Effects of Milling and Other Repairs on Smoothness of Overlays: Additional Testing on Construction Under Profiler-Based Smoothness Specifications

This technical memorandum provides additional information regarding smoothness on several thin asphalt overlay projects constructed soon after changes in Caltrans specifications for constructed pavement surfaces using the International Roughness Index (IRI) as the quality metric. The IRI data were collecting using inertial profilers, before and after construction, on overlaid surfaces employing one of three repairs—digouts, cold in-place recycling (CIR), mill and filling—or none. Because the data were collected after the close of the construction contract, they include the effects of any grinding that Caltrans required the contractor to perform prior to that close. However, the data provide a preliminary look at whether changes in the construction smoothness specification necessitate changes to any of the recommendations in a previous report regarding repairs before overlay. The results indicate that the recommendations in the previous report are generally being followed. The results also indicate that the previous recommendation to not include milling before overlay when IRI is less than 120 inches/mile or below 95 inches/mile may need to be revised under the new specification. However, additional data are needed, since only two projects with milling were included in this data set. A survey of district practices conducted in September 2017 indicated that decisions regarding the inclusion of digouts, milling, and CIR prior to overlay were based on addressing load-related cracking, not roughness. It was observed that decisions regarding pre-overlay repairs for the small set of projects reviewed have generally resulted in smoother existing pavements not being subjected to pre-overlay repairs, and digouts, milling, and CIR being used on successively rougher existing pavements.