Gilsonite asphalt grade is natural occurring hydrocarbon substances characterized by a high softening point (above 110° C) in the class known as asphaltite. They are mined much like other minerals and sold essentially in their native state. They are fully compatible with asphalt and have long been known as asphalt hardeners and reinforcing agents. Gilsonite applicable in asphalt is currently sold all over the world as an asphalt modifier in the form of a dry bulk solid granular powder.
Gilsonite powder benefits to asphalt pavements include increased stability, resistance to deformations problems such as rutting and shoving, resistance to water striping and increased load bearing ability. Gilsonite functions by making the pavements harder, stronger and increases asphalt’s adhesion to aggregates.
It is generally regarded that Gilsonite reduces pavements’ low temperature properties making them susceptible to thermal cracking. Gilsonite melted into hot asphalt will reduce penetration and increase viscosity of the asphalt binder. Gilsonite may also be mixed with aggregate prior to combining with the asphalt binder.
Gilsonite modified asphalt pavements have been particularly successfully in highly stressed traffic areas. Gilsonite, as the majority constituent, has been combined with virgin polymers such as styrene – butadiene – styrene (SBS) and Ethyl Vinyl Acetate (EVA). Gilsonite modified asphalt binders generally do not increase asphalt binder content requirement in pavement mixtures.
Performance grading of asphalt binders and pavement mixtures became a reality with the conclusion of the, “FHWA” 50 million dollar, Strategic Highway Research Program, “SHRP”, in March of 1993. “SHRP” developed new asphalt binder specifications and test criteria based on the engineering properties related to pavement performance.
The new emphasis is on low temperature performance of aged binder materials. Low temperature flexibility of aged asphalt binders became significant. Performance Grade “PG,” asphalt is based on the predicted temperature performance both high and low of asphalt binders. Neither Gilsonite nor post vulcanized crumb rubber have performed well under “SHRP” evaluations. “SHRP” specifications will cause increased demand for modified asphalt as state departments of transportation adopt the “PG” specifications.