Asph alt is the main material for road construction. After three years, they require repair, and then the annual restoration of operational properties. The concrete road is vastly superior to the asph alt road in many respects, but its use is limited.
The reasons for this are as follows:
- insufficient construction budget;
- poor performance;
- climate;
- transport loads;
- shortage of needed grades of cement;
- terrain.
Concrete roads are a national treasure in the US (pictured below).
Even in the 50s in America and the West they realized their advantage and construction went on at full speed.
Earlier, concrete roads in Russia were laid out from slabs, driving a car resembled the movement of a train at the junctions of rails. Now it is poured on the spot and the coating is even.
What are concrete roads for?
Concrete road has the following advantages:
- easy to prepare concretemixes;
- high speed styling;
- high strength and durability;
- smooth surface with good tire grip;
- better visibility than asph alt due to good reflectivity.
Concrete roads have the operational advantage of transferring the load from a rigid concrete slab to a large portion of the base. This is especially evident in the spring. Asph alt deflection is often irreversible, as can be seen from the appearance of ruts and waves. Concrete pavement reduces such deflection, while achieving fuel savings of up to 20%.
Environmental benefits associated with the absence of soil pollution by oil products that are released from the asph alt. Lower fuel consumption reduces emissions into the atmosphere. A harder finish is said to produce more noise, but the increase is negligible.
The influence of terrain on road construction
Automobile concrete road is being built using different technologies. Every project is different. In mountainous areas, the road follows the terrain.
When building highways, they try to straighten it: depressions are filled up, hills are cut off, tunnels are built through mountains, overpasses and bridges are built. To ensure a normal speed regime, builders try to avoid steep ascents, descents and turns.
For different road constructions, the main classification is made according to the materials of the top surface, which can be asph alt orconcrete. Asph alt needs to be repaired after 3-4 years. Some long-distance roads begin to be rehabilitated before construction is complete. A concrete road costs 80% more, but it does not require repair for the first 10 years of operation. Its durability reduces operating costs. If the laying of a concrete road is done well, it will last for several decades without major repairs.
Road structure
The construction of concrete roads is made from the following layers:
- extra,
- underlying;
- concrete pavement.
Soil preparation
Concrete pouring is preceded by soil preparation and the manufacture of a leveling layer. The soil must be dense. This is easy to check by sticking a steel bar up to 12 mm thick into it. It should enter to a depth of no more than 60 cm. If the compaction is insufficient, the pillow will further sag and the concrete will collapse.
The soil is pre-rolled. Particular attention is paid to this when it is added. In this case, rolling is done in layers. Soil compaction is done at optimal moisture. The number of passes and the type of roller should be selected experimentally, making a trial rolling. If the humidity is below the permissible value, the soil should be moistened. If it is excessively damp, it is dried by loosening, adding sand, slag, or other means.
Water disposal
When concrete roads are built, the technology provides for the removal of thawed, storm andflood waters even before the construction of the subgrade. Work in this regard is carried out both within the city and beyond.
The installation of a concrete road with precipitation removal is necessary in order to increase the service life and improve driving conditions. On the surface of the road, water is dangerous for vehicles when it is moving. The adhesion to the canvas deteriorates, splashes from under the wheels interfere with the view, and ice also forms when freezing. To remove it, the road surface must be inclined in 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 single-slope or dual-slope. Places where water can accumulate are leveled and covered with non-draining soil.
Outside the city, water from the roadway is removed into road ditches. Their width is 1-2.5 m. Water is collected in them and discharged into water intakes: a sewer, a natural or artificial reservoir, a river bed. To do this, a slope of 1-4% is created in the ditch, reinforced with lawn grass, cobblestone, detrital or concrete stone.
In settlements, water is collected through trays in the city sewer. The evacuation devices are constantly cleaned to ensure the required throughput.
Water that seeps into the ground is a danger to the road. It is discharged through seepage layers such as gravel. It contains drainage pipes with slots or holes. They can be plastic, concrete or ceramic.
Works on the removal of thaw, storm and flood from the road stripwaters are made before the construction of the subgrade.
Laying bedding
A sand cushion 20-40 cm thick is made on the ground. You can do without it, but it significantly prevents moisture from rising upwards from the soil and improves drainage. It is necessary to prevent blurring 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 made of clay, peat, and any other that is capable of accumulating water. It is partially cut off and stones of large fractions are poured to the bottom, and then gravel. The height of the layers after rolling is about 30 cm. The costs and how long the concrete roads will be built depend on their preparation. The minimum base thickness depends on the type of soil and climate zone. It is determined by the tables. Geotextile is laid between all layers of different materials.
The leveling of each layer is carried out in compliance with the design longitudinal and transverse slopes.
Stone base materials are usually reinforced with substances that have astringent properties. It can be cement or industrial waste: granular metallurgical slag with the addition of quicklime, ash from thermal power plants, ground slag. The layers must be monolithic, which is achieved through the use of binders and careful rolling.
For the passage of construction vehicles, an increase in the strength of an additional bottom layer is often required. To do this, it is strengthened with astringents.
Formwork
Formwork is made from lumber in heightfill, which is 100-150 mm. When choosing it in height, it should be borne in mind that ribs are made at the edges of the concrete slab, which increase its strength. The thickness of the boards must be at least 50 mm. They are coated with a compound that facilitates detachment from the frozen plate. Wooden formwork is subject to strength requirements from the expansion of fresh concrete and the forces arising from the operation of the tamper bar.
If heavy road machines are used for compacting and finishing concrete, a powerful steel formwork is installed. It does not warp and lasts much longer. It features a midsole for added stability at the base.
Formwork sections are lined up and securely fastened. This is especially important if the vibration of concrete is done by heavy machines. In places where the level of the base decreases, layers of lean concrete are poured under the formwork for greater stability.
Concrete Roads: Slab Manufacturing Technology
Expansion joints are placed before the concrete is placed, allowing the slabs to move vertically and horizontally as they expand or contract.
1. Expansion joints
Pouring sections are completely separated. To fill the joints, energy-absorbing materials are used: insulating cardboard, soft wood, cork with bitumen. To protect the upper section of the seam from debris and stones to a depth of 40-50 mm, it is necessary to waterproof with a sealant. If it is not done in time, when the slabs expand, the concrete may break off due to stones.
Seam spacing in temperate climatesreaches 20-30 m. The reliability of the coating for long slabs is 50%, and for short slabs - 85%. It is characterized by resistance to cracking between overhauls. The solidity of the coating is maintained by steel rods placed in the seams.
They are installed through the side edges or using a special device on the concrete paver. When the gaps between adjacent slabs are at a distance of more than 6 m, intermediate seams are installed on top of the coating to a depth of 1/3 of the concrete thickness. Such false seams are also made along the axis of the road.
The width of the two lanes of the road is 6-9 m. A temperature-shrinkage seam is also made between them so that longitudinal cracks do not form.
2. Concrete placement
The litter layer is covered with waterproof paper, waterproofing or moistened. Concrete is laid in thickness at a time. If reinforcement is used, first a layer 30-40 mm thick is poured, a mesh is laid on it, and then the formwork is completely filled.
Concrete must be applied quickly as it has a short pot life. It must not be diluted with water, as this will lead to a deterioration in the mechanical properties of the plate.
Due to the large volumes, ready-made factory concrete is delivered to the pouring site. After unloading from the vehicle, it is leveled by a special machine equipped with powered blades. The mixture is discharged in 1 m3and evenly placed, otherwise a large pile will have a higher density at the base than elsewhere. ATDuring the leveling process, this unevenness persists, which can lead to increased shrinkage of poorly compacted areas. In this case, depressions are formed on the surface of the plate. The best option is to evenly lay concrete in 2-3 layers.
3. Concrete compaction
Concrete compaction equipment is a bar made of wood or metal, which is affected by pneumatic hammers mounted on it. It is immersed in the concrete mixture and moves inside it. When the processing of the site ends, the beam is lifted and transferred to another site.
When using reinforcement, the vibrating bar should be 5-7 cm above it.
The vibrating machine contains, in addition to the vibrating screed, which is located in front.
Special requirements are imposed on the plasticity of the concrete mix. It should be sufficiently mobile, but not too liquid, otherwise it will sag, flow through the formwork - strength deteriorates.
After a slight hardening, the concrete slab is poured with water so that cracks do not form from drying. It is covered with sand, straw mats, burlap or tarpaulins. A modern way to protect against evaporation is to spray a hardening sealant on the surface of the plate. The film-forming substance is applied to the entire surface and side faces. Before this, it is required to remove excess moisture from the coating.
Poor quality concrete results in frequent road repairs.
Conclusion
Concrete road construction technology is constantlyimproved by the following:
- Increasing the qualifications and experience of specialists.
- The availability of multifunctional and high-performance equipment.
- Improve technical equipment to reduce manual labor.
- The use of new modern materials.
Despite the high cost, the cost of repairing concrete roads is much less than repairing asph alt roads.
