A comprehensive laboratory evaluation of the factors affecting the Micro-Surfacing interlayer bond strength

This paper presents the results of a comprehensive laboratory 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 asphalt pavement surface. Several factors were investigated, which included: the type of tack coat material, the tack coat application rate, and the residual asphalt binder content of the micro-surfacing mix, the number of micro-surfacing layers, and the existing pavement surface texture. Two types of pull-off tests and a torque shear test were used to evaluate the interlayer bond strength of laboratory prepared samples. Statistical analysis was conducted on the results of the conducted bond strength tests. The results indicated that samples 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 (0.0068 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. The use of double layers of micro-surfacing generally resulted in lower bond strength compared to the use of a single layer for micro-surfacing application. In general, the bond strength was not significantly affected by the existing pavement surface texture.