n added directly onto the aggregate mix as solid prills or as molten liquid via a dosing meter. Marshall tests performed on mixes produced in this manner indicated no difference in stability or flow as compared to premixing with the binder5. In the United States, Sasobit® has been blended with the binder at the terminal and blown directly into the mixing chamber at the same point cellulose fibers were being added to an SMA. Commercial supplies of Sasobit® are available in 20 kg bags and 600 kg super-sacks.
GRANITEROCK WMA TRIAL
The Quarry Road WMA trial is the first application of the Sasobit® warm mix in California, and the project should provide quantifiable results for further evaluation and implementation of this new technology.
The Quarry Road project called for 330 tons of the warm mix containing the Fischer-Tropsch wax, Sasobit®. The WMA mix was paved in a one lane strip that has 540 meters (1800 feet) in length, 3.9 meters (13 feet) in width, and 64 mm (2.5 inches) in thickness. For easy evaluation of the long term performance, a control HMA section was built just aside from the WMA trial section. The only difference for the WMA mix comparing to the control HMA mix was the addition of 1.5% of Sasobit® wax by weight of the asphalt binder. The Sasobit® wax was pre-blended with the asphalt binder before it was pumped into the asphalt tank.
There were no changes required at the production plant when blending the warm mix, other than lowering the mixing temperature. Graniterock produced the warm mix at its Astec drum plant in Aromas, CA at a temperature of 270°F and 250°F (Control HMA mix was produced at the same plant at 305°F). The placement and compaction temperatures were lowered accordingly for WMA mix. As shown in Figure 3 and 4, there was significant difference between the emissions indicated by the smoking from the dumping of the truck load.
The lab and field testing results are encouraging for this new technology. The WMA mix achieved good compaction of 97.7 percent under the normal compaction pattern with an average of 50°F temperature reduction. The lab testing results indicate that the WMA mix will perform similar or even better than the HMA control mix in terms of air voids, stability and moisture damage sensitivity.
The added cost of the Sasobit material was almost fully compensated by the fuel saving (up to 37% with 50°F temperature reduction) due to the lower mixing temperature. The benefit of low emission and less odor, better pavement durability due to less aging, and the potential to promote low temperature or night paving capability are just extras.
Emission is one of the biggest issues with the rubberized asphalt mix. The production rate is limited to approximately 1000 tons per day because of the restriction for maximum allowed emission. The WMA technology appears to be able to significantly reduce the emission of asphalt plant therefore allows a significant improvement in the plant production rate for rubberized asphalt mix.
A message from NCAPA asphalt bulletin6 indicates that HMA industry needs to be cognizant of the current environmental regulations that HMA industry will face in the coming years. Several limits including NOx and CO2 limits have been developed and implemented. This is evident in Environmental Protection Agency (EPA)’s implementation of the National Ambient Air Quality Standard (NAAQS) and the recent adoption of the San Joaquin Valley Air Pollution Control District (SJVAPCD) Rule 4309. International Agency for Research on Cancer (IARC) will conduct a major study of asphalt fume research and make a determination as to whether asphalt fume is carcinogenic. All these major efforts will have significant effects on how the industry produces HMA.
How we address these challenges will determine the future of HMA as a viable and environmentally friendly road building material. With all the benefits on energy consumption saving and a commensurate reduction in CO2 emissions and a reported up to 90% reduction in fumes7, the WMA technologies appear promising though there is still a lot to 