Laboratory Validation of Surface-Initiated Transverse Cracking of Asphalt Pavement

Field pavement transverse cracking typically can be grouped into two categories, namely thermal cracking that initiates at the surface of the pavement and propagates downward, and reflective cracking that initiates at the pavement layer above the existing pavement cracks or joints and propagates upward. Recently, another transverse cracking phenomenon was noticed in some field investigations but was less studied. Cracks were observed from both the surface and the bottom of field cores, but they cannot be visually observed from the middle layer. In addition, the surface and the bottom cracks lined up well, showing the tendency of meeting each other. This study aimed to evaluate the causes of such transverse cracking phenomena by laboratory tests. Hamburg equipment was used as the evaluation equipment. Some samples were prepared with a saw cut notch 0.33 inches in depth and 0.25 inches in width, and some samples were prepared without the notch at the bottom. The results showed that such a crack type could have happened when samples are aged, the base below the sample is soft, and a notch exists in the bottom layer. A potential mechanism is when the wheel load moves on one side of the existing transverse cracking (the near side), as the specimen on this side tends to bend downward under the wheel load, especially when the support is relatively soft. If without constraint, the other side of the specimen (the far side) should consequently be tilted upward. However, the bonding with the base layer and the self-weight of the specimen restrict the upward movement of the far-side specimen. Therefore, the tensile stress at the surface of the specimen directly on top of the bottom crack is created. At the same time, the bottom crack has the potential of being squeezed and pushed together.