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  • Discussion relating to commuter rail, light rail, and subway operations of the MBTA.
Discussion relating to commuter rail, light rail, and subway operations of the MBTA.

Moderators: sery2831, CRail

 #1486997  by BandA
 
Didn't MBTA (or Amtrak) have a bad experience with cement ties? And the cement slabs used on the Red Line Alewife extension?

My limited understanding is that wood does better with freeze/thaw cycles, and cement is needed to retain the gauge precisely for high-speed rail (NEC).
 #1487002  by MBTA3247
 
Several railroads have had bad experiences with concrete ties. As I recall, the Braintree Line had a major problem with them around 20 years ago. My understanding is that it's an issue with bad batches of concrete.
 #1487013  by CRail
 
The T seems to have abandoned them. Old Colony had a major tie replacement project relatively recently (and those lines are relatively new anyways), and any time there's a track replacement where concrete ties are involved, at least on the transit side, wooden ties are being placed.

It was once explained to me by a civil engineer that concrete performs well under compression but terribly under tension. Concrete ties are enforced with rebar, which expands and contracts with the temperature. Steel also expands when it rusts, creating tension on the concrete causing it to crumble.
 #1487034  by Arlington
 
The only choice for GLX is wood or concrete, and it sounds like the MBTA system-wide answer is "wood" (making it theoretically possible that the temporary CR wood ties and CWR rails could MAYBE be repurposed for GLX outbound, if they can grind the rail to transit specs)

OFF TOPIC: Plastic/Composite ties are available, and have been slowly moving to market since 2011 made from car-bumper plastic scrap. It looks like they're too expensive to use in regular running track applications(like the CR & GLX through Somerville), and cost-limited to uses where the expense of changing ties is the real life cycle cost (tunnels, bridges, crossings, embedded, turnouts, and diamonds)
Last edited by CRail on Thu Sep 27, 2018 11:38 pm, edited 1 time in total. Reason: Unnecessary quote removed.
 #1487322  by troffey
 
CRail wrote:The T seems to have abandoned them. Old Colony had a major tie replacement project relatively recently (and those lines are relatively new anyways), and any time there's a track replacement where concrete ties are involved, at least on the transit side, wooden ties are being placed.

It was once explained to me by a civil engineer that concrete performs well under compression but terribly under tension. Concrete ties are enforced with rebar, which expands and contracts with the temperature. Steel also expands when it rusts, creating tension on the concrete causing it to crumble.

The Old Colony lines concrete ties failed after about ten years, which the T blamed on manufacturer error:
https://cdn.mbta.com/uploadedfiles/Abou ... tation.pdf" onclick="window.open(this.href);return false;

I believe they've gone strictly with wood ties since.
 #1487619  by jonnhrr
 
Seems that just about every country in the world outside the US is able to use concrete ties without issues. I wonder why.

Jon
 #1487626  by Bramdeisroberts
 
Concrete inevitably fractures and spalls in any situation where it's exposed to moisture and frequent freeze/thaw cycles, whereas wood is far more resilient under those same conditions.

Most countries where concrete ties are the standard have neither the harsh, wet, and cold winters of the Northeast and Canada nor the ample access to cheap wood, and so instead they go with concrete. Here, we have far harsher winters than most of Europe does, and far better access to cheap lumber, and so wooden ties are the standard.

It's not just the northern US and Canada, though, as JR Hokkaido and the Swedish/Norwegian railway systems all seem to also use wooden ties extensively on their main lines for the exact same reasons.
 #1487663  by jwhite07
 
There is such a thing as a steel crosstie. In fact, there are some in use in our area - the west end of the yard lead into CSX's intermodal yard in Worcester has steel ties installed a few years ago during the yard's expansion. I suppose they'd require some kind of insulating pads under the rail in signalized or electrified territory, not clear on how that works.
 #1487671  by Bolo42
 
I've actually done some research on this.
Concrete ties have difficulty in the Northeast due to rail-seat deterioration (the area of the tie directly under the rail). When fine particles infiltrate this area, the moisture, friction and freeze/thaw cycle causes the concrete to crumble, ultimately exposing the pre-stressed reinforcing wires causing them to rust and loose tension, etc. Otherwise concrete ties would be more economical in the Northeast due to their increased durability over wood.
Some current research is looking at using higher grade concrete for the top portion of the ties for one solution. Otherwise, unless the issue is caught and fixed with epoxy before the tie deteriorates too much (the deformations in track geometry caused by rail-seat deterioration can be caught with track geometry cars) the tie needs to be replaced.
Of course, it doesn't help that when concrete ties were first designed in the US, they were done from a manufacturing perspective to make them easier to manufacture, rather than an engineering perspective to be able to adequately withstand the forces that act upon them.
 #1488001  by artman
 
jonnhrr wrote:Seems that just about every country in the world outside the US is able to use concrete ties without issues. I wonder why.

Jon
Wood is generally unavailable for many purposes in many western European countries due to forests having been cut down centuries ago.
 #1488011  by Arlington
 
^ Exactly. Europeans don't have the forests, and so tend not to use wood where we would: telephone poles, rail ties, housing-framing. And North America has gotten good at growing, pressure-treating, and engineering wood products as a result.
 #1488081  by EuroStar
 
We also abuse our ties (and rails) more and generally do less maintenance on the right of way than what is typically done in Europe. European cars, both passenger and freight are substantially lighter than ours. Their train consists are shorter, with freight trains rarely exceeding 40 cars in length. They also pay much more attention to good drainage there. The ballast typically consists of larger aggregates than what we use here and gets cleaned by ballast cleaners that remove broken down stones every so many years. In the US most railroads have never heard of ballast cleaners, much less used one. As Bolo42 points out water is the enemy of the concrete ties and in order to achieve their claimed 50 years life those ties need good drainage.
 #1488559  by Arlington
 
Complete GLX Construction Update (FMCB Oct 15) Mostly shows the phases of moving the CR south/west so that the ROW can be widened and walled on the future CR side (and then subsequent phases on the GLX side).
 #1488911  by bozepravde15
 
Anyone have any info/links regarding the exact location of the new carhouse and how it will connect to the mainline? I haven't found anything on this (admittedly I'm not the best at combing through some of this) and I have a hard time picturing where it will be and how it will connect. Will it connect to the line before the split to Union Square or after?
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