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Low Emission Asphalt (LEA)
Frequently Asked Questions

Are chemical additives necessary for this process?

Yes they are. All of the developmental work done on this process found that chemical additives are essential to the products success. The chemical additives play many roles in the process - as an adhesion promoter, an aid in coating, and as a workability aid.

How much chemical additive is required?

Depending on the mix design, type of aggregates and binder used, this amount could vary, However, we generally use around 0.4% additive by weight of asphalt.

Can a continuous drum mix plant be used to produce LEA?

Yes it can. However, in order to optimize the low energy process, it is necessary to first coat the heated coarse aggregate fraction with asphalt binder before introducing the wet sand fraction into the mix through the RAP collar. In some plants, this may require a slight modification to the existing plant to move the asphalt further into the drum.

What additional equipment is required at the HMA plant to produce LEA?

The LEA process is controlled by four parameters in the plant - cold sand (or RAP) moisture content; heated aggregate temperature; mix discharge temperature; and additive flow rate. A microwave moisture must be installed on the wet sand (RAP) feed belt along with a shower if additional water is required. A readout for the heated aggregate temperature is desired however this is often not possible - so the inlet baghouse temperature can be used to help guide the process. A contact probe to measure mix discharge temperature is added to insure proper temperatures. And finally, a simple pump and metering system to insure the proper dosage of additive is injected directly into the asphalt line. The entire system is connected to a control module which monitors these parameters during LEA production. All of this equipment is provided by McConnaughay.

Are there any complicated license agreements involved with this process?

No. While the LEA technology is protected by a worldwide patent, McConnaughay will install all of the necessary equipment in your plant and as long as all of the chemicals are purchased through us, you are granted a sub-license to use the LEA technology.

Can moisture left in the mixture cause a problem?

In hot mix asphalt (HMA) it can cause a problem. But what is important is where in the mix is the moisture located. For HMA moisture left in the mix is located typically in the pores of the coarse aggregate due to insufficient drying of the aggregates. Under sunlight and traffic, this moisture will leave the coarse aggregate, breaking the bond between the asphalt and aggregate - leading to stripping and flushing. With the LEA process, the coarse rock is completely dried and the moisture that remains in the mix is in the form of discreet water droplets in the asphalt phase. These trace amounts moisture may eventually leave the mixture but will not cause any damage in doing so.