Asphalt Layer Coefficient

Recent research conducted at the NCAT Test Track indicates a need to update a critical value used in pavement design to determine the required HMA thickness. This value, called the layer coefficient, is a measure of a layer’s relative strength contribution to the overall pavement structure.   The American Association of State Highway and Transportation Officials (AASHTO) recommends using a HMA layer coefficient of 0.44, and this is based on the results from the AASHO Road Test conducted from 1958 to 1960.  Research from NCAT shows that this parameter can be updated to 0.54, resulting in approximately 18.5% thinner pavements for a more optimal design.  For more information on the layer coefficient study, click here.

Other references for NCAT's layer coefficient study:

Full length report on NCAT's website

Article in ASCE Journal of Civil Engineering

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