Concrete in the roadbed

While walking on an unimproved rail trail on the ex-PRR Chautauqua Branch near Corry, PA, I was surprised to find concrete buried in the roadbed. The pieces of concrete that were exposed were a bit wider than a railroad tie, and I found several stretches of the roadbed where there would be a lot of these protruding out of the ground beneath were the tracks once were. Was this a common practice in building railroads? It appears the only purpose the concrete could have served was to stabilize the roadbed. The soil in this part of the country can be quite wet and interlaced with a lot of springs that are very near the surface. Has anyone else ever see concrete in the roadbed along abandoned rail lines?