Officials in Hall County are looking at ways to upgrade gravel and failing asphalt county roads with fly ash. The county has 813 miles of roads,  629 of which are gravel and 184 that are asphalt. Officials believe they can save money by using fly ash to stabilize and strengthen the subgrade for new construction. A fly ash subgrade could allow the county to reduce its pavement thickness by 1 to 1.5 inches, which translates into a savings of $35,000 to $55,000 a mile, an official said.