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 the demonstration project was to determine the benefit of additional compaction and show that additional density could be obtained through improved techniques. This project effort included two major components: (1) a literature search to serve as an educational component regarding the best practices for increasing density, and (2) the construction of 10 field demonstration projects. Eight of the 10 states improved densities by at least 1% compared to a control section on their field demonstration projects. There were at least two pavement sections (a control and at least one test section) constructed within each of the 10 states that participated in this field demonstration project. Many of the states constructed more than two pavement sections for a total of 38 sections. There were many variables, including mixture type, construction equipment, and procedures between states and within states. A summary of the methods that states used to obtain increased density generally fell into one of five categories: (1) improving the agency’s specification by including or increasing incentives and increasing the minimum percentage 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.

A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the Mechanistic–Empirical Pavement Design Guide developed in NCHRP Project 1-37A, which has drawn much attention among asphalt technologists. The objectives in this study were ( a) to consider and compare different analysis techniques for construction of the master curve and ( b) to measure and analyze the effect of permanent strain on samples that have been evaluated with one of the simple performance tests, dynamic modulus. It was found that differences existed in the calculated asymptote values and the shape of the master curve, depending upon which method was adopted. Recommendations are made for modifications to the testing protocol and for further work to determine the effect of permanent strain at higher test temperatures.

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