Shortly after construction fat spots began to appear throughout the project on a 3-in. Hot-mix asphalt (HMA) overlay of an existing portland cement concrete pavement. The fat spots appeared to occur at the end of truck loads. After time the fat spots developed into potholes and the asphalt appeared to be stripped from the aggregate at the bottom of the potholes. Some rutting and shoving also developed at the fat spots. The objective of this study was to evaluate the HMA and to determine potential causes of the fat spots. The test plan included inspecting the pavement visually and obtaining core samples from fat spots, adjacent to fat spots, and from random locations throughout the project. Rut-depth measurements were also obtained. The cores were tested for asphalt content, gradation, void content, and slag content. Several of the asphalt mix layers were split into top and bottom halves, and the asphalt content and gradation of each half were compared. The asphalt cement from several cores was recovered, and the viscosity and penetration were determined. The results of this study indicated that the most likely cause of the fat spots was contamination of the HMA with some solvent (probably diesel fuel) during the placement operation.
Abstract