Warm Mix Asphalt Pavement Design

Submitted by:Janmejaya BarikRoll no- 12010008Branch- Civil

OVERVIEW Introduction What is Warm mix asphalt? Mechanisms involved in temperature reduction Laboratory design of warm asphalt mixes Mechanical performance of warm asphalt mixes Guidance on mixing, laying and compaction of warm asphalt m

ixes Benefits and drawbacks of WMA Comparison between life-cycle cost analysis of WMA and HMA conclusions

INTRODUCTION Over the last two decades, the production and appliance of asphalt mixtures have been improving, particularly to achieve economic and environmental objectives. Recently, the improvement has paid more attention to the reduction of energy consumption throughout the process, without changing the in-service mechanical performance of these asphalt mixtures. There is a growing international pressure on the reduction of fossil fuels consumption and the emission of greenhouse effect gases (GHG), such as CO2 (carbon dioxide). If a significant temperature decrease could be achieved within the production practice of asphalt mixtures, while the workability of the material is adequate and mechanical performance attained is the same as or even better than HMA, the gain for the environment and the society in general would be significant.

What is warm mix asphalt?

Hot Mix Asphalt (HMA) is a result of drying and heating mineral aggregates, and bitumen at temperatures above 140oC.

If a significant temperature decrease could be achieved within the production practice of asphalt mixtures, while the workability of the material is adequate and mechanical performance attained is the same as or even better than HMA, the gain for the environment and the society in general would be significant.

From this concept Warm Mix Asphalt (WMA) developed which require lower production temperature.

Mechanisms Involved in Temperature Reduction

Organic additives Chemical additives Foamed bitumen technologies

ORGANIC ADDITIVES Addition of an organic wax to bitumen or blending to asphalt

concrete mixtures, reducing the viscosity of the binder.

When the asphalt cools, the additive crystallizes forming a lattice structure of microscopic particles. 

Sasobit- produced from natural gas using the Fisher–Tropsch(FT) process

Asphaltan-B- blend of wax obtained by solvent extraction from lignite or brown coal (Montan wax) and fatty-acid amides

Thiopave™- a technology that uses a Sulphur-enhanced additive.

CHEMICAL ADDITIVES Chemical additives may reduce the mix and compaction temperatures

around 30oC

Aggregates are heated before mixing, the water within the emulsion vaporizes during the production process and the binder covers the aggregate particles

Package of products such as surfactants, emulsification agents, aggregate coating enhancers and anti-stripping additives

Rediset™ WMX and Cecabase RT- surfactant and adhesion agents

Evotherm™ - emulsification agent

FOAMED BITUMEN TECHNOLOGIES Bitumen foam is generally obtained by adding a small amount of

cold pulverized water into preheated bitumen

Foamed bitumen is obtained mixed together with aggregate at an ambient temperature or previously heated at a moderate temperature (under 100oC)

Subcategorised - water based & water containing

Water mixing technologies- -Low Energy Asphalt (LEA)

-Warm Asphalt Mixes foam (WAM-foam™ )

Laboratory design of warm asphalt mixes

Superpave (AASHTO R 35) -in the USA

Marshall method (EN 12697-34:2004 + A1 and EN 13108-1:2006), among other European methods, such as the French one - in Europe

Based on gyratory compaction

Foaming plant - Wirtgen WLB10

Recommended amount of some available WMA additives

Additive Addition rate range

Typical addition rate

Organic additives:Astec PER 0.5–0.75% by total

weight of RAP (only for high levels of RAP)

__

Asphaltan-B 2–4% by weight of the total binder

2.5% by weight of binder

Sasobit 0.8–4% by weight of the total binder

1.5% by weight of the total binder

SonneWarmix™ 0.5–1.5% by weight of the total binder

0.75% – maximum recommended for unmodified, virgin mixes

Chemical additives:Cecabase RT 0.3–0.5% by weight of

binder __

Rediset™ WMX 1.5–2.5% by weight of binder

__

Evotherm™ About 5% of diluted chemical package by weight of binder

__

Mechanical performance of warm asphalt mixes

Vary in a large range depending on the specific WMA technique applied as well as the type of material fabricated

Temperature and loading characteristics plays significant influence on performance

Affected properties : -Water sensitivity -Stiffness modulus -Resistance to fatigue -Resistance to low temperature fracture -Resistance to permanent deformation

Water Sensitivity Water sensitivity or water damage - suffering a

substantial reduction of resistance of some asphalt mixtures over the years in the presence of water

Causes rutting and/or cracking development. Failure of the binder aggregate interface and/or the cohesion

within the binder–filler mastic Moisture left behind during the construction process can also

increase the water susceptibility of asphalt mixtures. Surfactants - bridge between the asphalt binder and the

aggregate surface, promoting adhesion and resisting the action of water

Non-limestone fine aggregates, by adding 2% of hydrated lime powder as anti-striping agent.

BY increasing slightly the production temperature

Stiffness modulus

Stiffness (stress/strain ratio) decreases as manufacturing temperature decreases as coating of coarse aggregates particles and bonds between them improve

Stiffness modulus depends on the type of additive, compaction method and temperature

WMA mixes had higher stiffness moduli than HMA

Crystallisation due to wax additives can ensure good stiffness values for WMA dense-graded asphalt

Mixes with wax additives had consistently higher modulus values than the other types of WMA

Resistance to fatigue

Fatigue tests induces continuous damage on the specimen until failure occurs

WMA usually suffer more fatigue damage at lower strain levels than HMA

So, WMA preferred in heavy duty pavements

For Sasobit WMA mixes fatigue performance decreases 22% as compared to HMA

Resistance to low temperature fracture

Very important in very cold climates

In WMA the bonding at the interface binder-coated aggregate is still in doubt at low in-service temperature

Differential thermal contraction within asphalt mixes at very low temperatures thermal cracking micro-cracks development

WMA with wax additives or Evotherm™ at 200C exhibit similar or better performance than the HMA

Resistance to permanent deformation

Essential in hot climates

Mixture resistance to permanent deformation decreases as production temperature decreases

At high temperature(around 50 or 600C), the rut depth induced on the material increases as the number of wheel passes raises

WMA with wax additives (Sasobit) has a improved resistance to rutting at higher in-service temperature

Guidance on mixing, laying and compaction of warm asphalt mixes

Products added in form of pellets or pastilles are preferably added by means of a pneumatic feeder

In batch plants additives are introduced directly into the mixer

Thiopave™: conveyor belt system used directly feeding the mixing drum or the pug mill

Liquid additives: injected from a heated container into the plant’s binder line by means of a dosing pump, or pre-blended into the binder

Zeolite(powdered): added by means of a com- pressed air system. In drum plants

Benefits of WMA

POLLUTANTS REDUCTION IN PERCENTAGE

CO2(carbon dioxide) 30–40% SO2(sulfur dioxide) 30–40% VOC (volatile organic compounds) 50%CO (carbon monoxide) 10–30%NOx (nitrous oxides) 60–70%dust 25–55% for asphalt aerosols/fumes 30% to 50%polycyclic aromatic hydrocarbons (PAHs)

30% to 50%

Significant reduction on pollutant and GHG emissions

Doesn’t need curing time before opening up to traffic and does not require a sealing layer

As operating temperature and emissions are lower, easier for plants to be allowed in the proximity of urban areas

Viscosity of the stiff binder decreases and the drop of temperature with time is less allows higher haulage distances reduces the risk of compaction troubles requires less time to cool the laid Better workability

Reduction of the energy consumption up to 35%

Drawbacks of wma

High initial production cost

Carbon emissions related to the production of additives may be higher

On long-term performance may face some struggle

In-service moisture susceptibility of WMA is sometimes higher

Comparison between life-cycle cost analysis of WMA and HMA

production of raw

materials, constructio

nmaintenan

ce and repair

demolition

Except WMA additives, constituent materials is approximately the same for WMA and HMA

Emissions associated with additives can balance the general reduction of by-product

Temperature reduction in WMA leads to significant decreasing on fuel consumption and CO2 emissions

Maintenance and repair would be more or less the same in both cases

Deposit or recycling for both types of technology is also same

conclusions WMA have a significant number of advantages comparing to HMA, basically associated with energy saving which lead to a major reduction of GHG emissions and pollutants. Laying and compaction operations are generally improved, as workability of WMA is adequate and the release of fumes and odours for workers is much lower.

But operation and maintenance of plants used for WMA production require additional care.

Even though some drawbacks have also been pointed out, benefits of WMA in a whole seem to surmount their drawbacks.

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2008. p.131–45. [2] EAPA. The use of warm mix asphalt – EAPA position paper. Brussels: EuropeanAsphalt Pavement

Association; 2010. [3] Zaumanis M. Warm mix asphalt investigation. Master of science thesis. Kgs.Lyngby:

Technical University of Denmark in cooperation with the Danish Road Institute, Department of Civil Engineering; 2010.

[4] Button J, Estakhri C, Wimsatt A. A synthesis of warm-mix asphalt. Report FHWA/TX-07/0-5597-1. Texas: Texas Transportation Institute; 2007.

[5] D’Angelo J, Harm E, Bartoszek J, Baumgardner G, Corrigan M, Cowsert J, et al. Warm-mix asphalt: European practice. FHWA, AASHTO, NCHRP. Report no. FHWA PL-08-007, Alexandria; 2008.

[6] Jullien A, Baudru Y, Tamagny P, Olard, F, Zavan, D. A comparison of environmental impacts of hot and warm mix asphalt. Routes roads 350. PIARC (World Road Association); 2011. p. 81–5.

[7] Prowell B, Hurley G, Frank B. Warm-mix asphalt: best practices. Lanham (MD): NAPA – National Asphalt Pavement Association; 2011

[8] Hurley G, Prowell B. Evaluation of Sasobit for use in warm mix asphalt. NCAT report 05-06. Auburn: Auburn University; 2005.

[9] Xiao F, Amirkhanian S. Effects of liquid antistrip additives on rheology and moisture susceptibility of water bearing warm mixtures. Constr Build Mater 2010;24:1649–55.

[10] Kim Y, Zhang J, Ban H. Moisture damage characterization of warm-mix asphalt mixtures based on laboratory-field evaluation. Constr Build Mater 2012;31:204–11.

[11] Kavussi A, Hashemian L. Properties of wma-foam mixes based on major mechanical tests. J Civ Eng Manage 2011;17(2):207–16.

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