GENERAL INFORMATION ABOUT PRESTRESSED CONCRETE SLEEPERS

The development and the usage of the reinforced concrete sleepers gained importance due to the scarcity of wood after the Second World War, the proliferation of CWR’s (continuous welded rail) and the progression on the concrete and prestressing technology.

B70 type concrete sleeper is used in newly-established conventional lines and high speed train lines with axle load of 22.5 tons and above.

Technical specifications and production standards of the material

The main materials that are used in the production of the standard concrete sleepers are as follows:

  • Steel prestressing wires
  • Plastic dowels
  • Face plate (fish bolts)
  • M 27 nut
  • M 16 nut
  • Long and short taper stud
  • Bolt (long and short taper)
  • Guide Antenna
  • Cement
  • Water
  • Concrete Additive
  • Aggregate

The requirements specified by the specifications and the concrete sleepers must comply with are as follows:

  1. Prestressed concrete sleepers shall be manufactured in accordance with the country standards.
  2. In the production of concrete sleepers, specially produced prestressing wire shall be used for reinforcement purposes.
  3. The aggregate and cement shall meet the criteria.
  4. The equivalent alkali content of the cement shall not be more than 0.6%.
  5. The total reactive alkali mass in the concrete shall not exceed 3.5 kg / m3.
  6. Pre-tensioning process will be released after a minimum compressive strength of 45 N / mm2 is reached at the concrete to prevent rapid curing drawbacks.

In the production of sleepers, basalt aggregate (sand 0,25-8 mm, aggregate 8-16, aggregate 16-32) has been used. The weight (loose, compact), specific gravity, water absorption, corrosion, organic and muddy matter amounts of the basalt aggregate are determined and given in the following table:

According to the standards, the manufacturer has to meet the following requirements regarding the concrete sleepers it manufactures and present it to the employer before production:

  1. Water / cement ratio and tolerances,
  2. The ratio, weights and tolerances of each material in the concrete,
  3. Percentage of angularity of aggregates
  4. Strength of produced concrete for 7 days and 28 days,
  5. Maximum value of releasement of pretension wires after 1,000 hours,
  6. Details and tolerances of the prestressing system used (separately for each prestressing wire),
  7. Applied vibration method,
  8. Curing time and curing temperature detail of concrete,
  9. Minimum pressure immediately before the releasing of prestressing wires,
  10. The method used for releasing the prestressing load,
  11. Points and conditions to be considered in the storage of sleepers after production.

In addition, the number of sleepers produced in design and approval tests as specified in the design and approval tests and the results should be shared with the employer.

Tests and evaluation criteria applied to concrete sleepers:

2 types of tests are required for acceptance of the conformity of concrete sleepers with standards and to be used on railways;

  1. Design and Production Approval Tests:
    These are a series of tests to determine the suitability of the design on a concrete sleeper or part of a concrete sleeper. It is generally desirable that independent organizations to perform these tests.
  2. Routine Acceptance Control Tests:
    Apart from the production control processes of the factory, product control tests are carried out under the supervision of the staff of the employer during sleeper acceptance. These tests are carried out on concrete sleepers which are chosen randomly among the sleepers to be purchased by the employer. These tests are also called Dimension and Labor Control tests.