New tires have a higher zinc level.
I hope you will be at this year's annual USCC meeting. If so perhaps we could have lunch. This works pretty well and in about a year the rubber has been eaten up and is gone. I can see two potential problems with that material. The environmental constraint you describe of 85 degrees C may indicate that the piles are too high for the aeration system to be effective for cooling on a great portion of the compost pile, or that there is no active aeration.