FHWA Demonstration Project for Enhanced Durability of Asphalt Pavements Through Increased In-Place Pavement Density, Phase 2

FHWA Demonstration Project for Enhanced Durability of Asphalt Pavements Through Increased In-Place Pavement Density, Phase 2

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    Final Report
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    Based on prior studies, a 1 percent increase to in-place density (or 1 percent decrease in air voids) achieved through improved compaction was estimated to improve the fatigue performance of asphalt pavements between 8 and 44 percent and improve rutting resistance by 7 to 66 percent. In addition, a 1 percent increase in in-place density was estimated to extend the service life by 10 percent, conservatively. Recognizing the importance of in-place density in building cost effective asphalt pavements, a Federal Highway Administration (FHWA) Demonstration Project was created for Enhanced Durability of Asphalt Pavements through Increased In-place Pavement Density. The objective of this Demonstration Project was to determine the impact of additional compaction on in-place density and how additional density could be obtained through improved techniques. Many States added additional compaction equipment and evaluated other methods that can help obtain additional in-place density. Phase 2 of this Demonstration Project included two major components: 1) a literature review to identify how much in-place density is enough, and 2) the construction of field demonstration projects in eight States. The literature review identified best practices for sufficient in-place density required for long-life asphalt pavements and provided examples of specifications from the State highway agencies (SHAs) that have successfully achieved the required in-place density level. The field demonstration projects were intended to support SHAs in evaluating their current density requirements for acceptance. Six of the eight States participating in Phase 2 improved in-place density by at least 0.5 percent on their demonstration projects. All the participating States averaged greater than or equal to 94.0 percent in-place density in at least one test section. Many of the States constructed more than two pavement sections for a total of 28 sections. Many variables were evaluated, including mixture type, construction equipment, and procedures between States and within States. A summary of the methods that States used to obtain increased in-place density generally fell into one of five categories: (1) improving the agency’s specification by including or increasing incentives and increasing the minimum percent in-place density requirements; (2) making engineering adjustments to the asphalt mixture design to obtain slightly higher optimum asphalt content (although not part of the original goal of the demonstration project); (3) improving consistency as measured by the standard deviation; (4) following best practices; and (5) using new technologies.
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