Re: Ballast question

A really hard clean stone such as granite or quartzite makes the best ballast. It's normally tested with the "Los Angeles abrasive" test, has sharp edges to interlock, and has a minimum of fines. Crusher run isn't great as ballast because of the fines, which retain moisture, but is great as subballast because it can be compacted into a really hard surface to support the ballast and track. Really sophisticated trackwork sometimes calls for asphalt for subballast. Usually it is recommended that 8" of ballast be installed under wood ties and 12" under concrete ties. That's under the tie. Unfortunately, sub ballast and ballast add a significant cost to trackwork, especially new, and railroads sometimes tend to try to cut corners with it, usually to their regret later. We used slag from the Pueblo mill as ballast on the connector track through the Pueblo Army Depot to TTC. Slag is OK (but ugly) in areas of low rainfall, but not in rainy or damp areas due to the acids it creates. They "eat" the rail.