I've been considering using asphalt millings as a floor in my chicken run. I figured this would give my chickens some grit and make it easier to clean out the run from time to time. It would also keep the mud down. My driveway is currently made out of millings so the chickens have access to them anyways when free ranging. I'm concerned about the possible toxicity of the petroleum based asphalt millings leeching into the eggs. Has anyone found any research to confirm or dispute this idea? I could use gravel instead, however the chickens will still have access to my driveway most days anyways. Thoughts??