Asphalt concrete is a composite heterogeneous material comprised of aggregates bonded together by bitumen binder. The mechanical behaviour of this material shows great dependence on loading rates and time (e.g., creep, relaxation). Such heterogeneity in the internal structure and complex behaviour of asphalt concrete present a challenge for numerical methods to fully capture its responses under different loading rates and durations, especially when large deformation and crack development are present in the material. This study proposes a modelling approach capable of capturing the behaviour of asphalt concrete under different loading rates and durations. In this approach, the heterogeneous internal structure of asphalt concrete is naturally reproduced by the discrete element method (DEM). In parallel, a new inter-particle contact model is developed for the DEM to describe the grain-level behaviour of asphalt concrete. This contact model couples a viscoelastic-damage law with a cohesive-elastoplastic-damage law, enabling the contact model to characterise the rate and time dependency, viscoelastic damage, and plastic-damage behaviour of asphalt concrete. Moreover, thanks to the use of DEM, the proposed approach can naturally capture crack initiation and development. Through comparisons and verifications with a wide range of experiments on asphalt concrete, including the relaxation test, creep test, and dynamic semi-circular bending test, the proposed approach shows its capability of overcoming the limitations of previous DEM models in reproducing the complex behaviours of asphalt material under various loading conditions. Insights into the failure mechanisms of asphalt material under complex loading conditions and its transitional behaviours from diffuse to localised failure can be thus naturally derived from the proposed DEM approach. This study demonstrates the effectiveness of the proposed approach for investigating the behaviour of asphalt concrete.

沥青混凝土是一种复合异质材料，由通过沥青粘合剂粘合在一起的骨料组成。这种材料的机械性能表现出对加载速率和时间（例如，蠕变、松弛）的极大依赖。沥青混凝土内部结构的这种异质性和复杂行为对数值方法提出了挑战，以充分捕捉其在不同加载速率和持续时间下的响应，特别是当材料中存在大变形和裂缝发展时。本研究提出了一种建模方法，能够捕捉沥青混凝土在不同加载速率和持续时间下的行为。在这种方法中，沥青混凝土的异质内部结构通过离散元法（DEM）自然地再现。在平行下，为 DEM 开发了一种新的颗粒间接触模型来描述沥青混凝土的颗粒级行为。该接触模型将粘弹性损伤定律与内聚弹塑性损伤定律相结合，使接触模型能够表征沥青混凝土的速率和时间依赖性、粘弹性损伤和塑性损伤行为。此外，由于使用了 DEM，所提出的方法可以自然地捕捉裂纹的萌生和发展。通过与沥青混凝土的松弛试验、蠕变试验和动态半圆弯曲试验等大量试验的比较和验证，该方法显示出其克服以往DEM模型在再现混凝土复杂行为方面的局限性的能力。各种载荷条件下的沥青材料。因此，可以从所提出的 DEM 方法中自然地得出对复杂加载条件下沥青材料的失效机制及其从扩散到局部失效的过渡行为的洞察。这项研究证明了所提出的方法在研究沥青混凝土行为方面的有效性。