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

Federal Highway Administration2019PDFTech ReportAschenbrener, T.Leiva, FabricioTran, Nam H.United States. Federal Highway Administration. Office of Asset Management, Pavements, and ConstructionAuburn University. National Center for Asphalt TechnologyUnited States. Federal Highway Administration. Office of Asset Management, Pavements, and ConstructionUnited StatesAsphalt pavementsDurabilityIn place densityAir voidsService lifeIn-Place DensityAir VoidsField CompactionDurabilityService LifeFHWA-HIF-19-052DTFH61-13-H-00027Aschenbrener, TimFinal ReportBased 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\u2019s 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.95