Correct Answer - Option 4 : Two-block concrete sleepers
Concepts:
The various types of concrete sleepers (prestressed, pre-tension, post-tension, and two-block) being manufactured by Indian Railways have been described below:
1. Mono-block prestressed concrete sleepers
The mono-block prestressed concrete sleeper consists of single concrete block and it is pre-stressed with high tensile steel strands of 3 mm diameter. This sleeper has been standardized with an overall length of 2750 mm and a weight of 270 kg approximately. The sleeper has a trapezoidal cross section with a width of 154 mm at the top and 250 mm at the bottom and a height of 210 mm at the rail seat.
2. Post-tension concrete sleepers
These are used for Broad Gauge tracks but the use of concrete sleepers using the post-tension method has not been successful on Indian Railways and its manufacture has since been stopped.
3. Two-block concrete sleeper
Two-block concrete sleepers are used in Meter Gauge yards. The sleeper consists of two cement concrete blocks, each weighting about 36 kg and consisting of reinforcement bars at top and bottom making it just like a RCC beam or slab element. These two blocks are connected by an angle tie bar.