Concrete vs Wood

[cole1020]

We all know North American railroads use either concrete or wooden ties. The Midwest seems to be entirely wooden ties, while in the Deep South and the Desert Southwest along with a few commuter railroads sprinkled around the country, there are a handful of lines that utilize concrete ties. Canada seems to be all wooden while down in Mexico, it seems to be all concrete. There are many pros and cons to both types of ties, but what dictates what type of ties are used? I’ve seen both wooden and concrete ties being used on busy and dead lines, on both high and slow speed lines, and both on lines that see heavy freight traffic and simple light rail lines. The only similarity I see is that concrete ties usually pop up more frequently in warmer climates, though there are still some concrete ties in colder environments. Would anyone happen to know why and for what reasons railroads choose to use these two types of ties?

[Saturnalia]

The main determinations are tonnage, curvature and ease of maintenance.

Switching wood to concrete requires changing every single tie, so it is a massive up-front cost that needs to be justified. You'll typically see lines converted to concrete or laid with it in areas with exceptionally high tonnage or lots of curvature. In those areas, the benefits of concrete are its superior gauge restraint - especially important in curves - and to some extent they can typically handle more tonnage over their lives, in general. Wood ties tend to start giving up their ability to hold gauge in curves, which when combined with the rail wear can easily end up with a wide gauge condition. Concrete ties, meanwhile, really do not give up anything until they actually fail completely.

Transit lines may opt for concrete to start with, if they can afford it, since they'll last a long, long time in those low-tonnage environments and uptime is important to those systems. It's a lifetime maintenance reducer in those cases.

However, this lifespan does not justify for most medium and low density freight lines, where the up-front conversion is expensive and there simply is not benefit when a wood tie will typically do 30-50 years no problem in most of the country. There are some areas, particularly in the southeast, where wood tie degradation is significantly faster due to bugs and fungi. However, dual-treatment of ties, popular now for the last few decades, has furthered wood tie life generally, especially in those areas. This conversion process becomes even more arduous if the existing ballast is not fit for concrete ties. Limestone is particularly poor ballast for concrete ties, because the ties grind up the ballast, rather than the other way around. This results in poor surface, more movement, and more grinding. The ballast will turn to mud. While granite - the superior ballast - will grind the concrete on the other hand, if proper track surface is maintained with a good, tight tamp, this movement and thus wear will be minimal. Plus, it is easier to replace worn ties than fouled ballast. This is why you'll almost never see concrete ties founded in anything other than granite or other high-strength stone.

Another factor to consider is what one is going to do in turnouts. With concrete ties, every turnout tie is different, so if a replacement is needed, it must be ordered to be that specific tie - keep in mind there are roughly 100 ties in a typical mainline crossover turnout - often from a specific manufacturer and usually with a long lead time. So many places with concrete ties will still use wood in turnouts, since that is not a problem. You can put a 10' wood tie anywhere you need a 10' tie, simple as that.

Another major consideration is ease of maintenance. Concrete ties weigh a lot more so they're more difficult to handle, and also typically involve other specialized equipment and fasteners. Concrete ties also require a specialized inspection according to FRA regulations, since they can and often will experience failure modes not readily visible to a track inspector.

Finally, BNSF and UP have by and large embraced concrete much more than CSX and NS. Last I knew, NS' top engineer basically held the stance that NS wouldn't ever put in a single concrete tie under his watch!

[AARR]

Thank you Saturnalia for an excellent explanation

[amessmann]

The only similarity I see is that concrete ties usually pop up more frequently in warmer climates, though there are still some concrete ties in colder environments. Would anyone happen to know why and for what reasons railroads choose to use these two types of ties?

I would expect that the 'greater use in warmer climates' pattern you notice is due to ice formation in colder temperatures. Both concrete and wooden ties will be porous to an extent which would allow water to make its way in. When water freezes, it expands which I assume could crack a concrete tie. Wooden ties however are a lot less brittle, at least I imagine, and would be able to flex to accommodate the ice formation.

IIRC there was a concrete tie craze back in the 2010s, where they were widely deployed. Pretty soon after, reports of widespread cracking began to surface and it seemed as if the practice became "special cases only" from that point on.

In addition, thank you Saturnalia for the information. In hindsight, it makes total sense that concrete ties would hold the gauge better than wooden ones, especially in curves. That solid strength is a double-edged sword as with more strength, and less ability to flex, the tie becomes more prone to cracking due to its brittle nature.

[TC Man]

Let's not forget lesser known composite ties. Strangely, there are composite ties in Boardman Yard in Traverse City of all places! Saw them this spring when GLC MOW was working on a switch. I asked them what they were as they looked like model railroad ties (very black). They said MDOT got a batch of them and they stuck them here and there as ties were needing replacement.

[Saturnalia]

Let's not forget lesser known composite ties. Strangely, there are composite ties in Boardman Yard in Traverse City of all places! Saw them this spring when GLC MOW was working on a switch. I asked them what they were as they looked like model railroad ties (very black). They said MDOT got a batch of them and they stuck them here and there as ties were needing replacement.

Junk. Somebody's trash that somebody else tried to turn into a tie.