Optimization Method for the Number of Design Gyrations Based on Relative Performance.

Abstract

The Texas Department of Transportation (TxDOT) has recently established Hamburg Wheel Tracking Device (HWTD) specification criteria for Superpave mixtures. This has introduced a performance related feature to an otherwise volumetric mix design approach structured to ensure the rutting performance of asphalt mixtures. The Superpave mixture design procedure is itself geared towards the production of ne resistant mixtures. This, together with the new HWTD performance criterion tends to promote mixtures with lower binder contents. While this is advantageous for rutting resistance, there are reports that these mixtures are prone to cracking, which is becoming the single largest problem for asphalt pavements in Texas.  

In an attempt to produce mixes with higher binder contents to alleviate cracking problems, TxDOT has investigated the possibility of modifying the current design criteria established for Superpave mixtures, Initial research investigating the influence of lowerning the 4 percent volds in the mir anterion to 3 and aven 2.5 percent has resulted in increased optimum binder contents but has proven detrimental for those mixtures using softer binders. The Superpave misture design method does not account for mixes with stiff polymer-modified asphalts currently being used. Furthermore, the concentration of coarse aggregate in the mix and the influence of nominal maximum aggregate size are not accounted Ar 

The study reported in this article outlines a reliability-based mixture design procedure based on a performance related approach geared towards determining revised N compaction levels to increase binder contents in asphalt mixtures without compromising rating performance An extensive experimental program has been devised to investigate the performance characteristics of asphalt mixtures designed using the revised N levels and to account for the nominal maximum aggregate and the concentration of coarse aggregate in the mix, The procedure found strong support for decreasing current levels under most conditions, except when high-volume facilities in war environments. The number of design gyrations for most condition in Texas could be lowered to 75 to 85 from improved fatigue performance, without significant loss of rutting resistance.