Enhanced Durability of Asphalt Pavements through Increased In-Place Pavement Density

A new initiative by the Federal Highway Administration (FHWA) is examining the impact of improved density on the durability of asphalt pavements. The first step was a literature review of prior studies to examine the effect of improved compaction on the life of asphalt pavements. The literature review by NCAT researchers found that a 1% increase in in-place density could increase the service life of a pavement by conservatively 10% (NCAT Report 16-02).

For the second part, the FHWA provided grants for 10 state departments of transportation (DOTs) to construct at least one test section to demonstrate how increased density can be obtained. For each project, a control section was constructed using compaction procedures normally used by the contractor. Test section 1 was constructed using the same mix and compaction equipment but using best practices for compaction with the goal to reach a 1-2 percent higher density. Some DOTs elected to construct a second test section where an altered mix design and/or additional rolling equipment was used to help ensure higher density. The DOTs were required to submit a proposal to the FHWA outlining their approach to improve density in test section 1 and test section 2 (if used). The 10 DOTs selected were Alaska, District of Columbia, Florida, Indiana, Minnesota, Oklahoma, Pennsylvania, Virginia, Washington, and Wisconsin.

Prior to construction on each project, the Asphalt Institute conducted a one-day workshop to present best practices for improving in-place density. The goal of test section 1 was to use these improved rolling techniques to improve compaction but not to add additional equipment. By using these best practices, the process would hopefully provide higher density without significantly increasing construction cost.

Each project also included a mandatory pre-construction meeting for the agency and contractor and a representative of NCAT to ensure that everyone was familiar with the construction plans and the proposed methods for improving density in test section 1 and test section 2 (if used).

A Material Transfer Vehicle Provides Asphalt Mix to the Paver on I-75 near Lake City, Florida.

During construction, NCAT representatives observed and documented compaction procedures and recorded the locations of test sections, rolling procedures in each test section, mix type and laboratory quality assurance data, in-place density, and other information important to the project. After project completion, the NCAT representative prepared a short report of their observations.

Vibratory Rollers Immediately Compact the Hot Mix Behind the Paver on I-75 near Lake City, Florida.

All projects were scheduled for completion in the 2016 construction season. All of the information collected during construction is being compiled into a report documenting quality assurance data and observations. This information will be useful for others who want to improve density and those who may monitor the condition of these sections as they age.