Details of Gilsonite Usage

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Details of Gilsonite Usage

1. Mix with Asphalt

Glance Pitch and Graliamite are 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 is currently sold all over the world as an asphalt modifier in the form of a dry bulk solid granular powder.

Gilsonite s 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.

Mixing Gilsonite into Bitumen

This is a fairly simple procedure. A bitumen tank with a propeller stirrer with enough agitation action to create a vortex is recommended. The best choice is a “lightning” mixer or some other type of electrically powered mixer. An explosion proof motor is preferred if large dust concentrations are likely to occur.

Gilsonite should be added slowly at the vortex. Provisions should be made to recirculate the hot bitumen through recirculation piping. The most important item is that the minimum temperature should be about 170 to 175° C. Anything significantly less than this will extend mixing time. For typical (5-10%) substitution concentrations, 2-4 hours of mixing after addition is completed should be sufficient. For master batch concentrations (over 10% Gilsonite) recirculation overnight is preferred.

Meltable Bags

It may be much easier to pre-package Gilsonite into small, polyethylene bags with a measured amount of Gilsonite and toss them onto the hot aggregate in a batch plant. The sidewall thickness of the bag should be about 2 mils (0.005 cm). The aggregate temperature should be around 180°C. It is the aggregate temperature that is melting the bags and the Gilsonite, not the heat from the bitumen. Therefore a temperature of 150-165°C entering the pug mill is acceptable, as long as the aggregate is sufficiently heated.

In either case, spraying Gilsonite onto aggregate or tossing bags into the pug mill, we conservatively recommend increasing the mixing time an extra 15 seconds. This will insure the Gilsonite is melted properly and dissolving into the bitumen. Finally, it is possible to just scoop or shovel a precise number of kilos of Gilsonite per batch onto the hot aggregate, no re-packaging  just hand labor.

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