Failure Modes in Unbonded Concrete Overlays

Abstract

Unbonded concrete overlays (UBOL) consist of a new Portland Cement Concrete (PCC) layer placed on an existing PCC pavement. The new concrete layer is separated from the existing pavement by an interlayer system, allowing these overlays to be placed on distressed PCC pavements. The interlayer system usually consists of a thin open graded or dense graded hot mix asphalt (HMA) layer or a non-woven geotextile fabric. An effort is currently being undertaken to develop a mechanistic-empirical design procedure for UBOLs. To develop this procedure it is necessary to identify the distresses that commonly develop in these pavement structures. Performance data from in-service pavements at the Minnesota Road Research Facility (MnROAD), in Michigan and Missouri, as well as data in the Long Term Pavement Performance (LTPP) database was reviewed. It was found that primary cracking mechanisms include longitudinal cracking in the wheelpath, at random locations and at mid-lane, and transverse cracking due to reflective cracking, reflective distress and erosion along the transverse joint. Many of these distresses appear to be at least partially caused by breakdown of the interlayer.