Railroad tie
Railroad ties are traditionally made of wood, but prestressed concrete is now also widely used, especially in Europe and Asia.
As of January 2008, the approximate market share in North America for traditional and wood ties was 91.5%, the remainder being concrete, steel, azobé (red ironwood) and plastic composite.
One advantage of this method of construction was that it allowed horses to tread the middle path without the risk of tripping.
The stone blocks were in any case unsuitable on soft ground, such as at Chat Moss, where timber ties had to be used.
Their greater weight ensures improved retention of track geometry, especially when installed with continuous-welded rail.
Concrete ties need to be installed on a well-prepared subgrade with an adequate depth on free-draining ballast to perform well.
A study done as part of Euronoise 2018 proved this false, showing concrete sleepers to be an average of 2dB(A) quieter than wooden ones, however with a greater acoustic sharpness on straight stretches of track.
Historically, steel ties have suffered from poor design and increased traffic loads over their normally long service life.
These aged and often obsolete designs limited load and speed capacity but can still be found in many locations globally and performing adequately despite decades of service.
There are great numbers of steel ties with over 50 years of service and in some cases they can and have been rehabilitated and continue to perform well.
Steel ties are utilized in nearly all sectors of the worldwide railroad systems including heavy-haul, class 1s, regional, shortlines, mining, electrified passenger lines (OHLE) and all manner of industries.
[11] In some main track applications the hybrid plastic tie has a recessed design to be completely surrounded by ballast.
Although it was the first instance of plastic sleepers being installed on mainline track in the country, they have previously been used on narrow-gauge railways.
Compared to conventional ties, the volume of ballast required is reduced due to the load-spreading characteristics of the Y-tie.
[28] For curves the three-point contact of a Y steel tie means that an exact geometric fit cannot be observed with a fixed attachment point.
[36][37] Bi-block (or twinblock) ties consist of two concrete rail supports joined by a steel bar.
Frame ties (German: Rahmenschwelle) comprise both lateral and longitudinal members in a single monolithic concrete casting.
The two sleepers adjacent to a joint may be 12 inches (305 mm) wide where the formation is soft or the traffic is heavy and fast.
The fractional inch spacing at the fishplate corresponds to the thermal expansion gap allowed between the rail ends.
Due to the presence of wood preservatives such as coal tar, creosote or salts of heavy metals, railroad ties introduce an extra element of soil pollution into gardens and are avoided by many property owners.
In the UK, new oak or pine beams of the same length (2.4m) as standard railway sleepers, but not treated with dangerous chemicals, are available specifically for garden construction.
In Germany, use of wooden railroad ties as building material (namely in gardens, houses and in all places where regular contact to human skin would be likely, in all areas frequented by children and in all areas associated with the production or handling of food in any way) has been prohibited by law since 1991 because they pose a significant risk to health and environment.
