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.
If the bitumen cannot be heated higher than 170°C then you may consider using Selects other Grade (60/70 mesh) or Selects Grade (200mesh) rather than HMA Modifier Grade (175°C softening point) for modification. However, each one of these Selects grades will require slightly more Gilsonite to be added, relative to HMA Modifier grade, to achieve the same level of bitumen modification. The dry Gilsonite should be poured into the hot bitumen slowly. If it is added too fast then it may agglomerate, or "ball up" at the surface. If this happens then some manual stirring to disperse the agglomerations may be required.
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