Evaluation of the Interlayer Bond Strength of Micro-Surfacing Mixes

This paper presents the results of the first study to evaluate the effects of the tack coat and micro-surfacing mix properties on the interlayer bond strength between the micro-surfacing layer(s) and existing pavement surface. Several factors were investigated, which included the type of tack coat material, tack coat application rate, and the residual binder content of the micro-surfacing mix. To this end, a total of 14 field micro-surfacing test sections were installed on Ohio State Route 03 in Wayne County, Ohio. While the first seven sections were constructed with a single micro-surfacing layer, the other seven sections had double micro-surfacing layers. Five tack coat application rates and two residual binder contents were evaluated. The testing plan involved obtaining core samples from the constructed sections 1 week, 4 months, and 12 months after construction. The obtained field cores were tested in the laboratory using two types of pull-off tests and a torque bond strength test. The results of bond strength tests on obtained field cores and the statistical analysis performed on these results indicated that sections with no tack coat had significantly lower bond strength than those with tack coat with at least 0.05 gallons per square yard (gsy) total application (0.0083 gsy residual application rate). Furthermore, results indicated that the use of 0.75% lower residual asphalt binder content in micro-surfacing mixes resulted in significantly lower bond strength between the micro-surfacing and existing pavement. The tack coat material properties had some effect on the interlayer bond strength; however, this effect was statistically insignificant.