Highly modified asphalt (HiMA) mixtures, which have an increased structural contribution, potentially allowing for a reduction in pavement thickness without sacrificing performance, are having a big impact in Florida. The Florida Department of Transportation (FDOT) began using HiMA six years ago to address severe rutting observed in high-stress locations, such as truck weigh stations, agricultural inspection stations, and high-volume intersections and interchanges. Since then, the agency has placed more than 500,000 tons of HiMA mixtures on over 39 projects across the State and expanded use of HiMA to other types of applications.
One of the first HiMA projects built by FDOT was on a pavement section on Interstate 10 between two large truck stops, where the combination of heavy axle loads and slow-moving traffic resulted in severe rutting, exceeding 2 inches in some areas. To address these failures, FDOT planned to reconstruct the highway section using a Portland cement concrete pavement. However, FDOT instead milled the section to a depth of 2.5 inches and replaced it with a dense-graded HiMA mixture. While this was meant as a stopgap measure, the pavement performed so well that it was left in place and reconstruction was cancelled. After six years of service, rutting and cracking remains minimal.
FDOT performed a preliminary analysis and concluded that HiMA projects only need to last 10 months longer than conventional asphalt projects to pay for the increase in cost. There is strong evidence from projects in Florida and other States to suggest that the HiMA binder will add significantly more years of life than that.