Development of Technologies to Evaluate Hot Mix Asphalt Adhesion through Tack Coat

Graduation date: 2017Flexible pavements consist of multilayers, which form the pavement structures. Since the strength of the bond at interface between layers plays a significant role in improving the structural integri-ty and the performance of pavement structures, tack coat materials and methods used for their application during construction are important in providing an adequate bond strength between pavement lifts. Tack coat is a bituminous liquid asphalt (a mixture of water, asphalt binder, and an emulsifying agent) and usually applied to provide a bond between pavement lifts. The absence of the tack coat adhesion at the interface between layers leads to increased stresses in the pave-ment structure. An inspection procedure to monitor the performance of the interlayer bond dur-ing the pavement use phase and identifying bond failures is critical to improve pavement man-agement systems and develop more effective pavement design strategies. In this study, two dif-ferent devices were developed at Oregon State University to evaluate the tack coat performance in the field. \ud \ud First, the wireless Oregon Field Tack Coat Tester (OFTCT) device was developed to predict the long-term performance of the in-situ tack coat bond strength and to evaluate the impact of pave-ment surface cleanliness before tack coat application on bond strength. Correlations between OFTCT field test results and the results of laboratory shear tests conducted with cores taken from the field were investigated to determine the effectiveness of the OFTCT tests. A new heat-ing system (an adjustable heat gun and environmental chamber) was developed to reduce the tack coat’s curing time in the field and control temperature during testing. The results indicated that the OFTCT device can be successfully utilized in the field to differentiate between clean and dusty surfaces before tack coat application. By using wireless sensors controlled by a laptop, practicality of the device was improved to reduce the testing time. The correlation between OFTCT and laboratory shear test results was determined to be statistically significant (R² = 0.5189). OFTCT was able to identify the tack coats with high and low interlayer shear strength (ISS).\ud \ud Second, a new low cost field test device, Oregon Field Torque Tester (OFTT), was developed to evaluate the long-term post-construction tack coat performance of pavement sections. Correla-tions between OFTT field test results and the results of laboratory shear tests conducted with cores taken from the field were investigated to determine the effectiveness of the OFTT tests. The peak torque values at failure measured by the OFTT were observed to be highly correlated with the measured lab shear strengths. To conclude, both of the developed devices are expected to be adapted as field tests to evaluate the performance of tack coats in the field and to mitigate pavement distresses observed on roadways