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The use of vacuum distilled residues from the re-refining of used motor oils as blend stock in paving grade bitumen has occurred in isolated markets in North America for more than 30 years. Recently in the United States the increasing need for low stiffness bitumen for use in high binder replacement mixtures, coupled with economic considerations, has led to an expanding market for these products. Little in-depth investigation into the long-term impact of these additives on mixture performance has taken place until recently. Conflicting studies from researchers in Canada and private organizations have been published. Here, we review the eight-year performance of four virgin mixture test sections placed on a county highway Minnesota. Three test sections used PG 58-28 bitumens from different crude sources, one of which contained approximately 8% of the re-refined engine oil residuum. The fourth utilized PG 58-34 polymer-modified bitumen. Pavement distress surveys were conducted over the eight year period. Tests of the original bitumen following extended laboratory aging were conducted. Properties of the recovered bitumen from eight-year-old field cores were correlated to pavement distress. Double Edge Notched Tension (DENT) tests were conducted on 20-and 40-hour PAV residues of the original bitumen. Iatroscan and extensive rheological testing were conducted on laboratory aged bitumen and on bitumen recovered from laboratory aged mixtures and field cores to determine the colloidal index, rheological index and the extent to which laboratory aged and recovered bitumen materials were m-controlled. Also evaluated were three test sections constructed at the Minnesota DOT MnROAD test site. A comparative study of and PG 58-40 (PMA +re-refined engine oil bottoms) were evaluated over eight years. Bitumen used on the projects was tested as described above. The PG 58-40 exhibited the worst performance. The results of binder evaluations correlated to the fatigue cracking observed in the field with the test sections containing the re-refined engine oil residuum exhibiting the most extensive fatigue cracking. Based on this investigation we provide recommendations for test criteria to identify bitumens that could increase an asphalt mixture's likelihood to exhibit poor durability and fatigue cracking performance.

An emphasis on environmental stewardship has prompted the use of warm-mix technologies aimed at allowing for production of conventional asphalt mixtures at reduced temperatures. Successful use of warm-mix asphalt (WMA) in field demonstrations has created a need for development of mix design procedures. A major impediment in development of these procedures is the evaluation of the effect of WMA technologies on asphalt binder and mixture workability. The objective of this study was to introduce a new test methodology for estimating asphalt binder workability by measuring the lubricity effects of a surfactant-based additive as well as binder foaming processes through novel use of the dynamic shear rheometer with a new testing fixture. The new test allows measuring the coefficient of friction of binders at various temperatures, loading rates, and normal force. Asphalt binder lubricity measurements were correlated mixture to workability tests defined by the compactive effort required to densify a mixture to 8% air voids. Mixture testing was conducted at temperatures ranging from 90°C to 135°C. Results of asphalt binder workability testing demonstrated a significant reduction in coefficient of friction due to the use of a surfactant-based WMA additive and identified a need for revised procedures for evaluation of foamed asphalts. Both warm-mix processes demonstrated enhanced mixture workability relative to the hot-mix asphalt; however, significant differences were not realized until compaction temperatures were below those normally used in production.

Moisture damage–related distress is a primary concern limiting the application of cold-mix asphalt (CMA) as an alternative to hot-mix asphalt in the field. Thus, a simple and effective method is needed in the materials selection process to identify moisture susceptible materials. This study presents a modification to the boiling test procedure specified in ASTM D3625 based on the concept that a mix designer can limit moisture damage by controlling coating quality. The test was modified to present CMA-specific sample preparation guidelines and to remove subjectivity from the test by quantifying coating according to image analysis. Coating quality was evaluated with the coating loss ratio, defined as an index to compare coating before and after the boiling of cured loose mixtures. The relationship between coating quality and moisture resistance was verified with two separate tests: the AASHTO TP-91 binder bond strength test and the AASHTO T-283 tensile strength ratio test. The binder bond strength test provided a direct measure of the bond between binder and aggregate and how it was influenced by moisture. The effect of coating quality on bulk mixture performance was evaluated through comparison with the tensile strength ratio test. All compacted mixtures were produced with a newly developed CMA mix design method to maintain air void levels between samples. Results show that image analysis can be effectively applied to quantify the results of the boiling test, and rankings from all three tests are consistent; this efficacy suggests that the evaluation of coating quality with the modified boiling test can be used as an effective initial evaluation of the potential for CMA moisture susceptibility.