Warm Mix Asphalt - DAV

5/26/2018 Warm Mix Asphalt - DAV

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Warm mixasphalts

GUIDELINES

Tips and tricks developed by

professionals for professionals


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Warm mix asphaltsTips and tricks developed by professionals for professionals

Fundamentals ......................................................................................3Basic principles ........................................................................................3Glossary ..................................................................................................4Application..............................................................................................6

Basic Engineering Concepts ................................................................6

Materials ..............................................................................................7Binders and additives ..............................................................................7Viscosity modifying organic additives ......................................................8

Fischer-Tropsch-waxes ..........................................................................8Fatty acid amides ..............................................................................10Montan waxes ..................................................................................10

Viscosity modifying mineral additives ....................................................11Function of additives ............................................................................12

Viscosity modifying organic additives ................................................12Viscosity modifying mineral additives ................................................13

Asphalt mixtures ................................................................................14

General information ..............................................................................14Admixture of viscosity modifying organic additives ..............................17Admixture as ready-mix product ........................................................17Introducing additives into the mixing chamber ..................................17Inline blending of additives with bitumen ..........................................18Admixture in combination with stabilizing additives ..........................20

Admixture of viscosity modifying mineral additives ..............................21Storing and hauling the asphalt mix ......................................................22

Rolled asphalt ....................................................................................22

Mastic asphalt....................................................................................23Laying ..................................................................................................24Preparing the job site ............................................................................24Preparing the base ................................................................................24Laying of rolled asphalt..........................................................................25Laying of mastic asphalt ........................................................................27

Hand laying and floorings ..................................................................27Laying by paver..................................................................................28

Improving workability ............................................................................29Release to traffic....................................................................................30Site management ..................................................................................31

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Tests ....................................................................................................32General information ..............................................................................32Type testing ..........................................................................................32Factory production control ....................................................................36Compliance tests ..................................................................................37

Recommendations for specifications,

warranty claims and invoicing ..........................................................38Specifications ........................................................................................38

Warranty claims and invoicing ..............................................................39Asphalt recycling ................................................................................40

Procedures and experiences abroad ................................................41

Annex

References ..........................................................................................43

Additional information about the German Asphalt Paving

Association (DAV) and further DAV-Guidelines ..............................44

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Publisher:

Deutscher Asphaltverband e.V.(German Asphalt Paving Association.)Schieffelingsweg 653123 BonnGermanyFon +49 228 97965-0Fax +49 228 97965-11E-Mail [email protected] www.asphalt.de

Authors:

Dipl.-Ing. Richard Mansfeld, Hirschfeld (chairman)Dipl.-Ing. Rudolf Barth, LeipzigDipl.-Ing. Frank Beer, HamburgDipl.-Ing. Peter Breitbach, KrefeldDipl.-Ing. Daniel Gogolin, Bochum

Dr.-Ing. Friedrich Pass, BottropProf.Dr.-Ing. Martin Radenberg, BochumLabor-Ing. Gerhard Riebesehl, HamburgDipl.-Ing. Siegfried Sadzulewsky, DorstenHans Wlfle, Memmingen

Translation:

Nicolette QuigleyQuigley Translations, Heidelberg

Layout:

Elke Schlter communication agency, Alfter

April 2009, english translation July 2009


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Introduction

During hot mix asphalt laying bitumen emits fumes and ae-

rosols. Their concentration is determined by various

factors such as the temperature of the asphalt. The

higher the asphalt tempera-

ture, the higher the concentra-

tion of fumes and aerosols.

For occupational health and

safety reasons asphalt tem-

peratures should be kept as

low as possible during pro-duction and laying.

Reducing viscosity by ad-

ding organic and mineral

additives has proven to be an

easy and viable method to keep

asphalt temperatures below the stan-

dard temperatures. Aside from tempera-ture reductions, admixed additives can yield

even more benefits, such as improved workability,

higher deformation resistance, and the possibility to

open the road to traffic after a

shorter time period.

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2

Introduction

These methods were designed origi-

nally for mastic asphalt (gussasphalt)

floorings in buildings, because pro-

duction and laying temperatures reach

their highest values in this area. Since

these methods have so many advan-tages they were soon used for mastic

asphalt in road building and finally also

for rolled asphalt.

In 2006 the German Road and Transportation Research Asso-

ciation (FGSV) published Guidelines for Warm Mix Asphalt [1]

which describe various temperature reduction methods. The

FGSV Guidelines are under review while these guidelines are

being printed.

Based on these experience the guidelines in this brochure

explain temperature reduction methods for rolled

asphalt and mastic asphalt, highlight special aspects

that are important for practical applications and give

tips and tricks for asphalt mixture production and lay-

ing as well as for site management and testing.


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At the beginning of 2008 the german

committee for hazardous substances

(Ausschu fr Gefahrstoffe) which

reports to the Federal Minister of La-

bor and Social Affairs [2] cancelled

the suspension of the threshold valueof 10 mg/m for fume and aerosol

emissions released from bitumen in

hot mixes produced for mastic

asphalt applications. Since then mas-

tic asphalts may only be produced,

supplied and laid at reduced tempe-

ratures below 230 C. This method

only works safely when adding vis-

cosity modifying additives.

Mastic asphalt types addressed in

these guidelines have an upper tem-

perature limit of 230 C. These types

are used as wearing courses in road

building as specified in TL-Asphalt

StB 07 and ZTV Asphalt StB 07, as a

waterproofing layer for bridge decks,

and as interior flooring material.

Benefits when using warm mix asphalts:

Bitumen releases less fumes and aero-sols during hot mix processing

Based on a rough estimate a 10 degree tem-perature decrease leads to a 50% emissionreduction.

Energy savings and CO2 emissionreductions

A temperature reduction of 30 degreesyields savings of 9 kWh of energy per ton ofasphalt mix produced. This corresponds to0.9 liters of heating oil per ton of asphaltmix. Accordingly, CO2 emissions also drop.

Basic principles

1

Fundamentals

3


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CO2-emissionCO2 mass that is emitted from a plantbased on one ton of produced asphalt

mix.

Water of crystallizationWater that is resident in a crystallinebody. Normally, one or more water mo-lecules are bonded to a substance mo-lecule. The water in zeolites, however, isnot part of the crystal lattice but resideson certain lattice sites. Water of crystal-

lization is only loosely bound and isdriven off by heat without changing thezeolite structure.

Temperature reductionProducing and laying asphalt mixes attemperatures lower than the referenceproduction temperatures for the asphaltmixture type.

Glossary

4

Fundamentals

Basic principles

Improved deformation resistanceAfter having added viscosity modifying or-ganic additives to reduce viscosity the defor-

mation resistance of asphalt improves inwarm to hot ambient temperatures.

Section can be opened to traffic at anearlier stage

Asphalts that are produced and laid with vis-cosity modifying organic additives and at re-duced temperatures are ready-for-use withina shorter period of time.

Compaction aidWhen using these asphalts at moderate orno temperature reductions their compacta-bility improves significantly. This is especiallyadvantageous when asphalts have to be laidby hand or during adverse weather conditi-ons. The targeted degree of compaction canbe achieved without fail and it is easier to laythin layers.

Reduced susceptibility to aging of thebinder

Lower production and laying temperaturesreduce thermal aging of the binder.


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5

Viscosity modifying mineraladditivesMinerals (e.g. zeolite) containing physi-

cally or chemically bound water (e.g.water of crystallization) which are addedto the asphalt mix during production toreduce mixing and laying temperatures.

Viscosity modifying organicadditivesSubstances that change the rheologicalproperties of the binder in such a way

that mixing and laying temperatures canbe reduced.

Viscosity modifying bindersBinders whose rheological properties arechanged by adding appropriate additivesin such a way that mixing and layingtemperatures can be reduced. Ready-for-use viscosity modifying binders arealso described as ready-mix products.

Zeolites

Crystalline alkali silicate or alkaline-earth

silicates containing water of crystalliza-tion that is consistently driven off byheat without changing the crystal struc-ture. The silicates absorb other com-pounds instead of the released waterand can also be used as ion exchangers.


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Basically all asphalt types and grades canbe produced and laid at a reduced tem-perature and with modified viscosity.

Using warm mix asphalt is essential forthe following situations:

The specifications for asphalt mix de-sign, base, and the asphalt layers setforth in the bulletins TL Asphalt-StB and

ZTV Asphalt-StB also apply for warm mixasphalts. All these rules and regulationsalso apply for asphalt laying at reducedtemperatures, excluding the sections go-verning binders and asphalt-mix tempe-ratures.

6

Fundamentals

Application

2

Basic engineeringconcepts

Mastic asphalt

Construction sites

that can be

closed off onlyfor a short time

(airport runways,

construction

work at night)

Construction

sites under

adverse

weather conditions(e.g. off-season)

Traffic and industrialareas with special

high loads


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7

Binders and additives

3

Materials

Ready-to-use modified binders (ready-mix products) or additives of all sortsare supplied to produce warm mix/visco-

sity modified asphalts. There are viscositymodifying organic additives and viscositymodifying mineral additives.

The Federal Highway Research Institute(Bundesanstalt fr Straenwesen) archi-ved experiences that include all viscositymodifying binders (ready-mix products)and viscosity modifying additives that

delivered proof of performance. This ar-chive can be downloaded under theheading Lessons learned about theuse of ready-mix products and addi-

tives for warm mix asphalt [3] atwww.bast.de ( Special Subjects

Highway Construction Technolgy

Reduced-Temperature Asphalt De-

sign). (Remark: The archive itself is avai-lable only in german, see link at ref. [3])

The ready-mix products consist ofstraight bitumen or polymer modified bi-tumen in accordance with TL Bitumen-

StB and of viscosity modifying organicadditives which will be described in de-tail. Additives have to be distributed ho-mogeneously in the binder and shouldnot impair the storage ability of the bin-ders.

When handling suchready-mix products

users should consultthe information provi-ded by the manufac-turer in the relevantproduct informationsheets.


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8

Viscosity modifying

organic additives

Viscosity modifying organic additives are

either used to produce viscosity modifiedbinders or are added during the asphalt-mixing process.

Ready-mix products are produced inspecial mixing plants and then shippedready-for-use. This ensures a homoge-nous distribution of the additive in thebinder.

The viscosity modifying organic additivesused so far can be separated into threedifferent groups (Table 1).

Fischer-Tropsch waxes

Fischer-Tropsch paraffins are long-chain

aliphatic hydrocarbons which are produ-ced from syngas (carbon monoxide andhydrogen) under a high pressure cataly-tic process.

FT-molecules have a different chain-length than paraffins that are naturallyfound in mineral oil.

This explains why FT-paraffins have dif-ferent physical properties and why theycannot be compared with naturallyoccurring bituminous waxes.

FT-paraffins are completely soluble inbitumen at temperatures above 115 C.They form a homogeneous solution withbase bitumen on stirring and produce amarked reduction in the bitumensviscosity during its liquid state.

During cooling the FT-paraffins crystallizeand form crystallites in the bitumen.This, in turn, increases asphalt stabilityand its deformation resistance.

Materials


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9

*) Percentage by weight of binder

Appearance

Structure

Properties

Effect

in road

bitumen50/70

Fischer-Tropsch waxes Fatty acid amide Montan wax(amide wax)

white powder white powder brown powderor prills or prills or prills

Long-chain aliphatic Fatty acid Montanic-acidhydrocarbons diamide ester

Drop point [C] 114 to 120 140 to 145 110 to 140

Congealing point [C] 100 to 105 135 to 142 100 to 130

Dynamic

130 C 11 to 15 not measurable 20 to 200

viscosity 140 C 9 to 13 13 to 17 not determinedin mPas at

150 C 8 to 12 9 to 13 5 to 15

Additive [% by weight] 3,0* 3,0* 2,5 to 3,0*

Increase of R&B25 to 35 40 to 55

manufacturerssoftening point [C] information

Decrease of needle15 to 25 10 to 15

manufacturerspenetration [1/10 mm] information

Table 1 Identification of substances viscosity modifying additives

and their effect

(e.g. using road bitumen 50/70)

Substance

Name


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Fatty acid amides

Fatty acid amides are synthesized long-chain aliphatic hydrocarbons. Fatty acid

amide molecules have a different chain-length than paraffins naturally found inmineral oil.

This explains why fatty acid amides havedifferent physical properties and whythese amides cannot be compared with

naturally occur-ring bituminous

waxes.

Fatty acid amidesare completely

soluble in bitumen at temperatures above140 C. When stirring the mix they forma homogeneous solution with the basebitumen and produce a marked reduc-tion in the bitumens viscosity during itsliquid state.

During cooling the fatty acid amides cry-stallize and form crystallites in the bitu-men, thus increasing asphalt stabilityand its deformation resistance.

Montan waxes

Montan waxes and their derivativesare obtained during lignite processing

and consist of high-molecular hydro-carbons with a melting range from 110to 140 C.

This explains why Montan waxes havedifferent physical properties and whythey cannot be compared with naturallyoccurring bituminous waxes.

Above their melting range Montanwaxes are completely soluble in bitu-men. When stirring the mix they form ahomogeneous solution with the basebitumen and produce a marked reduc-tion in the bitumens viscosity during itsliquid state.

During cooling the Montan waxes cry-stallize and form crystallites in the bitu-men, thus increasing asphalt stabilityand its deformation resistance.

Montan waxes can be added directly tothe mixer which would require additio-nal mixing time or into the mobile stirrerfor mastic asphalt.

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Materials

H H HOI I I

H C C C CI I IH H H

H2


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Viscosity modifying

mineral additives

Natural and synthetic zeolites are used

as viscosity modifying mineral additi-ves. Zeolites are framework silicateswith a porous structure that canaccommodate and release foreignmolecules without changing their ownshape. They retain their shape andsize.

In chemical engineering they are used

as catalysts with a selective structure.Different pore sizes trigger differentreactions. Only A-type-zeolites with apore size from 2 to 5 (1 = 1010 m)are used in road building.

A-type-zeolites are only able to reactto water because their active centersare inside the structure, i. e. theyrelease and absorb water. This is whyzeolites are also called molecularsieves.

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Table 2 Identificationof substances

viscosity modifying

mineral additives

Name Zeolite

Appearance

Structure

Properties/effect

A-type-zeolites are sold as whitepowder or as powder with a yellowishdye.

Particle size distribution and densityare used as characteristic values.

Their particle size distribution provides

information as to how to handle andprocess zeolites.

Density provides information about theporosity of the structure.

Three-dimensional framework silicateswith highly porous structures, largevoids or channels.

Their pore size ranges from 2 to 5

(1 = 10-10

m).Zeolites retain their shape and size.

Zeolites can absorb foreign moleculesinto their structure and release themagain without changing their ownshape.

Zeolites do not react with their outersurface because all the active centers

are located inside the pores and voids. Water absorption and release are re-

versible and do not impact the alumi-nosilicate structure.

Natural and synthetic zeolites contain6 to 12 % and up to 25 % water, re-spectively.

This water is selectively released attemperatures from 70 to 220 C.

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12

Materials

Effect

Viscosity modifying

organic additives

Viscosity modifying organic additives

(either as ready-mix or as admixture foran asphalt mixing plant) reduce binderviscosity at high temperatures and thusallow lower mixing and laying tempera-tures. At asphalt temperatures below theadditives congealing point this reducedviscosity is offset again or the effect is

even reversed (see picture below), i.e.

the binder in the asphalt regains its ori-ginal stiffness or is even stiffer than acomparable, conventional binder. Thismeans that the binder now contributesmore to the deformation resistance ofthe asphalt.

V

iscosity

10 180

Temperature [C]

Modified

Basic correlation between temperature and

viscosity when using viscosity modifying

organic additives.

Laying and mixing

temperature range

Ambient temperature

range

Non-modified


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13

Viscosity modifying

mineral additives

Typically, natural and synthetic zeolites

are used as viscosity modifying mineraladditives. Natural zeolites have 6 to 12 %of their mass entrapped as water in theircrystalline structure and synthetic zeoli-tes up to 25 %. This corresponds to 1 to1.5 liters of water of crystallization perton of asphalt.

Zeolites are added to the mix with the

filler during mixing. As the mixing tem-perature increases the zeolites slowlyrelease their absorbed water into thebitumen which is dispersed throughoutthe mixture in the form of very fine dro-plets. This leads to a marked reductionof the workable viscosity of the bitumen.The asphalt mix produced with this

method can be laid even at lower tem-peratures without any problems.

As the asphalt and the binder cool off

the fine mist condenses. The bindersviscosity regains its original level and thebinder and the asphalt mix producedwith the binder regain their originalproperties.

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14

4

Asphalt mixtures

Warm mix asphalts can be produced innormal asphalt mixing plants. Functioningexhaust stacks at best even insulated

which ensure that exhaust temperaturesare above the dew point even during lowaggregate temperatures in the dryer drumare of essence for flawless productionprocesses.

Adjusting the speed of the dryer drummight be helpful to reach the right ag-gregate temperature. The burner output

and the dryer drum throughput have tobe matched with the drum speed.

Pre-heaters for fillers have proven towork well when producing masticasphalt because any asphalt mix tempe-

rature can be produced in an instantwhen cold and hot fillers are mixed.

Production temperatures and transpor-tation times should be planned in a waythat the reference temperatures forwarm mix asphalt behind the screed

specified in table 3 are kept.

General information


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1515

Empirical values for reduced mix tem-peratures for rolled asphalt when atransport vehicle with a normal canvascover leaves the mixing plant and takes30 minutes to reach the site are:

Outside temperature Reductionabove 20 C 15 to 30 degrees10 to 20 C 15 to 25 degreesbelow 10 C 0 to 15 degrees

The asphalt mixture temperature should not be reducedwhen temperatures are below 10 C or during strong winds.

70/100130 to 150 C Minimum 120 C50/70

30/45140 to 160 C Minimum 130 C25/55-55 A

10/40-65 A 150 to 170 C Minimum 140 C

30/45Minimum 200 C20/30 200 to 230 CMaximum 230 C25/55-55 A

10/40-65 A 210 to 230 C Minimum 210 CMaximum 230 C

Asphalt type

Rolled asphalt

Mastic asphalt

Table 3 Reference values for asphalt mix temperatureswhen producing warm mix asphalts

Type and grade Reference temperatures Reference temperatures

of binder for warm mix asphalt for warm mix asphaltat production behind screed


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16

Asphalt mixtures

Hopper doors might be difficult toopen upon start of production be-cause of lower temperatures.

It is vital to set up a precise schedulefor production, storage, transport andlaying.

The mixture should not be kept toolong in the silo.

Scope of possible temperature re-duction depends on the weather(outside temperature, precipitation,wind etc.) which has a strong impacton laying.

When setting the right temperature

for the mixture keep in mind whichasphalt mixture was produced inthe last batch (it takes more time to

reduce the mixing plant temperaturethan to increase it!) and/or whetherthe asphalt mixing plant has to beheated to the right production tem-perature.

Aggregates should be as dry as possi-ble to minimize water content in the

emissions. Make sure that all the aggregate

particles are entirely coated withbinder. If necessary, extend the mi-xing period or change the additionsequence of components.

For quality reasons you should notswitch to asphalt mixture types/gra-

des requiring standard productiontemperatures between mixing low-temperature batches.

The following guidance is given for asphalt mixtures produced

at reduced temperatures:


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17

Admixture of viscositymodifying organic additives

Admixture as

ready-mix product

Ready-mix products with viscosity modi-

fying organic additives are available onthe market for all sorts of different appli-cations. They can be easily processed instandard batch plants and are handledthe same way as standard road bitumen.It makes sense to lower storage tempe-ratures in the bitumen storage tank tomatch viscosity. If necessary the time setfor bitumen injection into the mixer has

to be monitored and/or adjusted. Youshould follow the manufacturers in-structions.

Ready-mix products must have storagestability.

It is absolutely necessary that only onespecific binder grade is charged into thetank. Even small amounts of other gradescan change binder properties.

Ready-mix products should be the firstchoice to ensure consistent quality. Whenno ready-mix is used the mix can be mo-dified at the asphalt mixing plant.

Introducing additives

into the mixing chamber

Fischer-Tropsch-waxes and fatty acid

amides have to be in a liquid state toensure homogeneous distribution in themix (mastix). This necessitates a changein the mixing sequence. A mastic has tobe produced with a minimum bindercontent higher than 15 % by weight be-fore blending in the additives and beforethe rest of the components are added.The fines and the filler components have

to be metered in such a way that thetotal binder amount in the mixed batchyields a mastic with a binder content ofat least 15 % by weight. Make sure thatthe mixing chamber has a filling rate ofat least 35 % and that the mixer outletis tight enough to prevent bitumenleakage. Remix for at least 15 secondsafter introducing the additive. Only thenare the remaining aggregates added tothe mixer and the mix is agitated foranother 15 seconds.

This modified production process increa-ses the overall batch production time to65 seconds. (The mix time does not haveto be extended when using ready-mix

products!)

Feeding additives into the mixer should

be more the exception than the rule!


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Inline blending

of additives

Additives can be blended with the bitumen

stream at the asphalt mixing plant by usinga melting system or an ejector for the in-troduction of solids into the bitumenstream.

After having passed through the meltingsystem the molten additives are fed directlyinto the bitumen weigh bucket. The hotbitumen and liquid wax are blended and

then pumped into the weigh hopper at theasphalt mixing plant, thus creating a visco-sity modified binder.

It is important to ensure that thedosage of the relatively small quantities of

additives is integrated into the processcontrol of asphalt mixture production. Thisleads to a high degree of accuracy andallows a modification of all conventionalbitumen grades and types.

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Asphalt mixtures


Simply incorporating the additives

instead of modifying the productionprocess as described above should beavoided, as extended mixing timescannot guarantee a perfect and ho-mogeneous dispersion in the batch.

The additives can be introduced directlyinto the mobile stirrer when producingmastic asphalt. All additives should be

added while the mobile stirrer is beingfilled. You will have to wait at least 60minutes before placing the mixture.

Melting system principle


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An ejector works like a water-jet pump.

The binder that is to be modified is pushedthrough a tapered section of the pipe.This creates a vacuum upstream of thetapered section. This vacuum can drawsolid and liquid additives into the binderstream and thus allows their homogene-ous distribution.

As the binder temperature is higher than

the melting point of the additives the ad-ditives will melt and dissolve in the liquidphase of the binder.

The system bypasses the conventional

binder feed to the scale. The admixture isadded to the mix by volume which is basedon the delivery rate of the binder and theadditive. Addition rates may range from2 to 12 % by mass of binder.

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Ejector

Existing

binder feedPump

PI PI

LS

FQ

FQ = ControlLS = Level sensorPI = Pressure indicatorM = Engine

M

Ejector system principle

to the mixer

Hopper

Prills

Bitumen

Screw conveyor


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20

Asphalt mixtures

It is not necessary to extend mixing

times for these two methods; the bitu-men storage capacity at the asphaltmixing plant is not affected either. It isalso very easy to produce small batches.

Admixture in combination

with stabilizing additives

Modified fiber pellets are another

option to introduce viscosity modifyingadditives into the mixer. Fiber pelletsconsisting of stabilizing additives (cellu-lose fibers) and viscosity modifyingadditives can be metered into the mixvia the feed systems for stabilizingadditives which are part of the asphaltplant.

When selecting fiber pellets and deter-mining their quantity it is important tomake sure that the amount of modifiedfiber pellets is carefully adjusted tomatch the binder content. This meansthat both the fibers and the wax mustbe proportioned accordingly. Mixingtimes are the same as recommended forregular stone mastic asphalt.



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21

Zeolites are introduced directly into the

mixer before the required binder quan-tity is added.

Zeolites come as a (synthetic) white or(natural) yellowish powder which can beused the same way as fillers.

In asphalt mix designs the amount ofzeolites introduced into the mix needs to

be accounted as filler .

An automatic feed system meters andfeeds the zeolites from the silo into theplant. This method also works with aportable silo.

Small quantities can be added manually.

The required amount comes in paperbags and is then added to the mixer.

Zeolites are introduced with the filler orafter the filler was added. The mix hasto be stirred at least for 5 seconds beforeadding the binder.

As with fibers, zeolites should be kept in

a weatherproof and dry storage area.

Admixture of viscositymodifying mineral additives


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Temporary silo storage is possible forall warm mix asphalt types.

For older silos keep in mind that tem-peratures will be lower at the disch-arge gates (gates may get sticky).

The mixture should not be kept in thesilo for an extended period of time.

Usually transport vehicles do not needa release coating.

Warm mix asphalt mixes should behauled as quickly as possible to thejob site.

Avoid journeys that take longer than60 minutes.

The production temperature shouldbe increased by 5 degrees if the in-terval between loading and unloa-ding exceeds 45 minutes.

Ensure that the mix is carefully andcompletely covered during transpor-

tation to avoid premature cooling ofthe asphalt mix, especially at theedges.

Remove the cover (tarpaulin) only im-mediately before unloading.

We recommended the use of insula-ted tipper bodies. Vehicles with ther-mal insulation ensure even greater

efficiency.

22

The following rule of thumb

applies:

Short journey =lower asphalt mix

temperature

Long journey =

higher asphalt mix

temperature

Asphalt mixtures

Rolled asphalt

Storing and haulingthe asphalt mix

Some basic guidelines should be considered when handling

warm mixes:


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Mastic asphalt

Mobile stirrers are cauldrons that areused to ensure that the mastic asphaltmass is brought without any majorchanges and quality losses from theasphalt mixing plant to the job site,and to increase the degree of homoge-nization.

Viscosity modified mastic asphalt ishauled the same way as conventionalmastic asphalt. Mobile stirrers workwith horizontal or vertical agitators.

The following aspects should be considered when using

a mobile stirrer:

The asphalt mix must be homoge-neous and its filling level above themeasuring device to allow exacttemperature readings.

The temperature dial should bechecked in regular intervals andshould allow calibration to ensurethat the reference temperatures arekept.

Drivers must be informed that theyare handling temperature-reducedmastic asphalt and that it is vital to

keep the asphalt mix at the set tem-perature. Otherwise the mix mightsegregate and/or the binder might bedamaged.

Temperatures should be checkedwith a handheld thermometer (aprobe thermometer is the bestchoice) during laying.

Pursuant to Section 2.3.4. of theterms in ZTV Asphalt-StB 07 roadbitumen may not remain longerthan 12 hours in the stirrer and po-

lymer-modified bitumen no longer8 hours. In addition, the (actual)maximum retention time should bedetermined according to the varyingtemperatures and binders. Regulati-ons do not allow the temperature toexceed 230 C.

23

Release coatings should be used assparsely as possible when handlingmastic asphalt in buckets and wheel-barrows. Water entrapped in therelease coating will evaporate andcause temperature drops. When themass is poured and water from therelease coating is entrapped in themastic asphalt mass the mat will

show blisters.


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24

Preparing the job site Preparing the base

5

Laying

All parties involved in the warm mix siteshould be provided with detailed infor-mation about the pavement materials.

When warm mix asphalts are laid forthe first time it would make sense toask engineers at the different bitumenand additive manufacturers for on sitehands-on instructions.

When working at lower asphalt tempe-ratures the tack coats need to be appliedvery carefully and homogeneously to

safeguard sufficient adhesion. The basehas to be dry and clean.


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25

Laying of rolled asphalt

The production temperature has to beset to a level that ensures that the re-ference temperatures for warm mix

asphalt behind the screed specified inTable 3 under Section 4 Asphalt mix-tures are met, taking due account ofweather and transportation conditions.

Special reference is made to theTips and tricks for laying rolled

asphalt listed in the Guidelinesfor rolled asphalt pavements of the

German Asphalt Pavement Association,DAV (see Annex 2).

FertigeDecke

Fertiger

1015 cm

Excerpt from Section 4, Table 3

Fertiger 2

Fertiger 1

mind.

15 cm

Rolled asphalt

Table 4 Reference temperatures for warm mixrolled asphalts behind the screed

Type and Grade Reference temperatures for warmof base binder mix asphalt behind the screed

70/100Minimum 120 C

50/70

30/45Minimum 130 C

25/55-55 A

10/40-65 A Minimum 140 C

Variante 2Walzverdichtung:Variante 1

++ = besonders geeignet+ = geeignet = bedingt geeignet = wenig geeignet

Excer

ptfro

mthe

DAV-g

uideli

nesTip

sand

trick

s

forlay

ingrolle

daspha

lt(Ava

ilable

only

inge

rman)


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26

Laying

Laying technology has to be especiallyeffective since there is only a small timewindow during which warm mix rolled

asphalts can be laid. Therefore the follo-wing aspects should be kept in mind:

Constant laying speed,

continuous charging with mix, constant temperature control, rolling operations close to the paver, check the degree of compaction

(e.g. with the density gauge), fast initial rolling (including the

edges),

short rolling zones, adjust the surface level around iron-

work right after the paver has passed,

gritting with small aggregates to pro-vide enhanced skid resistance (where

applicable) at the latest after thesecond roller pass,

aim to finish compaction at 100 C,depending on binder viscosity

When placing asphalt at lower tempera-tures there will be areas where the matcools more quickly (edges, spandrels) as

is the case with normal laying tempera-tures. Here, however, cooling will have amuch greater impact because tempera-ture levels are lower.

During adverse weather conditions anddifficult laying conditions (city centers,trumpets, islands etc.) the time windowcan be extended by elevating the tempe-

rature.


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The purpose of temperature-reductionmethods for mastic asphalt describedin this guideline is to ensure that the

maximum temperature of 230 C whichhas been in effect since January 2008(see Introduction) and set forth inthe bulletins TL Asphalt-StB 07 andZTV Asphalt-StB 07 can be observedwithout sacrificing quality. Followingare some recommendations as to howmastic asphalt should be handledand laid at a maximum temperature of

230 C.

Hand laying and floorings

Due to the lower laying temperature ofmastic asphalt the time window to

work on the surface is smaller thanwith mastic asphalts laid at higher tem-peratures prior to 2008.

Particularly dense subgrades (concrete,sheeting, mastic asphalt protective layer)have to be dry. Otherwise moisture willbe entrapped which will cause conside-rable blistering. When laying masticasphalt in civil engineering make surethat the base is dry or take measures todry damp surfaces. Shoe soles or wheelsof wheel-barrows or dumpers can also

bring moisture into the building and ontothe surface.

27

Laying of mastic asphalt

Fast and timely blinding and gritting,

short journeys from the stirrer to the jobsite (e.g. use lifts in civil engineering),

changes in the flow behavior of the masticasphalt mass (especially when dealingwith sloped gutters, ramps withstrong inclinations etc.).

Therefore special attention should be given

to the following aspects:


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28

Laying

Laying by paver

Aspects to consider:

The base must be clean and dry.

Check the contact area of the screedunit.

Mastic asphalt should not be laid toofar ahead of the screed.

Take into account rapid cooling of theedges.

Level out the mastic asphalt mass withthe spreading plough, also around theedges of the screed.

Remove the entire cold material.

Avoid that gritting chips are sunk intothe material (due to lower viscosity).

Ensure that the guide battens are in

direct contact with the ground (themastic asphalt mass might underflowthe battens; sunken edges)

When placing hot layers next to coldlayers: Pre-heat the connecting surfa-ces with a heating system.

Rolled mastic asphalt: Time the begin-ning of rolling so that the gritting par-ticles cannot be fully pressed into thesurface during initial rolling; on theother hand, ensure timely application

of these aggregates in order for themto stay connected to the mastic film onthe surface - even when it is windy!

The gritting particles that are appliedshould be pre-heated. Supplying theaggregates in thermally insulated hop-pers proved to work very well in thepast. Poor adhesion due to aggregate

particles that are too moist or too coldwill cause insufficient skid resistance.

. Do not produce gritting particles du-ring mastic asphalt production.


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Weather conditions might require lesstemperature reductions or no tempera-ture reductions at all. Lower viscosity ofthe binder allows better laying and com-paction of the asphalt mix.

This advantage can be used for the fol-lowing aspects:

Hand-laid areas,unfavorable laying conditions (strong

wind, low outside temperature, etc.), mixes that are difficult to compact, long hauls, thin layers paved with hot mixes.

Improving workability

Compaction work of the paver screed has tobe adjusted to the respective asphalt mix(asphalt base courses and asphalt bindercourses need a higher degree of compaction).

Normally, a high compaction screed is not ne-cessary when placing surface course material.

Initial rolling should be performed withmedium weight rollers (6 to 8 t) withoutvibration.

The second and subsequent compaction passescan be performed in the vibration or oscillationmode and with heavy rollers.

When laying surface course materials com-paction should preferably be carried out withstatic or oscillating rollers.

Shoulders should be compacted only afterthe asphalt mat has reached a sufficientdegree of deformation resistance and whileit is still compactable.

Gritting should be carried out after thesecond roller pass, if possible.

29

Conditions and recommendations to consider:


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Experience has shown that roads can be opened to traffic at an earlier

stage when using additives. General conditions, such as air tempera-

ture, layer thickness etc. should be taken into account.

30

Laying

Release to traffic

The asphalt mix should be laid atthe lowest possible temperature.

Measure the temperature of thelaid asphalt course on the surface

and in the core. Use a density gauge to check the

degree of compaction.

If necessary, use signage after re-lease to traffic: Avoid tracking!

To ensure initial skid resistance werecommend that excess aggregates

are swept off only after the road isopened to traffic and after the sur-face course has fully cooled.

The following matters should also be addressed:


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31

Site management

You should consider in particularthe following aspects:

Additional instructions for the pavingcrew,

plan the job according to the materialthat is used,

ensure constant asphalt mix supplythat is adjusted to laying capacities,

make available the right pavers androllers,

set up a detailed work flow plan,especially if the road has to be re-opened to traffic very quickly,

have additional machines and staffon hold if the mix is laid simultane-ously by hand and by paver at roadjunctions, bus bays, ironwork etc.,

ensure that the same number ofrollers is available as for conventionallayings,

revert the laying direction (see pic-ture) when placing one layer imme-diately after another.

Reverse laying direction

1st layer 2nd layer

Laying direction for 1st layerLaying direction for 2nd layer

Beginning of construction work

Appropriate site management has toensure that asphalt materials with awarm mix design can be laid without

any mistakes.


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32

General information Type testing

6

Tests

Ensure that the relevant sections inthe guidelines TL Asphalt-StB and ZTVAsphalt-StB are observed. The 2006

edition of the Bulletin for warm mixasphalt (Merkblatt fr Temperaturab-senkung von Asphalt - M TA) [1] isunder review as these guidelines arebeing printed. The information in the re-vised bulletin will supersede these gui-delines in the event of discrepancies.

Some viscosity modifying organic addi-

tives (e.g. fatty acid amides) interactwith aggregate surfaces. This meansthat standard hot extraction will notguarantee full reclamation. In such cases

the ring and ball softening point is oftenlower than in the case of virgin viscositymodified binders. The manufacturersprovide information as to how achieve anearly full recovery of the additive.

Asphalt mixes for warm mix asphalts(both rolled asphalt and mastic asphalt)are CE-marked even if they fail to meet

the guidelines in TL Asphalt-StB be-cause such mixes can be identified inthe respective European material mix

standards of theEN 13108 series.

When using grade designations (on de-

livery notes etc.) for warm mix for rolledasphalt make sure that you not onlycite the (short) designation accordingto TL Asphalt-StB 07 but specify thecharacteristic of the warm mix, e.g. byusing the abbreviation TA.


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Type tests for asphalt mixtures withviscosity modified organic additivesor viscosity modified binders are per-formed pursuant to TL Asphalt-STB 07.The suitability test has to be carried outagain when the viscosity modifying or-ganic additive or the viscosity modifiedbinder (ready-mix) is changed. As a ge-neral rule, the ring and ball softening

point of the viscosity modified binderin use has to be determined upon deli-very and after extraction.

When carrying out the extractions thefollowing extraction conditions shouldbe uniformly set to minimize fluctuati-ons caused by method variations:

Washing cycles: 6 Extraction time: 90 minutes Determination of the ring and ball

softening point for the reclaimedbinder.

The ring and ball softening point deter-mined in this setting will be part of thecontract and will serve as reference valuefor compliance tests.

You should also be aware of the follo-

wing aspects when conducting typetests for projects with reduced layingtemperatures and if you have had no ex-perience so far with viscosity modifiedasphalt mixtures.

33


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For rolled warm mix asphalt

Experience has shown that Marshall spe-

cimens required to determine densityshould not be produced at standardcompaction temperatures of 135 5 C

(road bitumen) or 145 5 C (polymer modifiedbitumen) when usingasphalt mixtures that in-clude viscosity modifiedbinders and/or viscosity

modifying organic addi-tives.

The optimal asphalt mix composition and

the reference density at compactiontemperatures (VT) of 135 C and 145 Care determined by carrying out a refe-rence test with a non-viscosity modifiedbinder. Specimens for asphalt mixesmanufactured with a viscosity modifiedbinder or viscosity modifying organicadditives should be produced at severaldifferent compaction temperatures (e. g.

110, 120, 130, 140, and 150 C) to de-termine the relevant temperature (VTTA)for the production of specimens.

34

Tests

Type testing

Asphalt (reference mix)Asphalt (with viscosity modified binder)

VTTA VT

2,420

2,410

2,400

2,390

2,380

2,370100 110 120 130 140 150 160 170

Compaction temperature [C]

DensityofMarshallspecimen

VTTA = VT - VT


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35

The temperature where the volumetric

density and reference density match isthe relevant compaction temperaturewhich must be used to determine the re-ference density at the Marshall specimenduring compliance testing. This rule alsoapplies when using viscosity modifiedbinders (ready-mix products) or viscositymodifying organic additives to improveworkability/compactability, i. e. also du-

ring laying without temperature reduc-tion.

So far practice has shown that the diffe-rence between reference compactiontemperature and applicable compac-tability temperatures for warm mixasphalts does not cover the entire rangeof potential temperature reductions onsite. Often it was possible to attain evengreater temperature reductions on thejob site.

Laboratory tests conducted with rolled

asphalts treated with viscosity modify-ing mineral additives (zeolites) willnot yield any specific results, since theeffect of zeolites is limited by time andcannot be ascertained in the lab.

Zeolites do not change the ring and ballsoftening point of the binder. Thereforethe softening point need not be deter-

mined and extractions (for suitabilityand compliance tests) can be per-formed with the normalextraction settingsaccording to applica-ble rules and regula-tions.

In asphalt mix de-signs the amount ofad-mixed zeolites isaccounted for as filler;zeolites are also regardedas filler in the testing procedure.

Annex 1 of the M TA [1] providesadditional information on this matter.


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For mastic asphalt

Stirring resistance should be deter-mined according to Annex 2 of the

M TA [1] to qualifywhich effect tempera-ture changes (tempera-ture range from 180 to230 C). have on theworkability of masticasphalt. As these guide-lines are printed deve-lopment of a new stirrer

is under discussion. (seepicture on left).

Particularly when one orseveral components of the asphalt mixare changed (fine or coarse aggrega-tes, fillers, binders, additives) it doesmakes sense to (re-)determine thestirring resistance

The ring and ball softening pointshould be verified before and after thetest to control if disproportionate bin-der hardening impacts the test results.

Fr GussasphaltDIN EN 13108-21 is applicable for fac-tory production control (FPC) at the

asphalt mixing plant. Factory produc-tion control is carried out accordingto Section 4.2. of TL Asphalt-StB 07.Contractors tests during laying arecarried out according to Section 5.2 ofZTV Asphalt-StB 07.

The ring and ball softening pointshould be determined in regular inter-

vals and compared with the results ofthe type test (see pp 32/33 in theseguidelines) when using viscosity modi-fying organic additives.

It also makes sense to take and re-tain samples of the viscosity modifiedbinder.

Viscosity modifying mineral additiveshave no effect on the ring and ballsoftening point.

36

Tests

Type testing Factory production control


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37

Compliance tests

Mastic asphalt (variant B) produced with viscosity modifying organic additives

has a markedly lower temperature but the same stirring resistance.

300

280

260

240

220

200

180

160

140120

100

80

60

40

20

0200 210 220 230 240 250 260

Temperature [C]

Stirring resistance MA 11 S Variant AStirring resistance MA 11 S Variant B

Stirringresistance[Ncm]

! !!

Compliance tests should be carriedout according to Section 5.3 of ZTVAsphalt-StB 07.

The ring and ball softeningpoint of reclaimed bitumen de-termined in the type test is usedas reference value to allow as-sessments against the contractterms.

This is the reason why identicaltesting conditions have to be en-sured during compliance testing

(see the extraction setting sug-gested on pp 32/33 etc.).

The relevant compaction tempe-rature ascertained in the suitabi-lity test has to be used whenproducing Marshall specimensfor the compliance test.


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For specifying mastic asphalt you cancopy the wordings in Section 113Asphalt designs of the (german)

standard specification index to preparespecifications for the pro-duction of mastic asphaltlayers. These wordings al-ready include text moduleswhich describe the admix-ture of appropriate addi-tives.

You should only use ready-mix productsor additives according to the most recentversion of Lessons learned about theuse of ready-mix products and additivesfor warm mix asphalt [3]. These Les-sons learned are available as downloadunder www.bast.de (only in German,see page 7 of these guidelines)

The specifications must include type andgrade of the required base binder. Forrolled asphalts you are required to spe-cify the use of ready-mix products or ad-ditives to be added to meet the mainobjectives of the construction project:

Objective: Temperaturereduction:

(e.g. Temperature reduction by at

least 20 degrees by adding viscositymodifying organic or viscosity modi-fying mineral additives or by usingviscosity modified binders (ready-mixproducts).)

Objective: Improvingworkability/compactability

(in special cases, e.g. where hand

laying is necessary): (e.g. Admixtureof viscosity modifying organic or vis-cosity modifying mineral additivesor use of viscosity modified binders(ready-mix products) to improveworkability.)

Objective: Increasingdeformation resistance:

(e.g. Admixture of viscositymodifying organic additives oruse of viscosity modified bin-ders (ready-mix products) toimprove deformation resistanceunder thermal load. Effective-ness must be proven.) (e.g.wheel tracking test)

38

Specifications

7Recommendationsfor specifications,

warranty claims andinvoicing


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Objective: Earlier releaseto traffic:

(e.g. Admixture of viscosity modi-

fying organic additives or use of vis-cosity modified binders (ready-mixproducts) to allow earlier releaseto traffic. Client and contractor willagree on site when the constructionsite will be opened to traffic.)

You should be aware of the conditionsspecified in the Type testing section

in these guidelines and cite thesesettings in the specifications; this alsoincludes the extraction settings and theinstructions regarding the temperaturedetermination for the production ofMarshall specimens for rolled asphalts.

When adding viscosity modifying or-ganic and/or mineral additives at theasphalt mixing plant or to the mobilestirrer type and amount of additivesused in the type test and intendedfor in-situ laying have to be docu-mented (according to Section 2.3.2.of ZTV Asphalt-StB 07).

Production and laying temperaturesshould not be lowered when laying tem-peratures are below +10 C or when

considerable cools down of the mix isexpected due to wind impact.

If an earlier release to traffic is stated asobjective the contractor should selectappropriate products to ensure that thisgoal can be attained.

Generally, the bidder should have built

reference projects. If this is not the casethe bidder should prove that his site ma-nager and the paving crew are trainedaccordingly.

The provisions in the agreed rulesand regulations (e.g. ZTV Asphalt-StB,ZTV BEA-StB) will apply.

39

Warranty claims and invoicing


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Experience has shown that RAP con-taining viscosity modifying organic orviscosity modifying mineral additives

can be rexycled without any problems.

The use of viscosity modifying organicadditives leads to a marked increase inthe ring and ball softening point. There-fore the ring and ball softening point isnot an effective criterion to assess the

quality of such RAP.. The suitability ofthe asphalt mix produced with this kindof RAP has to be verified in an initial type

test.

When adding viscosity modifying mine-ral additives it seems that no specialaspects have to be considered when re-cycling such asphalt because the binderdoes not change.

40

8

Asphalt recycling


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41

9

Procedures andexperiences abroad

In addition to the viscosity modifyingorganic and mineral additives descri-bed in these guidelines there are even

more technologies in use throughoutthe world:

Admixture of chemical additives, Use of bitumen emulsions, Process technologies, Use of foamed bitumen.

These technologies are distinguishedaccording to the following aspects:

Hot mixes (hot mix at conventionaltemperatures),

Warm mixes (temperature reductionby ca. 30 degrees),

Half warm mixes (mixing and layingtemperatures below 100 C, mostly

at around 90 C) and Cold mixes (mixing and laying at

ambient temperatures).

Process technologies often use specificaddition sequences or the two-phaseprocess.

When following a specific sequence thecoarse aggregates are charged into themixer, bitumen is then added and mixed

with the coarse aggregates. The fineaggregates and the filler are added inthe last sequence.

When applying the two-phase processall aggregate sizes are fed into the mixerwith the addition of a soft binder andmixed. A hard binder is added after thisfirst mixing phase. The two combined

binders thus yield the desired or requiredbinder.

Some processes which are mostlypatent-protected combine one ofthese process technologies with thefoamed bitumen effect where bitumenis foamed with a conventional methodor where the foaming effect is createdby adding moist aggregates to the mix.


46/52

Detailed overviews of these technologiescan be found in the FHWA publication[4] or at the European Asphalt PavementAssociation www.eapa.org [5].

The technologies and their designati-ons which are often connected tocompany names are not listed here.

42

Energyconsumptio

n

Warm mixes Hot MixesCold mixes

Heating

Vaporization

Warming

Half warmmixes

0 20 40 60 80 100 120 140 160 180

Temperature [C]

Proceduresand Experiencesabroad


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References

[1] Merkblatt fr Temperaturabsenkung von Asphalt (MTA), Ausgabe 2006.FGSV Nr. 766 www.fgsv-verlag.de

[2] Nur noch mit abgesenkter Temperatur, Reinhold Rhl, BG Bau und Obmann

des Gesprchskreises Bitumen. asphalt, Heft 4/2008 www.asphalt.deLiteratur)

[3] Erfahrungssammlung ber die Verwendung von Fertigprodukten und Zustzenzur Temperaturabsenkung von Asphalt, published by Bundesanstalt fr Straen-wesen (BASt), Bergisch Gladbach www.bast.de FachthemenStraenbau-technik temperaturreduzierte AsphaltbauweisenErfahrungssammlungorwww.bast.de/cln_005/nn_42746/DE/Aufgaben/abteilung-s/referat-s5/

temperaturreduzierter-asphalt/erfahrungssammlung,templateId=raw,property=publicationFile.pdf/erfahrungssammlung.pdf).

Valid version when printing these guidelines: May 2008(The archive is available only in german. For the english websites of BASt seepage 7 of these guidelines)

[4] Warm mix asphalt: european practice. Publication no. FHWA-PL-08-007,US Federal Highway Administration, February 2008www.international.fhwa.dot.gov Fax: +1 202 366 9626)

[5] The use of Warm Mix Asphalt EAPA-Position Paper 2009. European AsphaltPavement Association, www.eapa.org

43

Annex 1


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Additional information about theGerman Asphalt Paving Association (DAV)

and further DAV-guidelinesMore information about the German Asphalt Pavement Association

DAV and the German Asphalt Research Institute DAI as well as

an overview of their publications (brochures, guidelines and

research reports) you will find on the internet:

www.asphalt.de

Annex 2

44


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45

Notes


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46

Notes


51/52

Notes

47


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Deutscher Asphaltverband e.V. Schieffelingsweg 6 53123 Bonn GermanyFon +49 228 97 96 5-0 Fax +49 228 97 96 5-11E-Mail [email protected] Internet www.asphalt.de

S* W G!H

W/# 13-2720457 H!/%G$/,F, +49 40 78 115 711F +49 40 78 115 882!'@#$.*.".!'."

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