Performance of Concrete Overlays in Iowa

It has often been claimed that concrete overlays are a cost effective, low maintenance preservation tool used to extend pavement life. However, there has been relatively little data to confirm this. The State of Iowa has a long history of using concrete overlays as a means of extending the life of all types of roadways and as such provides an interesting opportunity to examine their performance over time. The work described in this paper summarizes the activities and findings of a study conducted for the Iowa Highway Research Board. Existing databases operated by the Department of Transportation and Iowa State University were analyzed to assess the performance of overlays. Pavement condition data such as IRI, transverse cracking, longitudinal cracking, D-cracking, spalled joints and faulting were compared with design details of the overlays such as bond type, thickness and joint spacing. The data indicate that in general overlay performance is very good in that about 90% of 3100 km of overlays are still in acceptable condition at ages up to 35 years. The paper discusses the details behind this finding