Ballast is the name for the small rocks under tracks that absorb some of the vibrations from trains, and to create them I had to get busy with some rocks. I had made rocks in the past and they were relatively low poly which is perfect for what I was looking for.
I created a basic plane in Maya and populated it with loads of those scaled down rocks to make it look like pebbles! Ingenious eh?
Once I was happy with the density I baked out normal and ambient occlusion maps, for extra depth information and more aesthetically accurate.
What this allowed me to do is focus less on the albedo, as the information needed really was already here. I used a cool technique by snapping the same asset to the edge of the plane and the grid, I was able to create a seamless tile without doing any post process work.
I found an albedo I had been using for some rocks and added a little variation to it, and the finished material looks awesome! (Marmoset render)