FAYETTEVILLE, Ark. - Although researchers develop superior paving materials, such as Superpave, and government entities mandate their use, drivers continue to encounter roads that buckle, crack and wear out prematurely. University of Arkansas researcher Kevin Hall found that one significant reason for this was that the engineers and workers directly involved in specifying and supplying the asphalt were not aware of the necessary construction practices for the new mixes.

"Although Superpave design specifications are well understood by most designers and suppliers working on high-volume roadways, problems arose when local projects began using Superpave," explained Hall, professor of civil engineering. "We realized that there was an acute need for information at the local level regarding necessary specification and construction practices, both in Arkansas and nationally."

Hall recently presented his findings and the details of the Arkansas Superpave seminars at the Transportation Research Board meeting in Washington, D.C. They will appear in the upcoming issue of the Transportation Research Record on Technology Transfer. He is currently preparing a handbook to facilitate conduct of Superpave seminars throughout the United States.

Hall studies hot-mix asphalt concrete (HMAC) flexible pavement, which covers more than half of the roadways in the United States. Until 1990, virtually all HMAC roads in Arkansas and most other states were made by the Marshall method and produced a very dense asphalt. However, in 1990 the national Strategic Highway Research Project defined a new way to mix HMAC called Superpave.

Designed for the particular location where it is installed, Superpave models the fundamental characteristics of the materials rather than relying on the contractor’s experience. State and local highway departments, who bear the burden of building and maintaining more than 3.9 million miles of paved roads, began implementing Superpave aggressively in 1993. In 1997 Arkansas implemented the Superpave asphalt design system for all state and federal highways and eliminated the use of Marshall-based mixtures on state roads in 2003.

"Unlike Marshall-type HMAC, which is made up of both small and large rocks, Superpave aggregate has mostly large rocks," Hall explained. "This provides more strength than old pavements, but it also means water moves through Superpave in a different way."

Problems arise because individuals specifying materials for low-volume county roads and city streets often order a mix that meets "state specifications," assuming it is the same Marshall mix that has been used for years. Suppliers send the mix currently being produced in their plant, which is often a Superpave mix being prepared for high-volume highways.

"This common situation illustrates the need for programs to explain Superpave technology to engineers, city and county officials, local suppliers and others working on paving projects for lower-traffic-volume roadways," explained Hall. "We needed a true technology transfer, which is an active interaction between information suppliers and ultimate users that results in actual innovation."

To meet this need, Hall developed a no-cost, one-day seminar, which he presented at nine locations around the state. Locations were selected to ensure that no participant had to travel more than an hour to attend. The 226 participants ranged from engineers to county judges to dump truck drivers.

"Localization of the programs was key for two reasons," Hall said. "First, participants were able to attend at no cost, which is an important issue for small governments on tight budgets. Second, HMAC mixtures vary across the state and this allowed the program to address the unique problems in a given area. An added benefit was that it allowed local personnel to interact with the local asphalt producers."

The seminars took an informal, hands-on approach to allow the audience to draw on personal experience and actively participate in the learning experience. Each seminar began with a three-hour informal discussion on Superpave HMAC specifications and construction issues. During a lunch provided on-site, participants watched two videos on HMAC construction issues. The afternoon was devoted to a field trip to a local hot-mix asphalt plant to show how hot-mix asphalt is produced.

Discussion of specifications looked at typical local practices, including the specification of "state mix" for asphalt roadways. Elimination of Marshall-based mixes from the "state mix" and criteria for specifying Superpave mixes were stressed, with emphasis on "what needs to be done" vs. "what has been done."

The contribution of local HMAC providers was key, according to Hall. "Even within a relatively small state such as Arkansas, significant differences exist in materials used for HMAC. Local producers were able to provide participants with site-specific information concerning mixtures and aggregates, including cost information and case studies."

Because seminar cost was a critical issue, the seminars were developed through a grant from the Mack-Blackwell National Rural Transportation Study Center. Additional funding was provided by the Arkansas State Highway and Transportation Department (AHTD) and the Arkansas Asphalt Paving Association (AAPA).

"AAPA was the true champion of the cause. They enlisted local providers, initiated contact with the Arkansas County Judges Association and the Arkansas Municipal League and provided course materials," Hall said. "And since this involved transfer of technology used at the state level to the city/county level, the technology-transfer program personnel from AHTD were also eager to participate."