Abstract Manager

Asphalt concrete (AC) surfaced flexible pavements are the prevalent pavement structures in Canada and elsewhere, and AC overlays are the common treatments to extend their lifecycle. Several methods have been in use for overlay design, which provided a reasonable variation of overlay requirement for a change in any design input. However, highway agencies are facing challenges to implement the AASHTOWare Pavement ME Design (PMED) software because of concerns related to some models and inconsistencies in predicted distresses including significant variations among software versions. This study aimed to evaluate the suitability of the latest version of the software for flexible pavement AC overlay design.

In August - September 2023, TAC ME Design Subcommittee completed several design trials for flexible pavement overlay design using the PMED software v3.0 and following variable inputs: i) climate data from nine weather stations across Canada; ii) three existing pavements with varying strength, surface condition, layer materials and subgrade, iii) AC mill depth, iv) AC overlay thickness, and v) traffic load.  

Preliminary analysis showed that AC overlays on milled surfaces do not reduce the predicted roughness as compared to straight overlays. An increased traffic load results in an increased roughness with some inconsistencies. AC overlays on milled surfaces result in higher total rutting as compared to straight overlays. An increased overlay thickness results in an inconsistent variation of predicted total rutting. An increased traffic load results in slight increase in the predicted total and AC layer rutting with unexpected variations among climatic areas. The total rutting is governed by rutting in subgrade and granular layers. No design input affects the predicted bottom-up fatigue cracking (BUFC), except traffic load. Higher fatigue cracking in existing pavements correspond to higher reflective cracking with inconsistencies among climatic areas. Increased mill depths provide no or unexpected effect on the predicted reflective cracking. There is no or negligible variation of transverse cracking among input variables. In general, transverse reflective cracking is unaffected by milling or overlay thickness with some exceptions and inconsistencies. The predicted top-down fatigue cracking (TDFC) remains unchanged for all inputs, except traffic load, with a higher TDFC in colder climatic areas as compared to warmer climatic areas.

The objective of this paper is to present the above stated trial results including detailed analyses and findings. The presented information may help agencies and interested individuals in assessing the suitability of the PMED software for flexible pavement overlay design.