Investigation of ultra-rapid-setting emulsion for tack coat applications

The presence and the proper application of bituminous tack coat between pavement layers are critical elements to the effective functionality and longevity of multilayered flexible pavements. This study assessed the performance of a newly developed ultra-rapid-setting (URS) emulsion as a tack coat, with particular emphasis on its adhesive properties. The experimental testing matrix included physical and rheological tests consistent with relevant specifications of the Pennsylvania Department of Transportation and Superpave® binder grading. Bonding performance was evaluated on the basis of results from shear tests conducted with a modified Marshall setup and the Superpave shear tester (SST). The results revealed that the new product set faster than the typical cationic rapid-setting emulsion (CRS-1h) used as a control tack coat in this study. The physical and rheological properties of the URS residue indicated a reduction in density, stiffness, and viscosity. The changes in the properties of the residue, however, were not significant enough to alter its performance grade. Results from the modified Marshall test at 25 C and SST tests at 25 C and 51 C revealed similar values for shear strength for both types of emulsions. The strengths of the specimens with the CRS-1h tack coat were slightly higher than those of the URS when tested in the modified Marshall setup, while the opposite was true for the SST setup at 51 C. This study demonstrated no statistical difference between the performances of the two products regarding adhesion for all conditions and tests performed.