It was on a roadbed with concrete ties that the French TGV high speed train established a world record of 237 « miles per hour in 1981. Concrete crossties are not only strong and stable enough to handle these new super trains, but they are also more durable and require less maintenance than the wood ties so common in America. Concrete ties will function without failing for 40 to 50 years versus 25 years for wood.
Other benefits of concrete ties include: lower track maintenance costs; potential for higher safe speeds; fuel economy, averaging a significant 2 percent; and longer rail life, especially on curves. With prestressed concrete the number of ties can also be reduced significantly. Wood ties are set 19 « inches on centers, while concrete ties can be set at 24 inches, resulting in a saving of 609 ties per mile.
The prestressed concrete crosstie is a sophisticated member. To meet Amtrak's specifications a tie was designed using 7000-psi concrete reinforced by eight lengths of 3/8-inch diameter 270-K strand, prestressed to 72 percent of ultimate strength. In our operations, the 7000-psi concrete usually exceeds the specification substantially. We use an 8.0-sack design, with a water reducing admixture added. The Kansas plant uses a 3/8-inch limestone coarse aggregate; in Massachusetts, granite of the same diameter is crushed on site. Slumps are held as low as possible usually about 2 inches consistent with good placement practice.