Influence of operational tolerances on HMA performance

This study focuses on determining the effects of variability on key mix design factors, such as asphalt content, gradation, and density, on the laboratory performance of different HMA samples that were produced in the laboratory. Mixture variables were kept within specified limits as per allowable operational tolerances, and performance was monitored through the evaluation of the results obtained from volumetric properties and laboratory tests, such as flexural fatigue test, Hamburg wheel-tracking test, and overlay tester. A series of statistical analyses were conducted to develop relationships between the key mix design factors and the observed laboratory performances of each type of mixture. From the analysis, the effects of the main variables on the results of the performance tests used in this study were found.Finally, a statistical sensitivity analysis was conducted to reveal the relationship between different tolerance levels and mixture performance. Based on the findings of this sensitivity analysis, recommendations to revise the current TxDOT operational tolerances and performance-based pay adjustment factors for contractual jobs were provided that not only commends high quality and a consistent end product but also promotes superior performing mixtures based on the analysis of laboratory data.

► The AC content and F/B ratio have a significant effect on the performance of the mix.
► The fineness modulus has an inverse relationship with the rutting performance.
► The proposed pay adjustment schedule rewards consistency and superior performance.