Warm mix asphalts

Warm mix asphalts (WMAs) are asphalts produced, handled and compacted at temperatures lower than those of conventional hot asphalts. This is achieved by lowering the viscosity of the binder using additives or applying foaming processes, both known as WMA systems. The aggregate mix gradation is the same as for the hot mix variety. 

Producing and using WMA have environmental and paving benefits. 

In the environmental aspect, fuel energy savings, reduction of greenhouse gas emission and reduction of bitumen fumes, and hence, improvement of workers welfare, are achieved. 

The fuel energy savings may be 20% to 35% on the plant, depending on the WMA system, which is equivalent to approximately 1.5 to 2.0 L of fuel per tonne of material. The reduction in greenhouse gas emission is closely associated with the reduction in energy consumption, that is, 20% to 35% reduction of C02 eq, which translates to approximately 4.1 to 5.5 kg of CO2 per tonne of mix. The reduction of bitumen fumes is in the magnitude of 30%, while more optimistic studies are indicating reductions of up to 90% behind the paver (Croteau and Tessier 2008). 

In the paving aspect, compaction and transportation are facilitated, the paving season is extended into the winter/cold months, WMA facilitates higher rates of reclaimed asphalt (or RAP) in recycling, the usage of WMA allows quick return of traffic and multiple lifts with WMA can be overlaid sooner (Croteau and Tessier 2008). 

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Figure 5.8 Classification by temperature range (temperature and fuel usage are approximations). (From D Angelo J. et al., Warm-Mix Asphalt European Practice. Technical Report FHWA-PL-08-007. Washington. DC FHWA, Office of International Programs, Department of Transportation, 2008.)...

Source NCHRP Report 69 i. Mix design practices fi>r Warm Mix Asphalt. Washington, DC Transportation Research Board, 20 i i. 

Anderson R.M. and R. May. 2008. Engineering Properties, Emission and Field Performances of Warm Mix Asphalts. Interim Report, NCHRP 9-47. Lexington, KY Asphalt Institute. 

Austerman A.J., WS. Mogawei and R. Bonaquist. 2009. Investigation of the influence of warm mix asphalt additive dose on the workability, cracking susceptihility, and moisture susceptihility of asphalt mixtures containing reclaimed asphalt pavement. Proceedings of 54th Annual Conference of the Canadian Technical Asphalt Association. Laval, Quebec, Canada Polyscience Publications Inc. 

Croteau J.M. and B. Tessier. 2008. Warm mix asphalt paving technologies A road builder s perspective. Proceedings of 2008 Annual Conference of the Transportation Association of Canada. Laval, Quebec, Canada Polyscience Publications Inc. 

Diefenderfer S.D. and A.J. Hearton. 2010. Performance of Virginia s Warm-Mix Asphalt Trial Section. 

EAPA. 2010. The Use of Warm Mix Asphalt. Position paper. Brussels, Belgium European Asphalt Pavement Association. 

NAPA. 2011. Warm-Mix Asphalt Best Practices, 3rd Edition. Lanham, MD National Asphalt Pavement Association. 

Prowell B.D. 2007. Warm Mix Asphalt - The International Technology Scanning Program-Summary Report. Washington, DC FHWA, U.S. Department of Transportation. 

When recycling is predominant, the hot aggregate, fines and reclaimed asphalt pass through the double-barrel and mixing takes place in a twin-shaft pugmill or rotary mixer. Hence, the double-barrel dryer/mixer is called double RAP dryer (ASTEC Industries Inc. 2014). With the addition of the Green Pac, an option offered by the same company, the double RAP dryer produces warm mix asphalt. 

Hansen K.R. and A. Copeland. 2013. Annual Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage 2009-2012. Information Series 138. Lanham, MD NAPA. 

Several PG asphalt binders were used in combination with nonfoaming warm mix asphalt additives, i.e., Cecabase , Evotherm , Rediset , and Sasobit . 

CN-01 Use Warm Mix Asphalt (WMA) in place of Hot Mix Asphalt CN-02 Recycle and Reuse Construction and Demolition Materials CN-03 Implement a Construction Vehicle Idling Plan CN-04 Specify Low-emission Construction Vehicles and Equipment CN-05 Specify Energy Efficienf Temporary Lighting During Constmction... 

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