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The heart of this new Terex warm mix asphalt system lies in an expansion chamber that provides single-point mixing of water and heated liquid AC just prior to the entering the drum. A three-way valve installed to the liquid AC supply line allows producers to choose between running traditional hot mix and diverting binder flow to the expansion chamber for making foamed asphalt.

A high pressure, five horsepower, piston-type pump operating in a closed-loop system accurately injects water into the asphalt. “It’s really a simple system. Other than the water pump, there are no moving parts,” Nelson mentions.

Once the water and hot AC are mixed in the expansion chamber, the foamed asphalt is immediately piped into the drum to evenly coat the virgin aggregate and RAP. The pipe is designed to fit the producer’s specific drum mixer and is equipped with up to 24 spray nozzles, in which at all times all nozzles are used to coat the aggregate and RAP regardless of whether the plant is running at 200 or 500 tons per hour.

“The system can produce up to 500 tons per hour of warm mix asphalt,” Emerson explains. “Our system will work with either volumetric or mass-flow metering systems,” Musil adds.

Positive field results

Originally, Lehman-Roberts planned to produce the warm mix asphalt for a paving project Desoto County, MS. However, due to the inclement weather during the evaluation and since this was the first time the producer worked with the new mixing process, company officials decided to move the evaluation to a more controllable application.