In one of the various news stories leading up to the rebuilding of the CTA Dan Ryan line, it was mentioned that the original (1969) limestone ballast is being removed and replaced with granite ballast. What are the various pros and cons regarding the use of limestone ballast?
Limestone is softer than granite or trap rock, so it fractures and abrades more easily under load, and that produces fines that foul drainage to a greater extent than the harder rock product.
And its a great fertilizer
Was limestone more widely accepted as a good ballast in the past? I remember the C&O (ex-Pere Marquette) main line through my home town getting re-ballasted with fresh limestone often, and thinking that it sure looked a lot spiffier than the “gravel” that GTW used. I actually thought that CNW’s use of granite from an on-line quarry was unusual (and impressive!).
The Minneapolis & St. Louis RY. used “red rock” crushed red limestone on their main line out of Minneapolis during their final phase of track improvement. I don’t know how far they applied it southward, but it may have been used all the way to Peroia. They got it from the long established red rock quarry near Shakopee, MN.
There are indications that they once used crushed gray limestone. I don’t know where they got it, but I associate it with Minneapolis along the river.
I don’t believe that crushed limestone was considered unacceptable for use as ballast. It just was not the best. But price and availability were factors in addition to performance over time.
Soo Line served Dresser, WI where there was a big trap rock quarry, and they used trap rock extensively for ballast.
The “fines” from degraded limestone ballast will also ‘cement’ together (some limestones being the raw material to make Portland cement). Also, limestone fines eventually turn into clay. Finally, limestone dust can be pretty corrosive to rail steel.
- Paul North.
I think your observation explains the downside of limestone. Reballasting costs money, so if you have to do it “often” it is definitely time to consider a better quality of rock, such as others have already described. Limestone may have been adequate in the old days with much lighter axle loads but not for heavy tonnage.
John
Trackmen want the stuff not to degrade and also to drain. It locks-up OK, but mechanical action breaks limestone down quickly. One of the tests that materials engineers perform is the LA Abrasion Test which tells you a lot about how come granite is so much superior to limestone.
Crushed slag from steel mills had the prerequisite edges, but broke down and failed like limestone. Fortunately, the steel mills don’t generate much of that in the newer electric arc furnaces. (did that stuff ever eat ties though!)
Real railroaders (even desparate ones) don’t allow gravel into their track structure, period. Put that stuff in french drains or concrete.
The Milwaukee Road used some kind of gravel. I don’t know if it was washed or screened to any extent, but it was not crushed, angular, or sharp. It ran from a rock size of about 3/4" down to fines. The rocks looked like the colors of limestone, but it was hard and shiny more like marble. I don’t know where it came from, but they must have had a good source on their system. I am sure abrasion would have been negligible, but drainage was slow. It would grow weeds very well.
I would guess that trap rock would make good ballast because it is angular and can be a sharp as a knife, and hard enough to ring like a bell.
I agree that the CNW “pink” ballast was sharp looking.
Mudchicken, can you elaborate why gravel isnt used? Is it too smooth and small?
Ed
“Diamonds are a girls best friend.” Could they also be a railroad’s?
Assume a process existed to turn carbon into diamond of similar size, texture and price as “Pink Lady” ballast. Diamond is a hard material.
Is diamond too hard? Would diamond tear aside the binding ties that no man should tear asunder like a divorce attorney?
Wheeler pit run… The pit was near Janesville Wis for years. Later the Milw started buying crushed Lannon stone from nearby Waukesha for local use.
Randy
I suspect what was available locally had a large influence on what the railroad used.
I recall railroads in Michigan’s Upper Peninsula around 1960 having “stamp sand”. as ballast. This is course rock particles (about 1/8" as I recall) with sharp edges left by the copper mines.
The Milwaukee also had a gravel quarry just west of Miles City for track ballast.
I’ve seen gravel roads made with crushed limestone. They eventually turn to dust roads under moderate traffic.
Limestone on roads is crushed and includes the fines because it needs the fines in order to be compactable. When it is compacted, it looks just like hard mud. The individual rocks are not visible. If it is dry, it will be dusty with a thin coat of loose fines on the surface. The appearance is not due to the rocks having broken down to dust.
The fact that limestone breaks down under load is relative. Limestone is softer than granite or basalt, but it is still quite serviceable for road base and railroad ballast. The choice for railroad ballast depends on cost of material and transportation, and the cost of maintenance such as cleaning and resurfacing for application for a given amount of traffic and tonnage.
The C&O (ex PM) had online limestone quarries at the Petoskey end, and perhaps other areas. There is no granite in the southern peninsular of Michigan.
I remember the Black Mesa/Lake Powell coal mine to power plant RR was ballasted with river gravel which turned out to be unstable because of roundness.
MP173 - You want the ballast to lock-up, support & drain the track structure. You want to put track on a bed of ball bearings and watch it head for the fences upon addition of heat & lateral forces?
You will not find any major railroad allowing ballast to be round river run ballast in its industry track specs or standard plans.
More than once a year here, a new industry track has been rejected for use because a contractor substituted gravel for approved ballast.
Pre 1940, what DRGW called “gravel” was in reality less than 3/4" crushed rock.