Types Of Concrete Sleepers

Concrete Sleeper refers to a railway tie made of concrete, reinforced with steel. According to the reinforcement method, concrete sleepers can be divided into two types: prestressed concrete sleepers and ordinary reinforced concrete sleepers. The former has better crack resistance and consumes less steel. 

1. By manufacturing process, concrete sleepers are divided into two categories: ordinary concrete sleepers and prestressed concrete sleepers.
2. By reinforcement diameter, concrete sleepers can be categorized into steel cord (high-strength steel wire, abbreviated as "cord") and reinforcing steel (high-strength rebar, abbreviated as "reinforcing steel").
3. In China, concrete sleepers are classified into three types, type I concrete sleepers, type II concrete sleepers and type III concrete sleepers. Let's take a look at the following three types.

The Type I concrete sleeper is designed to support an axle load of 23 tons, a maximum speed of 85 km/h, and a track density of 1,840 sleepers per kilometer. It is suitable for medium- and light-duty tracks. However, with the ongoing development of the national economy and rail transport, both the axle loads of locomotives and rolling stock and the total weight passing through the tracks have steadily increased. As a result, the bearing capacity of the Type I sleeper is no longer sufficient to meet these evolving demands, leading to increased wear and a reduced service life. Consequently, Type I concrete sleepers are being gradually phased out from use on railway lines in China.

The Type II concrete sleeper is designed to withstand the heavy loads and high-frequency repetitions typical of heavy-load tracks, with a focus on fatigue reliability as the key design criterion. It is based on a design standard that accommodates an annual traffic volume of 60 million tons, axle loads of 25 tons for locomotives, 23 tons for freight cars, a maximum speed of 120 km/h, and a rail weight of 60 kg/m. This makes it suitable for heavy-duty and secondary heavy-duty tracks. Compared to the Type I sleeper, the Type II sleeper has improved bearing capacity, with the positive bending moment in the track cross-section increased by 13% to 25%, the positive bending moment at the middle section increased by 8.8%, and the negative bending moment at the middle section increased by 14% to 41%.

Due to various issues with Type II sleepers on heavy and secondary heavy tracks-such as transverse cracks on the upper surface, longitudinal cracks along bolt holes, cracks at the ends, lateral longitudinal cracks, and diagonal cracks at the shoulders-the failure rate of these sleepers has averaged 1.2% per year. As a result, they are no longer suitable for the load-bearing requirements of heavy and extra-heavy tracks. To meet the needs of more robust track structures, Type III concrete sleepers were developed. These sleepers are available in two versions: with or without shoulders, and in two lengths: 2.6 meters and 2.5 meters. The design parameters are based on a maximum axle load of 23 tons for locomotives (three-axle), a maximum speed of 160 km/h, and a sleeper density of 1,760 sleepers per kilometer. Type III sleepers are primarily used for extra-heavy tracks.