Lab Corner Summer 2006 – Density and performance

Quantifying the Effect of Asphalt Pavement Density on Performance

Unlike many commercial products in the United States, new asphalt pavements have not typically come with warranties on performance. As such, the client (state highway agency) usually identifies certain properties that are believed to be related to performance and establishes incentives and disincentives for the supplier based on compliance with property criteria.

One major performance property specified that affects pavement performance is the density of the hot mix asphalt layers that constitute the overall pavement system. Obtaining an optimum initial construction density allows the asphalt mixture to have a proper balance of strength and durability, while at the same time maintaining reasonable construction costs. Failure to achieve proper initial and ultimate density can reduce the performance of the asphalt pavement, leading to a shorter pavement life and more frequent rehabilitation needs.

The Kentucky Transportation Center at the University of Kentucky has partnered with the Asphalt Institute to conduct a coordinated research program that will: (1) quantify the effect of initial construction density on asphalt pavement performance; (2) validate the relationship between initial construction density and ultimate pavement density; and (3) identify material and construction variables and quantify their effect on the ability to reasonably achieve specified target density during construction. Phase 1 of the research has just started with an expected completion date of approximately 18 months.

By obtaining a better understanding of the relationship between density and asphalt pavement performance, more appropriate specification limits and pay adjustments can be developed that directly relate to serviceability and long-term performance. Ultimately, the results of this research may also help producers transition more smoothly to end-result (warranty) specifications. The implementation of these results will not only increase asphalt pavement life, but also contribute to a reduction in user delays and accidents coincident with future work zones.

For more information on the Asphalt Institute’s Research Program, please contact Mike Anderson (, Director of Research and Laboratory Services.