Effects of Binder Modification on Aggregate Structure and Thermovolumetric Properties of Asphalt Mixtures

Modifiers have been widely used to improve the engineering value of asphalt binders and the performance characteristics of asphalt mixtures. Recent studies have confirmed that binder modification can influence mixture performance by two mechanisms: improving the mechanical properties of the continuous phase (i.e., binder or the asphalt–mineral filler mastic) of the mixture and changing the initial or inherent aggregate structure of the mixture (i.e., aggregates’ packing). A study identifies the relative importance of these two mechanisms on the low-temperature response of asphalt mixtures by using both experimental testing and finite element model analysis. This study uses three modifications: elastomeric, plastomeric, and a combination of elastomeric and plastomeric (i.e., hybrid). The low-temperature mechanical characterization of asphalt binders and mastics are measured with the bending beam rheometer and the glass transition temperature test. Mixture performance at low temperatures is evaluated with the asphalt thermal cracking analyzer. Internal structure of the aggregates is quantified by two-dimensional imaging analysis by using the recently developed Image Processing and Analysis System. Results indicate a significant relation between indexes describing the internal structure of the aggregates and the laboratory performance indicators at low temperatures. Experimental and finite element model simulation results confirm that modification enhances mixture responses by improving the initial internal structure of the aggregates, thus allowing a more favorable distribution of thermal strains within the binder. These results suggest new opportunities to optimize mixture resistance to cracking through binder formulation.