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Publication Number: FHWA-SA-97-021
Date: March 1997
Nearly two-thirds of States have adopted or are in the process of adopting the Superpave binder specification, which is the first step in implementing the Superpave system. Many States are already planning to take the next step - namely, implementation of the Superpave volumetric mix design procedures by 2000, in line with the target date set by the Asphalt Technical Working Group. These States are making the right choice, according to the findings of the Strategic Highway Research Program (SHRP) assessment project. By producing longer-lasting pavements, the Superpave system can stretch highway dollars and save motorists time and money.
The assessment of the Superpave system focused exclusively on the role of the asphalt binder in mix performance. The properties of the binder have a significant effect on the performance of an asphalt mix, leading TTI to estimate that switching to the Superpave binder specification could increase the service life of an asphalt overlay by 25 percent, to 10 years from 8 years. Based on States' experiences, the Texas Transportation Institute (TTI) estimated that one-fourth of the asphalt paving projects in the United States use binders that do not meet the Superpave binder specification.
Those conservative assumptions yield tremendous potential savings over a 20-year period. If, for example, all highway agencies adopt the Superpave binder specification within 5 years, TTI calculates that the savings to highway agencies nationwide could reach $637 million each year. Even if it takes highway agencies 10 years to implement the specification, the annual savings could still reach $484 million.
The potential savings to motorists are even more impressive. Because longer-lasting overlays will mean fewer maintenance-related delays and less wear and tear on vehicles, TTI calculated that motorists could save as much as $1.7 billion per year over a 20-year period if highway agencies were to adopt the Superpave binder specification within 5 years. If it takes 10 years to adopt the technology, the savings to motorists could still reach $1.3 billion per year.
Superpave research was the single biggest item in the SHRP budget, costing $53 million. All told, research, development, and implementation of the Superpave binder specification will cost an estimated $230 million over 20 years. But even if highway agencies take 10 years to fully implement the Superpave binder specification, they'll still save more than twice that amount every year for the next 20 years. Motorists will save more than five times that much every year.
States that have already built Superpave pavements agree that the new system should produce longer-lasting roads.
TTI's analysis included consideration of the following factors:
By producing longer-lasting pavements, the Superpave system can stretch highway dollars and save motorists time and money.
Traditionally, engineers have tested binders for characteristics such as viscosity or penetration. These tests do not measure a binder's low-temperature properties. As a result, highway agencies do not always choose the best binder for a job. The Superpave binder specification, in contrast, classifies binders according to the pavement temperatures under which they will serve.
The Superpave binder specification sets forth the physical properties that all binders must have; what varies, however, is the temperature at which those properties are reached. The properties indicate a binder's ability to resist rutting and low-temperature cracking.
Pavement designers determine the pavement temperatures expected at the project site and then select the appropriate Superpave binder grade. For example, a Superpave binder classified PG58-22 will meet the required physical properties at pavement temperatures ranging as low as -28 ºC (-18 ºF) and as high as 58 ºC (136 ºF).
More detailed information on the benefits-versus-costs analysis of the SHRP products, as well as more than 100 case studies of how highway agencies are using those products, are available at the RoadSavers home page.
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