Performance Evaluation of REOB Modified Asphalt Binders and Mixtures

Abstract

This study evaluated a limited number, but well-controlled group of asphalt binders of the same PG grade made with a wide range of REOB contents; 0%, 2.5%, 6% and 15%. The most practical indicator of the possible presence of a considerable quantity of REOB with measureable changes to the rheological and performance characteristics was the difference between the BBR m-value temperature grade and the BBR S stiffness temperature grade, DTcritical. When a binder exhibited a large DTcritical it was associated with larger differences in performance losses depending on the binder tests and to a lesser extent the mixture test. The DTcritical performance disruption was made worse by oxidative aging by means of double PAV conditioning as well as holding the binder at extended low temperatures before testing. The impact of REOB on moisture damage resistance showed higher moisture sensitivity with increasing REOB content, but it did not interfere with liquid anti-strip additives. Mixture cracking tests results were mixed. Low temperature relaxation, strength and fracture measured with TSRST showed the fracture strength had slight increases or decreases with 2.5% and 6% REOB and could be interpreted as unaffected. Aging also improved the average strength of these mixes. However, the strength of the highest 15% REOB mix was measurably decreased and made worse by aging. The impact of REOB on intermediate temperature fatigue cracking performance depended on the aging condition and whether stress-control or strain-control performance was considered. To minimize risks a best practice needs to be developed which includes a maximum use level, taking into account both the variability of REOB and the effects on asphalt binders from different sources. Asphalt binder specifications might be refined by placing lower limits to BBR stiffness or a maximum allowable DTcritical. More focus should be placed on intermediate REOB levels such as near 10% to the 6% used in this study to better identify performance pitfalls and performance benefits from REOB and the corresponding DTcritical.