Pavement Preservation Journal, Summer 2015, Vol. 8, No. 2
For many years and for many reasons, road agencies in both the United States and Canada have been increasing the use of warm mix asphalt (WMA) designs.
Recently the many HMA producers have chosen the foaming method to make WMA, as in most cases that will meet the minimum state specification requirements. In doing so they also have included additives for anti-strip where needed.
As the season gets later in the year and working conditions get colder, or if the hauls from the plant to the site are quite long, loss of heat in a mix causes many contractors to add a WMA additive as a compaction aid to meet minimum state requirements with cooled mixes.
In Europe the specifications simply are based on performance requirements, and the vast majority of the major contractors over the last two years have chosen a product called ZycoTherm as a nanotech-based anti-strip which provides a chemical instead of physical bond, yet also providing warm mix performance and better coating and wetting, allowing for greater flexibility and workability, the manufacturer says.
A lab protocol developed by Zydex Industries supports these attributes, the maker says. The lab protocol closely simulates plant and field conditions, which provides a new method of determining optimum dosage for anti-strip, and then adds only 0.05 percent for the WMA benefits needed.
In the lab, the addition of ZycoTherm was carried out on the basis of the instructions for “mixing report with asphalt binding agent/mixing report for asphalt mixtures” provided by the customer. A special mixer with a Cowles agitator for producing emulsions was used for this purpose.
The ZycoTherm additive was mixed with the bitumen heated up to 160 deg C (320 deg F) for at least 10 minutes. The resulting bitumen then was added to the preheated stone in the mixer and the mixing process was started. Using the Cowles agitator and mixer provides for high shear blending, which simulates plant and field conditions. This is extremely important as high shear is required to sufficiently disperse this material into the bitumen.
Contractors using ZycoTherm have noted a faster wetting and coating cycle, which has enabled them to complete projects more efficiently.
