Evaluation of Internal Resistance in Asphalt Concretes

International Journal of Concrete Structures and Materials, Dec 2012

Composites are somewhat more difficult to model than an isotropic material such as iron or steel due to the fact that each layer may have different orthotropic material properties. In finite element literature the asphalt mixes are represented by using rectangular meshes, not the actual picture of their cross-sections. Asphalt aggregate size and distribution in the asphalt concrete sample, aggregate shape, and fractured surface effects are ignored. In this research, the actual image of the sample including all these effects were directly considered in the finite element. The samples, were cut into cross-sections and were scanned. The image-processing toolbox of Labview was utilized in obtaining the rectangular gray images of the scanned images. In the rectangular sample the aggregates were white and the asphalt binders were black. The grayscale images were converted by LABVIEW into the format required by ANSYS as an input file, with the same dimensions. The nodes at the bottom of the model were constrained in both x and y directions. Left and right edges were symmetry and top was free. Certain amount of pressure was applied along the top surface to simulate the tire pressure.

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Evaluation of Internal Resistance in Asphalt Concretes

Yousef Zandi Muhammet Vefa Akpinar Composites are somewhat more difficult to model than an isotropic material such as iron or steel due to the fact that each layer may have different orthotropic material properties. In finite element literature the asphalt mixes are represented by using rectangular meshes, not the actual picture of their cross-sections. Asphalt aggregate size and distribution in the asphalt concrete sample, aggregate shape, and fractured surface effects are ignored. In this research, the actual image of the sample including all these effects were directly considered in the finite element. The samples, were cut into cross-sections and were scanned. The image-processing toolbox of Labview was utilized in obtaining the rectangular gray images of the scanned images. In the rectangular sample the aggregates were white and the asphalt binders were black. The grayscale images were converted by LABVIEW into the format required by ANSYS as an input file, with the same dimensions. The nodes at the bottom of the model were constrained in both x and y directions. Left and right edges were symmetry and top was free. Certain amount of pressure was applied along the top surface to simulate the tire pressure. 1. Introduction A major concern in asphalt pavement roads is excessive permanent deformation (rutting) resulting from heavy truck loads. Rutting appears as longitudinal depressions in the wheel paths and increases with increasing numbers of load applications. Safety concerns such as steering problems and decrease in bearing capacity on asphalt pavements are the results of rutting. The asphalt pavement layer must exhibit high resilient moduli and show low permanent deformation in order to reduce and rutting in the asphalt pavement. Rutting (permanent deformation) in an asphalt-concrete layer is caused by a combination of densification (volume change) and shear deformation. Shear deformations caused primarily by large shear stresses in the upper portions of the asphalt-aggregate layer(s) are dominant. Granular materials have a major function in the structural capacity of a highway pavement. Because approximately 85 % of the total volume of asphalt concrete mixtures consist of aggregates, the performance of the asphalt concrete is greatly affected by the properties of the aggregate blend (Ahlrich 1996; Ahlrich 1995; Zakaria and Less 1996). They provide a foundation that supports asphalt concrete layers and helps to support the pavement. One of the most important properties of an aggregate blend is its size gradation, which defines the percentages of different particle sizes that are present in the blend. Gradation affects almost all the asphalt concrete properties, including durability, stability, stiffness, permeability, workability, fatigue resistance, frictional resistance and moisture damage. The primary objective of 2002 AASHTO (American Association of State Highway and Transportation Officials) was to advance the state-of-the-practice from empirical to mechanistic related design procedure. AASHTO Joint Task Force on Pavements (JTFOP) to initiated an study objective of developing mechanistic pavement analysis suitable for use in future versions of the AASHTO guide. Rutting associated test techniques for asphalt pavement materials are empirical. It is important that a mechanistic procedure be developed which will reasonably predict the permanent deformation under loading by heavy traffic. Finite element (FE) analyses provide significant basis for the development of mechanistic analysis. Available FE programs are powerful tools for studying stressstrain analysis in pavement structure. Pavement rutting cannot be estimated with sufficient accuracy and reliability using current mechanistic procedures which are based on either (1) linear viscoelastic models or (2) layer-strain algorithms. However, FE techniques are now available that are well adapted to the analysis of permanent deformation in pavement structures. They can effectively handle complex constitutive relationships as well as the transverse distribution of traffic. 2. Objective In order to determine the rutting of the asphalt pavement layer for a given mix type, permanent deformation parameters of the mix can be developed from laboratory testing. These parameters can then be used to predict the permanent deformation of the material taken in the field and from the image and FEM analyis is the optimum use of unbound granular materials as a structural layer in pavements can be determined. In this research, the actual image of the sample were directly considered in the FE. In the FE literature the asphalt mixes are represented by using rectangular meshes, not the actual picture of their cross-sections. 3. Materials and Methods 3.1 Sample Preparation The preparation of the samples were followed according to superpave protocols. Fifteen centimeter diameter samples were prepared by a superpave gyratory compactor. Aggregate gradations use (...truncated)


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Yousef Zandi, Muhammet Vefa Akpinar. Evaluation of Internal Resistance in Asphalt Concretes, International Journal of Concrete Structures and Materials, 2012, pp. 247-250, Volume 6, Issue 4, DOI: 10.1007/s40069-012-0021-0