Gajewski Marcin D, Król Jan B
Faculty of Civil Engineering, Warsaw University of Technology, 00-637 Warsaw, Poland.
Materials (Basel). 2022 Dec 14;15(24):8946. doi: 10.3390/ma15248946.
This paper presents the results of a research study and analysis conducted to determine the degree of anisotropy of asphalt concrete in terms of its initial elastic properties. The analysis of asphalt concrete was focused on determining the effective constrained stiffness modulus in three mutually perpendicular directions based on the finite element method. The internal structure of the asphalt concrete was divided into the mortar phase and the mineral aggregate phase. Static creep tests using the Bending Beam Rheometer were conducted for the mortar phase to fit the rheological model. The aggregate arrangement and orientation were analysed using an image analytical technique for the mineral phase. The Finite Element Method (FEM) meshes were prepared based on grey images with an assumption of plane strain in 2D formulation. Using the FEM model, the tension/compression tests using selected characteristic directions were conducted, and the effective constrained stiffness moduli were estimated. This study showed a dominant horizontal direction for all coarse aggregates resulting from the normal force of the road roller and paving machines during laying and compaction on a road site. Depending on the values of the mortar's mechanical parameters and the load direction, the effective stiffness modulus might differ by ±20%. Based on the FEM analysis, this result was proven and commented on through an effective directional modulus evaluation and a presentation of internal stress distribution. Depending on the shape and orientation of the aggregates, it was possible to observe local "stress bridging" (transferring stresses from aggregate to aggregate when contacting). Moreover, the rheological properties of the mortar were considered by assuming two limiting situations (instantaneous and relaxed moduli), determining the bands of all possible solutions. In the performed FEM analysis, the influence of the Poisson ratio was also considered. The analysed asphalt concrete tends to be isotropic when the Poisson's mortar ratio is close to the value of 0.5, which agrees with the physical expectations. The obtained results are limited to particular asphalt concrete and should not be extrapolated to other asphalt mixture types without prior analysis.
本文介绍了一项研究的结果，该研究旨在确定沥青混凝土在初始弹性特性方面的各向异性程度。对沥青混凝土的分析重点在于基于有限元法确定三个相互垂直方向上的有效约束刚度模量。沥青混凝土的内部结构分为砂浆相和矿质集料相。对砂浆相进行了使用弯曲梁流变仪的静态蠕变试验，以拟合流变模型。对矿质相使用图像分析技术分析集料的排列和取向。基于灰度图像并在二维公式中假设平面应变来制备有限元法（FEM）网格。使用有限元模型，在选定的特征方向上进行拉伸/压缩试验，并估算有效约束刚度模量。该研究表明，由于道路施工现场铺设和压实过程中压路机和摊铺机的法向力，所有粗集料都存在一个主导水平方向。根据砂浆力学参数的值和荷载方向，有效刚度模量可能相差±20%。基于有限元分析，通过有效方向模量评估和内部应力分布呈现对该结果进行了验证和评论。根据集料的形状和取向，可以观察到局部“应力桥接”（接触时应力从一个集料传递到另一个集料）。此外，通过假设两种极限情况（瞬时模量和松弛模量）来考虑砂浆的流变特性，确定所有可能解的范围。在进行的有限元分析中，还考虑了泊松比的影响。当泊松砂浆比接近0.5时，所分析的沥青混凝土趋于各向同性，这与物理预期相符。所获得的结果仅限于特定的沥青混凝土，未经事先分析不应外推到其他沥青混合料类型。
