An empirical pavement design method such as the American Association of State Highway and Transportation Officials (AASHTO) 1993 pavement design guide uses structural layer coefficient (ai) value to determine thickness of each layer material or to convert a selected layer thickness to structural number (SN). Any change in material composition and properties will affect the ai value, which will directly affect the required thickness of that layer in a logical manner. However, there are concerns regarding the sensitivity and trends of predicted distresses using the AASHTOWare Pavement Mechanistic‐Empirical Design (PMED) software for different design inputs including material properties and the consistency among the PMED software versions. Two sets of design trials were completed between November 2023 and February 2024 in this study, using the latest web version (v3.0) of the PMED software, to assess the effect of hot mix asphalt (HMA) in‐place compaction, which ranged from 90 to 97%, and the voids in mineral aggregates (VMA), which ranged from 13 to 17%, on the predicted distresses. Climatic data from nine to ten weather stations across Canada were used.
The analysis showed that a lower density/compaction (increased air voids) in an HMA mat results in an increase of predicted IRI, total and HMA (i.e., asphalt concrete) layer rutting, bottom‐up fatigue cracking (BUFC), and thermal cracking (TC), but an inconsistent variation of top‐down fatigue cracking (TDFC). Increased VMA and asphalt cement (AC) content results in a reduction of predicted IRI, BUFC, TDFC and TC, and an increase in total and HMA layer rutting. In general, the predicted distresses were shown to be very sensitive to changes in HMA density (air voids), VMA, and AC content. The impact of climatic condition on predicted distresses was not shown to be as expected or practically experienced. This paper presents the details of these trials including trend analyses and findings.