MINIMUM CRUSHED AGGREGATE REQUIREMENTS

An accelerated pavement testing facility has been developed by Purdue University for the Indiana Department of Transportation. The test facility includes a test pit in which prototype scale pavement sections can be installed. The Accelerated Pavement Tester (APT) loading system has the capability of applying moving wheel loads to the test sections. An initial study utilizing the accelerated pavement test facility has been conducted at Purdue University to determine the minimum crushed aggregate requirements in asphalt mixtures in Indiana. This study addresses effects of various constituents of the asphalt mixture on pavement rutting. The factors included in this study are aggregate type, percentage of crushed gravel, percentage of natural vs. crushed sand, and asphalt content. Combinations of these factors and their levels resulted in 27 sections being tested. Rutting was documented for each test section during APT operation. Marshall mixture design and laboratory tests provide comprehensive information on mixture properties. As a result of both the laboratory and APT results, recommendations are provided for using gravel in asphalt mixture. A finite element program, ABACUS, was used in this study to model the pavement structure and permanent deformation. An approximate approach was used to simulate the APT conditions. A creep model was used to represent the actual pavement rutting. Based on the mixture performance in APT, material constants in the creep model were backcalculated. Regression analyses were conducted to correlate these material constants with mixture physical properties. Mixtures tested with the APT were also tested in a laboratory wheel track device. After these results were evaluated, two of the original mixtures were retested in the APT.