Quantitative Methodology for Improving Fatigue Resistance of TxDOT Superpave Mixes by Accounting for Expected Pavement Performance
Jorge A. Prozzi
The University of Texas, ECJ 6.112, Austin, TX 78712
Tel.: (512) 232-3488, Fax: (512) 475-8744,
The Texas Department of Transportation (TxDOT) has recently implemented Hamburg Wheel Tracking Device (HWTD) testing and set specification criteria for their Superpave mixtures. This implementation has introduced a performance-related feature to an otherwise volumetric mix design procedure originally conceived to ensure the rutting resistance of asphalt mixtures. With the addition of the new HWTD specification, asphalt mixtures in Texas tend to have even lower binder contents than before. Although, this is desirable for rutting resistance, it could result in mixtures that are dry and prone to cracking, which is becoming the single largest performance problem for asphalt pavements in Texas.
In an attempt to produce mixes with higher binder contents to alleviate cracking problems, The University of Texas is investigating modifications to the current design criteria, specifically, the specification of the laboratory compaction effort or Superpave’s Ndesign.
This research paper will present the revised mix design procedure based on a performance-related approach geared towards determining revised Ndesign compaction levels to increase binder contents in asphalt mixtures without compromising rutting resistance. An extensive experimental program has been devised and is underway to investigate the performance characteristics of asphalt mixtures designed using the revised Ndesign levels and to account for the nominal maximum aggregate size and the concentration of coarse aggregate in the mix. Performance will be investigated through performance-related tests as well as actual performance as recorded by TxDOT Pavement Management Information System (PMIS).
The revised procedure will allow the determination of optimum laboratory compaction effort based on a reliability-based approach, which allows the designer to fine-tune the optimum binder content by balancing rutting and cracking resistance of the mixtures.
PRESENTER'S QUESTIONS: I would like to receive comments, suggestions, and feedback from the meeting's attendees on the following matters:
1- For other Superpave users, are you aware of similar research aimed at revisiting Ndesign recommendations based on mix performance (lab or field)? If so, do you have access to mix design and pavement performance data that can be shared with us?
2- Several European countries have performance-based mixture design methods, are they significantly better of than those using volumetric-design? Performance-based mix design is more costly, do the benefits over the life of the pavement justified the increased cost? Are there hard data to this effect.
3- Please provide feedback on the proposed reliability-based approach, is it practical enough to be implemented by highway agencies? What can be done to make it more easier to understand and user friendly?
PRESENTER'S STATEMENT: This work is still in progress, and has not been submitted for presentation or publication at another meeting.