Quantification of Effects of Bitumen Surface Treatments on Material Properties of Existing Asphalt Pavement

Abstract

Bituminous surface treatments (BSTs), or chip seals, can be placed soon after (e.g., within 1 year) the underlying asphalt layer is paved, toward the end of the life of the existing asphalt layer, or sometime in between. The placement of a BST, especially soon after the underlying asphalt layer has been placed, mitigates the oxidation of the asphalt in the underlying layer as well as the infiltration of surface water into the pavement structure, which helps to reduce the raveling, frost heaving, and cracking of the underlying asphalt layer and to preserve the pavement’s integrity. However, few studies, if any, have evaluated the effects of BSTs quantitatively. This study quantifies the effects of BSTs on the material properties of the underlying asphalt layer based on laboratory testing of field samples. Asphalt layer field cores were extracted from pavements without a BST and with a BST as a control in the same project, for two field projects in Washington State. The mixture tests included dynamic modulus, creep compliance, and indirect tensile fracture tests on field cores of underlying asphalt layer. The asphalt binder was extracted from the asphalt layers at different depths to evaluate the aging gradient throughout the pavement depth; this evaluation included performance grading, multiple stress creep and recovery, and monotonic tests. Testing results suggest that placement of a BST soon after hot mix asphalt (HMA) paving reduces the oxidation of the HMA. When the BST is placed on the HMA, no aging gradient exists in the top two layers of the HMA. When the HMA pavement is subjected to long-term aging, no aging gradient in the HMA layer is evident, regardless of whether a BST is present or not. Therefore, this study explained/confirmed that the placement of a BST immediately after the HMA layer is placed could be beneficial for reducing cracking in HMA.