Abstract
A large portion of Canada’s highway network is low traffic volume roads with thin pavement structures.
Currently, no generally accepted design method is available for these roads. As such, pavement design
and/or construction methods vary widely among the jurisdictions. The AASHTO 1993 guide recommends the same design approach for thin asphalt (<100 mm asphalt) pavements as the conventional flexible pavements, but with a lower level of reliability. These design outcomes are cost prohibitive in most cases considering traffic uses. This paper examined the suitability of the AASHTOWare Pavement ME Design (PMED) software for the design of thin asphalt pavements.
In 2022, the Transportation Association of Canada (TAC) Mechanistic‐Empirical (ME) Pavement Design
Subcommittee completed extensive design trials for thin asphalt concrete (AC) pavements using the
PMED software. These design trials used varying climate data across Canada, subgrade soil types,
base/subbase thickness combinations, and asphalt concrete (AC) thicknesses that ranged 50 mm to 150 mm. The trial results have shown uniform trends of the predicted total rutting when the AC layer
thicknesses were ≥60‐80 mm, depending on the subgrade stiffness. Uniform trends for the predicted
bottom‐up fatigue cracking were observed when the AC thicknesses were ≥100‐105 mm. The predicted
AC layer rutting were inconsistent among the design variables. There was no noticeable effect of varying
AC layer thickness on the predicted top‐down fatigue cracking.
Very good correlations (with R2 values >0.98) were observed between the AC layer thickness and the
predicted IRI as well as between the AC layer thickness and the predicted total rutting. Overall, these trial
results indicated that PMED software can be used to design pavements with a minimum AC thickness of
approximately 100 mm (4 in.) considering all type of distresses. However, considering only the IRI and
total rutting criteria and ignoring small irregularities in the trends of predicted IRI and total rutting in
pavement designs for low traffic volume roads, an AC thickness of as low as 50 mm could be used when using the PMED software.
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