November 2006 issue: Concrete Railroad

[BellmoreBob]

Many thanks to William D. Middleton for the article and photos: Concrete railroad: Delaware, Lackawanna & Western pioneered the use of reinforced concrete in its bridges and structures.  It reminded me of the day I brought two friends, construction engineers of smaller structures, on an automobile trip to show them the Starrucca Viaduct (fitted stone, without mortar, 1848).  On the way home, we stopped also at Tunkhannock (modern reinforced concrete, 1915).  My companions instructed me that Tunkhannock was showing the effect of the different expansion in temperature of the metal reinforcement vs. the surrounding concrete.  Not civil engineers, they claimed that Starrucca was in better shape.  Comments?  (Both men are now deceased.)

[Flint Hills Tex]

Just for the record: I am not any kind of engineer and the only thing I've had to do with construction was helping build some houses. In the town where I live, the railroad runs under two street bridges, the first, a reinforced concrete bridge built during the 70's, the other, a fitted stone bridge, much older and narrower (1 lane). Both bridges have to put up with modern day traffic, including tractor trailers. The reinforced concrete bridge looks better to the eye; nevertheless, the local authorities have put up pylons and traffic signs limiting the traffic on it by tonnage and direction (the pylons only permit traffic to cross the bridge in one direction at a time, making it effectively also a one lane bridge). The fitted stone bridge has no posted weight limitations, but walking under it, one sees white residue seemingly seeping out from between the stones. The rails underneath are extremely corroded, and upon asking a knowlegdable person, I was told that this was caused by the salt used on the road during the Winter. Despite this, the bridge continues to serve its purpose without any limitations. As a lay person, I am certain that the fitted stone structure is more sound and long lasting than the reinforced concrete. There are bridges over major rivers that were built by the Romans, and still carry traffic! At the same time, the reinforced concret bridges on the German Autobahn need replacement about every 30 to 50 years.