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WMA Technologies and Production Principles

My WMA publications


Zaumanis. Warm Mix Asphalt., K. Gopalakrishnan et al. (eds.), Climate Change, Energy, Sustainability and Pavements, Green Energy and Technology, Springer-Verlag, (2014), DOI: 10.1007/978-3-662-44719-2_10

Zaumanis, Martins, and Juris Smirnovs. 
Analysis of Possibilities for Use of Warm Mix Asphalt in Latvia.” 
In Civil Engineering. International Scientific Conference. Proceedings. Vol. 3. Jelgava, Latvia, 2011.
Laboratory Evaluation of Organic and Chemical Warm Mix Asphalt Technologies for SMA Asphalt.” 
The Baltic Journal of Road and Bridge Engineering 7, no. 3 (2012): 191–197. doi:10.3846/bjrbe.2012.26.
“Laboratory Evaluation of Warm Mix Asphalt Properties.”
5th International Conference “Bituminous Mixtures and Pavements.” Thessaloniki, Greece, 2011.
Development of Calculation Tool for Assessing the Energy Demand of Warm Mix Asphalt.”
Procedia - Social and Behavioral Sciences 48 (January 2012): 163–172. doi:10.1016/j.sbspro.2012.06.997.
“Laboratory Testing of Organic and Chemical Warm Mix Asphalt Technologies.” 
St. Louis, MO, USA: National Asphalt Pavement Association, 2011

My book:                                          My Masters thesis:  







Aquablack WMA

MAXAM Equipment

Water injecting nozzle

Not necessary

Double Barrel Green


Water injecting nozzle

Adhesion additive recommended

Low Emission Asphalt (Low Energy Asphalt outside US)

McConnaughay Technologies & LEACO

Hot coarse aggregate mixed with wet sand

Adhesion additive required

Ultrafoam GX

Gencor Industries

Water injecting nozzle

Adhesion additive recommended


Shell and Kolo-Veidekke

Foaming process using two binder grades

Adhesion additive recommended

Warm Mix Asphalt System

Terex Roadbuilding

Water injecting nozzle

Adhesion additive recommended



Water injecting nozzle

Adhesion additive recommended

LT Asphalt


Binder foaming + hygrophilic filler

0.5-1.0% of hygroscopic filler by mixture weight


PQ Corporation

Synthetic zeolite

0.25% by mixture weight



Synthetic zeolite

0.3% by mixture  weight








Fischer-Tropsch wax

2.5-3.0% of bitumen weight in Germany

1-1.5% of bitumen weight in US (Drüschner, 2009; D'Angelo, u.c., February 2008)



Paraffinic hydrocarbon blend

0.5-1.5% by weight of binder (Prowell, et al., 2012)

Asphaltan A

Romonta N

Romonta GmbH

Montan wax for mastic asphalt

1.5-2.0% of bitumen weight (Damm, u.c., 2003)

Asphaltan B

Romonta GmbH

Rafined Montan wax with fatty acide amide for rolled asphalt

2-4% by mixture weight (Chowdhury, u.c., December 2008)

2.5%by mixture weight (D'Angelo, u.c., February 2008)

Licomont BS 100


Fatty acid amide

3% of bitumen weight (Drüschner, 2009)



Sulfur and organic compound

25% binder replacement

BituTech PER

Engineered Additives

Plant extracts

0.5-0.75% of RAP+RAS mass

3E LT or Ecoflex



Yes, not specified






Rediset LQ

Akzo Nobel

Catonic surface active agents

0.4-0.75% of binder mass

Evotherm ET


Chemical bitumen emulsion

Delivered in form of bitumen emulsion

Evotherm DAT


Chemical package plus water

0.4-0.7% of binder weigth

Evotherm 3G


Surface-active agents, waxes, processing aids, polymers

0.4-0.7% of bitumen weight


CECA Arkema group

Chemical package

0.2-0.4% by mixture weight

Rediset WMX

Akzo Nobel

Cationic surfactants and organic additive

1.5-2% of bitumen weight

Warm-Mix L

Star Asphalt

Amide based chemical package

0,5% of bitumen weightW

Three different WMA production technologies exist in the market: 

- Foaming techniques (which are divided into water-based and water containing);
- Organic or wax additives;
- Chemical additives.

The available products are listed on left and they use use at least one of these technologies, but some of them are combine benefits of several techniques. 

Foaming Technologies

Foaming technologies use small amounts of cold water injected into the hot binder or directly in the asphalt mixing chamber. This can be accomplished by using foaming nozzles, by adding zeolite, or by introducing a portion of wet aggregates (Zaumanis, 2010). The water rapidly evaporates and is encapsulated in the binder, producing large volume of foam which slowly collapses before the binder reverts to its original characteristics (Capitao, 2012). The foaming action in the binder temporally increases the volume of the binder and lowers its viscosity, which improves coating of aggregates and improves mix workability. In the foaming processes enough water must be added to cause foaming action, without adding too much to cause stripping. 

The optimum foaming water content is generally identified as the amount in percentage of the foamed asphalt content that would achieve the highest expansion ratio and longest half-life. A higher expansion ratio promises larger surface area to coat the aggregates and a longer half-life will provide lower viscosity for a longer period ensuring enough workability of the mixture (Ozturk and Kutay, 2012). Fu et al. (2010) showed that even a small change in the bitumen temperature or water content can significantly change the foaming parameters and concluded that better bitumen foaming parameters tend to promise higher mixture strength.

Several different methods of introducing water into the mixture have been used. Many producers offer some type of nozzle (or series of nozzles) as illustrated in Figure X.3 to inject a small amount of cold water into the asphalt binder stream. Most water injection systems add 1-2% water by weight of asphalt binder. The water creates steam which is encapsulated in the binder resulting in foaming and a large volume increase of the binder. This decreases the viscosity thus allowing it to coat the aggregates at lower temperatures (Perkins, 2009). The nozzles are computer controlled to adjust the foaming rate.

Double Barrel Green nozzle

Other popular way of foaming the binder is by adding finely powdered synthetic zeolite that has been hydro-thermally crystallized (Figure X.4). It contains about 20 percent water of crystallization which is released by increasing the temperature above 85°C. When the additive is introduced in the mixture at the same time as the binder, water is released as a fine mist, which foams the binder thus reducing the viscosity. Six to seven hours of increased workability due to controlled foaming has been reported (Chowdhury and Button, 2008; D’Angelo et al., 2008). Foaming additives are typically added at 0.25-0.30% by weight of mixture.

Advera zeolite

Production Technology

Foaming system WMA technology producers offer their own production kit that can be fitted to contractors’ plants. An example is illustrated in Figure X.6. The foaming nozzle must be installed in-line with the binder addition system. It must be supported by a water supply system (water pump, reservoir tank) and water metering system. A bitumen expansion chamber is required in most cases. The water addition processes can be controlled through a control unit from the plant operation center. Special attention should be given to maintain the ability to easily switch between the WMA and HMA production systems. The maintenance of the nozzles is another important issue as they may require special treatment and/or cleaning between the batches or after each production.

Warm Mix Asphalt System water tank with water pump (right)
and foam expansion chamber (left)

Zeolite additives in a batch plant can be added into the pugmill using a weight bucket or by blending in line with the binder. In a drum mix plant, they can be pneumatically fed into the drum via the RAP collar or using a specially built pneumatic feeder that introduces the additive in the binder line. The additive develops into a dispersed steam when it comes in contact with hot binder; therefore it must be introduced to the binder directly before addition of the aggregates.

Organic Additives

Above their melting point organic (wax) additives reduce the viscosity and increase the lubricity of binder. In the mixing process this allows coating of the aggregates at lower temperatures, as illustrated in Figure X.7. After the pavement has cooled and the additives crystallize, they tend to increase the stiffness of the binder and asphalt’s resistance against plastic deformation. The type of wax must be carefully selected to ensure that its melting point is higher than the expected in-service temperature and to minimize embrittlement of the asphalt mixture at low temperatures. A temperature reduction range of 10-30°C can be expected compared to HMA (Zaumanis, 2010).

Viscosity change of wax-modified binder

Sasobit is one of the most widely used organic additives. It is a Fischer-Tropsch (FT) wax in the form of white powder or granulate (Figure X.8). It is a long-chain aliphatic hydrocarbon wax with a melting range between 85°C and 115°C, high viscosity at lower temperatures, and low viscosity at higher temperatures. According to Drüschner (2009), with the addition of 3% Sasobit by binder mass, the binder softening point is decreased by 20-35°C and the penetration falls by 15-25 1/10mm. This accounts for the reported increased resistance to rutting of Sasobit-modified mixes (D’Angelo et al., 2008; Chowdhury and Button, 2008). In the U.S. the most common introduction of additive is at 1.5% by mass of binder. Some reports note slightly reduced low temperature cracking resistance when wax additives are used. Qin et al. (2014) report a 2.0 to 3.5°C increase in the limiting low temperature grade when Sasobit was used at a 1.5 to 3.0% dose. Other waxes have similar effects on binder as the described product.

Production Technology

Wax additives are usually delivered in granular form. They can be added to asphalt mixtures in several different ways. The most effective method for ensuring homogeneous mixing is pre-blending with bitumen at a refinery, a terminal, or an asphalt plant. However, in this case it must be ensured that the wax is stable and stays homogeneous in the binder storage tank. In another method, the wax additives can be heated in a separate tank and injected in a liquid state in-line with the binder addition. The granular form of the additives also allows direct addition of the additive into the asphalt mix using a pneumatic feeder, a weight hopper or an existing fiber addition system. However, in this case it must be ensured that the additive is homogeneously distributed and well blended with binder. To ensure this it may be necessary to extend mixing time (especially in batch plants).

Chemical Additives

Chemical additives are the third type of WMA technology that is commonly used. A variety of chemical packages are used for different products. They usually include a combination of emulsification agents, surface active agents, polymers and additives to improve coating, mixture workability, and compaction. These products generally improve the adhesion of binder and aggregates thus eliminating the need for additional adhesion additive. Most additives are designed to not change the grade of the binder. Chemical additives may reduce the asphalt mixing and production temperature by up to 30°C (EAPA, 2010; Capitao et al., 2012).

Rediset WMX granules

Production Technology

Chemical additives are most often provided in a liquid state and are readily soluble in asphalt binder. This results in relatively minor modifications to the asphalt plant. Additives can frequently be easily added to the binder using existing plant equipment, such as the liquid anti-strip additive in-line injection system. If no such equipment is available, a volumetric pump with a precise metering system can be installed. In some cases the additive may require heating to ensure flow. Liquid additives are mostly stable in the binder and can therefore be added at the binder terminal, or the storage tank at the asphalt plant. A stirring unit for bitumen is necessary if additive is introduced into the bitumen tank. In some cases the additive may be pre-blended by the producer and delivered in the form of bitumen emulsion. Some products can also be delivered in granular form (see Figure) and can be added similarly to waxes.