Feasibility Of Virtual Laboratory For Asphalt Mixtures And Pavements

The objective of this study is to develop a Virtual Testing Laboratory for Asphalt Mixture (VTLAM) in senior undergraduate and graduate student education. The virtual lab is based upon computer simulation, and will be Internet supported. Therefore, in the future, students can access the lab 24-7 (24 hours a day, 7days a week) to conduct test without location limits. In the computer program, the authors propose to simulate mixture properties using the advanced micro-fabric discrete element method. The program will employ the microfabric discrete element method, which has the ability to consider aggregate-aggregate contact by using the distinct/finite element method with the assistance of mixture internal microstructure. The asphalt concrete is a multiphase material which has different properties from the original components which are aggregate, mastic, and air voids. The physical properties and performance of asphalt mixture is governed by the properties of aggregate (shape, surface texture, gradation, skeletal structure -microstructure, modulus, etc.), properties of asphalt binder (grade, complex modulus, relaxation characteristics, cohesion, etc.), and asphalt-aggregate interactions (adhesion, absorption, physio-chemical interactions, etc.). The numerical analysis is based upon the microstructure components of the asphalt mixture. In addition, the aggregate, binder/mastic, and mixture properties will be provided by a database according to different aggregate types and binder grade. The authors will work with local research agencies to establish a comprehensive laboratory database. The virtual lab will help senior and graduate students to evaluate asphalt mixture performance by calculating the material parameters. In the future, the virtual lab can be used to evaluate and predict asphalt mixture rutting, fatigue cracking, thermal cracking, and other distress. The final target is to help students and engineers in design of asphalt mixture and asphalt pavement when a fully developed virtual laboratory for Asphalt Mixture is established. It is expected that the expanded virtual lab can be used in pavement distress simulation and pavement design in the future. It is also expected that, after the completion of this lab, the education, especially distance learning will become very easy because the students can access the lab without time and location limit. Backgrounds of Virtual Laboratory for Asphalt Mixtures and Pavements Paving asphalt concrete is multiphase material which has different properties from the original components—aggregate, mastic, and air voids. The physical properties and performance of HMA is governed by the properties of aggregate (shape, surface texture, gradation, skeletal structure, modulus, etc.), properties of asphalt binder (grade, complex modulus, relaxation characteristics, cohesion, etc.), and asphalt-aggregate interactions (adhesion, absorption, physio-chemical interactions, etc.). The asphalt concrete pavement is a very complicate composite with a gradation of aggregate and a certain P ge 11639.2 amount of asphalt after mechanical compaction. Figure 1 shows the aggregate for typical asphalt mixture, different sizes of coarse aggregate in mixture after image processing, and asphalt mixture construction. a. Aggregate stockpile b. different aggregate size c. asphalt concrete construction Figure 1. Asphalt Mixture and Construction The development of micromechanical models started about a hundred years ago, beginning by Voigt (1889), Einstein (1911), and Reuss (1929). During this time, a number of research studies addressed micromechanical models with both non-interacting and interacting particles. In models with non-interacting particles, geometries were either specified or not specified. Some simple micromechanical models for describing various purposes for different composite materials include Hirsch’s Model (Hirsch, 1962), Counto’s Model (Counto, 1964), Paul’s Model (Paul, 1960), the Arbitrary Phase Geometry Model (Hashin & Shtrikman, 1962), the Composite Spheres Model (Hashin, 1965), the generalized self-consistent scheme model (Kerner 1956, Christensen & Lo, 1986), the Mori-Tanaka model (Mori & Tanaka, 1973), and Christensen et al. model (2003). Recent studies have shown that existing micromechanical models, such as the composite spheres model and the arbitrary phase geometry model, do not adequately describe the complex microstructure of asphalt concrete (Buttlar & You, 2001). Existing micromechanical models are overor under-predicting the stiffness of asphalt concrete. This is due primarily to the inability of the models to properly predict the contribution of aggregate interlock to the overall response of the mixture. Therefore, a new micromechanical modeling technique for asphalt concrete is needed to improve the understanding of the fundamental properties of asphalt concrete. Some advanced micro-mechanical modelings are used to study granular materials or asphalt concrete. Kose et al. (2000) and Masad et al. (2002) report the strain distribution within asphalt binders in asphalt concrete using 2D finite element with the linear elastic properties of the binder and aggregate. Chang et al. (1999) also derived an expression for elastic moduli of an assembly of bonded granulates, based on the response of two particles connected by an elastic binder. Chang and Meegoda (1997) proposed a micromechanical model based upon the discrete element method (DEM) to simulate hot mix asphalt (HMA). Rothenburg et al. (1992) developed a micromechanical model for asphalt concrete to investigate pavement rutting. An innovative feature of this research P ge 11639.3 considered inter-granular interactions in the presence of binder and aggregate-binder interaction. In recent years, microstructure-based micromechanical models were proposed by Buttlar & You, 2001; You & Buttlar, 2002; You, 2003; You & Buttlar, 2004; You & Buttlar, 2005; You et. al., 2005, using discrete element (DE) model and finite element (FE) approaches. The proposed models are novel due to the consideration of the material’s true microstructure – including the inclusion of the matrix of the material. In addition, the models allow large displacement between particles in the material, which is desired in engineering, military, and aerospace. The virtual test concept was developed in many areas such as virtual test of nuclear bomb, hospital, museum, and library. A computer simulation using micro mechanics computation is virtually conducted to measure the material properties, simulate an engineering phenomenon, or even a design of asphalt concrete mixture based upon the ingredient. Figure 2 illustrates the general procedure of the virtual laboratory for asphalt mixtures and pavements. In the illustration, asphalt mixture is tested using the virtual laboratory to predict the performance in pavement structure design.