"From the story: "The MBTA does not plan on purchasing
concrete ties in the future. The new ties on the OCRR are
Somebody up there has a brain.
I _know_ how widespread concrete ties are in Europe.
I _know_ how others in this forum tout their advantages
vis-a-vis wood ties.
But from my observations over the past 30+ years of running
over them, they don't seem to holding up well in American
usage, insofar as those advantages were supposed to be.
This goes _beyond_ the recent case of "defective" ties used
by Amtrak, Metro-North, and perhaps others, that came from
that supplier down around Maryland (or was it Delaware or
NJ?). I can't say whether it has to do with subsurface
preparation, ongoing maintenece (which doesn't happen much
after the ties are installed), or something else "in the
American railroad scheme of things".
It seems that in many places, the concrete ties last no
longer than a good wood tie (by "good wood tie" I refer to a
tie that was properly creosoted, like they did in the old
days) -- and in some usages, much LESS longer.
Some areas in particular that concrete ties don't hold up:
- Insulated rail joints -- modern insulated joints are
usually "pre-constructed" from two short pieces of rail,
with the insulated connection bolted/cemeted together. They
are then spliced into position and the end joints are
spot-welded with the running rails. With wood ties
underneath the insulated joint, the wood acts as a "shock
absorber" between the ballast and the rail itself as the
weight of the train passes over the joint. The entire
assembly (both rails and the joint itself) can "move"
slightly up and down as a unit. But with concrete ties,
there can be no "give" between the weight of the train and
the ballast. Nothing there to absorb the shocks. What
happens next is the ties begin to wear from the bottom up
(in a battle of concrete vs. rock, concrete loses). Now, as
the train passes over there is the brute force impact each
time at the joint itself. The result is that, over time, the
joint gives out. Ultimately the insulated joint deteriorates
to the point where it feels like it's going to just break
under impact. The track department can go in, replace a few
of the concrete ties, and tamp up the ballast, but once one
of these pre-constructed insulated joints loses it's
"initial integrety", it's doomed.
- Bridge decks -- this is where concrete ties adjoin a
highway (or other) underpass which uses a wooden tie bridge
deck. (Aside: in many places it's impossible to rebuild the
deck with a concrete "bathtub" and concrete ties do to
clearance limitation underneath, or wire clearances
overhead.) No matter how carefully the track department
surfaces the concrete ties on either side of the deck, it
seems like the surfacing doesn't keep its trim too long. The
result is a heave due to uneven rail heights on either side
of the deck. (My solution, which they ought to consider,
would be to run about 20 wood ties on either end of the deck
before they transition back to concrete.)
- Tunnels, station platforms, wet spots -- anyplace where
there is the possibility of moisture building up between the
bottom of the ties and the ballast, there's going to be
problems. Without fail, the bottom of the ties will begin
grinding against the ballast and result in an unstable
surface above. This came to be so bad in the "East Haven
Tunnels" on the Shoreline that they finally went in, removed
all the concrete ties, and re-installed wooden ties, which
might need replacement individually as they wear, but don't
become dangerously unstable as do concrete ties. Wasn't
there a derailment in Washington State where an Amtrak train
literally had a bad stretch of concrete ties crumble to
pieces underneath it?
I've no doubt that the concrete can be used to advantage in
_some_ places. But again, from what I've seen, around these
parts, the promise seems to have been much more enticing
than the payoff...