Tests Confirm Less Pavement Rutting with RET-Modified Binder with DuPont™ Elvaloy® RET Asphalt Modifier
Polymer-modified asphalt (PMA) is proving reliable as a way to reduce pavement rutting. From its earliest use in Oregon 1991, to the paving projects being undertaken now around the world, RET is proving to be a top performer, and an easy product for asphalt producers to use, to meet higher performance specs. The following studies compare DuPont™ Elvaloy® RET and other choices, for rut resistance.
Cumulative Strain Tests Compare EVA, SBS and Elvaloy®
A Citgo Savannah 67-22 base asphalt and limestone aggregate were studied by Mathy Technology and Engineering Services, Inc., to determine the impact of four different polymer additives on both the modified binders and the mixes they produced.
The modifiers were an EVA, an SBS, an SBS with cross-linking, and Elvaloy®. Newly developed cumulative strain testing for PG binders was used as an alternative to conventional DSR testing, since it better predicts actual road performance.
"Elvaloy® ... modifier outperformed both SBS crosslinked and non-crosslinked systems as well as an EVA system."
U.S. Federal Highway Administration Tests 11 Binders for Rut Resistance
Eleven asphalt binders including RET-modified (Elvaloy®) were studied by the U.S. Federal Highway Administration (FHWA) with diabase aggregate, using a French Permanent Rut Tester, a Hamburg Wheel Tracking Device and dynamic shear rheometry.
The FHWA report ranked the modified binder made with Elvaloy® as the best performer.
Modified Binder Rheology and Wheel Tracking Studied in Mexico
Mexican researchers at SURFAX S.A. de C.V. conducted rheology tests to analyze the rutting susceptibility of neat and modified asphalts. Four modification technologies were compared: Elvaloy® RET, EVA, air-blown (oxidized), and SBS-modified.
The modified binder made with Elvaloy® ranked best overall, for reduced rutting at different temperatures (including the highest temperatures studied.) A Spanish wheel tracking device verified the findings.
"In rheology characterization, asphalt modified with Elvaloy® was the only one that fulfilled the specified values of elastic recovery in repeated creep test, and had the higher failure temperature."
Advancing Asphalt Test Methods for Rutting and Fatigue
In a comprehensive review of asphalt testing methods, Hussain Bahia and coauthors describe advances from traditional Superpave elastic recovery, toughness and tenacity tests for predicting the durability of polymer-modified asphalt mixes. Their study included work by the University of Wisconsin at Madison to assess 19 binders, including 8 made with Elvaloy® RET, for resistance to permanent deformation and fatigue.
"The results show that modification with SBS and Elvaloy® additives can significantly improve resistance of binders to rutting and fatigue damage"
Accumulated Strain to Failure: RET vs SBS and Others in Granite Aggregate Mix
Mathy Technology & Engineering Services, Inc., tested and compared asphalt binder and mix properties for RET-modified and other binders, used with a high-quality granite aggregate.
Their study recognized that dynamic shear rheometer (DSR) generated data (such as phase angle) for polymer modified binders, was not fully predictive of real-life rutting resistance. Accumulated strain to failure was studied, and a new method (repeated creep and recovery) was proposed.
"PG binders produced with Elvaloy® will perform as well as or better than a similar PG grade produced with a SB modifier. In addition the Elvaloy® modified binders were produced using 3 different asphalt sources and all performed very well in both the binder and mixture tests."
RET versus Crumb Rubber for High-Temperature Rut Resistance
Binder and mix properties related to rutting were studied by DuPont™ for an RET-modified binder (using 1.5% Elvaloy® RET) and three other binders with different levels of 80-mesh crumb rubber blend as the modifier. Binders were measured for cumulative strain, and mixes were evaluated for high-temperature resistance to deformation using a torsional flow procedure. Crumb rubber pricing and addition rates (6%, 12% and 18%) are included for comparison with Elvaloy® from a cost perspective as well.
"Comparing 12% CRM and 1.5% Elvaloy®, the Elvaloy® has two orders-of-magnitude greater resistance to deformation."
Reduction of Rutting with DuPont™ Elvaloy® RET
Loaded "French wheel" and "Hamburg wheel" tests are among those used to simulate the dynamics of heavy and repeating traffic loads. These tests and newer dynamic shear rheometry (DSR) based tests ... such as Multiple Stress Creep Recovery (MSCR) ... consistently show outstanding rut resistance for pavements made with RET.
One state's DOT shared with DuPont™ scientists results of Hamburg wheel test results, comparing two PG 64-28 grade asphalts. One grade was modified by air blowing; the other by adding Elvaloy® RET. Both passed SHRP binder tests for their grade rating; however, the grade modified by adding Elvaloy® RET clearly resisted rutting much better (see chart).
In this test, rut depth of 20 mm occurred with the air-blown product after 10,000 cycles. In contrast, after twice as many cycles, ruts were only half as deep (10 mm) in the product made with Elvaloy® RET.