Performance, Analysis, and Repair of Ultrathin and Thin Whitetopping at Minnesota Road Research Facility

Abstract

Thin and ultrathin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997 the Minnesota Department of Transportation constructed several thin and ultrathin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. Different techniques for repairing ultrathin whitetopping were investigated. Various techniques were also used to deter reflective cracking, including various bond-breaking materials and full-depth sawing at strategic locations along the longitudinal joint to prevent cracks from propagating into adjacent panels at misaligned transverse joints. Four of the six sections had present serviceability indexes (PSIs) greater than 3.5 before the repairs, showing that a good level of performance has been maintained after 4.7 million equivalent single-axle loads. The two sections that exhibited the largest drop in PSI were the overlays with 1.2- × 1.2-m (4- × 4-ft) panels. The repairs made in sections containing these panels have brought the PSI back up to an acceptable level (PSI > 3). The thin and ultrathin whitetopping test sections at Mn/ROAD have shown that whitetopping is a viable rehabilitation alternative for asphalt pavements. The importance of choosing an optimum panel size was exhibited. It has also been shown that when necessary, it is easy to repair ultrathin whitetopping sections. Various techniques for repairing each type of distress have been summarized.