By Dwight Walker, P.E.
This is the second in a series of articles on warm mix asphalt (WMA). The first article, published in the Spring issue of Asphalt magazine, gave an overview of WMA. This article provides more details on some of the technologies, as described by the suppliers.
The WMA products and processes included in this article are listed for information only. The Asphalt Institute does not endorse any particular proprietary product or technology. There may be additional WMA technologies available.
To view the first article in this series click here.
Akzo Nobel Rediset™ WMX
Rediset WMX is a WMA system with additives made to reduce mixing and paving temperatures and provide moisture resistance properties. The Rediset system enables the production of hot mix at up to 60°F (33°C) lower temperature versus normal hot mix. This can reduce fuel consumption by at least 20 percent and lower CO2 emissions. The lower temperature during mixing and paving also reduces smoke and fumes from the mix.
Rediset comes in a free-flowing, pellet form. It is added to the asphalt binder prior to mixing or directly to the mixing unit. The mixing plant does not have to be modified. Rediset is added at the rate of 1.5 to 2 percent of the binder. It does not require modification of the mix design and does not change the PG grading of the asphalt binder.
Rediset improves the cohesive strength of the asphalt and reduces rutting and moisture sensitivity of the mix and in the final pavement. The underwater Hamburg Wheel Tracking test shows that Rediset will improve the pavement cohesive strength on par with or better than lime or cement.
Astec Double Barrel Green®
Astec, Inc. launched the Double Barrel Green System in June of 2007 as an option that can be included with any new Astec Double Barrel drum mixer/dryer or added as a retrofit. The system uses water to produce foamed warm mix asphalt by injecting it into the mix along with the liquid asphalt cement. The injection of water causes the liquid asphalt to foam and expand in volume. The foaming action helps the liquid asphalt coat the aggregate at a lower temperature.
The benefits of the Double Barrel Green system include:
- No smoke and no smell because the light oils in liquid asphalt never reach the boiling point.
- The ability to run high percentages of recycle mix with a standard grade of asphalt.
- Approximately 14 percent less fuel is used corresponding to a 14 percent increase in production (greater temperature reduction results in bigger fuel savings).
Astec has introduced the Green Pac™ warm mix system, which can be retrofitted to continuous mix and batch plants from any manufacturer. By offering the Green Pac System, Astec expands the benefits of its Double Barrel Green warm mix system to any asphalt plant owner or operator.
Maxam AQUABlack™ Solutions Warm Mix System
Maxam’s AQUABlack Solutions warm mix system is designed a plug-in system. The completely assembled AQUABlack foaming unit can be installed in an existing A/C line. It then connects the self-contained high pressure water metering system to a water supply and runs power to the control to produce warm mix asphalt. This system’s key is to form and entrain micro-bubbles that are retained throughout the mixing process.
Maxam has also refined its AQUABlack Solutions foaming gun. The design of the stainless steel construction foaming gun forms, mixes and entrains micro-bubbles in the asphalt binder via a series of high pressure jets, a compression nozzle and a static mixing chamber. The foaming gun forms and entrains micro-bubbles in the binder, modifying the binder’s physical characteristics until compaction during the rolling process. The gun is a highly machined assembly with no moving parts to wear and the only removable parts are the stainless steel jets, which are easily removed from outside the insulated, stainless steel housing.
Additional features include all steel heated enclosure for the pumping system, water tank and valving for accurate metering, automatic air purge for freeze protection and fully automatic PLC-based, touch-screen control. A Maxam AQUABlack System retrofits onto any plant. Users can run more RAP, reduce fuel consumption, improve worker safety, use no chemicals, reduce emissions, produce longer hauls and increase equipment life.
MeadWestvaco (MWV) Evotherm warm mix technology is a next generation paving solution that introduces the potential to reduce carbon emissions associated with asphalt paving. Evotherm’s technology enables asphalt mixes to be produced at temperatures more than 100°F lower than traditional hot mix asphalt applications.
The substantially lower production temperatures provide numerous benefits:
- 60 percent reduction of greenhouse gas emissions
- Up to 75 percent reduction in photochemical smog emissions
- Nearly 80 percent drop in sulfur dioxide
- 55 percent documented energy savings during the production and application of WMA
- Improved worker safety due to the handling of cooler temperature materials
- Streets and roadways are reopened quickly due to cooler final service temperatures after placement and compaction of the asphalt is complete
- Performance and durability greater than or equal to traditional hot mix asphalt.
Evotherm is a chemical additive that is injected at the mixing plant or at the asphalt terminal. Paving with Evotherm can increase RAP utilization, haul distances, paving seasons and pavement service life. Evotherm performance has been proven in over 300 projects in over 25 states, as well as in France, Spain, Canada, Mexico, South Africa, and China. Since 2005, Evotherm has also withstood rigorous accelerated testing at the NCAT test track.
PQ Corporation Advera WMA
Advera WMA is a warm mix asphalt technology first introduced in Europe over 10 years ago. The synthetic zeolite technology produces a sustained, time-release foaming of the asphalt binder at a true warm mix asphalt production temperature, 250°F, without modifying the PG grade of the binder.
Advera WMA contains 20 percent moisture, which is structurally and chemically bound in the zeolite. The zeolite releases this moisture over a sustained period of time from the 4 Angstrom pore causing micro-foaming. This small amount of micro-foam (0.05 percent water by the weight of mix) gives long lasting workability until the temperature drops below 212°F. This wider paving window allows for long hauls, cold weather paving, and the ability to pave over crack sealant successfully.
Advera WMA has been tested with dense and open graded mixes, in base and wearing courses throughout the USA and Canada. It can be used with any HMA plant, batch or drum. Advera WMA is introduced into the plant using a feeder, with minor modification to the plant — the addition of a port near the asphalt line in a drum plant and into the pug mill in a batch plant. One dosage level, 0.25 percent of the weight of the asphalt mix (5 pounds per ton) is used for all mixes.
Sasobit is a long-chain aliphatic hydrocarbon that is produced by Sasol Wax in South Africa using the Fischer-Tropsch process. It is completely soluble in asphalt at temperatures greater than 240°F (115°C). It forms a homogenous solution with the base asphalt upon stirring and produces a marked reduction in the asphalt’s viscosity. This enables mixing and handling temperatures to be reduced by 20 to 55°F (10 to 30°C). During cooling, Sasobit crystallizes and forms a lattice structure in the asphalt increasing the asphalt stability.
Sasobit can be blended into hot asphalt at the mixing plant using a simple stirring device. A high-shear mixer is not required. The blended asphalt is stable and does not separate. Sasobit can be used with polymer-modified asphalts. The reduced viscosity provided by adding Sasobit improves the workability and compaction of modified binders.
Hamburg Wheel Tracking tests have shown that Sasobit-modified binders display increased rutting resistance. Sasobit does not significantly affect the low temperature behavior of asphalts. The low temperature properties are determined by the base asphalt.
Suit-Kote Low Emission Asphalt
Low Emission Asphalt (LEA) is a warm mix technology that has been used in dozens of projects across New York State since 2006. It is based on the Low Energy Process developed in France and relies on a chemical additive and sequential mixing to yield a 35 to 50 percent reduction in energy consumption over HMA. LEA also reduces greenhouse gas emissions, uses existing HMA mix designs, improves working conditions, and minimizes plant modifications.
The liquid chemical additive rate is approximately 0.5 percent of asphalt binder content and aids in workability, adhesion, and aggregate coating. The production sequence is modified so that the additive is combined with the asphalt prior to coating hot coarse aggregates. Wet sand is then introduced, which creates a foaming action. The wet sand fraction, which could be as high as 40 percent of the total mixture and could contain 0 to 100 percent reclaimed asphalt pavement (RAP), is unheated in this process. The final produced mix temperature is around 210°F and can be paved at temperatures as low as 170.
LEA production is compatible with both drum and batch plants, but it does require that the plant have a RAP system for delivery of the up to 40 percent unheated fraction. A mobile trailer contains the necessary equipment to enable production of LEA.
Additional information on warm mix asphalt is being developed as more experience is gained. The website www.warmmix.org is a very good source of information.
We’ve included a chart so readers can easily find more information on each process.
WMA Suppliers Chart
|Advanced Concepts Engineering Co. LEA-CO
|Akzo Nobel Rediset WMX
|Arkema Group CECABASE RT
|Astec Industries Double Barrel Green
|Gencor Industries Green Machine
|Maxam Equipment Inc. AQUABlack Solutions
|MeadWestvaco Asphalt Innovations Evotherm
|PQ Corporation Advera WMA
|Sasol Wax Americas, Inc. Sasobit
|Suit-Kote Low Emission Asphalt
|Terex Roadbuilding Warm Mix Asphalt System