Why do we modify asphalt binders? What impact do the various forms of modification have on the performance of asphalt pavements? How should we evaluate a new modifier? How does this impact state DOT approvals?
Such questions have always been asked by asphalt suppliers and DOT agencies. However, during the summer of 2014 the possible impact of a modifier in the New England region highlighted the necessity to understand the supplier’s evaluation steps and the approval processes of state agencies…
Re-Refined Engine Oil Bottoms: Don’t Jump on the “Banned”-wagon too Quickly
By Karissa Mooney, HollyFrontier Refining & Marketing, LLC
February 10, 2015
Re-refined Engine Oil Bottoms, or REOB, are one of several products obtained in the refining of recovered engine oil (see the diagram below). REOB have been used in the paving industry since the 1980s, with current annual production around 160,000 tons. This represents about half a percent of all Performance Graded binders produced in the United States.
REOB are used from 3 to 10 percent by weight in order to obtain low temperature binder properties. The effects of REOB on binder properties depend on the base binder. Generally, REOB will soften the base binder, resulting in a one PG grade drop in low temperature properties. This resulting PG grade reduction is based on 2 percent REOB (m-value) and 4 percent REOB (stiffness). REOB are used to soften a base binder to obtain improved low temperature properties and in higher RAP and RAS mixes to counteract the stiffness of the recycled materials in the binders.
A ban and its aftermath
In 2014, state DOTs in New England discovered that REOB were being used by a regional asphalt mix supplier. Based on limited existing technical information on REOB, this discovery led to a ban on REOB in the area while the University of Massachusetts at Dartmouth evaluates the impacts of REOB on pavement performance.
Additionally, through efforts by the North East Asphalt User/Producer Group, a task group was developed to generate a list of known modifiers. The task group is evaluating how the list will be implemented, such as an approved list or as examples of known modifiers with proven performance.
Ron Corun with AMAP member company Axeon offered perspective on the situation. “The New England states are jumping the gun with a ban based on very limited data,” Corun says, “but I can understand the frustration of the DOT engineers.”
Corun noted a parallel with the use of polyphosphoric acid as an additive. “In some ways this is a repeat of the PPA issue,” he says. “That additive was used to meet specifications before mix testing or verification showed long-term performance. The PPA industry scrambled to conduct those studies after the fact. That’s what’s happening now with REOB.”
Corun says, “The burden should be on industry to do testing and verification, ideally before we start using a new additive.”
Research digs into REOB
During the annual 2015 Transportation Research Board meeting, a session was held pertaining to the history, refining process, and chemical footprint of REOB. Tony Kriech from Heritage Research Group presented on the history and refining process. The process to collect the “waste engine oil” is regulated by the U.S. Environmental Protection Agency, which labels these oils as non-hazardous.
Once the material is collected by the refiner, it is checked for PCBs and the volatiles are removed. The REOB material is the non-distillate fraction after atmospheric and vacuum distillation of the base oil. Since REOB is refined from engine oil, it is the highest boiling point fraction of the paraffinic lube oils. According to FHWA’s Terry Arnold, the various chemistries and viscosity of the REOB will vary by manufacturer. Additive packages are added into the engine oils to inhibit oxidation, and REOB may contain varying amounts of zinc, molybdenum, styrene butadiene, phosphorus, sulfur, calcium, iron, and copper.
During FHWA research, the complexity of the REOB chemistry was evaluated when blended with asphalt and Ground Tire Rubber (GTR). The asphalt may contain sulfur, iron, molybdenum, and zinc (from hydrogen sulfide scavengers). Whereas the GTR may contain sulfur, calcium, silica, iron, copper, and zinc, the FHWA project has utilized the X-Ray Fluorescence Spectroscopy (XRF) analysis to determine the presence of REOB in a binder. However, due to the overlapping chemistries of base asphalt binder and other modifiers, the XRF can detect the presence of REOB although it may be difficult to quantify the actual percent in the binder.
Developing guidelines and moving forward
Currently, research is ongoing at various institutes and agencies regarding the impact of REOB on pavement performance. These projects will evaluate rutting and fatigue using short term and long term aging, and the impact of combining various types of modifiers to produce an engineered binder. The research will provide the industry with the guidelines for use of REOB, which will enable the suppliers to produce a quality binder using appropriate dosage levels.
AMAP believes REOB will continue to have a role to play as an asphalt modifier, in all of the United State including New England. As crude sources change and sustainable products are developed, the properties of the asphalt binder will vary and the need for engineered binders will grow. The industry needs to foster collaboration between the suppliers and the agencies to ensure that implementation of products is not hindered by the unknown, but is accepted based on a validation process that uses the best available engineering tools.