Zeolite in Warm Mix Asphalt
Warm Mix Asphalt produces reduced emissions, allows for an extended paving season, and reduces workers' exposure to harmful toxins.
A number of benefits were consistently identified as driving the development of Warm Mix Asphalt (WMA) in Europe. These benefits include environmental aspects and sustainable development concerns, or “green construction,” particularly reduction of energy consumption and the resulting reduction in CO2 emissions, and improvement of field compaction. Improvements in the compactability of WMA mixes can also facilitate an extension of the paving season and allow the possibility for longer haul distances. Another important consideration is the welfare of workers, particularly with gussasphalt or mastic asphalt, which is produced at much higher temperatures than HMA.
A number of suppliers’ presentations in Norway (Norwegian and Italian data), Belgium (Netherlands data), and France included data that indicated reduced plant emissions. Reduced emissions were reported in Germany, but no data were presented.
Data from the Bitumen Forum relate emissions to temperature: “At temperatures below 80 °C (176 °F), there are virtually no emissions of bitumen; even at about 150 °C (302 °F), emissions are only about 1 mg/h. Significant emissions were recorded at 180 °C (356 °F).” Problems observed in the United States with increased emissions—particularly CO and VOCs—potentially due to unburned fuel, were not reported in Europe. The smaller plants used in most cases in Europe have correspondingly smaller burners, making it easier to adjust the burner to run at lower temperatures.
Reduced Fuel and Energy Usage
Reports indicated that burner fuel savings with WMA typically range from 20 to 35 percent. These levels could be higher if burner tuning was completed to allow the burner to run at lower settings. Fuel savings could be higher (possibly 50 percent or more) with processes such as low-energy asphalt concrete (LEAB) and low-energy asphalt (LEA), in which the aggregates (or a portion of the aggregates) are not heated above the boiling point of water. It does not appear that any change in electrical usage to mix and move the material through the plant has been considered in the analysis of potential fuel savings.
Although paving benefits may not have been a driving force in the development of WMA technologies, they may be particularly attractive to U.S. contractors and agencies. Several paving-related benefits were discussed, including the following:
- Ability to pave in cooler temperatures and still obtain density
- Ability to haul the mix longer distances and still have workability to place and compact
- Ability to compact mixture with less effort (assuming typical conditions, not cold weather or long haul)
- Ability to incorporate higher percentages of RAP
- Ability to place thick lifts and open them to traffic in a short time period.
Reduced Worker Exposure
Enforcement of a new European Union regulation called Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) was implemented in June 2007. It requires chemical suppliers to provide information to workers on potential exposure and to set derived non effect levels (DNEL). Asphalt binders are included under these regulations. Research has shown a strong correlation between production temperatures and asphalt fume production. It is anticipated the DNEL levels will set asphalt application temperatures at less than 200°C (392°F). While this is well above the temperature at which HMA is placed, particularly in the United States, it is lower than the temperatures used for the production of mastic asphalt. Although mastic asphalt usage is relatively small, it is a technology that European agencies want to continue to specify. This seems to be a driving force toward WMA in areas where mastic asphalt is routinely used. Mastic asphalt, not used in the United States, should not be confused with stone matrix asphalt.