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Date of Award

2015

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering (PhD)

Administrative Home Department

Department of Civil and Environmental Engineering

Advisor 1

Zhanping You

Committee Member 1

Jacob Hiller

Committee Member 2

Qingli Dai

Committee Member 3

Desheng Meng

Abstract

User defined heterogeneous model for asphalt concrete has been well developed recently with the recognition that X-Ray image based model is costly and time consuming. A comprehensive literature review showed that user defined heterogeneous model for asphalt concrete has been widely used in the discrete element (DE) modeling, while rarely seen in finite element (FE) modeling, especially in the three-dimensional (3D) scheme. Motivated by this, a novel idea of creating 3D user defined FE model based on DE models is proposed in this study. In addition, the accuracy of the model shall be evaluated since user defined models are created with computer-aided algorithms. The internal structure, including air void distribution, aggregate orientation, contact points, etc., are good indices for such evaluation. In this regard, this study proposed approaches to analyze the internal structures of both the user defined model and the real asphalt concrete sample. Besides of the model reconstruction and internal structure analysis, this study aims to model real aggregate shapes and to establish an aggregate model library. An innovative approach was proposed to create 3D aggregate models with close shape to real aggregates. At the end of this study, a numerical simulation on asphalt concrete beam fracture behavior was carried out to show an application of the user defined models.

For the 3D FE modeling based on DE models, two approaches were proposed: virtual cross sectional scanning and input file creating. The virtual cross sectional scanning was similar to the real X-Ray scanning. Two-dimensional (2D) virtual cross sectional images were obtained first, then the 3D models were obtained through the stack of slices of 2D images. The idea of input file creating was to obtain the nodal and elemental information of each cubic element, based on which an input file was written. Both the two approaches turned out to be viable to create 3D FE models. After that, the aggregate angularity and internal structures of the user defined models and real asphalt concrete samples were analyzed. The aggregate angularity and the internal structure of real asphalt concrete sample were acquired through image processing by user-written programs in MATLAB. The internal structure analysis of asphalt concrete models were achieved through calculations in the DE simulation software particle flow code in 3D scheme (PFC3D). The aggregate angularity and internal structure of the asphalt concrete models and real samples were found to be overall comparable. The real aggregate shape modeling was achieved through two steps. First, the 3D outline of individual aggregate particles were obtained based on X-Ray scanning. Then, a sphere growth algorithm was utilized to fill the internal region of the 3D outline. A case study of four aggregate particles showed that sphere clumps with the growth algorithm can model real aggregate shapes well. Then these four aggregate models were saved to establish an aggregate model library. Finally, DE and FE models of an asphalt concrete beam were created using the aggregate models from the library. The results of the simulation of asphalt concrete beam fracture behavior showed that the simulation results agreed well with the experimental results, indicating that user defined heterogeneous model is viable for the numerical simulation of asphalt concrete.

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