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Micromechanical modeling of I-FIT asphalt concrete specimens

机译：I-FIT沥青混凝土标本的微机械建模

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Analytical and numerical micromechanical models have been previously used to understand fracture behavior of heterogeneous materials like Portland cement concrete or asphalt concrete (AC). In this study, the behavior of asphalt concrete was studied during a semi-circular bending (SCB) fracture test, Illinois Flexibility Index Test (I-FIT), using micromechanical level finite element models. The models were validated in multiple steps using the strain fields calculated with the digital image correlation (DIC) technique as well as the global scale forces measured in the same experiment. The micromechanical model was developed to evaluate the effects of microstructural features such as aggregate gradation, aggregate distribution, and void space on fracture behavior of AC. The model focused on pre-peak behavior and assumed that AC consists of aggregates and mortar. Aggregates were considered linear elastic with material constants reported in the literature, while the mortar was assumed linear viscoelastic. Mortar was defined as the combination of binder, air voids, and material passing 2.36?mm sieve. Mixture theory was utilized to characterize the mortar as viscoelastic using binder’s dynamic shear rheometer results, elastic properties of fine aggregate material, and air voids volume from the AC mix design. The validated FEM was used to perform a parametric study aimed at determining the effect of aggregate gradation and binder properties on the applied load, opening strains and stresses, and energy around the crack tip. Nine aggregate gradations and three binders were studied; ten replicates for each aggregate gradation-binder combination were considered. In order to create the replicates, a Python script that fabricates artificial aggregate gradations and randomly distributes aggregates in the I-FIT geometry was created. It was found that mortar properties, rather than air voids, binder content, or fine material, were heavily correlated to energy and applied load of the I-FIT specimen.
机译：分析和数值微机械模型以前用于了解像波特兰水泥混凝土或沥青混凝土（AC）等异质材料的断裂行为。在这项研究中，使用微机械水平有限元模型在半圆形弯曲（SCB）骨折试验中研究了沥青混凝土的行为，伊利诺伊州柔韧性指数试验（I-FIT）。使用用数字图像相关（DIC）技术计算的应变场以及在同一实验中测量的全局比例力来验证模型。开发了微机械模型以评估微观结构特征，例如聚集级别，骨料分布和空隙空间的效果对AC的断裂行为。该模型专注于预峰值行为，并假设AC由骨料和砂浆组成。聚集体被认为是用文献中报道的材料常数的线性弹性，而砂浆被假定线性粘弹性。砂浆被定义为粘合剂，空隙和通过2.36Ωmm筛的材料的组合。使用粘合剂的动态剪切流变仪结果，细骨料材料的弹性特性以及AC混合设计的空隙量，混合理论用于表征砂浆作为粘弹性。经过验证的有限元件用于执行参数研究，该研究旨在确定聚集体梯度和粘合剂性能对施加的负载，打开菌株和应力的影响，以及裂纹尖端周围的能量。研究了九粒聚集级和三个粘合剂;考虑了每种聚集级级粘合剂组合的十个重复。为了创建复制，创建了制造人为聚合渐变和随机分发I-FIT几何中的聚合的Python脚本。发现砂浆性能，而不是空气空隙，粘合剂含量或细材料，与I-FIT标本的能量和施加负荷严重相关。

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