ABSTRACT

Strength and fracture-based tests have been developed to assess the cracking potential of asphalt concrete (AC). The major difference between them is the presence of a notch in fracture tests. The objective of this study was to investigate the correlations between AC strengths and energy-based indices obtained from these tests, theoretically and experimentally. Theoretically, the role of a notch is presented and validated experimentally using 13 various AC mixtures. Strength tests, Indirect Tensile Test (IDT) and Indirect Tensile Cracking Test (IDEAL-CT), and a fracture test, Illinois Flexibility Index Test (I-FIT) were used. In addition, digital image correlation (DIC) was utilised to monitor crack development and path, compute crack propagation speed, and identify location and mode of energy dissipation. Brittle AC exhibits limited plasticity in both strength and fracture tests. Hence, a correlation is, theoretically, expected between strength and fracture test results. Conversely, ductile AC exhibits high plasticity in a strength test, but limited plasticity in a fracture test due to the notch presence, which amplifies the stress around the crack tip. Hence, theoretically, no correlation is expected between strength and fracture test results. Both tests reported lower index values for brittle AC mixtures, but no trend for ductile AC mixtures. Using DIC, the process zone (PZ) magnitudes of strength specimens, such as IDEAL-CT, were greater than the fracture-process zone (FPZ) for fracture specimens, such as I-FIT. Although I-FIT exhibits a single well-defined crack path, its Flexibility Index (FI) variability is a direct result of crack propagation speed, which is a function of the AC inhomogeneity. The FI captures AC material-inherent variability, which is useful for AC risk assessment to control AC pavement premature cracking.

摘要

已经开发了基于强度和断裂的测试来评估沥​​青混凝土 (AC) 的开裂潜力。它们之间的主要区别在于断裂测试中存在缺口。本研究的目的是从理论上和实验上研究从这些测试中获得的交流强度和基于能量的指数之间的相关性。从理论上讲，使用 13 种不同的 AC 混合物来展示和验证缺口的作用。使用强度测试、间接拉伸测试 (IDT) 和间接拉伸开裂测试 (IDEAL-CT)，以及断裂测试、伊利诺伊柔韧性指数测试 (I-FIT)。此外，数字图像相关（DIC）被用来监测裂纹的发展和路径，计算裂纹的传播速度，并确定能量耗散的位置和模式。脆性 AC 在强度和断裂测试中表现出有限的可塑性。因此，理论上，预期强度和断裂测试结果之间存在相关性。相反，韧性AC在强度试验中表现出高塑性，但由于缺口的存在，在断裂试验中塑性有限，这会放大裂纹尖端周围的应力。因此，理论上，预计强度和断裂试验结果之间没有相关性。两项测试均报告脆性 AC 混合物的指数值较低，但韧性 AC 混合物没有趋势。使用 DIC，强度试样（例如 IDEAL-CT）的过程区 (PZ) 幅度大于断裂试样（例如 I-FIT）的断裂过程区 (FPZ)。尽管 I-FIT 表现出单一的明确定义的裂纹路径，其弹性指数 (FI) 可变性是裂纹扩展速度的直接结果，裂纹扩展速度是 AC 不均匀性的函数。FI 捕获 AC 材料固有的可变性，这对于 AC 风险评估以控制 AC 路面过早开裂很有用。