NRRA: Service Life Enhancement of Substrates Overlaid with Thin Overlays (UTBWC, Chip Seals, and Micro-Surfacing)Status: CompleteReport Date: 08/03/2020 Summary: Non-structural overlays such as ultra-thin bonded wearing course (UTBWC), chip seals, and micro-surfacing are commonly applied as a preventive maintenance method to extend the service life of a pavement. They are generally placed over flexible substrates, which include flexible pavements that have received bituminous interventions on bituminous upper layer (BOB), flexible pavements that have received bituminous interventions on concrete layer (BOC), and flexible pavements that have not received any intervention since constructed on aggregate base (BAB). These treatments have been widely applied, thus driving the need to conduct an analysis to determine the service life enhancements of these overlays using Weibull analysis. There are various factors that affect the expected service life of these preventive maintenance techniques such as the condition of the substrates and the maintenance window. The RSL – service life enhancement since intervention – for all treatments from two agencies (MnDOT and NDDOT) appear to be relatively close to each other, except for the BOC substrates overlaid with micro-surfacing. All treatments have a pattern of wear-out failures, which are an indication that the treatments are effective in providing life extensions because the cause of failures is not random. Some of the interventions are second or third and these collectively synergistically improve service life of the substrate, for which further investigations are recommended. Additional data from other state members and an update on these existing data (MnDOT and NDDOT) in five years would enhance the performance curves and improve the accuracy of estimated remaining service life. Final Deliverables: Report #NRRA202003 Related Materials: Related Research: