Concrete road: construction technology

The main material for the construction of roads is asphalt. In three years, they need repair, and then an annual restoration of operational properties. The concrete road considerably exceeds asphalt in many respects, but its application is limited.

The reasons for this are the following:

• Insufficient budget for construction;
• Low productivity;
• climate;
• Transport loads;
• Shortage of necessary grades of cement;
• The terrain.

In the United States, concrete roads are the national treasure (photo below).

Back in the 1950s, in America and the West, they understood their advantage and construction was well under way.

Previously, concrete roads in Russia were laid out of slabs, driving by car resembled the movement of a train at the junctions of rails. Now it is poured in place and the coating is smooth.

What are concrete roads used for?

The concrete road has the following advantages:

• Ease of preparation of concrete mix ;
• High speed stacking;
• High strength and durability;
• A smooth surface with good grip with tires;
• Better visibility than asphalt due to good reflectivity.

Concrete roads have operational advantages, which consist in transferring loads from a rigid concrete slab to a large part of the base. This is especially evident in the spring period. The deflection of asphalt often occurs irreversibly, as can be seen from the appearance of ruts and waves. The concrete cover reduces this deflection, while achieving fuel savings of up to 20%.

Environmental benefits are associated with the absence of soil contamination with oil products, which are released from the asphalt. Reducing fuel consumption reduces emissions to the atmosphere. It is believed that a harder coating produces more noise, but this increase is insignificant.

Influence of the terrain on road construction

An automobile concrete road is built using various technologies. Each project is different. In mountainous areas the road repeats the terrain.

When building highways, they try to straighten it: hollows are falling asleep, the hills are cut, tunnels are being built through the mountains, overpasses and bridges are being built. To ensure a normal speed mode, builders try to avoid steep climbs, descents and turns.

For different road designs, the main classification is made from topcoat materials, which may be asphalt or concrete. Asphalt must be repaired in 3-4 years. Some roads of great length begin to be rebuilt when the construction is not finished yet. Concrete road costs 80% more expensive, but it does not require repair for the first 10 years of operation. Its durability reduces operating costs. If the concrete road laying is executed qualitatively, it serves several decades without major repairs.

Structure of the roadway

The construction of concrete roads is made of the following layers:

• additional,
• Underlying;
• Concrete covering.

Soil Preparation

Pouring with concrete is preceded by preparing the soil and making an equalizing layer. The soil should be dense. This can be easily verified by sticking a steel rod up to 12 mm thick in it. It should enter a depth of not more than 60 cm. If the seal is not sufficient, the cushion will subsequently crawl and the concrete will collapse.

Primer pre-roll. Particularly this is given attention when it is poured. In this case, the rolling is done layer by layer. Soil compaction is done at optimum humidity. The number of passes and the type of rink should be selected experimentally, making a test roll-out. If the humidity is below the allowable value, the soil should be moistened. If it is excessively moist, it is dried by loosening, adding sand, slag, or other means.

Wastewater

When concrete roads are built, the technology provides for the removal of melted, storm and flood waters from them before the erection of the roadbed. Work in this plan is carried out both within the city and outside it.

The construction of a concrete road with the removal of precipitation is necessary in order to increase the service life and improve driving conditions. On the surface of the road, water is dangerous for transport when it moves. The adhesion to the canvas deteriorates, splashes from under the wheels interfere with the survey, and ice forms during freezing. To remove it, the road surface must be inclined in the transverse and longitudinal directions, and drainage layers are also made. The base under the road is leveled and a slope is created in it, which can be a single-pitched or two-pitched one. Places where water can collect, level and fall asleep with undrained soil.

Outside the city, water from the roadway is removed into the road cuvettes. Their width is 1-2.5 m. The water is collected in them and diverted to the water intake: a gutter, a natural or artificial pond, the river bed. For this, a gradient of 1-4% is created in the cuvette, reinforced with lawn grass, cobblestone, detrital or concrete stone.

In settlements, water through the trays is collected in the city sewer. Devices for its removal are constantly cleaned to provide the required throughput.

Water, which seeps into the ground, is a danger to the road. It is drained through layers of seepage, for example, gravel. It contains drainage pipes with slots or holes. They can be made of plastic, concrete or ceramics.

Work to remove from the road strip thawed, storm and flood waters are made before the construction of the roadbed.

Laying of the litter layer

On the ground is a sand cushion thickness of 20-40 cm without it you can get by, but it significantly prevents the upward flow of moisture from the ground and improves drainage. It is necessary to prevent blur and frost heaving, leading to the appearance of depressions and the formation of cracks in the concrete monolith. The greatest problems are created by soil from clay, peat and any other that is capable of accumulating water. It is partially cut off and stones of large fractions are buried on the bottom, and then gravel. The height of the layers after coiling is about 30 cm. From their preparation depends the costs and how much time concrete roads will be built. The minimum thickness of the substrate depends on the type of soil and climatic zone. It is determined by tables. Between all layers of different materials laid geotextiles.

Leveling of each layer is carried out in accordance with the design longitudinal and transverse slopes.

Stone base materials are usually strengthened with substances that have astringent properties. This can be cement or industrial waste: granulated metallurgical slag with the addition of quicklime, ash from thermal power plants, ground slag. Layers should be monolithic, which is achieved through the use of astringent compounds and thorough rolling.

For the passage of construction machines, it is often necessary to increase the strength of the additional lower layer. For this, it is strengthened with astringent compounds.

Formwork

The formwork is made from sawn timber according to the height of the pouring, which is 100-150 mm. Choosing it in height, it should be borne in mind that at the edges of the concrete slab, ribs are made, increasing its strength. The thickness of the boards should be at least 50 mm. They are covered with a composition that facilitates detachment from the frozen plate. To the timber formwork, the requirements of strength from the rip-off of fresh concrete and the forces arising from the operation of the ramming beam are required.

If heavy road machines are used to compaction and finish concrete, a powerful formwork of steel is installed. It does not warp and lasts much longer. At its base there is a sole that increases stability.

The formwork sections are installed in a line and securely fastened. This is especially important if the vibration of concrete is made by heavy machines. In places where the base level is lowered, layers of lean concrete are poured under the formwork for greater stability.

Concrete roads: technology for making slabs

Before laying concrete, temperature joints are set, allowing the plates to move vertically and horizontally as they expand or contract.

1. Temperature seams

The filling sections are completely separated. To fill the seams, a material that absorbs energy is used: insulating cardboard, softwood, cork with bitumen. To protect from debris and stones of the upper section of the seam to a depth of 40-50 mm, it is necessary to make a waterproofing sealant. If it is not done in time, with the expansion of the slabs, the concrete can split from the stones.

The distance between seams in a temperate climate reaches 20-30 m. The reliability of coating for long plates is 50%, and for short ones - 85%. It is characterized by resistance to cracking between major repairs. Monolithic coating is supported by steel rods located in the seams.

They are installed through the side faces or using a special device on the concrete paver. When the gaps between adjacent slabs are more than 6 m apart, intermediate seams are set on top of the coating to a depth of 1/3 of the thickness of the concrete. Such false seams are made along the axis of the road.

The width of two lanes of the road is 6-9 m. A temperature-shrinkage joint is also made between them, so that longitudinal cracks do not form.

2. Concrete laying

The litter layer is covered with waterproof paper, waterproofing or moistened. Concrete is stacked in thickness at a time. If reinforcement is used, a layer 30-40 mm thick is first filled, a grid is laid on it, and then the formwork is completed.

The concrete mix should be applied quickly, as it is viable for a short time. Dilute it with water it is impossible, because this will lead to a deterioration of the mechanical properties of the plate.

Due to large volumes, ready-made concrete is delivered to the pouring site. After unloading from the car, it is leveled by a special machine equipped with blades with a drive. The mixture is discharged 1 m ³ and evenly distributed, otherwise a large pile will have a higher density at the base than in other places. In the process of equalization, this unevenness is retained, which can lead to increased shrinkage of low-compacted areas. At the same time, hollows are formed on the surface of the plate. The best option is a uniform laying of concrete in 2-3 layers.

3. Concrete consolidation

The equipment for compacting concrete is a bar made of wood or metal, which is affected by pneumatic hammers fixed on it. He immerses himself in the concrete mixture and moves inside it. When the treatment of the site ends, the bar is raised and transferred to another site.

When using reinforcement, the vibrating beam should be 5-7 cm above it.

The vibrating machine contains, in addition to the vibrating machine, also a leveling beam, which is located in front.

The plasticity of the concrete mix requires special requirements. It should be sufficiently mobile, but not too liquid, otherwise it will be drifted, flowing through the formwork - strength deteriorates.

After a small hardening, the concrete slab is watered to prevent cracks from drying out. It is covered with sand, straw mats, burlap or tarpaulin. A modern method of protection against evaporation is the spraying on the surface of the plate of the hardening sealant. The film-forming substance is applied to the entire surface and the side faces. Before this, it is required to remove excess moisture from the coating.

The poor quality of the concrete mix leads to the need for frequent road repairs.

Conclusion

The technology of construction of concrete roads is constantly being improved, thanks to the following:

1. Improvement of skills and experience of specialists.
2. Availability of multifunctional and high-performance equipment.
3. Improving technical equipment, which reduces manual labor.
4. The use of new modern materials.

Despite the high cost, the cost of repairing concrete roads is much less than for repairing asphalt.