Shear Properties and Various Mechanical Tests in the Interface Zone of Asphalt Layers

Abstract: Over four decades, researchers have extensively focused on bonding flexible pavement layers. Scholars have concentrated on the partial or complete lack of interlayer bonding between asphalt layers, which is the primary cause of premature pavement failures, such as cracking, rut-ting, slippage of wearing courses, and decline in pavement life. These defects are observed within the high horizontal force areas owing to increased speed, braking, and sharp angles when entering or exiting highways and the variations in paving materials, traffic load, and climatic factors. Var-ious studies have investigated the debonding of flexible pavements, and test methods have been developed to find effective solutions. This review is aimed at summarising and discussing certain factors influencing shear strength performance, such as tack coat material, surface characteristics of multi-layer construction of flexible pavements, and different mechanical shear tests. First, bonding in the interface zone area and its Effect on the shear strength performance is reviewed. Subse-quently, the types of materials and construction methods and their effects on the bonding quality of the interface zone area are clarified. Finally, the linear relationships between certain effects and the Ability of nanofibers to improve the emulsion properties are discussed. However, no agreement on the optimum tack coat could be obtained owing to the variety of surfaces. Hence, a milling surface is recommended for higher shear strength. The shear test is the most used method for verifying the interlayer bonding strengths, and continuous research endeavours are recommended to analyse debonding in multi-layer asphalt pavements.摘要：四十余年来，研究者们始终围绕柔性路面层间粘结技术开展了大量系统性研究。学界重点关注沥青层间部分或完全粘结缺失的问题——该问题正是引发路面过早失效的核心诱因，具体表现为开裂、车辙、磨耗层滑移以及路面使用寿命缩短。这类缺陷多发于高横向力区域：该区域因车辆高速通行、制动操作、进出高速公路时的急转弯工况，加之摊铺材料、交通荷载与气候因素的波动变化，更易出现上述病害。 已有多项研究针对柔性路面层间脱粘问题展开探索，并开发出各类测试方法以寻求有效解决方案。本综述旨在梳理并探讨影响层间抗剪强度性能的若干因素，包括粘层油（tack coat）材料、柔性路面多层铺装的表面特性，以及各类机械式抗剪测试方法。首先，本文对界面区域的粘结状态及其对抗剪强度性能的影响进行了综述；随后，本文明确了各类粘结材料与施工工艺的类型，并阐释了其对界面区域粘结质量的作用效果；最后，本文探讨了部分影响因素与纳米纤维（nanofibers）改善乳化液（emulsion）性能的能力之间的线性关联。 然而，由于路面表面类型多样，目前尚未就最优粘层油方案达成统一共识。因此，为获得更高的抗剪强度，推荐采用铣刨处理后的路面表面。抗剪测试是验证层间粘结强度最常用的手段，未来仍需持续开展研究工作，以深入分析多层沥青路面的层间脱粘问题。