Future Enhancements Being Developed
December 12, 2023Three major enhancements are being developed within fiscal year 2024 which are listed below. Two of the enhancements are directed towards the software based on requests from multiple users, while the other enhancement was also requested by users but is focused on local calibration – updating the Guide for Local Calibration.
1. AASHTO ‘Guide for Local Calibration of the Mechanistic-Empirical Pavement Design Guide’ (LCG)
The AASHTO ‘Guide for Local Calibration of the Mechanistic-Empirical Pavement Design Guide’ (LCG) was first published in 2008. Written a few years before the first AASHTOWare Pavement M-E Design (PMED) program was developed, the LCG did not have a specific pavement design tool to reference and was meant to inform generically about the process of locally calibrating a pavement design.
Now, with many States having adopted PMED as their pavement design tool, the LCG is being rewritten both to incorporate use of PMED as the primary design tool, and the AASHTOWare Calibration Assistance Tool (CAT) as the means of automating much of the local calibration process. The new LCG will also provide examples of actual pavement distress model calibrations, using the CAT, for new AC, JPCP, semi-rigid and AC overlay designs.
2. New Rehabilitation Design Strategy and Default Material Properties of Cold in Place Recycled and Full Depth Reclamation for Pavement Design
Full depth reclamation (FDR) and cold in-place recycling (CIPR) of the existing asphalt layers are not directly included in the PMED software as rehabilitation design strategies. The use of FDR and CIPR, however, are common rehabilitation strategies for flexible pavements with extensive deterioration. One reason why in place recycling techniques has become popular within the past couple of decades is the focus on pavement sustainability and conserving resources.
FDR and CIPR are addressed in the Mechanistic Empirical Pavement Design Guide (MEPDG) Manual of Practice but are defined as a new flexible pavement. The MEPDG Manual of Practice provides a brief overview on how to consider the use of various recycling techniques for rehabilitation design, but this requires a lot of assumptions by the user. The assumptions are related to the default layer properties, as well as simulating the recycled pavement layers.
To facilitate the use of the PMED software, multiple users have requested that FDR and CIPR techniques constitute a new rehabilitation design strategy. The purpose of this effort is to provide a rehabilitation design strategy that can be included directly in the PMED software. The inclusion of a separate rehabilitation design strategy will ensure more consistent use of recycling techniques in rehabilitation design using the PMED software, as well as reduce the uncertainty of the assumptions being made by the designers regarding the layer properties.
3. Integrate MSCR Asphalt Designations to Determine Input Level 3 Defaults
The “AASHTO M 332-18, Multiple Stress Creep Recovery (MSCR)” test has been implemented by multiple agencies throughout the USA and Canada. At present, the MSCR test is not accepted by the PMED software but is recommended for a better evaluation of asphalt binder modifications. Many agencies in North America are planning to use AASHTO M 332 in the specifications. The inclusion of Level 3 binder grade selection corresponding to the MSCR characterization will allow users to select binders that are more representative of their current practices and naming conventions.