Fighting the causes of pavement cracks
When was the last time you closely inspected a road in your everyday life? There were likely cracks – whether they were impossible to miss or so small they were invisible to the eye.
Cracks happen when temperatures change, and the pavement expands and contracts beyond the binder’s ability to stretch or compress to conform to the movements. Studies have shown by creating a more resilient binder at a molecular level, ELVALOY™ Reactive Elastomeric Terpolymer (RET) asphalt modifier can prevent cold and thermal cracks.
Bending beam tests demonstrate cold-temperature performance
The cracking temperatures for asphalt binders provided by the Bending Beam Rheometer (BBR) and Thermal Stress Analysis Routine (TSARTM) were studied by the U.S. Federal Highway Administration (FHWA Report RD 02 075). Low-temperature mixture properties provided by the Thermal Stress Restrained Specimen Test (TSRST) were used to validate these asphalt binder tests. An emphasis was placed on evaluating the performances of mixtures containing polymer-modified asphalt binders with identical Superpave performance grades (PG's) and similar base asphalts, but varied modification chemistries. ELVALOY™ RET broadly outperformed grafted SBS these tests, in granite and limestone aggregates tested.
|ASPHALT MIXTURE DESIGNATION||TSRST FRACTURE TEMP.|
|Test #1||Test #2||Test #3|
|STOA = 2 h|
|SBS LINEAR GRAFTED||-29.6||-34||-35.5|
|SBS RADIAL GRAFTED||-32.2||-30.1||-29.1|
Wheel path cracking: Northern Ontario (Canada) pavement trial
The paper on the North Ontario Pavement Trial by Queens University and the Ontario Ministry of Transportation evaluates the usefulness of various asphalt binder and mixture properties for predicting field performance in terms of top-down fatigue cracking. Reference is made to Canada Highway 655 north of Timmins, Ontario, where a pavement trial was constructed during the summer of 2003. Seven test sections (one with ELVALOY™ were placed in two lifts for a total of 90 mm hot mix asphalt on new granular material. Asphalt binder content was 5.2 percent.
During January 2004, the pavement temperature at 5 mm depth reached -34ºC on two occasions - a rare condition. In early 2005 the air temperatures reached around -40ºC on six occasions, while the pavement at 5 mm depth reached below -30ºC on five occasions. The distress observed after the first winter provided insight into mitigation of transverse and wheel path cracking.
"Sections 1 [ELVALOY™ and 5-7 ... have performed very well without showing signs of early distress. ... Sections 1 and 5 have sustained almost no damage thus far ... Section 1, with the lowest stiffness, has so far been free of cracking," study expert wrote.
Compare the cycles to failure for eight asphalts, including one made with ELVALOY™ RET
Eleven binders were used in this study of fatigue failure. They included eight polymer-modified binders of PG70-28, using the following polymers: ELVALOY™ terpolymer (RET), styrene-butadiene-styrene (SBS) linear-grafted, SBS linear, SBS radial-grafted, ethylene-vinyl-acetate (EVA), EVA grafted, ethylene styrene interpolymer (ESI), and chemically modified crumb rubber. Bending beam fatigue tests were performed according to the AASHTO provisional test method TP8-94 (10). The tests were conducted in the strain-controlled mode at a high strain level of 1000 microstrains and at a test temperature of 19C.
Several different data analytical methods were compared, with a consistent result. The mixes made with ELVALOY™ RET far outdistanced the other samples in terms of cycles to failure.