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Adhesion Promoters for Bitumen

This booklet gives an introduction to the problem of adhesionbetween bitumen (asphalt cement) and surfaces and how thisadhesion can be improved by additives known variously as"adhesion promoters", "antistripping agents", "wetting agents","antistrips" or "adhesion agents" in the different regions of theworld. In this booklet we have used the term "adhesion promoters"to include all additives to bitumen designed to improve adhesion.

The largest use of bitumen (asphalt cement) is in road constructionand the discussion is mainly directed to adhesion in roadmaterials, but adhesion and wetting can also be an issue inbituminous coatings and filled bitumens as well as with relatedbinders like tars and resins. Some examples are given in the"Applications" section.

That roadways can suffer water damage is well established.The symptoms of water damage are various and include ruttingand shoving, loss of chippings from surface dressings (chipseals),ravelling of surface layers leading to potholes, susceptibility tofreeze-thaw damage, cracking and bleeding. But the underlyingproblem on a micro scale is loss of adhesion between the binderand the aggregate.

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All road materials can be damaged by water.Experience has shown that there are fewaggregates which completely resist the action ofwater under all conditions. The water may enterthe pavement structure in several ways:

• water inside or on improperly driedaggregate

• rainfall seeping through shoulders, cracksor porous pavements

• subsurface water from higher groundproducing a hydrostatic head

• capillary water from the subgrade• or water vapour from the subgrade

Some things make the pavement moresusceptible to moisture damage, such as:

• mix designs low in binder and open ingrading

• inadequate compaction so the material hashigh voids

• inadequate subsurface drainage• a high content of clay fines and dusty

aggregate surfaces• and where water vapour can condense

under impermeable layers

Bitumen (asphalt cement) is an oily material oflow polarity with little chemical affinity foraggregate, whereas the aggregate has a highaffinity for water. This means bitumen is easilydisplaced by water. In practice the adhesionbetween bitumen and aggregate depends on thesource of the bitumen and the chemistry of theaggregate surface.

Aggregates may be of an "acidic" type whosesurfaces have a tendency to become negatively

Silica content of road aggregates

How Adhesion is Affected

charged, or "basic" with surfaces which havea tendency to become positively charged.Acidic aggregates include those with highsilica contents, while basic aggregates includecarbonates.

Bitumens, especially those of high acid value,have a tendency to become negativelycharged and thus adhesion problems occurparticularly, but not exclusively, with acidicaggregates.

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Effect of climate. Percentage of sites showing moisture damage in USA

Water damage is more likely in wet climates andhighly trafficked roads are liable to show theeffects of any damage most quickly. But waterdamage can occur in all climates as shown by astudy of moisture damage in the USA.

The chemical affinity between bitumen andaggregate can be improved by the addition ofsmall quantities of chemicals which change the

nature of the aggregate surface or the natureof the bitumen.

These chemicals are known as "adhesionpromoters". The use of adhesion promoterscannot eliminate all the moisture damagecaused by poor design, bad constructiontechniques or poor materials, but it can reducetheir effect in practice.

Effect of water on binder coating.Sample on the right contains

adhesion promoter

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Adhesion

We can recognize two aspects of adhesion:• taking hold (wetting): the binder comes in intimate contact with the aggregate• keeping hold (resistance to stripping): the binder stays in contact with the aggregate

during the lifetime of the road.

Wetting

Adhesion problems can occur beneath the binder film

Poor wetting can be avoided by the modificationof the binder or by the modification of theaggregate surface. Chippings can be precoatedwith bitumen or kerosene or with a watersolution of adhesion promoters. The idea is tomake the surface more receptive to the bitumen.

The more usual approach is to modify thebinder by the addition of adhesion promoters(wetting agents) so that it has more affinityfor the aggregate. Normally 0.5-1.0% of anadhesion promoter is sufficient to ensureactive adhesion.

How to ensure good wetting

Bitumen is highly viscous with little chemicalaffinity for the surface of aggregates so itspreads only with difficulty. To ensure goodwetting it is necessary to reduce its viscosity andto modify the chemical nature of the bitumen orthe aggregate.

Bitumen viscosity can be reduced by heating oradding solvents, and to some extent the highviscosity can be overcome by using lots ofmechanical energy such as intensive mixing.Additives like polymers or fillers like lime whichhave the effect of increasing binder viscosity canimpede wetting and may require the use ofhigher temperatures or longer mix times. Forhot mix a maximum binder viscosity of 0.2Pa.s(2 poise) at the mix temperature is generallyconsidered necessary for good coating.

A rough or dusty aggregate surface will makespreading more difficult. A damp or water-wetsurface will in most cases make it impossiblefor an untreated binder to coat the aggregate.Bitumen has much less affinity for the aggregatesurface than water and little ability to displaceit. The ability of the binder to displace waterfrom aggregate surfaces is known as "active"adhesion.

Poor wetting can be recognized by the presenceof uncoated surfaces in mixes and early loss ofchippings from surface dressings. But even whenthe aggregate is apparently well coated withbitumen, a dust or water layer may preventintimate contact and the establishment of theadhesive bond.

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Resistance to stripping is sometimes called"passive" adhesion. Passive adhesion can beensured by the addition of adhesion promoter(antistripping agent) to the binder. Typically0.2-0.5% is sufficient to impart water resistance.The effect of the adhesion promoter is long-lasting and the resistance to stripping can beseen many years after the construction of theroadway.

Stripping

There is only one cause of stripping: watergetting between a bitumen film and anaggregate surface, replacing the bitumen as thecoating of the aggregate. Stripping can showitself by cracking or deformation in a mix, atendency for the bitumen to flush to the surface,loss of structural strength, ravelling, loss ofchippings from surface dresssings anddetachment of seals from the underlyingsurface. In many cases an examination of thematerials will show uncoated aggregate surfaces(stripping).

Smooth-surfaced aggregates will not hold thebinder film as well as rough-surfaced aggregatesand so are more likely to strip.

In the most simple case stripping is theretraction of the bitumen film from the surfaceof the aggregate–a type of dewetting. But it canalso show itself as a detachment of the bitumenfilm from the the stone or substrate caused bywater penetrating the film or coming out of thestone itself.

The aggregate may appear coated but thebinder can be easily removed. This may beassociated with the formation of soluble saltsat the interface. In favourable circumstancesdetached films may partially reattach on dryingout.

How to prevent stripping

Stripping in hot mix specimens. The sample on the topcontains adhesion promoter

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How Adhesion Promoters Work

Adhesion promoters are surface activematerials which concentrate at the interfacebetween bitumen and the aggregate surface.They displace most of the weakly adsorbedcomponents of the bitumen to form strongchemical bonds to the aggregate surface.

While the head groups on the surface activeagents bind strongly to the aggregate surface,the hydrocarbon "tails" of the molecules arecompatible with the bitumen. The adhesionpromoter thus acts as a bridge between thebitumen and the surface which resists the actionof water.

The adhesion promoters can be introduced intothe system by addition to the binder. Althoughadded to the binder, the molecules of theadhesion promoter quickly find their way to theinterface where they bind so strongly to the

Adhesion promoter molecules act as bridge betweenaggregate and bitumen

aggregate surface that the binder film can pushaway any water present (active adhesion).

Typical adhesion promoter moleculesLeft: Diamine typeBelow: Amidoamine type

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Other Benefits of Adhesion Promoters

Age-hardening

Adhesion promoters ease the spreading ofbinder over the aggregate surface and help todisperse fillers in asphalt mixes. The result isfewer uncoated particles and a more consistentmixture which compacts easier.

This is in contrast to the addition of lime andcement fillers, occasionally used to improve thewater resistance of mixes, which tend to stiffenthe binder and so impede spreading.

Adhesion promoters not only improve theadhesion between the binder and aggregate.Because of their chemical nature they can slowdown the age-hardening of the binder.

Bitumen oxidizes both during the mixingprocess itself, during the storage of the mix andmore slowly during the lifetime of the roadway.The effect of this oxidation is a hardening of thebitumen and a loss in flexibility of the roadwaywhich can lead to cracking.

The hardening during mixing is simulated in thelaboratory by the Rolling Thin Film Oven Test(RTFOT) where hot binder is exposed to astream of air. The viscosity of the binder is thencompared to an untreated sample.

The slower age-hardening during the life of theroad can be simulated by the so-called pressureageing vessel (PAV) test developed as part of theSuperpave protocols developed in the USA. Inthis test the bitumen is exposed to air in anautoclave and then its rheology is compared tothat of an untreated sample.

The increase in stiffness of binders before andafter RTFOT and PAV tests, as measured by theDynamic Shear Rheometer, shows the tendencyto age during mixing and service.

The results show reduced age-hardening withtreated binder which should lead to lesstendency for fatigue cracking during the servicelife of the pavement.

As roads are designed for longer lifetimes,oxidative hardening and stripping becomesignificant factors contributing to early failure.The combined effect of improved adhesion andslower hardening on the lifetime of the roadwaymakes the use of adhesion promoters even morecost-effective.

Mixing and Compacting

Adhesion promoter reduces the age-hardening of bitumen

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Hot Mixes

Most asphalt mixes are made hot with dryaggregate. The use of adhesion promotersensures complete coating of aggregates that aredifficult to coat and also improves the durabilityof the roadway. Typical use levels range from0.2-1.0% on the binder.

In contrast to treatment with lime or lime slurryadhesion promoters are required at much lowerlevels. They do not form dust and the treatedbinder coats more easily. There is also evidencethat mixes containing adhesion promoterscompact more easily.

Tests on specimens using the NottinghamAsphalt Tester show that mixes containingtreated bitumen maintain their load bearingcapacity (stiffness modulus) even whenimmersed in water.

Applications

Chip spreading

Surface Dressing (Chip Seal)

Surface dressing (chip sealing) involvesspreading chippings over a sprayed seal ofbinder and rolling in. The binder cools rapidlyon the road surface leading to high viscosityand wetting problems which can be made worseby wet and dusty aggregate.

This is an application where "active" adhesionis essential and typically 0.5-1.0 % adhesionpromoter is added to the binder. Alternativetechniques include precoating the chippingswith a mix of diluted binder and adhesionpromoter or the spraying of a diluted watersolution of adhesion promoter before spreadingthe chippings, so-called interfacial dope.

There have been several field studies whichdemonstrate beyond doubt that the use ofadhesion promoters in surface dressing leads toresistance to early rain, an ability to cope withmore dusty aggregate and less loss of chippingsin the long term. Not surprising that one authorconcluded: “Although the cost of adding a smallamount of adhesion promoters is small, thesavings to be made are incredible”. The use ofadhesion promoters in surface dressing isspecified by many national authorities.

Compacted mixes containing adhesion promotersresist the effect of water.

Indirect Tensile Stiffness Modulus after Immersion

soak time (days)

28 mm base course using 100pen bitumen

no treatment0.4% adhesion promoter0.8% adhesion promoter

stiff

ness

mod

ulus

MPa

0 5 10 15 20 25 30

3000

2500

2000

1500

1000

500

0

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Hot Recycling

If partly coated surfaces are obvious in thereclaimed asphalt, adhesion promoters shouldbe used.

Bituminous Coatings

Bitumen is used for waterproofing, sealingand corrosion protective coatings. Many ofthe same problems with coating and waterresistance seen in road construction materialsalso apply to these coatings. Where thesubstrate is cold and could be damp, then itis necessary to ensure active adhesion by theuse of adhesion promoters at a level of 0.5-2%on the binder.

Emulsions

The use of cationic bitumen emulsions usuallyensures good adhesion in both road andindustrial applications. There may be caseswhere additional water resistance is required.Adhesion promoters can be added to the binderbefore emulsification and usually at a level of0.2-0.5%.

Anionic emulsions generally provide pooradhesion to siliceous (acidic) aggregates and tometallic or stone substrates. Adhesion of anionicemulsions is improved by adding adhesionpromoters to the binder before emulsification,typically at a level of 0.2-0.5%, or to thefinished emulsion.

Cold Mixes

Asphalt mixes can be made without heating ifthe binder is of sufficiently low viscosity. Typicalapplications include road oil mixes, common inScandinavia, and reinstatement and repairmaterials made with fluxed or cutback binders.

Because the process is carried out cold, theaggregate is usually not dried or heated sothe binder may have to displace water fromthe surface. In these cases an active adhesionpromoter is essential.

Typical use levels range from 0.5-1.5%. Theadhesion promoter also ensures that strippingdoes not occur during the stockpiling of themixes.

Precoated Chippings

Chippings are lightly coated with bitumen oroil to ensure adhesion in surface dressing orwhen rolled into hot rolled asphalt surfaces toimprove skid resistance. Adhesion promotersare added to the coating material to ensuregood adhesion.

Prime Coats

In some countries cutbacks or road oils are usedfor priming and to control dust on road basesduring construction. Because the road base iscold and damp, adhesion promoters should beadded to the prime coat to ensure activeadhesion and rainfastness.

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Use of Adhesion Promoters

Dosage

Dosing of adhesion promoters can be done atdifferent stages in the mixing and applicationprocess.

Akzo Nobel Asphalt Applications can supplycustom-built equipment for the dosing ofadhesion promoters for either batch orcontinuous hot mix plants or provideinformation to assist the installation of asuitable system.

At refineries and bitumen distributor centressimilar equipment can be used to add adhesionpromoters inline when the bitumen is loadedinto the distribution tanker.

Dosage equipment for adhesion promoters

Surface Dressing

In some applications, mainly surface dressing(chip seal), the bitumen is treated with a passiveadhesion promoter at the refinery or the depotto ensure the long term adhesion performanceof the seal. Adhesion promoters can be dosedinto the bitumen line as the spray tanker isfilled.

To enable surface dressing to continue duringwet weather conditions, additional activeadhesion promoters can be added on-site directto the spray tanker as necessary. A solidpelletised form of adhesion promoter is mostconvenient to add by hand under thesecircumstances.

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Heat Stability

Adhesion promoters are quite stable in coldbitumen and maintain their antistripping effectover many years.

Adhesion promoters slowly lose activity in hotbitumen. This loss in activity depends on thesource of the bitumen and mainly due to thereaction of the alkaline amine with the acidiccomponents in the bitumen. Activity is lostmore quickly in bitumens with higher acidvalues such as those from Venezuelan crudesand particularly at higher temperatures.

Treated binders should not be overheated andshould be stored for as short a time as possiblebefore use. If extended storage of treated binderis unavoidable, then a special "heat stable"product should be selected.

Wherever possible the adhesion promotershould be added to the binder just before itgets into contact with the aggregate.

Hot Mix Plants

To minimize this loss of activity it is better toinject the product in-line via a metering systeminto the bitumen delivery line just before mixing.

Adhesion promoters are generally liquidproducts which can be stored in carbon steeltanks. Some products may require heating incold weather conditions. Consult the productdata sheet.

Bitumen (asphalt cement) is used as a binderand waterproofing agent in many industrialapplications such as sealants, mastics, roofingcompounds, pipe coatings etc.

Adhesion promoters are used in many of theseproducts to ensure a good water resistant bondor to displace water in cold applied systems.Akzo Nobel Asphalt Applications can give adviceon suitable products.

Storage

Industrial Applications

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Survey of Laboratory Tests forAdhesion and Adhesion Promoters

Compatibility Tests

Total Water Immersion Test (TWIT)Dry chippings are fully coated with binder, at atemperature related to the binder viscosity,allowed to cool, then covered with water. Whenapplied to emulsion or cutback binders, thecoated chippings may be allowed to cure beforebeing covered with water. After storage for atime and at a temperature specified by themethod, the coverage/stripping is estimatedvisually. When the water temperature is at100ºC, the method is known as "The BoilingStripping Test".

In modified tests the aggregate may be coveredwith a solution of salt to simulate the effect ofdeicing chemicals. For binders of low viscositythe method may be modified to measure activeadhesion by wetting the chippings before addingthe binder.

References to typical procedures:a) Germany: DIN52006 Effect of

Water on Binder CoatingsPart 1 (Emulsions)Part 2 (Active Adhesion)Part 3 (Cutback Binders)

b)France: NFT 66-018 Test forAdhesivity for a Cationic Emulsion

c) Austria: O Norm B3682 (1984)Testing of Adhesion Propertiesbetween Bitumen and Aggregatesby Stripping

d)Canada: Ontario Modified StaticImmersion Test (uses salt solution)

e) Norway: VTI Method 262 ActiveAdhesion Laboratory Method

f) USA: ASTM D3625-91 Effect ofWater on Bituminous CoatedAggregate Using Boiling Water

g) USA: ISSA Method TB149 TestMethod for Boiling Compatibilityof Slurry Seal Mixes

h) Akzo Nobel: AA2 Passive Adhesioni) Akzo Nobel: AA3 Active and Passive

Adhesion of Soft or Cutback Bindersj) Akzo Nobel: AAE1 (Emulsions)

Rolling Bottle TestChippings are coated with binder and coveredwith water in glass jars. The jars are rotated sothat the contents are agitated. Periodically thecoating of the stones is estimated visually.

References to typical procedures:a) Akzo Nobel: AA1 Rolling Bottle Test

Wet Mix MethodThe method is primarily designed to evaluatecold mixed materials. Wet aggregate is mixedwith binder and the coating is estimatedvisually.

References to typical procedures:a) Akzo Nobel: AA4 Wet Mix Method

Rolling Bottle Test

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Immersion Tray TestA film of binder in a shallow tray is covered withwater and chippings pressed into its surface.The chippings are removed after a specified timeperiod and the coverage of the face in contactwith the binder is estimated visually.

References to typical procedures:a) UK: Road Note 39 (3rd Ed)

Appendix D The Immersion Tray Testb) Australia: Victoria CRB 112.03

(1975) Adhesion of Binder to Stone

Plate MethodsA film of binder is placed on a metal plate. Wetor dry chippings are pressed or rolled into thesurface. The plate may be immersed in water.The adhesion of the chippings is determinedby blows to the back of the plate. Chippingswhich fall off are weighed or counted or thechippings are removed by pliers and the coatingdetermined. The use of wet chippings gives ameasure of active adhesion.

Tests Methods for Surface Dressing (Chip Sealing)

References to typical procedures:a) France: NF P98-274-1 Vialit

Adhesiveness Test for AnhydrousBinders

b) Australia: HDSA 305.01 (1988)Determination of AggregateStripping Value by the One Day PlateStripping Test

c) Australia: NSW T230 Resistance toStripping of Cover Aggregates andBinders

d) New Zealand: MWD B301-83Method of Measuring the ActiveAdhesion between a BituminousBinder and a Roading AggregateMaterial

Sand Mix MethodWet sand is mixed or shaken with a solution ofbinder in solvent. The colour and cohesion of thesand are determined. A black agglomeratedsand is a positive result.

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Test Methods for Compacted Mixtures

Immersion MethodsMixes are made and compacted, sometimes toa specified voids content. After curing the mixesare immersed in water for a specified time andat a specified temperature. The specimens maybe vacuum saturated to ensure waterpenetration. The stability, compressivestrengths, or tensile strengths of the specimensare compared with specimens which have notbeen immersed. The methods can also beapplied to field cores.

References to typical procedures:a) France: NF P98-251-1 Duriez Test

for Hot Mixesb) France: NF P 98-251-4 Duriez Test

for Bitumen Emulsion-aggregateMixtures

c) USA: ASTM D 4867-92 Effect ofMoisture on Asphalt Concrete PavingMixtures

d) USA: ASTM D 1075-94 Effect ofWater on Compressive Strength ofCompacted Bituminous Mixtures.

Modified Lottman TestMixes are made and compacted sometimes toa specified voids content. After curing thespecimens may be vacuum saturated with waterand subjected to one or more freeze-thaw cycles.The tensile strength or stability of the specimensis compared with specimens which have notbeen subjected to freeze-thaw.

References to typical procedures:a) USA: ASTM D4867-92 Effect of

Moisture on Asphalt Concrete PavingMixtures

b) USA: AASHTO T238 Resistance toMoisture Induced Damage

Exposure to Moisture VapourMixes are made and exposed to a moistatmosphere. The stability of the mix isdetermined after exposure.

References to typical procedures:a) USA: California CT307 Moisture

Vapour Susceptibility

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Abrasion TestsCompacted mix specimens are shaken in waterand the weight loss of the compacted specimensmeasured. Metal balls may be included toincrease the abrasion effect. In wheel trackingtests the surface of compacted specimens isabraded by a moving wheel.

References to typical procedures:a) USA: ISSA Method TB144

Aggregate-Filler-BitumenCompatibility by the Schultze BreuerRuck Procedure (has been applied tocured slurry seals and hot mixedmaterials).

b) USA: California CT360 SurfaceAbrasion

c) USA: Nevada DOT Durability ofCompacted Bituminous Mixtures bythe Dynamic Strip Method

d) UK: TRL Immersion Wheel TrackingTest

Test to estimate Coating ofHot MixesAdhesion promoters may improve the coatingof aggregates. The coating in hot mixes can beexpressed in terms of the coating of the coarseaggregate and the time required for goodcoating can be determined.

References to typical procedures:a) USA: ASTM D2489 Degree of

Particle Coating of BituminousAggregate Mixtures

SealantsA sample seal is made between two concreteblocks. The bond strength and otherperformance requirements are measured afterimmersion of the specimen in water.

References to typical procedures:a) USA: ASTM D5329-92 Sealants and

Fillers, Hot Applied for Joints andCracks in Asphaltic and PortlandCement Pavements.

Joints in Roofing LayersA specimen joint is immersed in water. Theleakage and tensile strength of the joint isdetermined.

References to typical procedures:a) Europe: UEAtc MOAT No 27:1983

General Directive for the Assessmentof Roof Waterproofing SystemsSection 5.2

Asphalt Roof CementsThe coverage of a wet surface placed in contactwith asphalt cement is determined.

References to typical procedures:a) USA: ASTM D3409-93 Adhesion of

Asphalt-Roof Cement to Damp, Wetor Underwater Surfaces.

Other Tests

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Adhesion PromoterCationic surface active agent which ensures athorough, irreversible water resistant bond betweenbitumen binder and aggregate.

Adhesion Promoter, Heat StableAdhesion promoter which maintains itsperformance after storage of treated binder athigh temperature.

Adhesion AgentAdhesion Promoter.

Adhesion, ActiveBitumen treated with active adhesion promoterdisplaces moisture from an aggregate surface andestablishes a bond between the mineral surfaceand the bitumen.

Adhesion, DynamicAdhesion between mineral aggregate andbitumen is resistant to the pumping effect ofvehicles on wet surface layers.

Adhesion, PassiveThe ability of an established bond between mineralsurface and bitumen to resist the effect of water.

Aggregate Mix, Dense GradedA mix containing aggregate which is graded fromthe maximum size down to filler with the object ofobtaining a bitumen mix with a relatively low voidcontent.

Aggregate Mix, Open GradedA mix containing little or no filler giving relativelylarge void spaces in the compacted mix.

Antistripping AgentAdhesion promoter providing passive adhesion.

BinderGeneral term for asphalt cement which includesbitumen, coal tar or polymer-modified bitumens.

BitumenDark viscous liquid, residue of the vacuumdistillation of petroleum. Predominantly aliphaticand cycloaliphatic. Known as asphalt in the U.S.A.

Bitumen, Acid ValueMeasurement of the acidity of bitumen expressedin milligrammes of potassium hydroxide requiredto neutralise one gram bitumen.

Bitumen, Blown and OxidizedAsphalt that is treated by blowing air through it atan elevated temperature to give it characteristicsdesired for certain special uses, such as roofing,pipe coating etc.

Glossary of TermsBitumen, Cutback

Bitumen containing 10-15% volatile solvent, e.g.kerosene, boiling range 150-200 ˚C.

Bitumen EmulsionAn emulsion of bitumen in water which contains asmall amount of an emulsifying agent.

Bitumen Emulsion, AnionicBitumen emulsion in which the droplets of bitumencarry a negative charge.

Bitumen Emulsion, CationicBitumen emulsion in which the droplets of bitumencarry a positive charge.

Bond CoatNew European terminology for tack coat.

Chip SealU.S. terminology for surface dressing.

Coal TarDark viscous liquid obtained from the carbonisationof coal. Predominantly aromatic in character.

Deferred Set MacadamRepair material based on fluxed or cutback binder.

Flux, Flux OilThick, low-volatile petroleum fraction which maybe used to soften bitumen.

GradationA general term used to describe the aggregatecomposition of a bituminous mix. When the exactpercentages of all aggregate essential to a goodmix are controlled through the percentage of eachsize aggregate used.

Hot MixRoad material prepared from a hot mixture ofbitumen and graded aggregate.

Hot Rolled Asphalt (HRA)Type of gap-graded dense mix with a smoothsurface texture, predominantly used in the UK,in which the fines and the binder form a loadbearing mortar.

ImperviousResistant to penetration by water.

Interfacial DopeAdhesion promoter applied as an aqueous solutionto the surface of freshly sprayed bitumen or to theaggregate surface before surface dressing.

PenetrationMeasurement of the hardness of bitumen by thedistance of needle penetration. High penetrationrefers to soft bitumen.

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Penetration MacadamTechnique in which bitumen emulsion or cutbackbitumen is sprayed on to an open graded aggregatemix, then compacted.

Porous AsphaltOpen graded wearing course material with gooddrainage and sound-deadening properties.

PrecoatsChippings coated with a small amount of bitumenor kerosene used in surface dressing or rolled intothe surface of Hot Rolled Asphalt.

Prime CoatLiquid binder sprayed on an unbound layer toprovide a good bond with hot mix.

RavellingLoss of material from the wearing course of aroadway under the influence of traffic.

Road OilHeavy petroleum fractions used as binder inNorthern Europe.

Soft BitumenFluxed bitumen, viscosity 2000-20000 mPa.sat 60 ˚C, popular in Northern Europe.

StrippingProcess whereby water displaces bitumen binderfrom the aggregate surface. Includes processeswhere water penetrates the film of harder bitumenscausing debonding.

Surface DressingSurface sealing technique in which chippings arespread on a sprayed film of hot bitumen, cutbackbitumen or emulsion.

Tack CoatAn application of low viscosity liquid bitumen oremulsion between layers of bituminous materialsto prevent slippage.

Warm MixRoad material produced from a mix of aggregateand soft bitumen at relatively low temperatures,100-120˚C, popular in Scandinavia.

Wearing CourseTop layer of the road pavement which isexposed to traffic.

Wetting AgentAlternative term for adhesion promoterreflecting the ability of treated binder tocoat aggregates.

References1. Premature Asphalt Concrete Pavement Distress Caused by

Moisture Induced Damage, S.R. Shatnawi & J van Kirk, TRBResearch Record 1417, 168-177 (1993)

2. Le Problème de l'Adhesivité Liants Hydrocarbones-Granulats, A-M Ajour, RILEM, Report 17 BM No3 1979

3. Relationship between Permanent Deformation of AsphaltConcrete and Moisture Sensitivity, N C Krutz & M Stroup-Gardiner, TRB Research Record 1259, 169-177 (1990)

4. Field Observations of the Behaviour of Bituminous Pavementsas Influnced by Moisture, W K Parr, Symposium on BituminousPaving Mixtures, 3-16, ASTM Special Publication 240 (1958)

5. Investigation of Moisture Damage to Asphalt Concrete and theEffect on Field Performence - A case study, T W Kennedy, R GMcGennis & F L Roberts, TRB Research Record 911, 158-165

6. Detachment of the Stone From Binder Under the Influence ofWater in Road Surface Dressings, H Kaqrius & G L Dalton, J InstPetroleum, 50, 481, 1-14 (1964)

7. A Laboratory Test System for Prediction of Asphalt ConcreteMoisture Damage, R P Lottman, R P Chen, K S Kumar, & L WWolf, TRB Research Record, 515, 18-26 (1974)

8. Surface Dressing Failures: A Review of Studies in Ireland,M C Cahill, I L Jamieson & J P M Sheedy 111.26,4th Eurobitume Congress, Madrid (1989)

9. Stripping of Asphalt Pavements: State of the Art, M A Taylor& P Khosla, TRB Research Record 911, 150-157 (1983)

10. Surface Active Agents in Bituminous Road Materials, D HMathews, J Appl Chem, 56-73 (February1962)

11. The Effects of Amino Antistrip Additives on Stripping ofBituminous Mixes, S Ramaswamy & E W Low, Highways andTransportation, 9-13 ( May 1990)

12. Early Performance of Some Antstripping Agents in OntarioPavements, F Field & W A Pheng, Annual Conference ofCanadian Technical Asphalt Association, Vancouver (1972)

13. Field and Laboratory Investigation of Stripping in AsphaltPavements: State of the Art Report, P S Kandal, TRB ResearchRecord 1454, 46-47 (1996)

14. The Cost Effectiveness of Using Cationic Amine AdhesionAgents in Surface Dressing Treatments, A R Woodside C Rogan,5th Eurobitume Congress, Stockholm (1993)

15. The Development of a Mathematical Model to predict ChipLoss in Surface Dressing AR Woodside C Rogan,5th Eurobitume Congress, Stockholm (1993)

16. The Use of the LIMPET Tester to Assess the Bond StrengthCharacteristics of Bituminous Materials, A R Woodside C Rogan5th Eurobitume Congress, Stockholm (1993)

17. Stripping in Asphaltic Concrete Mixes Observations and TestProcedures F Field & W Phang, Proceedings Canadian TechnicalAsphalt Association 12, 61-80 (1967)

18. Adsorption of Asphalt and Asphalt Functionalities ontoAggregates Precoated with Antistripping Agents, CC Curtis,J Baik, & Y W Jeon, TRB Research Record, 1269, 48-55 (1990)

19. Adsorption Behaviour of Asphalts on Siliceous and CalcareousAggregates, CJ Brannan, Y W Jeon, L M Perry, C W Curtis,TRB Research Record 1323, 10-19 (1991)

20. Identification of Chemical Types in Asphalts strongly adsorbedat the Asphalt Aggregate Interface and their relative Displace-ment by Water, H Plancher, S M Dorrence, J C Petersen AAPTProceedings San Antonio Texas (1977)

21. Improving Frictional Characteristics of Emulsion-based SealCoats with Antistripping Agents, A. A Selim, 68th AnnualMeeting, TRB Research Record 1217, 46-52, Washington(1989)

22. The Use of Adhesion Agents and their Effect, A R Woodside &P D McCool 1-37, 4th Eurobitume Congress, Madrid (1989)

23. Effects of Adhesion Agents on Asphalt Cements as measuredby the Schultze-Breuer Test, A C Brooker, J Barnat, & D Bohn,28th Annual Convention of ISSA, Tampa Florida (1990)

24. Improving Chip Retention and Reducing Moisture Susceptibilityof Seal Coat, A A Selim & T Tham. TRB Research Record 1392,20-26 (1993)