Evaluation of aggregate characteristics affecting HMA concrete performance

This report documents the outcomes of the ICAR study on the Evaluation of Aggregate Characteristics Affecting HMA Concrete Performance. This study was conducted with support from the Federal Highway Administration (FHWA) program on Simulation, Imaging, and Mechanics of Asphalt Pavements at Texas A&M University. The first outcome includes assessment of HMA sensitivity to aggregate shape characteristics. Aggregate shape is characterized through detailed measurements of angularity, form, and texture using the Aggregate Imaging System (AIMS). The shape characteristics are presented in terms of the distribution of the property in an aggregate sample rather than an average index of this property. The second outcome of this study is the development of a viscoplastic model for permanent deformation. The model accounts for the aggregate structure in the mix, which is related to the shape properties measured using AIMS. The model capabilities are demonstrated through matching the results of testing various mixes from the Accelerated Loading Facility (ALF) of the FHWA using the triaxial creep and strength tests. In addition, the model is used to predict the response of mixes that include aggregates with different shape characteristics in order to develop relationships between the model parameters and aggregate shape characteristics. As part of the model development, an experiment was conducted to capture and characterize damage evolution in HMA due to permanent deformation. HMA specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. Consequently, image analysis techniques were used to analyze damage distribution. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.