It is a German prestressed concrete sleeper that is used in the railway system and transfers the loads caused by the train to its underlying bed. In order to increase the strength and resistance to flexibility and slopes caused by the load and force of the train, this element is produced using high strength strands in pre-stressed form.
Pre-stressed concrete sleeper means concrete sleeper in which pre-stressed concrete blocks are used. In this type of sleeper, before the concrete is poured, steel cables or reinforcements that are subjected to tension are placed inside the block.
The production process of prestressed concrete sleeper includes the following steps:
- Design: First, the prestressed concrete sleeper must be designed. This includes determining the dimensions, geometrical shape, number and position of prestressed strands, type of concrete and the loads to be tolerated. In the design, the existing standards and regulations related to the production of the sleeper must be observed.
- Preparation of materials: The necessary materials for the production of prestressed concrete sleeper include concrete, prestressed strands, binders, dowels and connections. Concrete must be specified in accordance with existing standards for strength and mechanical properties.
- Formwork: After the design, the forms needed to produce the prestressed concrete sleeper are made. Templates should be designed based on the desired dimensions and geometric shape.
- Reinforcement: In this step, strands and connections are placed in the mold. The strands are cut to the required length and placed in the appropriate position in the mold. Then the strands are pre-stressed to the required amount using hydraulic jacks. This action creates a compressive force in the concrete, which increases the strength of the sleeper.
- Pouring concrete: the prepared concrete is poured into the mold according to the existing standards. Concrete must be poured evenly and smoothly in the mold so that it can have the necessary strength and resistance.
- Concrete curing: immediately after concreting, a tarpaulin cover is placed on the sleeper molds so that the concrete does not lose its water. About 3 hours after the end of concreting, after the initial setting of the concrete, the steam processing system is activated and for about 7 to 8 hours, the sleepers are processed using steam with a certain temperature and pressure in accordance with the existing regulations. 3 hours after the end of the steaming process, the tarpaulin covers are collected and 2 hours after that, the concrete samples are tested using a concrete breaker jack. If the concrete has reached the desired strength, the process of releasing the sleepers is done and the sleepers are marked and transferred to the depot after leaving the mold. Otherwise, more time is given to the concrete to reach the desired strength.
- Quality inspection and tests: After the sleeper is produced, it should be subjected to a quality inspection and relevant tests should be performed. These tests include compressive strength test, bending test, tensile test of pre-stressed strands and other relevant tests. Existing standards and regulations must be followed in these tests.
- Installation and use: After confirming the quality, the sleepers are installed and used in the rail system.
International and national standards and regulations related to the production of prestressed concrete sleeper may be different. Some of the famous standards and regulations in this field are:
- EN13230 standard: European standard for prestressed concrete sleepers.
- AREMA standard: American standard for the production and use of sleepers in the rail system.