Digital Specimen and Multiple Functional Digital Tester Technique for Performance Evaluation of Asphalt Mixes

The goal of this Innovations Deserving Exploratory Analysis (IDEA) project was to develop a 3-D digital representation of the microstructure of an asphalt concrete specimen and an asphalt mastic specimen and evaluate the performance of the "digital specimens" using modeling and simulation techniques. Therefore, the final product would be a computer program that reads processed computed-tomography images, reconstructs them into "digital specimens," and performs the stiffness test on them using the platform of a finite element code. The work was accomplished in two phases. In the first phase, a computer program to represent the microstructure of cylindrical specimens of asphalt concrete and mastic in digital format (digital specimen) and modules to link their microstructure to a finite element code for simulating the indirect tensile test and dynamic modulus test (digital test) were developed. The simulation models used elastic and viscoplastic material models for aggregate and asphalt, respectively. By using a rate dependent material model for asphalt binder, the numerical simulation of the indirect tensile test provided realistic response for the asphalt mixture when qualitatively compared with the experimental results. The model successfully captured the stress variation resulting from the presence of both aggregates and voids, and the test was able to distinguish performance differences of different mixes used in the evaluation. Work was also performed on the development of a method for parameter estimation using inverse algorithm based on simulation results and test data. The viscoplastic model for asphalt binder was refined and used to conduct realistic digital tests with the microstructure of the asphalt concrete mixture and mastic. Based on the comparison of simulated and observed test results, realistic models were selected and integrated into the digital specimen interface modules to generate a multi-functional digital "tester." In phase two, an attempt to implement the digital specimen and digital test technique at the FHWA's Turner-Fairbank Research Center will be made. Implementation needs to be conducted through training programs and workshops for demonstrating their applications in performance evaluation of asphalt concrete.