I've had a similar problem with trees that are next to our gravel road. The county dropped a dead Shagbark Hickory on my property and I told them, that I would cut it up. It was very old and was full of grit, from years and years of having cars driving up and down the road. When I counted the rings it was about 120 years old. I had to resharpen my chain about 8 times while cutting that up.