Tack Coat Optimization for HMA Overlays: Accelerated Pavement Test Report: Fid-Bau Portal

Tack Coat Optimization for HMA Overlays: Accelerated Pavement Test Report

I. L. Al-Qadi / S. H. Carpenter / Z. Leng / H. Ozer / J. S. Trepanier

Interface bonding between hot-mix asphalt (HMA) overlays and Portland cement concrete (PCC) pavements is one of the most significant factors affecting overlay service life. This study was performed to quantify the effects of HMA type, tack coat type, tack coat application rate, and PCC surface texture on the interface bonding and overlay performance through laboratory testing, accelerated pavement testing (APT), and numerical modeling. This report presents the outcomes of the APT, as well as the numerical modeling of pavement interfaces. The results of the laboratory testing are covered in a companion report. The APT built on and validated previously completed laboratory tests where an HMA overlay was placed on top of an existing PCC pavement having various surface textures including smooth, transverse tined, longitudinal tined, and milled. In addition, zebra sections were included to evaluate the effect of non-uniform tack coat application. Asphalt emulsion SS-1hP and cutback asphalt RC-70 were applied at three residual application rates, 0.02, 0.04, and 0.09 gal/yd2 (0.09, 0.18, and 0.41 L/m2); asphalt binder PG64-22 was applied at 0.04 gal/yd2 (0.41 L/m2). Two HMA designs, standard binder mix and moisture sensitive binder mix, were used along with the three tack coats. Twenty-five pavement test sections were constructed and loaded with the Accelerated Transportation Loading ASsembly (ATLAS) at the centerline. The tensile strains at the bottom of HMA, to quantify potential interface slippage, were measured for selective sections, and primary HMA rutting was analyzed for all sections. The APT results validated laboratory determined optimum tack coat application rate, which provided the lowest interface strain and surface rutting in the field. Both PG64-22 and SS-1hP showed better rutting resistance than RC-70. Milled PCC surface provided lower rutting than transverse-tined and smooth surfaces. The field testing also showed that PCC cleaning methods play an important role in the HMA-PCC bonding. Higher rutting depth was measured in sections with uneven tack coat distribution compared to that with uniform tack coat distribution. Field testing results dont show enough evidence to prove that using a moisture-sensitive mix will result in higher HMA surface rutting.