Assessing the Moisture Susceptibility at Interface of Asphalt Concrete Pavement Layers

Abstract

The asphalt concrete flexible pavement consists of many layers interconnected by tack coat binder. The resistance of the bonding tack coat to the impact of moisture that ingress through the cracks into the interface of asphalt concrete can cause premature matrix degradation of pavement structure. In this investigation, the influence of moisture susceptibility on the bond strength and horizontal deformation of three layers of asphalt concrete are assessed under repeated shear stresses. The suitability of two types of tack coat (Rapid curing cutback RC-70 and medium setting cationic emulsion CMS) to support the resistance to moisture damage have been investigated. Asphalt concrete slab specimens have been prepared with the aid of roller compactor for the typical three layers usually implemented in flexible pavement in Iraq (wearing, binder and asphalt stabilized base courses) with (12, 19.5 and 25) mm nominal maximum size of aggregate. Layers were bonded by tack coat after construction of the bottom layers. Core specimens have been obtained and subjected to moisture damage then practiced 1200 cyclic shear stresses in the Pneumatic Repeated Load System PRLS using a special manufactured mold. Control core specimens have been obtained and practiced 1200 cyclic shear stresses. Specimens were tested for bond shear strength. The bond shear strength and horizontal deformation under repeated shear stresses were analyzed and compared. It was concluded that the horizontal permanent deformation increases by a range of (4 -27) % and (2-57) % after moisture damage when RC-70 and CMS tack coat were implemented respectively at various application rates. However, the reduction in bond shear strength due to moisture damage ranges between (2-17) % and (5 -30) % for RC-70 and CMS Tack coat interfaces. CMS tack coat exhibits higher bond shear strength ratio BSSR than RC-70 tack coat for all the application rates and is recommended for use from the moisture susceptibility point of view. Keywords: Moisture Susceptibility; Interface; Asphalt Concrete; Bond Shear; Horizontal Deformation; Tack Coat;