Roughness progression of asphalt overlays in the C-shrp's LTPP study

The Canadian Long Term Pavement Performance (C-LTPP) study, initiated in 1989, involves 65 sections in the 24 provincial sites that received various thicknesses of asphalt overlays. This paper describes the impacts of these overlays on pavement roughness progression under comparative traffic loading, climate, and subgrade soil conditions. Progression of roughness for thin overlays (30-60 mm) is significantly higher on a national basis than for medium (60-100 mm) and thick (100-185 mm) overlays. Major factor effect findings are that: (a) in wet, high freeze zones, thinner overlays show a higher rate of roughness progression than thicker overlays, regardless of subgrade type; (b) in dry, high freeze zones, roughness progression for medium and thick overlays is relatively small; (c) in wet, low-freeze zones, thinner overlays combined with a fine subgrade show the highest rate of roughness progression. In conclusion, the C-LTPP experiment has provided valuable information on roughness trends after only eight years of observations.