Chapter 2: Benefits of WMA

A number of benefits were consistently identified as driving the development of WMA in Europe:

• Environmental aspects and sustainable development concerns, or "green construction," particularly reduction of energy consumption and resulting reduction in CO₂ emissions.
• Improvement in field compaction. Improvements in the compactability of WMA mixes can facilitate an extension of the paving season and allow the possibility for longer haul distances.
• Welfare of workers, particularly with gussasphalt or mastic asphalt, which is produced at much higher temperatures than HMA.

As discussed previously, one pillar of sustainable development is environmental protection. Reduction in the use of natural resources (fuel) and the production of CO₂ is a key element of sustainable development. Reduction of CO₂ emissions is mandated as part of the European Union's ratification of the Kyoto Protocol. It does not appear that the Kyoto Protocol directly impacts the HMA industry in Europe. However, the HMA industry has taken a proactive approach in investigating means of reducing CO₂ emissions. This was apparent in all of the countries visited.

Although they do not consider it a prime factor, some contractors acknowledged that improvement in field compaction was realized when using WMA technology. They saw this as an added benefit in ensuring adequate in-place density for long-term performance. More widely recognized were potential benefits of extending the paving season and potential for longer haul distances. As in the United States, many locations in Europe have climatic conditions that restrict HMA placement to warmer months. Extending the paving season and/or providing for longer haul distances can make the use of HMA more economical.

Contractors noted that reduced temperatures improved workers' comfort and productivity. The European Union is implementing new regulations to address worker exposure to all types of chemicals, including asphalt binder.

Several WMA technologies mentioned in this chapter will be described in Chapter 3.

Reduced Emissions

A number of suppliers' presentations in Norway (Norwegian and Italian data), Belgium (Netherlands data), and France included data that indicated reduced plant emissions. Table 4 presents the ranges in reductions. 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)."⁽⁹⁾

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.

*Reported as NO₂ NA-not available

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. No specific study was referenced for the suggested fuel savings.

Paving Benefits

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 to traffic in a short time period

Case studies were presented in Germany in which paving was completed with various technologies when ambient temperatures were between -3 and 4 °C (27 and 40 °F). Base, binder, and an SMA surface course were placed in Germany using Aspha-min. The base course contained 45 percent RAP. Ambient temperatures during placement ranged from 30 to 37 °F (-1 to 3 °C). The mix temperatures for the WMA behind the paver ranged from 216 to 282 °F (102 to 139°C). Better density results were obtained with the WMA than the HMA with the same or fewer roller passes.⁽¹³⁾ The ability to compact the mix at lower temperatures is achieved through the reduction in viscosity of the binder. Data were presented using Licomont BS 100 on the viscosity reduction effect at lower temperatures. Similar data were presented for Sasobit and Sübit (binder modified with Licomont BS 100). The Department of Eure-et-Loir in France also believes that WMA technologies can be used to extend the paving season. The ability to place and compact WMA at lower temperatures has not been investigated in Norway using the WAM-Foam process.

Actual production temperatures for WMA mixes produced during cool weather vary, depending on the WMA technology, ambient conditions, and haul distance. In most cases the production temperatures will most likely be reduced compared to HMA produced under the same conditions. In some cases, the production temperatures may be closer to that of HMA.

Similar to the potential for extending the paving season using WMA technologies, longer hauls may be facilitated by the reduced rate of cooling of WMA and the reduced viscosity of WMA at lower temperatures. Kolo Veidekke reported that it stored WAM-Foam in a silo for 48 hours and still had the ability to place and compact the mix. HMA containing Sasobit reportedly was hauled up to 9 hours in Australia and the material was still able to be unloaded. The Department of Eure-et-Loir in France also believes that WMA technologies can be used for longer hauls while maintaining workability.

WMA technologies may be beneficial with mixes containing high proportions of RAP in two ways: 1) the viscosity reduction will aid in compaction, and 2) the decreased aging of the binder as a result of the lower production temperatures may help compensate for the aged RAP binder, similar to using a softer binder grade. In Germany, a case study was presented in which 45 percent RAP was used in the base course. In the Netherlands, both LEAB and HMA are routinely produced with 50 percent unfractionated RAP. Trials have been conducted in Germany with 90 to 100 percent RAP using Aspha-min zeolite and Sasobit.

Overall, RAP usage in the United States appears to be higher than that in the countries visited. In Norway, Kolo Veidekke reported that it typically runs 7 to 8 percent RAP in all of its mixes. Milling is not used extensively in Norway, so its RAP supply is limited. Kolo Veidekke tries to run a consistent amount of RAP in all of its mixes. In its annual report, Colas reported that its U.S.-based operations averaged a recycling rate of 14 percent, compared to 3 percent in France.⁽¹⁴⁾ Colas' Northern Europe operations averaged an 11 percent recycling rate.

Several studies provided data to show that the WMA technologies acted as compaction aids and reduced the required compactive effort. Some of the technologies (Sasobit and Licomont BS 100 or Sübit) were initially used for their stiffening effect at high in-service pavement temperatures. During this use it was observed that the materials reduced viscosity at compaction temperatures, particularly when compared to other types of modifiers.

Finally, WMA technologies can be used to facilitate deep patches, such as those placed when repaving the Frankfurt Airport. Sasobit was used in the repaving of Frankfurt Airport. Twenty-four inches of HMA were placed in a 7.5-hour window. The runway was then reopened to jet aircraft at a temperature of 85 °C (185 °F). This may have significant implications either for trench patching or when rehabilitation strategies require multiple lifts to be placed in the same night.

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 noneffect 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 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. Mastic asphalt is described in Chapter 6.

French, German, and Italian data were presented that indicated reduced worker exposure when placing WMA. Direct comparisons of measurements of fumes and aerosols are difficult since different testing protocols and sampling periods are used in different countries. It should be noted that all of the exposure data for HMA were below the acceptable exposure limits. Tests for asphalt aerosols/fumes and polycyclic aromatic hydrocarbons (PAHs) indicated significant reductions compared to HMA. Data presented by the Bitumen Forum appear to result in a 30 to 50 percent reduction.⁽⁹⁾ Preliminary data from a forthcoming Italian study indicate even larger reductions.

In addition to reducing worker exposure, the lower mix temperatures also provide a more comfortable working environment. This may aid in worker retention. In Germany, one contractor also observed greater worker productivity when placing WMA compared to HMA.