TxDOT Research Library - TxDOT Research Project

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Improving Fracture Resistance Measurements in Asphalt Binder Specifications with Verification on Asphalt Mixtures Cracking Performance

What Was the Need?

The current performance grading (PG) specification for asphalt binders was developed during the Strategic Highway Research Program (SHRP). The PG was based primarily on the study of unmodified asphalt binders. Over the years, experience has proven that the PG system, while good for ensuring overall quality, fails in some cases to guarantee good rutting and cracking performance, particularly as it applies to today's binders modified in a variety of unknown ways. Specifically, recent studies on mixes with highly polymer-modified binders from Minnesota found that the Road mixes have substantially improved cold weather cracking properties over mixes currently used its Texas and still pass-TxDOT's Hamburg putting requirements.

Under project 0-6674 researchers investigated these softer but highly modified binders in the laboratory and built 11 field test sections in northern districts of Texas for validation. (Note that softer binders are often referring to those PGXX-28 and PGXX-34 binders; regular binders being PGXX-22 binders; and stiffer binders being PG76-X_N binders.) Eleven test sections are: four in SH 15 north of Amarillo, three in US 62 at Childress, and four in Loop 820 at Fort Worth. These projects were monitored for a maximum of 12 months which is too short of a time to draw definite conclusions. Also in previous project 0-6674, a statewide binder selection catalog was developed based on the results of laboratory tests and performance simulations of numerous overlay projects. Further work is needed to validate these recommendations.

Project Summary

The major objectives of project 0-6674-01 are to: (1) Continue monitoring the 11 field test sections constructed under project 0-6674 for the duration of 0-6674-01. This will provide the research team with a total of five years of performance data which should be adequate to validate the benefits of these softer binders in the colder areas of Texas; (2) Validate the statewide binder selection catalog building field test sections in West, South, and East Texas districts. The specific locations will be selected in coordination with the project team and TxDOT Districts; (3) Perform 40-year life cycle cost analyses with true cost and performance data on all field test sections to evaluate the benefit of using softer but highly modified binders; (4) Update the statewide binder selection catalog developed under previous Project 0-6674; and (5) Evaluate ten (10) most often used asphalt binders recently engineered with a variety of modification techniques using the asphalt binder tests recommended by previous Project 0-6674.

Project Number

0-6674-01

Status

Completed

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