A Testing and Evaluation Protocol to Assess Seal Coat Binder-Aggregate Compatibility
This research project was commissioned to develop a new testing protocol to assess the compatibility of asphalt binders and aggregates used in seal coats and surface treatments. The study encompassed physical, chemical and mechanical aspects of compatibility as well as the construction factors that affect the bond between the aggregate and binder in seal coats. Prior to the development of the testing protocol, a constructability review was undertaken to assess the conditions under which incompatibility between binders and aggregate occur. Four different tests were conducted on several aggregate-binder combinations; modified net adsorption test, TechMRT aggregate pull-out test, interfacial bonding (pull-out) test and the newly developed performance-based seal-coat aggregate-binder compatibility test. Based on the constructability review, aggregate-binder combinations were identified to represent the 'best' and 'worst' performing material combinations. These combinations were used to test the feasibility of the testing protocol to include both extremes of the performance spectrum. It was not the objective of this research project to test all possible aggregate-binder combinations using the newly developed testing protocol, but a sufficient number of tests were conducted to illustrate the feasibility of the newly developed testing protocol under the multitude of conditions experienced by TxDOT seal coats. In the end, several hundred tests were conducted using multiple aggregate-binder combinations. By analyzing the results of these four test methods, two testing protocols were recommended for possible implementation by TxDOT. The modified net adsorption test developed by the National Roads Authority of Ireland is recommended to evaluate the compatibility of uncoated aggregates and hot asphalt binders. The second testing protocol recommended for implementation is the performance-based sealcoat aggregate-binder compatibility test.