A Guide of Concrete sleeper

The concrete sleeper is one kind of railway sleeper just like wooden sleeper and steel sleeper. The concrete sleeper has a wide source of material. The good stability of concrete sleeper can meet the requirements of high speed and large capacity of the railway line. The concrete sleeper is not affected by weather, decay, insects and fire, and has a long life. However, it is easy to fail due to cracks, and because of heavy weight, it is difficult to change, also has poor elasticity.

As for the classification, concrete sleeper can be divided into various types according to different ways, details as follow:

1. According to the manufacturing process, it can be divided into two types: ordinary concrete sleeper and pre-stress steel reinforced concrete sleeper.
2. According to the diameter of the ribs, it can be divided into steel strings (high-strength steel wire, simply called string) and steel bars (high-strength steel bars, simply called ribs) concrete sleeper.
3. According to the railway types. For example, in China, concrete sleeper include I,Ⅱ, Ⅲ type.

Operating requirements of concrete sleeper

• In the section of concrete sleepers, the rails must be rectified (weld, sanded, etc.) when they have joint defects; the roadbed must be rectified when it has a tumbling, uneven sinking and frost damage exceeding 15 mm.
• The sleepers with inconsistent slopes of the track-bearing grooves shall be laid in sections and shall not be mixed. Damaged sleepers should be repaired before laying.
• Screw spikes are anchored with sulphur cement mortar.
• Concrete sleeper is heavy. Use appropriate tools when handling, loading, unloading and laying the sleepers. Try to avoid smashing, falling, bumping and bumping.
• The concrete sleeper has a trapezoidal cross section. It is inconvenient to install the anti-climbing device. It is necessary to tighten the rail fastening system to increase the joint strength between the rail track and the railway sleeper to prevent the rail from crawling.
• The fasteners of concrete sleepers should be used reasonably. Continuous welded rail and rails of 60kg/m and above must use rail clips fasteners; when using 70-type gusset fasteners, in the curved section of 800m and below, the outer side of the rail should be a widened iron seat.

Damage criteria of concrete sleeper

The concrete sleeper of main line and the hair line shall be kept free of failure, and there shall be no continuous failure (including the switch tie) in other sections. The criteria of serious damage of concrete sleeper as follows:

Failure criteria

• Obvious fracture.
• Longitudinal cracking: The seam width at the shoulder angle is greater than 1.5mm; Longitudinal horizontal cracks are basically penetrated (seam width is greater than 0.5mm).
• Transverse crack (or oblique crack) close to the annular crack (residual crack width exceeds 0.5 mm or length exceeds 2/3 shoulder height).
• The shoulder is broken and is close to losing support (the length of the break exceeds 1/2 of the length of the shoulder).
• Seriously lost.

Damage criteria

• The length of the transverse crack is 1/2 to 2/3 of the height of the sleeper.
• Longitudinal crack: longitudinal crack between two rail bolt holes (the slit width at the apex angle of the shoulder is not more than 1.5mm); the longitudinal horizontal crack is basically penetrated (the slit width is not more than 0.5mm).
• The length of the shoulder breakage is 1/3 to 1/2 of the length of the shoulder.
• Severe reticular cracking and falling off.
• The bearing groove is crushed and the depth is more than 2mm.
• Exposed steel bars (or steel wires) (the steel bars are not corroded and the length exceeds 100mm).
• The length of the oblique crack is 1/2 to 2/3 of the height of the pillow.

Special types of concrete sleeper

Broad concrete tie (sleeper slab)

The Broad concrete tie is a new important development in China, and the maintenance and repair work is small. It is a kind of "less maintenance" track structure.

Advantages of broad concrete tie

• broad concrete ties are generally densely covered, almost covering the top surface of the track bed, thus preventing the bed from being polluted and keeping the track bed clean for a long time;
• The contact surface of the broad concrete tie and the track bed is large, which can reduce the compressive stress of the train to the track bed;
• The track bed of the broad concrete tie has small deformation and stable track, which is suitable for heavy-duty and high-speed railway requirements;
• The maintenance of broad concrete tie is small, which can reduce the labor intensity and reduce the number of operations;
• The broad concrete tie has a neat appearance and beautiful appearance.

Concrete turnout sleepers

At present, prestressed concrete turnout sleepers have been applied on the railroad. The use of prestressed concrete turnout sleepers can improve the stability of the ballast. The geometrical dimensions such as gauge, horizontal and direction are easy to maintain, and the anti-super-high and ball-sand crawling diseases of the guide curve can be eliminated, and the maintenance workload is reduced by about one-third. The length of the sleeper is 2.6~4.8m, the step is 0.1m, the width of the bottom of the pillow is 300mm, the width of the top is 260mm, and the height is 220mm. All the ballasts are arranged perpendicular to the ballast of the ballast. However, the joint parts of the concrete turnout sleepers are more complicated, and it is not easy to replace and deal with after the damage. The concrete turnout sleepers has a large self-weight and poor elasticity, is not easy to be replaced by a single root.