While not necessarily trackside, this industry would have a home on any layout. Concrete is the most used man-made material on the planet. Gravel, sand, fly ash, and blast furnace slag are all products carried by rail and also used in concrete mixing. I took several pictures of a mixing plant, and will post a few here. These have been resized so they don't take up so much bandwidth, the originals are HUGE and very detailed. If you're interested in having all of them, send me a PM and I can email them to you.