is automated. To maintain the given direction of movement of the machine and the evenness of the surface of the coating, a tracking system is used. One of the designs of this system consists of two base wires stretched on metal racks with holders adjustable in height. The wire base is installed on both sides of the carriageway at least 100 m ahead of the concreting of the pavement. The installation is checked by leveling with an accuracy of ± 2 mm. Four electronic sensors are mounted on the paver frame to maintain a given level of the surface of the coating and one sensor for the direction of movement of the machine. Each sensor has a slot through which the base wire passes. There are microswitches on both sides of the slot.
When the movement of the machine deviates from the given direction or when the position of the working bodies deviates from the set level, the wire is pressed on one of the microswitches, as a result of which the relay system for turning on the electric motor of the reversing mechanism is activated to correct the direction of movement or the level of the position of the frame with the working bodies of the machine.
A sensor for maintaining a given direction of movement of the machine is suspended on the front corner of the machine frame. The adjustment is made according to the difference in the speeds of movement of the tracks of the machine, which have an independent drive. The position of the frame with working bodies is corrected by four sensors suspended on brackets in front and behind the machine.
With a reliable bearing capacity of the base, this system ensures the evenness of the surface of the coating with a gap under the triple rail of no more than 3 mm.
It should be noted that the slipform paver performs the complex operations of laying, compacting and finishing the pavement and eliminates the use of special concrete finishing machines. One of the caterpillar slipform pavers mastered by our industry is the DS-513 paver. At present, our industry has mastered the production of a set of machines DS-100 with sliding forms for high-speed construction of highways (Fig. 106). Such machines can be used for the construction of long-distance urban highways, approaches to large cities, ring (around the city) highways.

The DS-100 set includes nine main types of machines and equipment: subgrade and foundation profiler DS-97; conveyor loader DS-98 mounted to the profiler; concrete mix distributor DS-99; concrete paver DS-101; DS-103 trolley for transportation of reinforcing mesh trailed to the concrete distributor; vibratory loader DS-102 of reinforcing mesh trailed to the concrete paver; concrete finishing machine - tubular finisher DS-104; DS-105 machine for applying film-forming materials; asphalt-laying equipment DS-106.
In addition to the main ones, the set includes auxiliary machines: cross cutter DS-112; cutter of longitudinal seams DS-115; filler of joints DS-67; DS-107 trailer with MAE-537 tractor for transportation of machines and equipment of the set.
The kit also includes an automated continuous concrete plant SB-109 with a capacity of 120 m3/h. For the normal operation of a set of vehicles with a rate of at least 1 km of road per day, it is necessary to have two such plants.
Profiler DS-97 is used for loosening, distributing and profiling the top layer of the subgrade, as well as profiling various imported materials (sand, slag, gravel, gravel-sand mixtures, soils reinforced with binder materials, etc.) when installing frost-protective, draining and underlying layers and various bases for cement-concrete coatings. The working bodies of the profiler are the auger-mill, the front blade, the distribution auger and the rear blade. A vibrating beam can be additionally mounted on the profiler for compacting the structural layers. Travel speed of the profiler during preliminary profiling (scarring with a cutter) 1-2 m/min, during finishing profiling 6-7 m/min, when distributing materials 3-5 m/min, when arranging a stabilized base (mixing in place) 8-12 m /min and when spreading reinforced soil with simultaneous compaction 1-2.5 m/min. The width of the processed strip is 8.5 m, and with dump extensions - 9.5 m. The level and direction indicators in terms of the profiler and other machines are copy cords (strings).
Hinged conveyor-loader DS-98, consisting of a fan-type belt transport, is designed for reloading excess material to the roadside or to vehicles.
The DC-99 concrete distributor is used to receive concrete mix and other materials from vehicles (usually dump trucks) and distribute them evenly over a width of up to 7.5 m and a thickness of up to 50 cm. The working bodies of the concrete distributor are laying equipment, including a frame, receiving hopper with a belt conveyor and a mechanism for moving the hopper; distribution equipment, including a screw cutter and a dosing gate. Speed ​​of movement of the DS-99 car at distribution of concrete mix of 2-4 m/min. When constructing a reinforced cement-concrete pavement, a DS-103 trolley is attached to the distributor for transporting a reinforcing mesh (up to 7.35 m wide).
An additional replacement equipment for the concrete distributor or profiler is the DS-106 asphalt paver, which is also used for laying stabilized and other mixtures. In this case, on the concrete distributor, as well as on the profiler, a vibrating beam can be mounted to compact the laid mixtures.
Asphalt paver DS-106 consists of a semi-trailed pneumatic hopper and a screed hung in front of a concrete distributor or profiler. The bunker performs the role of not only a receiving, but also a distributing and dosing device with a rear wall adjustable in height.
The DS-101 concrete paver performs operations on the final distribution of the concrete mixture, semi-automatic laying of reinforcing bars along the axis of the machine and from the sides of the coating to connect concreted strips, the device of a longitudinal seam in freshly laid concrete with filling it with insulating tape and preliminary finishing of the coating. The working parts of the paver are a distributing auger, a first metering gate, a package of internal vibrators, a second metering gate with electromagnetic vibrators, two oscillating forming beams, a screed and side sliding moulds. Working bodies and sliding forms are mounted on an auxiliary frame, which is attached with special pins to the main frame of the concrete paver. Stacker travel speed up to 3.2 m/min.
When constructing mesh-reinforced coatings, the concrete paver is equipped with a reinforcing mesh vibrator DS-102. The vibratory loader is mounted on a semi-trailer two-support pneumatic wheel frame and is attached to the concrete paver using special rods. Two sections of vibratory hammers are attached to the frame with the help of an adjustable shock-absorbing suspension; the vibration of each section is carried out by two mechanical vibrators. The mesh immersion depth is regulated by two hydraulic cylinders.
The paver is equipped with additional equipment: a device for forming the edges of the coating; vibratory cutter of a longitudinal seam in freshly laid concrete; device for laying reinforcing pins.
Concrete finishing machine - tubular finisher DS-104 is designed for final surface finishing of cement-concrete pavement. The main working body of the machine is a smoothing thin-walled pipe, consisting of two sections and located diagonally in relation to the direction of movement of the machine. The screed pipe is equipped with a water spray system for wetting the surface of the coating during its finishing. Finishing of a covering is carried out by shuttle passes for 3-4 times.
The DS-105 machine for applying film-forming materials to the surface of concrete is equipped with a tank with a stirrer, a pump for pumping liquid and a spray device. The machine moves at a speed of up to 10 m/min, applying a thin layer of a moisture-proof film on the surface of the coating or laying out a roll of synthetic film to a width of 3.65 to 7.92 m.
The cutter of transverse seams DS-112 is mounted on a self-propelled pneumatic wheel trolley. The cutter has two carriages (each with two cutting discs) as working elements, which move simultaneously along the frame, cutting transverse seams in hardened concrete.
The DS-115 seam cutter is a four-wheeled trolley with a working body installed on it - a three-disc cutter for cutting longitudinal seams in hardened concrete.
Transportation of the entire set of DC-100 and auxiliary machines and equipment is carried out by two DC-107 trailers with a MAZ-537 tractor.
The set of machines DS-100 for high-speed construction of roads with cement-concrete pavement is designed for an annual output of 50-75 km, so the efficient use of machines can be achieved only if the subgrade is prepared in advance, vehicles are provided (heavy-duty dump trucks of the KrAZ-type 256B) and uninterrupted supply of inert materials and cement to factories preparing cement-concrete mixtures.

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Currently, two technologies are used in road construction in Russia:

• With the use of traditional asphalt concrete pavements, in which the binder is bitumen;
• Using cement-concrete coatings, in which the so-called road concrete is used.

traditional technology asphalt paving not very suitable for the Russian climate. Roads with such a coating are constantly being repaired, but their quality does not improve from this. Experience European countries, who began to build cement-concrete roads, showed the promise of such autobahns. And it's not even about moral old age asphalt concrete technology. It has been discredited by the wrong methods of its application.

Asphalt concrete roads, as an engineering solution, in Europe and the USA are concrete base on which there is a thin layer of asphalt applied. In Russia, asphalt pavement, in which the binder is not cement, but bitumen of the lowest quality, is laid at best on a monolithic base of low-quality “lean” concrete, and most often on gravel or sand bedding.

At present, only a small percentage of Russian highways has a concrete surface, mainly federal highways. Most of the Russian roads do not meet modern transport standards.

Advantages of concrete road surfaces

The technical and economic advantages of cement-concrete pavements over asphalt concrete pavements are undeniable:

• Sufficiently high strength allows the passage of heavy vehicles;
• High surface roughness allows high-speed traffic in rainy weather;
• Small wear of the roadway;
• Resistance of concrete for road construction to aggressive environmental influences;
• No dust;
• Small amount of current repair work;
• Durability in comparison with asphalt concrete roads, the service life reaches 50 years;
• Possibility of mechanization at all stages of construction.

According to experts, the continuation of the asphalt-bitumen strategy in the construction of Russian roads will not allow getting out of the vicious circle of "laying-repair", although huge funds are allocated annually for road maintenance.

The main differences between road concrete

The extreme nature of the operation of concrete pavements of autobahns is distinguished by the following negative factors:

• Cyclically changing freezes and thaws;
• Moisturizing and drying.

Due to such a set of negative impacts, the concrete roadbed is constructed from a special concrete material that differs from conventional types of concrete used in construction and landscaping. Concrete paths in a private house are poured with a completely different composition than a federal highway or an airfield runway.

Concrete road surfaces have the following positive characteristics:

• Increased wear resistance;
• High performance mechanical strength in compression and tensile bending;
• Low abrasion;
• Resistance to temperature changes;
• Frost resistance;
• Moisture resistance.

Comparative formulation of road concrete

Modern highways are constructed from heavy concrete, which incorporate heavy fillers with a fraction size exceeding 5 mm. The density of such concretes ranges from 1800-2500 kg/cu. m. Filler - gravel and crushed stone, which is based on basalt, granite, limestone.

It is important! For comparison, lightweight concretes, which include foam concrete, expanded clay concrete, wood concrete and other similar materials with a loose filling component, have a density in the range of 500-1800 kg / cu. meter.

For the construction of highways and urban roads, for transport routes at industrial facilities, in the construction of airfields, in the manufacture of curbs, heavy concretes are used with a high content of crushed stone filler and a reduced weight fraction of binder-cement, called "lean concretes". Such a dosage reduces the cost of producing a concrete mixture for an extended range of building structures, since a mixture of such a composition is cheaper than high-quality concrete compositions.

The composition of lean concrete includes:

• 1 weight part of binder-cement;
• 3 parts by weight of filler-sand;
• 5 or 6 weight parts of fillers - gravel or crushed stone.

The dosage of water is determined based on the requirements for road concrete of a given grade and the grade of cement used. Ordinary lean concrete is characterized by rigidity (F), which differs from ready-mixed concrete prepared according to the recipe regulated by GOSTs. In the range of produced lean concretes there are compositions with rigidity Zh1-Zh3 and super-rigid compositions SZh1-SZh3, however, the following grades are most popular:

• M100 V7.5 Zh4 and
• M200 V15 Zh4.

Road concrete is a slightly different composition compared to lean concrete.

The difference lies in the content of special plasticizers, which give road concrete a higher mobility compared to lean concrete, which is important when laying road concrete in the process of road construction. The indicator of the mobility of the mixture P1 is added to the marking of road concrete. For example, the designation of one of the grades of used concrete road mixes M150 P1 F100 W2 is class B12.5. The corresponding letters in the designation mean the following indicators:

• "P" - the mobility of the mixture;
• "F" - frost resistance of the mixture;
• "W" - water resistance.

Rationing the water-cement ratio W / C allows you to more clearly subdivide the strength characteristics for road concrete intended for a particular type of coating. In different climatic zones for concrete of single-layer pavements or the upper layers of two-layer road pavements, W / C is taken within 0.5-0.55. In the same two-layer coatings, the bottom layer is produced with a W / C index exceeding 0.6.

But for modernized coatings, the base is made from mixtures with non-standard W / C.

It is important! Road concrete should be delivered only by dump trucks, as the mixture is stratified in automixers, the characteristics and quality of road concrete are lost.

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Road repair equipment

Construction of cement concrete pavements

The technology of cement concrete pavement installation consists of the following operations: - preparatory work; - delivery of the prepared mixture to the installation site; – mixture distribution; – formation of a constructive layer; – compaction of the cement-concrete mixture; – surface finishing of cement concrete pavement; – maintenance of freshly laid concrete; - arrangement of seams; - sealing seams.

The preparatory work for the installation of cement-concrete pavements includes: 1) installation of copy strings, which ensure the evenness of the structural layers of the pavement and their planned and high-altitude location during the operation of concrete paving machines with sliding formwork; 2) installation of rail-forms for the operation of machine sets on rail-forms;

3) procurement and installation of reinforcement and structures of expansion joints.

The tension of the copy string is made from two sides for the operation of the concrete paver with a sliding formwork. Copier strings are fixed in brackets on racks. Racks are set using a theodolite and a level at a distance of 4-6 m from each other on curved sections and after 15 m on straight lines. Brackets are mounted on racks at a height of 0.5-1.0 m from the surface of the underlying layer. The deviation of the copy string from the vertical marks should not exceed ±3 mm.

Installation of rail forms is a labor-intensive operation performed with the help of surveying tools and a truck crane. Rail-forms are intended for the movement of a set of machines along them and at the same time they are a formwork for concrete.

Rail-forms should be installed on a planned base with a width of at least 0.5 m on each side of the concreting (made of crushed stone, gravel or soil reinforced with binders) or on a base widened for this under cover. It is not allowed to settle the base from the impact of concrete-laying machines during laying. To do this, the installed rail-forms should be run in with the heaviest machine of the set. Deviation of marks of rail forms after running-in should not exceed +5 mm. Directly before laying the concrete mixture, the rail-forms must be lubricated with inside used oil.

Rail-forms should be separated from concrete using devices that ensure the integrity of the side faces and edges of the laid layer, not earlier than 24 hours after laying.

When installing cement concrete pavements in areas of high embankments above pipes, on the approaches to overpasses, bridges, the coating layer is reinforced.

Metal meshes are installed in the design position using concrete crackers or reinforcing embedded parts.

Delivery of the prepared mixture to the place of laying can be carried out by various vehicles, taking into account the amount of work and the distance of transportation. The range of transportation of the mixture should be calculated taking into account the temperature and humidity of the surrounding air, on which the setting speed of the cement concrete mixture depends. According to SNiP 3.06.03.-85, the mixture must be delivered to the place of concrete work no later than 30 minutes at an air temperature of 20-30 ° C, 60 minutes - at a temperature of 10-20 ° C.

To control the fulfillment of this condition, it is necessary to keep a strict record of the order of movement of vehicles, if the CCB serves only this object, or each vehicle must be provided with accompanying documents (mixture passport), which indicate the brand of cement concrete mixture, the mobility of the mixture, the time of its preparation and installation place. In places of unloading, it is necessary to equip washing points for cleaning car bodies from the remains of the cement-concrete mixture. Motor vehicles must have a waterproof body with a smooth, even surface.

Long-term transportation adversely affects the quality of mobile mixtures. It is not recommended to transport mobile mixtures in vehicles without prompting on the way over a distance of more than 10 km on a good road and 3 km on a bad one. Concrete mixer trucks are used as concrete trucks with impulse. Concrete mixer trucks are also used for preparing concrete mix en route to the place of laying.

The range of transportation of dry mixes is limited for economic reasons by the distance over which ready-made concrete mixes can be transported with impulsion (slow rotation of the drum 3-4 rpm) without compromising the quality of the mix.

When installing cement concrete pavements, the most time-consuming operations are the distribution, formation, compaction and surface finishing of the cement concrete pavement. For the production of these operations, sets of concrete paving machines are currently widely used.

The development of concrete paving machine sets is carried out in two directions: the creation of high-performance concrete paving machines with sliding formwork and concrete paving machines using rail forms.

Slipform pavers are tracked machines designed for continuous laying of cement concrete pavements in the construction of roads, airfields, canals. Traditionally, for these purposes, sets of concrete-laying machines DS-100 and DS-110 were used, at present a number of companies are entering our market offering their services in updating the fleet of construction machines.

Wirtgen slipform pavers are highly economical. Their modular design allows the machine to be quickly reconfigured depending on the job ahead.

Sliding molds can be hung between the running gears or sideways using the "offset" (offset) method. Thus it is possible to use the same machine for a 7.5 m wide pavement and for a edging drainage tray, reinforcing strip, guide wall.

The unloading of the cement concrete mixture is carried out directly on the base in front of the concrete paver or concrete mix distributor, if the base is strong enough for vehicular traffic. Otherwise, the mixture is unloaded into a receiving hopper located on the side. From the receiving hopper, the mixture is fed by a conveyor to the distributor auger. The distributor screw consists of two parts, each of which can rotate in two directions. This ensures uniform distribution of the cement concrete mixture across the width. Wirtgen's SP 1600 slipform pavers make it possible to form two-layer cement concrete pavements in one pass. One concrete paver is used for the simultaneous laying of the concrete base layer and concrete cover.

The cement-concrete mixture for the foundation device is fed directly to the foundation in front of the concrete paver, and the mixture for the top layer of the cement-concrete coating is fed into the receiving hopper located on the side or in front of the concrete paver. From the receiving hopper, the cement-concrete mixture is fed by a conveyor to the working body, which distributes and compacts the top layer of the cement-concrete coating. Sliding formwork can form the side surface of the layer to be flat or curved for better adhesion between adjacent strips.

The formation of the mixture along the width of the coating is carried out by the concrete mix distributor or by the concrete paver itself. When using a distributor, the concrete mixture is distributed to a given width with a certain thickness margin for compaction. The margin for compaction is specified by trial concreting.

The compaction of the cement concrete mixture and the final formation is carried out by a concrete paver. To compact the mixture, the concrete paver is equipped with internal vibrators, vibrating bars and a screed.

When vibrating, the grains of crushed stone and sand are denser, and the air in the mixture is forced out. When compacting, different vibration frequencies are used. Low frequencies contribute to the compaction of larger particles, and high frequencies - to small ones. In this case, dense concretes are obtained with a short duration of vibration. The oscillation frequency is in the range of 460-1000 Hz.

The quality of vibrocompaction also depends on the duration of vibration. Its optimal duration depends on the workability of the mixture and is in the range of 60-90 seconds.

When vibrocompacting cement concrete surfaces, the upper layers are often enriched with excess water squeezed out from the thickness of cement concrete. This can lead to an increase in the porosity of the cement stone and a decrease in the strength of the top layer.

For the final finishing of the coating, the set of machines for the device of cement concrete pavements includes a concrete finishing machine - a pipe finisher. The working body of this machine is an asbestos-cement pipe suspended from the frame of the machine. By moving the pipe over freshly laid concrete, the surface is smoothed out. To prevent the destruction of the edges of the freshly laid coating during the first passes, the asbestos-cement pipe is installed at an angle to the axis so that the edges of the pipe do not reach the edges of the coating by 15-20 cm.

To remove the water squeezed out during vibration, the concrete finishing machine provides for hanging a moisture-absorbing cloth, such as burlap. At the end of the working shift, the burlap is thoroughly washed, cleared of cement laitance. The finishing machine also has an attachment for applying grooves to create a roughness. The average depth of the roughness grooves, determined by the "sand spot" method, depending on the required value of the coefficient of adhesion of the wheel with the coating, should be in the range of 0.5-1.5 mm. The texture of the treated coating must be uniform.

The next technological operation is the care of hardening concrete. This operation consists of a set of measures that provide favorable conditions for the hardening of the mixture laid in the coating. Measures include preventing the evaporation of moisture from concrete, which is necessary for the process of concrete structure formation, as well as protecting it from mechanical damage in the initial period of curing.

The duration of care is up to the set of design strength, but not less than 28 days.

To prevent the drying of concrete pavements, the surface is treated with film-forming materials, which can be used as powder (PM-86), lacquer "Etinol", bituminous emulsions. Bituminous emulsions are used less often, as the creation of a dark surface contributes to the heating of the coating, which is detrimental in the early stages of curing. To reduce surface heating after film formation, the coating treated with bitumen emulsion should be covered with a layer of sand 5 cm thick or a suspension of aluminum powder or lime mortar is applied to brighten the surface.

Currently, film-forming materials of the PM type are used to care for concrete. They are applied to the concrete surface in an amount of at least 400 g/m2 at an air temperature of up to 25 °C and 600 g/m2 at a temperature of 25 °C and above, as a rule, in two layers with an interval of 20-30 minutes.

Film-forming materials must be applied by spraying with a multi-nozzle distributor evenly over the entire exposed surface of the slab (including the side edges) after finishing the coating.

Film-forming materials of the PM type should be applied after the moisture has evaporated from the concrete surface (the surface becomes dull), and an aqueous bitumen emulsion should be applied immediately after finishing the surface of the concrete coating. In the event of a delay in the application of film-forming materials, fresh concrete must first be protected by applying a moisture depressant to prevent drying of the surface. As a depressant for moisture evaporation, a depressant of the DSSh brand should be used at a flow rate of 5-10 g/m2. Wet burlap is allowed. In the event of precipitation, rolled vapor-tight materials should be used.

To reduce the stresses arising from seasonal and daily changes in air temperature, expansion joints of compression, expansion and warpage are installed in cement concrete pavements.

At an air temperature exceeding that at which the coating was arranged, thermal elongation of the cement-concrete coating slabs occurs; expansion joints are arranged to ensure such an elongation.

The length of the concrete pavement increases in proportion to the distance between the expansion joints, the thermal expansion coefficient of the concrete, and depends on the difference in pavement temperatures at the moment and at the time of laying. In expansion joints, the coating is cut across the entire thickness of the slab and over the entire width. This is done with a wooden lining.

At air temperatures below that at which the cement concrete mixture was laid, the cement concrete pavement slab tends to shorten. Compression joints allow for shortening of concrete pavement slabs. When the length of the slab is reduced, the frictional forces between the coating and the base cause tensile stresses in the cement concrete coating. Compression seams reduce these stresses and the associated potential for cracking. In compression joints, the coating is cut across the entire width by 1/3 - 1/4 of the thickness, below this slot, and a crack occurs later.

Seams in the longitudinal direction are arranged with a coating wider than 4.5 m. This seam is called a longitudinal seam, or warp seam, as it allows for the possibility of thermal warping in the transverse direction and reduces the likelihood of longitudinal cracks.

Grooves of expansion joints should be cut mainly in hardened concrete with diamond discs when the concrete reaches a compressive strength of 8-10 MPa. The device of seams and grooves of compression seams is allowed in a combined way: laying in freshly laid concrete an elastic gasket and cutting a groove along it in the hardened concrete.

The expansion joint element (Fig. 4.15) should be securely fastened with pins before concreting in accordance with the project. Before installation in the design position, the board lining should be soaked in water for 24 hours or lubricated on all sides with liquefied bitumen. The pins of the transverse compression joints should be installed in the design position before concreting the pavement using supporting devices or embedded into freshly laid concrete by vibration immersion.

Rice. 4.15. Typical design of a transverse expansion joint: 1 - reinforcement; 2 - reinforcing body; 3 - wooden gasket; 4 - bituminous coating; 5 - plastic cap; 6 - rubber compensator

The start time for grooving the joints should be determined based on concrete strength data and verified by test cutting. During test cutting, chipping of the edges of the seams should not exceed 2-3 mm. With daily air temperature fluctuations of less than 12 °C, the grooves of the transverse compression joints in the coating should be cut on the same day. If it is impossible to cut all the seams in a row due to unacceptable chipping of the edges of the seam, control compression seams should be arranged through three or four slabs using a two-stage method: cutting a narrow groove of the seam with one diamond disk when the concrete compressive strength is reached about 5-7 MPa and subsequent cutting the upper part of the joint to the design dimensions when the concrete strength reaches more than 10 MPa. If it is impossible to install control seams using a two-stage method and cracks appear in the coating, control seams should be arranged in a combined way.

With a daily air temperature difference of more than 12 ° C, the grooves of the transverse compression joints in the coating laid before 13-14 hours should be cut on the same day. In the coating laid in the afternoon, to ensure crack resistance, control transverse seams should be arranged through two or three slabs in a combined way, and subsequent cutting of intermediate seams should be made in hardened concrete.

When arranging control transverse seams in a combined way, an elastic tape (gasket) with a thickness of 0.2-3.0 mm should be laid in the concrete, and then a seam groove in the hardened concrete should be cut along the tape. As an elastic gasket, polyethylene tape and other similar materials can be used after finishing the surface of the concrete pavement. Installation of the tape according to SNiP 3.06.03.-85 is not allowed if the concrete mixture has lost its mobility and the tape is not monolithic. The tape should be laid to a depth of at least 1/4 of the coating thickness and protrude 0.5-1.0 cm above the surface.

At the end of the work shift and in the event of a forced break in work, work transverse seams should be arranged, as a rule, by the type of warping seams using an attached formwork. The laying of the coating from the working joint should be continued after the formwork has been removed and the end of the slab has been coated with thinned bitumen or film-forming material. If an expansion joint is required at a given place, it is arranged at a distance of one plate before or after the working joint.

Joint sealing work is carried out in dry weather at an air temperature of at least +5 °C. Filling of joints cut in freshly laid concrete is carried out after 7 days, and in hardened concrete - immediately after they have been washed and dried.

Works on filling expansion joints with mastics prepared on the basis of bitumen should be carried out in the following sequence: and lay a cotton cord on the bottom of the groove of the joint; and lubricate the walls of the groove of the seam with liquefied bitumen; and fill the groove of the seam with mastic 2-3 mm above the level of the coating;

□ Cut off excess mastic that protrudes above the seam groove with a sharp scraper.

Sealing materials prepared on the basis of bitumen must be heated to a temperature of 150-180 °C before use.

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Concrete, cement-sand and mosaic (terrazzo) coatings

Cement-sand floors are used only in utility and service rooms, usually located in the basement floors, as well as on alcons, in boiler rooms, coal rooms, etc. with a rail and a novation plane, no more than 10 mm are allowed. With large gaps, irregularities are filled with a hard cement-sand mortar. When leveling the concrete base, the surface is pre-incised and thoroughly washed with water before laying the cement-sand mortar. Aligned places are compacted with surface vibrators and leveled without grout for better adhesion to the monolithic coating. When controlling the quality of mosaic floors, it is necessary first of all to check the quality of the raw materials: - the size of crushed stone and gravel is allowed no more than 15 mm or 0.6 of the coating thickness; - mosaic chips (fine crushed stone) and sand for mosaic composition should be made from polished hard rocks - marble, granite, basalt, etc. with a compressive strength of at least 600 kg / cm2; for monolithic floors it is allowed to use pure quartz sand; - for white or light-colored mosaic coatings, white (GOST 965-78) or bleached ordinary cement should be used; for bleaching, stone powder with a particle size of not more than 0.15 mm is added to ordinary cement from white or light stone materials with a compressive strength of at least 200 kg / cm2 in an amount of 20-40% of the mass of cement. In the manufacture of colored coatings, it is necessary to strictly control that for coloring only silk-resistant, light-resistant mineral pigments are added to white or bleached cement in an amount of not more than 15% of the volume of cement. The use of gypsum and lime for whitening cement is prohibited. Mosaic mixture (concrete) and cement-sand mortar are laid into the coating in strips (sections) not more than 2.5 m wide, bounded by slats that simultaneously serve as beacons. The height of the installed rails should be 30 mm, which after grinding provides a floor thickness of 20 and 30 mm in the high sections of the base. The mixture is placed 3-5 mm above the rails based on its compaction during vibration. The mixture is compacted with platform vibrators or vibrating screeds. Excessive vibration can cause most of the large grains to settle, resulting in a uniform surface after grinding and reducing the wear resistance of the concrete floor. Therefore, vibration and tamping must be stopped immediately after the appearance of laitance on the surface. After compaction, the surface of the coating is smoothed with steel trowels. Smoothing should be completed before the concrete or mortar begins to set. Sprinkling of cement on mosaic and concrete pavements during their smoothing is prohibited; ironing of cement-sand coatings is allowed only if indicated in the project. After compaction and smoothing, the beacon rails are carefully removed, and the grooves are filled with a mixture and smoothed with steel trowels to the same level as the compacted surface. As veins, depending on the pattern of the floor, strips of aluminum, brass, plastic are used, which can also serve as beacons at the same time. The upper layer of the mosaic mass is laid 1-2 hours after laying the lower layer and aligning the veins. The processing of the mosaic flooring is carried out similarly to the processing of single-layer simple mosaic floors. Before final grinding with fine-grained stones, the surface of the coatings must be washed with water, and small scratches and pores should be carefully rubbed with cement with the addition of stone flour (and for color coatings with the addition of pigment). When resuming the laying of monolithic floors after a break in work, the vertical edge of the hardened concrete or mortar is cleaned of the cement film, dust and dirt with steel brushes, moistened and primed with cement milk with wash brushes.
Rice. 39. Installation of veins in mosaic floors: a - varieties of veins; b - installation of veins; 1- glass vein; 2 i. 3- metal veins with various fasteners; 4 - plastic vein; 5 - mosaic mixture of terrazzo); 6 - cement-sand mortar. Compaction and smoothing of concrete and mortar in places of working seams is carried out until the seam becomes invisible. To increase the durability of cement-sand coatings, they are ironed. Ironing must be completed before the cement>sand mortar begins to set. Ironing of the hardened coating is prohibited. To improve the water resistance of concrete, mosaic and cement-sand coatings, fluates, liquid glass and calcium chloride are used. Surface impregnation of fluatam coatings (with aqueous solutions of fluorosilicic acid or its zinc, aluminum and magnesium salts prepared no earlier than 5 days before application) is carried out no earlier than 10 days after laying concrete or cement-sand coatings. Before impregnation, the coating is dried and thoroughly cleaned. It is necessary to control that the impregnation with fluates was carried out three times with intervals of at least 24 hours, and the concentration of the solution was increased with each subsequent treatment (3-7-G2% by volume). Impregnation of the coating with sealing compositions must first be carried out with liquid glass (GOST 13078-67) with a specific gravity of 1.07, and a day later - with an aqueous solution of calcium chloride with a specific gravity of 1.12. On the impregnation of the surface of the coating is an act. After the final grinding of mosaic and concrete floors before putting them into operation, walking on them and transporting materials, mechanisms and tools is not allowed. Finished mosaic and concrete floors are recommended to be sprinkled with wet sawdust, which is removed before putting the floors into operation. When accepting mosaic and concrete polished floors, check the grain. polishing quality, preservation of the veins in the presence of a pattern, the absence of noticeable scratches and potholes. Cement-sand floors must have a perfectly smooth surface. The horizontalness of the floor is determined by applying a control rail in different directions, visible gaps for all types of monolithic floors should not be more than 4 mm.

Asphalt is the main material used for road construction. After a few years, such a coating needs to be repaired, then its operational properties are restored annually. Concrete pavement is much better than asphalt pavement, but it is used to a limited extent. There are reasons for this, related to insufficient funding, low productivity, climatic conditions, insufficient amount of cement of the required grades, and relief areas. This technology is not particularly popular in Russia yet, since asphalt roads are much cheaper. However, we note that gradually the cost of these types of linen is slowly equalized. The construction of concrete roads, bridges, runways at airfields begins.

Advantages of concrete roads

Such coatings have certain advantages:

• the road made of concrete is of good strength, it does not need repair work. The coating can be used for at least four decades, and for asphalt this period is limited to a decade with annual repairs;
• automotive technology consumes less fuel. This is due to the fact that during the movement of a heavy vehicle, road concrete is not subjected to deformation, from which the vehicle needs less fuel to move a fifth;
• The coating is resistant to sudden changes in climatic conditions. It is not affected by heavy rains or sudden changes in temperature;
• there is a preservation of air purity, because cars need less fuel, the exhaust gases of which pollute the environment;
• natural resources are used sparingly. Limestone is used to make concrete, and oil is used to make asphalt.

Construction technology

The device of concrete roads includes certain stages:

1. The ground base is being prepared. It is rolled to achieve the desired density, if necessary, moistened or dried.
2. Water diversion is organized to prolong operational period blades and make driving safer.
3. The underlayment is being installed. It is a sandy layer, the thickness of which is up to two to four tens of centimeters.
4. The formwork structure is being assembled. Its elements are made of lumber, while taking into account the height of the fill.

If water seeps into the ground, the pavement is gradually destroyed.

The construction technology is complex, and each stage will be considered in detail.

Concrete road structure

The canvas includes certain layers:

• underlying - for its device, gravel is used, which drains groundwater, and sand, with which the resulting loads are compensated;
• reinforcing - represented by low-grade concrete that binds the bulk layer;
• the roadbed is a concrete surface.

The construction of a concrete road for heavy vehicles is made of stressed and non-stressed reinforced concrete, the reinforcing frame base in which does not allow the stone to crack from the weight of trucks.

In private types of construction work or when arranging a concrete pavement of roads on soils oversaturated with moisture, a waterproofing material is laid out on a sand cushion, which prevents the roadway from becoming very wet, followed by corrosion of stones and reinforcement. As a waterproofing material, ordinary roofing material is used.

Execution of work

Let's take a closer look at what this or that is. construction stage road concreting.

Training

Earthworks are difficult, and they are quite expensive. Their beginning is preceded by the preparation of a detailed design solution, the conclusions of which are based on geological studies of the area. If there is such an opportunity, then the concreting of roads is carried out horizontally, removing small hills or laying compacted rock in the recesses.

If a major highway is being built, then the layer fertile land removed in full, and for the construction of a concrete road in the yard, it will be enough to remove from fifteen to twenty centimeters of soil.

The prepared base is compacted by rollers and vibration mechanisms, which are characterized by a large weight.

This stage is considered a crucial moment, since the stiffness index and the integrity of the road surface depend on the strength of the base, even when dynamic loads are quite intense.

During earthworks, a drainage system is thought out so that it is possible to remove ground and rain moisture. For this purpose, the base is brought out in a plane, the inclined angle of which is from two to four degrees. Concrete gutters are installed on the sides of the road or slopes of a natural type are arranged, along the slopes of which water will enter the receiving wells or go into the ground.

Litter layer

A sand cushion is arranged, the thickness of which is twenty to forty centimeters. This element can be omitted, but it perfectly protects against moisture coming from the ground, improves the drainage process. The bedding layer is necessary to prevent erosion and heaving during frosts, which leads to the formation of depressions and cracks in the cast-in-place concrete.

Most problems appear on clay, peat and other areas of the terrain that can hold water. In most cases, such layers are partially removed, the bottom is covered with large stones and gravel. The rolled layer reaches a height of thirty centimeters. The costs and time required for construction will depend on such preparation.

The minimum thickness of the base depends on the type of soil and climatic conditions. Determine it according to a special table. If the layer is laid out from various materials, then a geotextile is spread between them.

Align the layers in accordance with the designed slopes. Stone backfills are strengthened with binders - cement, granulated slag from metallurgical production, to which quicklime is added, ash from thermal power plants, ground slag.

formwork

For the manufacture of this structure, boards are used, the height of which corresponds to the level of pouring concrete for the road. As a rule, it is equal to ten to fifteen centimeters. When determining its dimensions, it must be taken into account that ribs are arranged along the edges of the concrete to improve strength. The thickness of the boards should not be less than 5 cm. Each structural element should be covered special composition, which will facilitate detachment from the cured concrete.

Requirements are imposed on wooden formwork panels in terms of strength from expansion by their fresh concrete mass and the forces that arise as a result of tamping.

If heavy equipment is used for the construction of roads made of concrete, with which the concrete is compacted, then a formwork made of steel material should be installed. It will last much longer. At the heart of each element is a sole that improves stability.

Formwork sections are set in one line, firmly fixed. This is especially important if the vibrating of the concrete mass is carried out by heavy machinery. In places where the level of the base is reduced, lean concrete is poured under the formwork to improve stability.

Reinforcement

If the technological process of constructing a concrete road involves this type of work, then the reinforcement should be a metal mesh, the cell area of ​​which reaches 150 mm. sq. This choice of material will make it possible to avoid expansion and the appearance of cracks in the concrete thickness.

Laying of the reinforcing mesh is carried out in the process of pouring the concrete mixture at a height of three to four centimeters from the lower level. Before this, the poured concrete is leveled, the frame mesh is covered, and, if necessary, fixed. Now you can continue to work.

fill

The litter layer is covered with a material that is resistant to getting wet, waterproofing, or simply moistened. Road concrete, corresponding to GOST, is laid out in thickness in one go. When reinforcement is applied, the process is carried out in stages.

Concrete for the road, the brand of which meets all the requirements, is applied quickly, since it does not have a long pot life. It is not recommended to add water to the mass, because the mechanical properties of the coating will deteriorate. Since construction volumes are large, factory-prepared road cement is delivered to the place of work. The mixture is unloaded in one cubic meter and leveled to give the entire layer the same density.

The best option for laying a concrete canvas is two or three layers.

The concrete mixture is compacted by special mechanisms, represented by wooden or metal beams, which are acted upon by pneumatic hammers mounted on them. Such a device descends into the mixture, begins to move in it. Having processed one section, the beam is moved further.

If reinforcement is used, then the vibration device should be located five to seven centimeters above the upper edge of the frame.

In a special machine, in addition to the vibration device, there is also a leveling device located in front.

The concrete composition must be flexible and sufficiently mobile, but not too liquid, so that it cannot float, flowing through the formwork panels. All this will negatively affect the strength of the coating.

Seam cutting

A prerequisite is the device of expansion joints. This type of work is possible when concrete reaches a certain level of strength, which is 50 - 60 percent. In this form, the canvas is able to withstand the weight of not only the worker, but also a special tool for cutting seams.

In this way, the thermal expansion to which concrete is subjected to varying degrees is compensated. Road segments do not form cracks during seasonal changes.

Sawing is performed by jointing - a special tool. The distances between the seams are determined by design calculations. As a rule, for this, the thickness of the monolithic coating is multiplied by thirty.

To prevent moisture from getting into such seams, they are filled with mastic.

Materials for constructing a concrete web

M400 - universal concrete composition. Its strength allows it to withstand loads from various wheeled vehicles. The basis is Portland cement, which is resistant to moisture. Plasticizers are also added to the solution to improve hydrophobicity and strength.

The concrete mixture consists of:

• cement - 1 part;
• gravel - 5 parts;
• sand - 2 parts.

The composition of concrete and its characteristics are specified in the construction project.

Slab covering device

Concrete slabs for the road are made as follows:

1. Forms of the required size are being prepared, or formwork panels are being set up.
2. If necessary, a reinforcing cage is prepared to improve the strength of the plates.
3. Pouring is carried out with a ready-made concrete mixture, it is advisable to immediately tamper to remove air bubbles.
4. After some time, when the concrete hardens, you can remove the formwork and give the slabs time to gain the desired strength.

With the help of such material, you can make a concrete road with your own hands. Under all conditions, it will serve you well for a long time.

Conclusion

The concrete pavement of the road is durable, but needs some care. The resulting cracks must be immediately repaired so that they do not increase in size. To do this, use special putty compositions or concrete mortar. If a fracture has formed, the entire section of the concrete sheet should be removed.

Cement-concrete pavement is a capital hard type pavement designed for any heavy traffic.

Such coatings are different:

- high strength;

- durability;

- a safer level of traffic at night;

- high adhesion coefficient of the coating, which does not change when moistened;

— high level mechanization and automation;

- the ability to conduct construction work under adverse conditions;

- low wear of the coating (0.1-0.2 mm/year).

With all the above and obvious positive points, there are also disadvantages of these types of coverage:

- difficulties arising during the repair of the coating;

– impossibility to open traffic immediately after the completion of construction;

- the need for expansion joints.

Cement-concrete pavements with an embankment height of more than 1.5 meters are built in the second year.

​Requirements for road c/w coatings:

​Cement concrete must be strong and frost-resistant (F).

Frost resistance is estimated by the number of cycles of alternate freezing and thawing of water-saturated samples at the age of 28 days without a decrease in strength by more than 25% and a loss in weight of not more than 5%.

Road cement-concrete pavements are divided into grades that characterize its tensile strength in bending and compression.