Warm Mix Demonstration Projects in the U.S. as of Jan. 2007

Warm Mix Demos

AAPA 2010 Study Tour Warm Mix Asphalt

Warm Mix Demonstration Projects in the U.S.

Warm Mix Demos

AAPA 2010 Study Tour Warm Mix Asphalt

US Experience - ImplementationInitial client desires were that WMA provides equal or better performance compared to hotmixThe various states have approached implementation differentlycollaborative trials permissive specifications lengthy approval processes with laboratory and field evaluationlist of approved technologies/productsmaximum production temperatures (non-attainment areas, over crack sealing, etc)

AAPA 2010 Study Tour Warm Mix Asphalt

US Experience - WMADense graded asphaltOpen graded asphaltStone mastic asphaltCrumbed rubber asphaltConventional bitumens and polymer modified binders

AAPA 2010 Study Tour Warm Mix Asphalt

US Experience - ConcernsRuttingStrength issuesStrippingWater injection technologies in freeze climates (ravelling)Production issues ensuring the aggregate is dryPlant addition of WMA additives vs terminal blending

AAPA 2010 Study Tour Warm Mix Asphalt

US Experience WMA Mix DesignsMix designs are generally the hotmix design with the warm mix technology appliedSome minor allowance is made to WMA containing Advera and Asphamin as these become an inert filler (once the water is remove)Lower voids of a WMA mix design compared to the hotmix design (but binder content isnt adjusted)

AAPA 2010 Study Tour Warm Mix Asphalt

Warm MixHot Mix

AAPA 2010 Study Tour Warm Mix Asphalt

Questions?

*Nominal 20% fuel savingsNominal 20% reduction in CO2 emissionsNote general indication only as some WMA technologies do not reduce emissions (e.g. some surfactants)Initially, the benefits were viewed to only favour the contractor. This perception has changed as the client (DoTs) have realised greater durability and consistency of end product (especially compaction) i.e. improved pavement constructability.Some of the WMA technologies may not result in reduced emissions e.g. some of the chemical additives.

Growth in free water systems due to lower variable cost.Free water systems do not allow as great a temperature reduction as some of the chemical additives and rheological modifiers. Also, with free water systems there is a maximum production temperature (nominal 140C) to ensure that the water doesnt boil out, and, a minimum paving/compaction temperature (nominal 100C) to ensure that the steam bubbles dont collapse and lose the warm mix attributes. It was recommended that free water systems not be used in cold/freeze affected climatic zones although it is the dominant technology in Virginia.Niche applications of some systems in non-attainment areas and over crack sealing products.Indications were that WMA have a cost premium of @ $3-$5/t over hotmix.Astec Green, zeolite, Sasobit, ?, Evotherm 3G and Rediset WMX3 technologies Asphamin, Evotherm and Sasobit.Rutting via HVS and Hamburg Wheel Tracker early indications are that twice the degree of rutting is predicted in the laboratory but it is not being experienced in the field.Fatigue via 4 point bending beam WMA has a greater initial fatigue life.Moisture sensitivity is a grey area with some WMA reporting low values i.e. 50-70%. The specifications vary considerably, ranging from minimum values of 70% to 80% and some requiring a conditioning step i.e. 150C for 4 hours. Some states have a mandatory inclusion of hydrated lime and others require the use of an adhesion agent to comply with their local TSR requirements. It was indicated that WMA achieves a comparable stiffness to hot mix after 2 years in performance.*Collaborative trialsCalifornia CALTRANS still wants the performance of WMA to be equivalent or better than hotmix. They assess the WMA technology under the HVS (Heavy Vehicle Simulator) and subject to the results, include the technology/product on an approved list e.g. currently only Advera is approved. Contractor approval process includes undertaking a lab evaluation (rutting, moisture sensitivity and cracking) using relevant state test methods and three placement trials with 12 months monitoring (generally only by photos). California has the most stringent requirements for WMA and are slow on the up take i.e. being cautious.Texas requires laboratory rutting and stripping (Hamburg Wheel Tracker) and field trials (three with at least one in Texas). The WMA technology must be on the approved list currently includes all foam processes, Advera, Asphamin, Evotherm, Rediset WMX and Sasobit. A permissive specification exists, but a mandatory maximum temperature in non-attainment areas. Some local areas/counties have preferences, but this is mainly due to the push by the technology provider in such areas.Virginia approves the contractor to use the technology and uses a permissive specification.North Carolina has a list of approved technologies based on the use of the technology within the USA i.e. it doesnt have to have been used in the state. A collaborative approach existed and was described as being an appropriate mechanism to assess, introduce and monitor trials which were undertaken on secondary i.e. low traffic roads (e.g.