Tech Tips for Better Asphalt Processing

An asphalt mixing system can be simple or complex, but certain basic components are common to all controllable process heat, leak proof and pressure capable containment systems (piping and tanks), pumps, valves, agitation equipment, sensors and control systems.

But even with the basic components in place in a system, there is no guarantee of predictable and acceptable asphalt mixing and modifying results. Here are a few helpful 'Tech Tips' to help ensure better asphalt processing.

The asphalt and polymer modifiers must be compatible - lab testing should be done to confirm this.
Always begin the mixing process with a trained operator at the control system who has the technical experience to operate the system to produce consistent asphalt polymer blend.
Select a sufficient heat source. Reichel & Drews recommends using thermal fluid because it's easy to work with and a higher temperature can be achieved at a lower pressure.
The asphalt temperature entering a mixing system should be about 350° F (depending on the process). Rather than maintaining that temperature in a storage tank, utilize an in-line heat exchanger to raise the asphalt temperature on the way to the mixing system. This ensures the asphalt will be the ideal temperature before entering the mixing system.
Asphalt requires consistent heat so insulation plays a major role in the success of asphalt processing - typically three inches on tanks and one to two inches on pipes and valves. Use custom removable/reusable blankets with twist ties or snap fasteners for valves and pumps - these do a good job of insulating and maintenance.
The pumps should be positive displacement, heat jacketed, with shaft packing rather than mechanical shaft seals. Reichel & Drews recommends using reversing starters.
Popular valve choices are heat jacketed plug type or non-jacketed butterfly with pneumatic operators sized for a 50 psi plant air supply (fail closed).
Standard schedule 40 pipe can be heated with one of several techniques - external jacketing, pipe and tube tracing, or the less common method, internal tracing, where the heat source pipe runs inside the asphalt containment pipe (check welds carefully).
The typical mixing vessel used is vertical and from 1,000 to 4,000 gallons. Vigorous agitation is required to avoid polymer agglomeration, whether the goal is to disperse and wet-out dry ingredients or maintain agitation of an asphalt/polymer blend. A multi-speed or variable speed agitator provides the flexibility of doing both, but vertical agitators with single or dual 3-4 blade impellers and between 5 and 25 HP will usually suffice.