The demand for softer binder grades has grown in recent years due to higher levels of RAP (reclaimed asphalt pavements) and RAS (recycled asphalt shingles) being used in mixtures.

Re-refined engine oil bottoms (REOB), also known as vacuum tower asphalt extender (VTAE), is the non-distillable residuum from a vacuum tower in a used oil re-refinery. A FREE Asphalt Institute (AI) publication explains how and why REOB/VTAE is used as blending agent to soften binders.

“IS-235 State-Of-The-Knowledge, The Use of REOB/VTAE In Asphalt” combines all information on the topic into a single, 89-page resource. It was produced by the institute’s REOB/VTAE task force, made up of member company representatives, AI staff engineers, and a Federal Highway Administration representative.

IS-235 details the background of REOB/VTAE; health, safety, and environmental considerations; alternate tests; and aging protocols for characterizing physical properties of asphalt binders. There's also an extensive review of 26 previously published papers on the subject as well as a frequently asked questions section.

The book was introduced at the American Association of State Highway and Transportation Officials Subcommittee on Materials annual meeting in Greenville, S.C., on Aug. 4.