Re: Concrete RR Ties
Author: Ross Hall
Date: 06-18-2007 - 17:39
Last year BNSF started testing certain aspects of concrete tie conditions with somesort of a machine that measured give in the rail. They were having a problem with the anchors getting loose and allowing rail to shift under light equipment on curves i.e. empty grain trains and Amtrak. Rail was staying in place under heavy trains and locomotives, just light equipment and on curves. There isn't a whole lot that can go wrong with a concrete tie. Even if the tie cracks in two, it is still held together with significant amount of rebar under tension.
Concrete ties do not tolerate pumping at all, they grind up quite quickly when rubbing on rock ballast creating bright white spots on the roadbed when they do. They also don't tolerate derailments well either---if they rail anchors get knocked off the tie is done. (Epoxy can reanchor them on a temporary basis, but they get replaced later.) They haven't really set a lifespan for concrete ties, it depends on climate and traffic levels. They do last significantly better than wood. Some side notes. Rail head wear increases on concrete ties due to the firmness of the ride, but rail fatigue decreases due to reduced flexing (the firm ride) and ballast deck bridges that are sensitive to vibration are not good places for concrete ties as they transmit vibration that wood ties absorb. (A good example of this is the BNSF Latah Creek Trestle in Spokane that has imported super hardwood ties, rather than concrete ties. Don't recall the type of wood, but you can't drive a spike into one of them no matter how hard you try, they have to be predrilled and screws used.) The transition point between wood and concrete ties can become a pumping point on the wood side and railroads have been experimenting with extra long wood ties at the transition point to try and deal with the problem.