Limiting Strain Distribution Criteria for Perpetual Pavement Design Using AASHTOWare Pavement ME Design

Abstract

Perpetual asphalt pavement designs have been based on controlling horizontal strains at the bottom of the asphalt layer and vertical strains on top of the subgrade to prevent bottom-up fatigue cracking and subgrade rutting, respectively. Traditionally, single strain thresholds had been used as limits where damage accumulation begins and propagates. The concept of strain distributions was introduced at the National Center for Asphalt Technology (NCAT), and it was found to better represent the wide response spectrum in asphalt pavements caused by the different loading and environmental conditions. This concept was developed based on information and data collected from the NCAT Pavement Test Track, and from this a limiting strain distribution was created to assist with perpetual pavement design. Several studies analyzed the criteria using pavement responses calculated from PerRoad predicted strains in Test Track sections and existing perpetual pavements. A limitation of the AASHTOWare Pavement ME Design software is its inability to output the pavement responses necessary for perpetual pavement design. The objective of this study was to analyze pavement response data predicted from an integration of the AASHTOWare Pavement ME Design software outputs and a JULEA based program developed at NCAT to create a limiting strain distribution for perpetual pavement design using the AASHTOWare Pavement ME Design software. Strains were calculated for Test Track sections using these tools and based on the results a limiting strain distribution was developed. This limiting strain distribution was then further evaluated using eight sections that won Perpetual Pavement Awards. Results showed that the horizontal strain distributions obtained from Test Track sections could differentiate the sections with cracking and the sections that did not crack. In the further evaluation, the horizontal strain distributions from the perpetual pavements did not exceed the limiting strain distribution developed from the Test Track sections, except for a section which surpassed it by a small margin at the 80th and higher percentiles. Vertical strains were also determined for these pavements and the current 200 microstrains at 50th percentile design criteria was met by all the sections.