QUOTE: Originally posted by Overmod That's one thing they do. You might think they'd 'wash' out, but not so... More important, in my opinion, is that they get in between the pieces of ballast and spoil the integrity of what the ballast does. Remember that plain old dirt has lots of rocks in it. Too much dirt in ballast essentially gives you track that might as well be laid on... dirt. Fines in and around the ballast can physically work in between the rocks, and (via a variety of mechanisms) makes the trackwork less stable. There are aspects of physics which make migration of fines upward into ballast happen (I won't bore everyone going into them)
QUOTE: Originally posted by talbanese Stupid question - sorry to ask - What are FINES? Fines to me are something I have to pay when I park in the wrong spot.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
QUOTE: Originally posted by M.W. Hemphill To emphasize Overmod's comments, the asphalt is NOT acting as a load-bearing material for a point load, which is the case in asphalt paving for highways. It's acting as a separation between the ballast and the subgrade -- see Overmod's first sentence. That's the key sentence. It's poor practice to place ballast directly on the subgrade as the very properties that make ballast provide good drainage (large voids) also makes ballast susceptible to infiltration by fines. That's the point of the crushed rock layer between the ballast and the subgrade. It really doesn't matter if the asphalt crumbles or cracks; it's a plastic material and will be self-healing. This is utterly different than asphalt paving, which is meant to be a sealer and also a load-bearing material (which is why chipsealed roads or calcium chloride treatment is just as good under light loads).
QUOTE: Originally posted by Big_Boy_4005 I saw that photo in Trains recently, pretty cool. In that situation it looked like they were putting down a completely new line, something that isn't done very often anymore. This technique seems like it would add a fair amount of expense to a mile of track. It's not something that can easily be done when working on existing lines, even if it is effective. I'm also not sure how well it would hold up under different climatic conditions. It will be interesting to hear how well it's working in a few years. Once it has seen a fair amount of traffic and a couple of summers worth of heat. Will the ties and ballast have squished their way into the pavement? Will the ballast keep enough heat off the asphalt to prevent that from happening?
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QUOTE: Originally posted by garr I wonder if this would really work. It seems the weight of the trains would crumble the asphalt quickly even with the ballast helping spread the weight. Trucks, roughly 1/2 the weight of loaded freight cars, seem to do a number on the Interstates, which are paved very thickly with asphalt. Hmmm, maybe if the asphalt was very, very thick... Jay
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