Influence of Production Considerations on Balanced Mixture Designs

Abstract

Measuring or predicting mixture performance prior to placement has become essential for many state transportation agencies due to incorporation of more recycled materials into mixtures, utilization of binders formulated with various modifiers, and utilization of new and unproven technologies. Mixtures designed incorporating these elements in accordance with the current Superpave mixture design method have unknown performance as Superpave was never designed to compensate for them. Thus, agencies have interest in implementing the balanced mixture concept that requires testing for acceptable mixture performance during the design phase. The effect of production considerations on a balanced mixture design is not known. It is unknown if a mixture remains performance balanced during production due to factors like asphalt content, gradation and binder source variations. This study was undertaken to understand the influence of these production considerations on a balanced mixture design. Two Superpave mixtures, a 9.5 mm and 12.5 mm, were developed using the balanced mixture design approach using volumetric properties, one rutting test and one cracking test. These mixtures were then modified to represent production variations in asphalt binder content, gradation passing the No. 200 sieve, and asphalt binder source. All mixtures remained performance balanced when examining the production considerations in terms of rutting and cracking using the selected tests. Examination of other performance results, like moisture susceptibility, suggest it is possible to effectively unbalance the mixture design during production. This underscores the importance of proper selection of performance tests to address the performance needs of the agency.