The benefits of the Astec Warm Mix Green Pac System

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  • The benefits of the Astec Warm Mix Green Pac System

7th January 2014 - With the benefits of warm mix asphalt such as reduced energy consumption, lowered emissions, and elimination of visible smoke well-known in the asphalt paving industry, warm mix technology allows mix to be prepared and placed at lower temperatures, typically 30˚C to 50˚C lower than conventional hot mix. To achieve this, the viscosity of the bitumen must remain low at the reduced temperatures. Maintaining a low viscosity at lower temperatures allows mix to flow freely through storage, transfer and placement equipment and is more easily worked by hand.

Unfortunately, many technologies for warm mix production rely on additives, special bitumen’s, special procedures and/or special bitumen delivery systems to achieve low viscosities at low temperatures. These additives are expensive and add significant cost per ton of mix.
With the introduction of the new Warm Mix Green Pac System the need for expensive additives and special bitumen’s is eliminated by mixing a small amount of water into the bitumen to create microscopic bubbles. These small bubbles then act to reduce the viscosity of the bitumen coating on the rock allowing the mix to be handled and worked at lower temperatures.

Compact with easy maintenance
Promoted in the UK by BG Europa (UK) Ltd, the Green Pac System for batch plants comprises a bitumen foam manifold assembly and a skid mounted water delivery system. With the system foam bar mounted remotely from the pugmill, common problems, such as nozzle blockage experienced with other foaming systems are eliminated. A further benefit also allows the system to be fitted to batch plants which have limited access around the pugmill mixer.
Although the system is compact, it has been designed with the plant maintenance in mind. The self-cleaning water injectors require only periodic inspection and may be removed and replaced from the top of the unit without removing the front cover. The foaming chambers have no moving parts.

How the system works
Bitumen is pumped to the Green Pac System either from the main bitumen supply, via a metering system, or alternatively a positive displacement conversion kit allows bitumen to be drawn from an existing bitumen weigh kettle.
Water is delivered to the Green Pac System from the skid mounted corrosion free reservoir which is fitted with an automatic filling valve that keeps the reservoir full from the water supply. A positive displacement piston pump accurately meters water into the system, with the water pump speed modulated by feedback control to maintain the appropriate flow of water to the manifold in relation to bitumen flow. Water is injected into the bitumen through a series of all stainless steel injectors located above corresponding foaming chambers within the Green Pac System foam manifold. Bitumen flows through the foaming chambers where water and bitumen are thoroughly mixed to produce mechanically foamed bitumen. The foamed bitumen then flows from the Green Pac manifold down a delivery pipe to the pugmill mixer.

Expanding the benefits
With the introduction of the new Warm Mix Green Pac System, Astec has expanded the benefits of its exclusive Double Barrel Green Warm Mix System to any asphalt plant owner or operator.

Astec says that the Double Barrel Green System saves energy, eliminating smoke and emissions without compromising mix quality, using water to produce foamed warm mix asphalt that is odourless, smokeless and longer lasting.

Andrew Pettingale – MD of BG Europa, commented. "The Double Barrel Green System does not require the addition of expensive commercial additives. Instead, the injection of water along with the bitumen causes the bitumen to foam and expand in volume. The foaming action helps the liquid asphalt coat the aggregate at a temperature that normally is in the range of 110-130°C versus traditional temperatures of 150-170°C. With the Green Pac System, an operator can decrease fuel consumption 14% by decreasing the mix temperature just 30°C. Other benefits include the elimination of smoke and smell, an increase in production, and the ability to run higher percentages of recycled asphalt pavement (RAP)."

Bury St Edmunds based company, BG Europa (UK) Ltd, who promote and are stockists of genuine Astec parts in the UK can retrofit warm mix systems to continuous mix and batch plants from any manufacturer, bringing the benefits of the Astec warm mix system to all asphalt pavement plant configurations.

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