Technical Bulletin on Design and Construction of Crack Attenuating Mixes (CAM)

The crack attenuating mix for pavement maintenance and preservation. Developed under Texas Department of Transportation (TxDOT) Project 0-5598, this very fine mix is designed to pass both the current Hamburg wheel tracking test (HWTT) to ensure moisture susceptibility and good rut resistance and the strict overlay tester (OT) requirements to ensure good crack resistance. In several recent projects problems were found using the current volumetric mix design requirements to determine the optimal asphalt content (OAC) that meets both performance test requirements. This project proposes a new mix balanced mix design procedure that attempts to identify a window of asphalt contents where both cracking and rutting requirements are satisfied. This procedure will rapidly identify aggregate/asphalt combinations that will not work so that costly re-runs of the volumetric designs can be avoided. The procedure can also save money by identifying a window of asphalt content that will provide satisfactory performance. This technical bulletin gives the minimum aggregate properties, a description of the mix design procedure, an example CAM mix design, and a discussion of construction issues.