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Terex Warm Mix Asphalt System Delivers Single Point Mixing

Wed April 08, 2009 - National Edition
Construction Equipment Guide

The new Terex foamed asphalt system from Terex Roadbuilding allows producers to take advantage of the benefits of running warm mix asphalt without the significant costs associated with additives. By simply mixing water and hot liquid asphalt (AC) in the expansion chamber, the new system eliminates the need for additives that increase the cost of asphalt by dollars per ton. Since its introduction in mid 2008, dozens of Terex warm mix asphalt systems have been installed in the field, successfully reducing mix temperatures by 50 to 90 F (10 to 32 C), according to the manufacturer.

The system design consists of two main components: an expansion chamber and a programmable logic control (PLC) skid package. The single-mixing-point expansion chamber is based on the foamed-asphalt technology pioneered by Terex in 1998. Once the hot AC and water combine in the expansion chamber, the foamed asphalt is immediately injected into the drum. The injection pipe is sized to the drum with a variable number of spray nozzles to evenly and thoroughly coat the heated aggregate.

For field installations, the warm mix PLC unit comes complete in a water skid package. The PLC unit interacts with plant controls to meter a predetermined percentage of water with liquid AC. The skid also includes a 220 gal. (832.8 L) water tank and a variable frequency 5 hp (3.73 kW) electric motor. Featuring a belt drive that allows the producer to increase or decrease power output, the motor drives a highly accurate water pump, according to the manufacturer.

The PLC unit interfaces with most input signals from a variety of plant controls packages. The Terex warm mix asphalt system can be installed on any unitized counterflow drum mix plant. For new plant purchases, the control unit is integrated into the plant controls package.

Also contained in the skid package, a water meter verifies the correct percentage of water is injected with the hot AC inside the expansion chamber.

“By incorporating the meter, the Terex system goes a step beyond most other foamed asphalt units, which leave the operator to assume the correct percentage of water is added,” said Joseph Musil, product manager at Terex Roadbuilding.

The Terex warm mix system works by injecting a variable amount of water with hot oil inside the exclusive expansion chamber. The system injects and mixes up to 4 percent of water by mass weight of the liquid AC. Higher percentages of water result in more asphalt foaming action.

“In typical applications, producers inject 2 percent water,” said Musil. The Terex system is capable of producing up to 600 tph (544 th) of asphalt at a 4 percent injection rate, and producers can quickly switch between running warm and traditional hot mix designs with the new system.

Hot-oil jacketed modules ensure dependable operation of the warm mix system. The expansion chamber is insulated and jacketed, while the asphalt and water safety check valves are jacketed. The system’s injection pipe includes a heating coil built inside the pipe to keep the valves from clogging.

“The heating jackets, insulation and coil built into our warm mix system prevent the asphalt from cooling and subsequent system blockage,” added Musil.

Many producers continue to realize significant operating benefits of running warm mix asphalt. Mixing at lower temperatures helps to reduce odor and particulate, carbon dioxide and nitrous oxide emissions at the plant, while at the same time virtually eliminate “blue smoke” at the truck and paver. Warm mix asphalt helps to reduce the plant’s fuel consumption. Additionally, lower temperatures inside the drum potentially result in a longer drum shell life, according to the manufacturer.

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