Investigation of Clay Balls in Asphalt Pavement

Clay ball is a pavement surface defect which refers to a clump in which clay or dirt is 8 mixed with hot asphalt mixture. Clay ball is typically caused by a combination of aggregate 9 contamination of clay or soil, high aggregate moisture, and low production temperature at the 10 asphalt plant. It usually appears a few weeks or months after paving under traffic load, after being 11 liquefied and knocked from the pavement surface. Clay balls can be the source of potholing, 12 raveling, and other issues such as moisture infiltration and reduced ride quality. This paper presents 13 an investigation of the clay balls on US-31 one winter after construction in Hamilton County, 14 Indiana. In order to understand the pavement condition, their severity was measured using both 15 visual observation and infrared image collection system. In addition, a clay ball distribution pattern, 16 its density, and cores condition were evaluated. A precipitation effect on clay ball formation was 17 investigated for finding a cause of the clay balls. The investigation found that infrared image 18 collection system was appropriate in detecting the clay balls. The clay balls were elliptic in shape 19 with 1 inch to 4 inches in diameter, and the maximum clay ball depth is almost penetrating the entire 20 surface course. It was also found that the asphalt paving on the raining days or right after raining 21 could increase the potential of clay balls. Monitoring of aggregate moisture during construction on 22 or after raining days should be able to reduce the risk of clay balls. 23