Anti-Strip Resistance: Properties of an Asphalt Binder Can Be Enhanced by using DuPont Elvaloy® RET modified PMB
Stripping away of asphalt binder from an aggregate can result from weather, environmental and wear factors. Loss of binder reduces aggregate adhesion at the pavement surface, and eventually deeper into the mix as moisture damage penetrates further into the friction course.
The reduced moisture susceptibility of asphaltic cement enhanced by modification with DuPont™ Elvaloy® RET is shown in lab tests and improved pavement service life.
Documenting Improved Anti-Strip Performance
In lab settings and on real projects, paving experts are observing reduced moisture susceptibility for binders modified with Elvaloy®.
DuPont™ Elvaloy® RET fights stripping
Asphalt binder adhesion to aggregate is a key requirement for sustained pavement life. Factors affecting adhesion include moisture and temperature cycling, especially freeze-thaw cycles. Properly formulated binders made with resilient. moisture-resistant Elvaloy® RET have been shown to prevent stripping in lab studies, field trials, and real life motorways.
The Statz Freeze-Thaw Cycle Test
Pioneering DuPont scientist Bob Statz compared binders made with and without RET, using an oven and a freezer. Results showed clear differences in binder adhesion after repeated cycling.
Early scientific research showed Elvaloy® RET anti-stripping benefits
Robert Statz, Ph.D., was among the early DuPont scientists exploring the use of Elvaloy® as an asphalt polymer modifier. To simulate the effects of outdoor weathering, he subjected samples of binder-coated aggregate to successive freeze-thaw cycles.
Photos were taken (see left), showing better-sustained aggregate adhesion and binder presence for the sample made with RET-modified binder. This anti-stripping tendency of the reactive terpolymer has since been confirmed in government tests and in actual road performance.
FHWA Study Results
Elvaloy® RET modifier was among the materials tested in a broad binder study by the U.S. Federal Highway Administration. Stripping resistance was strong for the reactive polymer.
U.S. Highway Research Program Reports Moisture Resistance Results for Modified Asphalts
The objective of this research, guided by the U.S. Federal Highway Administration, was to determine the effects of 11 asphalt binders on the moisture sensitivity of mixtures, using a Hamburg Wheel-Tracking Device (Hamburg WTD).
The Hamburg WTD tests a slab of hot-mix asphalt submerged in hot water by rolling a steel wheel across its surface. The device tested side-by-side slabs simultaneously using two reciprocating solid steel wheels applying a 685-N load at an average speed of 1.1 km/h.
"The statistical ranking ... shows that only the mixture with Elvaloy® performed better than the PG 70-22 control mixture at a 5-percent level of significance."
Understanding the Performance of Modified Asphalt Binders in Mixtures: Evaluation of Moisture Sensitivity (FHWA-RD-02-029) by Kevin D. Stuart, John S. Youtcheff and Walaa S. Mowager
In India, Side-by-Side Lane Inspection
On a highway in India, binder made with DuPont™ Elvaloy® RET asphalt modifier was used alongside an unmodified binder. Lanes were photographed years later, and showed a visible difference in binder retention.