According to this
https://docs.google.com/viewer?a=v&q...tptvt4fFhUmBXA
an article from the 4th Int Symposium on Roof Technology; Re use of fly ash in shingle manufacture:
"A common specification among shingle manufacturers is a limit to the free lime content in filler. Roofing industry experience has shown that an excess amount of lime can react with certain asphalt constituents to greatly accelerate granule loss from the shingle, resulting in premature failure of the roof."