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On the noon news today they announced that Amtrak had another problem and that it would cause delays in some places. The concrete cross ties were cracking and needed to be fixed. this would cost about $23,ooo,ooo. Did anyone else hear this ? I am assuming that this is in the NEC as that it where Amtrak owns the tracks.
Posts: 1577 | From: virginia | Registered: Jun 2005
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It is on the news and several other rail related web sites. It appears to be some form of manufacturing defect, as the replacement ties are being provided without cost by the contractor. What Amtrak is out is the installation costs. Before anybody gets too exercised about the contractor getting off free, he is not. This sort of stuff is the way contracts are normally written. If the supplier of the material bore full liability for the cost of replacing them, he would have to be buying insurance or setting aside a fund to cover it. The cost of these things then get plugged into his bid price. It is known as sharing the risk.
Nothing I have seen gives any indication of what percentage of the total these represent. A hint: about 350 miles times an average of somewhere over 3 tracks and on average 2,640 ties per mile, and you have something like 2,600,000 ties in the corridor.
Concrete ties are very high strength concrete, normally 7,000 psi compressive strength or higher. For comparison, most structural concrete is in the range of 3,500 to 5,000 psi. Your driveway and house floor slabs are probably around 2,000 to 2,500 psi, and almost never deliberately over 3,000 psi.
When you get in this strength range, particularly is prestressed elements, which this is, you have to pay careful attention to the properties of the aggregate (sand and gravel) in it. Some rock reacts chemically with cement, and some has a strength lower than the cement mix. There are tests for all these properties, but you test samples, not every rock. Many of these tests have come about as the result of past problems.
Concrete ties are postulated to have a service life of around 50 years, but there are no 50 year old concrete ties out there yet. A wood tie is in track on average about 35 years, but it varies a lot depending on climate and traffic, and usually in their last few years in track in most tracks they are mostly just taking up space. Wood tie life would be quite a bit less in heavily used high speed tracks.
Concrete ties are also a lot less tolerant of uneven support and high impacts than wood ties.
Posts: 2808 | From: Olive Branch MS | Registered: Nov 2002
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