Study Influence of Gradation Limit at Interface Shear Strength between Double Asphalt Layer Specimens Using a New Direct Shear Device

Numerous factors influence flexible pavement performance, and the interface shear strength between pavement layers is one of the quality and protection indicators; it is the primary cause of premature pavement failures, such as rutting and slippage of the wearing course, which can decline pavement life. Various methods have been developed to analyse the shear strength on the interface zone in the flexible pavement; however, the typical method is a direct shear. Several studies have investigated the problem of poor bonding between pavement layers and highlighted that many factors affect interface shear strength, such as temperature, surface texture, tack coat material, and type of mixture material. This paper aims to study the influence of gradation limit on the shear strength between double asphalt layer specimens and develop a new direct shear device for shear strength measurement. This study also investigates the shear behaviour of the studied materials at different temperatures (30, 40, 50, and 60 degrees C). Experiments were carried out for hot mix asphalt (HMA) AC 10 as a top layer with three gradations and ACW 28 as a bottom layer with slow-setting emulsion (SS-h1) and rapid-setting emulsion (RS-h1). The result of the study showed that the essential factors that influence shear strength in the interface zone are the temperature and the gradation limit. For the emulsion type, there is a slight effect on the shear strength. Generally, the shear result based on the direct shear device developed in this study (UPM- ST) is reliable, and this relationship can be used to ensure that the limit of gradation and tack coat can improve shear strength.