Reinforced concrete sleepers: main types, characteristics

In this article we will talk about what these products are, as well as what are the features of their production and operation. Consider where used concrete sleepers used, and what are the requirements for manufacturers of this type of materials.

Initially, stone bars were placed under the railroad rails. A little later, the stone was replaced by wood, which not only possessed the best cushioning qualities, but was also easier in terms of machining. However, the situation changed dramatically only when the production of reinforced concrete sleepers began.

A bit of history

As already mentioned, the history of railways has several varieties of supports, which fit under the rails. All solutions had a number of operational flaws. For example, the stone was extremely difficult to process and had low amortization properties.

In addition, despite the apparent strength, these plates were not the most durable solution, since due to prolonged mechanical stress they cracked and came to a partial or total disrepair.

Slightly better deal with wood products. Such sleepers were smiled for protection from the negative impact of environmental factors. But the wood, sooner or later, despite the special treatment, decays. And, as a result, railway tracks need repair.

Despite good depreciation qualities, wood has one major drawback - this is the high price of sawn timber, even with the simplicity of their machining. The situation changed for the better in the second half of the twentieth century, when the first railroad sleepers were developed.

Despite the fact that wood products are still used on secondary branches, it is reinforced concrete structures that are reasonably considered the most modern and promising solution.

Main characteristics

Instructions for the use of reinforced concrete sleepers in the post-Soviet space has been tested for more than 40 years.

In accordance with GOST 23009, modern concrete sleepers are rail supports made in the form of beams with a variable size and shape of the section. The product is reinforced with reinforcing wire with a diameter of 3-6 mm, depending on the modification.

During operation, the product is placed on top of the ballast layer. As applied to conventional roads, large-size rubble is used as a ballast embankment, and a concrete base of slab type is used for the construction of the underground.

Products made of reinforced reinforced concrete, used as under-rail supports, are the optimal solution, both for joint and for other categories of tracks.

The relevance of these structures is explained by a number of technical and operational advantages, including:

• long operational resource;
• optimal indicators of resistance to the negative effects of environmental factors;
• resistance to mechanical stress;
• not susceptible to rotting during the entire service life;
• possibility of mounting on the tracks with any level of load;
• relatively low price;
• minimum costs required for maintenance;
• simplicity of laying and installation, in comparison with wooden analogs;
• absolute identity of sizes and shapes, which guarantees the convenience of transportation and shipment.

Are there any disadvantages that could adversely affect the use of these concrete goods?

There are few such flaws:

• First, it is the probability of fatigue failure of the concrete structure and, as a result, the need for periodic inspection of the tracks.
• Secondly, the weight of reinforced concrete sleepers (270 kg) makes it impossible to do it yourself without the use of special equipment. Therefore, in contrast to wooden analogues, concrete structures are installed by means of specialized tie-laying machines.

Scope and conditions of use

Sleepers manufactured using prestressed reinforced concrete are commonly used in the construction of railway tracks around the world.

Given the variety of climatic conditions in which these products are operated, as well as the varying degree of mechanical stress, increased requirements are made for the production of sleepers, as well as the quality of the finished product. As a result, depending on the favorable conditions of use, these concrete goods can be used in for 30-60 years.

The ubiquitous replacement of the usual wooden supports with reinforced concrete counterparts is explained not only by strength and durability, but also by tight deadlines for production.

For example, for the production of ready-to-install reinforced concrete goods, only a few hours are needed, which is very convenient when it comes to building a large branch and a constant supply of large volumes of building materials is necessary. Again, concrete products can be repaired and adapted for operational needs using diamond drilling holes in concrete.

Important: Sleepers manufactured by domestic manufacturers with the use of prestressed reinforced concrete in accordance with the requirements of GOST, surpass foreign analogues in their carrying capacity and material consumption.

Requirements for railway railway sleepers

As already mentioned, the operating conditions in which the cross ties are used place high demands on the production technology of these reinforced concrete products and, in particular, on the technology for producing prestressed reinforced concrete.

The following requirements are imposed on the material and the finished product:

• Strength, sufficient to transfer the prestressing power after a few hours (the time is set in accordance with the modification of concrete goods) at the end of the production process.
• Maximum possible consistency freshly prepared concrete.
• Accuracy of sizes and shapes - An order of magnitude higher than similar requirements for other categories of commonly used reinforced concrete and prestressed reinforced concrete structures. By these requirements are meant tolerances for the angle of inclination, the length and width of the individual structural elements. Especially strictly controlled dimensions in areas adjacent to the rails.

Important: In Western Europe, technical requirements that determine the quality of the source material used in the manufacture of concrete sleepers are governed by standard EN 13230. The strength class of the source material in domestic production is determined by the higher requirements given in GOST 26633.

Manufacturing technology

Regardless of whether the foundation is made of reinforced concrete sleepers or concrete goods will be used for its intended purpose, the strength of these structural elements will be guaranteed. The performance qualities of the finished products are provided by production technologies.

In spite of the fact that quite a few methods for manufacturing sleepers have been tested for more than fifty years, today the four most common production technologies that meet the requirements of international standards are commonly used.

• Technology carousel with delayed removal of the form. The peculiarity of this technological process is that the finished mixture is poured into molds and compacted. Removing the product from the form is carried out only after the achievement of the optimal strength indicators, sufficient for the application of force pre-stress. In the manufacturing process, special collapsible cassette forms are used, which can accommodate up to six units of the product. Due to the use of special tensioning mechanisms, the prestressing of reinforcing rods is provided, which is subsequently transferred to the concrete and ensures optimum adhesion to it. After the reinforced concrete sleeper is ready, the mold can be dismantled and immediately applied for the next production cycle. The name of the method is explained by the type of production process and the construction features of the forms used, which are located on the carousel type transport system. This method is widely used in Western Europe and is considered the most promising and technologically advanced.
• Linear technology. Regardless of the fact that the reinforced concrete half-sleeper is made for rail cranes or a full-size product, the production process can be implemented on the basis of linear technology. During the production process, a conveyor is used with a series of consecutive forms. The total length of the chain, as a rule, is not less than 100 meters. At the ends of the forms, special devices are used, which not only cover the form, but also transmit the prestress to the reinforcing bars. As the mixture dries, the force is transferred to the concrete.
• The technology of removal of the form with the subsequent voltage.

In this case, templates are inserted into the forms that will determine the location of the metal reinforcement. Then the concrete is poured into molds and compacted.

As it hardens, metal pins are inserted into the mixture, to which mechanical force is applied. After a short time, the form is dismantled and the templates are retrieved. The advantage of this method is that the process is essentially uninterrupted, and therefore a limited number of forms are necessary to obtain the desired result.

• Technology of removal of the form with a preliminary voltage. In this case, the form is removed as quickly as in the previous method. The only significant difference of this technological process is that the tension force is transmitted to the product not through the pins, but through the frames.

Features of installation, repair and disposal of reinforced concrete sleepers

Laying railway tracks with the use of concrete sleepers has a number of characteristic features.

Rails and concrete sleepers, at the construction of railways, are mounted on the initially prepared canvas on the basis of ground, sand and crushed stone. .

Laying is done by means of mechanized complexes, which allow minimizing the degree of use of physical labor. As a result, the cost of the installation process is reduced, and in addition, the implementation time for laying the track as a whole is reduced.

As previously mentioned, the operational life of concrete sleepers is limited to 30-60 years. But such parameters of durability are possible only if the condition of the tracks is regularly inspected for breakage and partial deformations.

For example, the condition of the screws securing the lining to the sleeper affects the operational state of the concrete goods. If the screw is broken and the malfunction is not detected in time, it is likely that the lining during the passage of the compound will hit the concrete, causing fatigue stresses in it. (See also the article Hardening of concrete: features.)

If the problem persists after a screw head breaks down, microcracks appear in a relatively short period of time in the concrete, which lead to the partial or complete destruction of the sleepers.

Upon expiration of the service life or due to natural damage, the sleepers must be replaced. At the same time, unsuitable for use of iron-and-steel systems must be disposed of.

Since cutting of reinforced concrete with diamond circles for the purpose of grinding is an unnecessarily expensive process, processing is carried out using special mechanized complexes. The main working element of the complex is a jaw crusher, which crushes concrete products to the consistency of medium or small sized crushed stone. (See also the article Hardening of concrete: how to do.)

Recycled sleepers can then be used as materials for backfilling pits or for forming embankments.

Conclusion

Now you know how much reinforced concrete sleeper weighs, how it is made and what its operational features are. It must be assumed that the use of these concrete goods will be relevant and in demand for a long time.

Indeed, even despite the development of fully plastic sleepers in Japan, it is precisely the conformity of GOST to concrete sleepers that guarantees the optimum combination of strength, durability and acceptable cost. You can find more useful and interesting information by watching the video in this article.