Evaluating the Performance of Concrete Overlays in Missouri

Abstract

The Missouri Department of Transportation (MoDOT) has used concrete overlays as a pavement rehabilitation method since at least the 1930s, with over 40 projects constructed in the last two decades alone. However, there has not been an integral effort to comprehensively evaluate the performance of those projects in relation to design parameters, as-built construction quality, traffic levels, or distress progression. The objective of this study was to undertake a critical analysis of concrete overlays in Missouri as a first step to recommend improvements to MoDOT’s overlay selection, design, and construction practices. MoDOT uses three types of concrete overlays: unbonded overlays (UBOL), big block overlays (BBOL), and bonded overlays (BOL). It was found that UBOL projects exhibited the lowest international roughness index values among all types of overlays. The most predominant distress for UBOL was longitudinal cracking, which appeared more often at the center of the slab or in the right wheelpath. Cracking in the right wheelpath was particularly evident on projects that used a slab width greater than 12 ft and asphalt shoulders. Although BBOL and BOL projects did not deviate from the standard slab size, the rightmost panels tended to exhibit more distress, which might also point to weak support around the mainline-shoulder area. Recommendations for future projects include revising the design thickness procedures to be site-specific, revising the thickness quality control practices, and the continued use of geotextiles as interlayers for projects that require a bond breaker.