Development of the Crack Sealant Adhesion Test (0-5457-2)

Crack sealants are widely used in Texas to prevent water from entering into lower structural layers thereby extending pavement life. However, most current crack sealants have been reported to have a very short life mainly due to adhesive failures. Although adhesive failure is known to be the major failure mechanism very little attention has been paid to measuring this property in the laboratory. The main objective of this project was to develop a performance related adhesion test using TxDOT's Overlay Tester. In this report the crack sealant adhesion test protocol developed in year 1 of this study was finalized. The final test protocol includes a molding jig, a detailed sample preparation procedure, an adhesion test protocol, and criteria for interpreting the results. In this study 13 sealants (some of them have never been used in Texas) were evaluated following the proposed test protocol. The results clearly showed that the crack sealant adhesion test can effectively differentiate the poor sealants from the good ones. Furthermore, based on these test results, a draft crack sealant special specification was proposed. This is different from the current specification, which is mainly based on crumb rubber content. The new special specification is based on the results of the new adhesion test. In addition to this performance test other complementary factors such as flash point, softening point, and viscosity have been included in the new specification. In the proposed specification, the sealants are classified as: Type A (min. 100 cycles to failure at 45 ºF), Type B (min. 400 cycles to failure at 45 ºF), and Type C (min. 400 cycles to failure at 33 ºF). In addition, preliminary recommendation on optimum sealant types were made for each district in the state based on climatic conditions (freeze thaw cycles). Finally, an experimental test plan was developed to validate the draft special specification.