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Design Methods for Hot-Mixed Asphalt­Rubber Concrete Paving Materials

James G. Chehovits

INTRODUCTION

The properties and use of asphalt-rubber materials forvarious paving and maintenance activities have been welldocumented in the literature. The majority of this literaturereports on properties of asphalt-rubber materials (1-12), and useof asphalt-rubber in stress absorbing membranes (SAM) andinterlayers (SAMI) (13-25). Research studies have shown thatasphalt-rubber materials have significantly modified physicalproperties when compared to asphalt cement. These modificationsinclude increased high temperature modulus, viscosity, andtoughness; increased elasticity, reduced temperaturesusceptibility, and less age hardening. In several states andcountries abroad, use of asphalt-rubber in SAM and SAMIapplications has become routine construction practice forrehabilitating deteriorated pavements and extending overlay life.

In the United States, asphalt-rubber materials have beenused on a limited basis as the binder for hot-mixed asphaltconcrete pavements. A recent survey by the Asphalt-RubberProducers Group (ARPG) indicated that at least 35 projects whichused asphalt-rubber binder were placed between 1975 and 1987 in 12states. Several research studies have been completed whichinvestigated use of asphalt-rubber as an asphalt concrete pavingbinder (26, 27). Additionally, there have been several welldocumented field test projects placed by several states (28, 29,30, 31). The literature indicates that several other countrieshave used asphalt-rubber binders for hot-mixed paving (32, 33, 34).

Limited information is currently available on methods to beused for designing hot-mixed asphalt concrete mixtures when usingasphalt-rubber binders. Vallerga (35) has suggested severalspecification changes which should be made when usingasphalt-rubber. Hoyt and Lytton (27) reported on a mixture designprocedure for asphalt-rubber paving mixtures which was used in alab research program that studied the feasibility of usingasphalt-rubber binder in dense graded airfield pavements.

The purpose of this paper is to describe design procedureswhich have been developed since 1984 as the result ofapproximately 30 hot-mixed paving projects which usedasphalt-rubber binder. Procedures for selecting the asphalt-rubbermaterial proportions and resulting desired properties, mixtureaggregates, and binder contents for dense, open, and gap gradedmixture types are presented along with suggested constructionguidelines and specifications.

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FACTORS WHICH INF~UENCE ASPHALT-RUBBER PROPERTIES

The interaction which occurs between asphalt and recycledrubber has been shown to be dependent on a variety of factors:

• Asphalt physical and chemical properties• Rubber physical and chemical properties• Time• Temperature• Mixing conditions (high shear or low shear)• Use of ad~itives

Each of these factors needs to be considered when developing anasphalt-rubber formulation for a specific use.

Asphalt Cement

Chemical and physical properties of the asphalt influenceseveral properties of the asphalt-rUbber. Stiffness (asphaltgrade) and temperature susceptibility will influence hightemperature and low temperature performance of the asphalt-rubber.Chemical make-up of the asphalt will influence the degree ofinteraction which occurs between the asphalt and the rubber.Asphalts which have higher degrees of aromaticity tend to dissolveand interact with rubber to a greater degree than asphalts withlower aromatic contents.

Rubber

Several characteristics of the rubber influence propertiesof the asphalt-rubber blend. Physical rubber characteristicsincluding particle size (gradation), shape (angular or elongated),·surface texture (as influenced by grinding method), andcontaminant presence (fibers, etc.) influence properties of theasphalt-rubber. Chemical compositional characteristics alsoinfluence blend properties. These characteristics include rubberhydrocarbon content, specific type of rubber polymer or blends(amount of SBR and natural), plasticizer content, andreinforcement type and content (carbon black and other materials).

Time and Temperature

Various research projects have shown that the time exposureand temperature of the asphalt-rubber blend influence physicalproperties. Increased time results in greater interaction.Increased temperature results in quicker interaction.

When physical properties of asphalt-rubber are monitored,the material will thicken (increase in viscosity) as the rubberparticles swell in the asphalt. After a period of time, dependingon temperature and materials properties, the rubber will begin tobreak down (devu1canize and melt), and viscosity will reduce.

Rate of devu1canization will also be influenced by themixing conditions. Because of these influences, it is importantthat asphalt-rubber blends be checked for appropriate propertiesat a variety of time periods which can occur during actual use.

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Mixing Conditions

The amount of shear, or intensity of mixing, will influencethe properties of the asphalt-rubber. Production mixing systemsare designed to' insure uniform wetting and suspension of therubber particles in the asphalt.

It is important that lab mixing procedures do not subjectthe asphalt-rubber to excessive amounts of shear which couldquicken the rubber devulcanization process.

AdditivesExtending oils can be used to soften the material for

improved low temperature performance and for improving the degreeof interaction between the asphalt and rubber. Adhesion agentscommonly used in asphalt paving (heat stable anti-strippingagents) can be used to improve film stripping resistance. Diluentswhich are used in asphalt-rubber chip seal application must not beused in hot-mixed applications.

TEST METHODS FOR ASPHALT RUBBER

The physical properties of asphalt-rubber have been shown in avariety of studies to be substantially different than forunmodified asphalt cement (1-12). Many of these studies have usedcommon asphalt test procedures as well as non-standard proceduresto attempt to quantify the modified physical properties ofasphalt-rubber. The non-standard procedures include SchweyerRheometer (2, 3), sliding plate viscometer (1,3), force ductility(2.3.8,10). torque fork viscosity (2.3.8.10). mechanicalspectrograph (I). and several others.

Physical attributes of asphalt-rubber which should considered forhot-mixed applications include:

• Viscosity at high temperatures for appropriate mixing andcompaction characteristics.

• Consistency at high pavementexperienced during the summer.

surface temperatures

• Consistency at moderate temperatures.

e Elasticity

• Low temperature characteristics

Testing methods which can be used to evaluate these attributes areas follows:

Viscosity

The Viscosity of asphalt-rubber materialstemperatures (250-400o F) can easily be monitored usingtype viscometers such as a Haake hand held portable(10) or a Brookfield viscometer (ASTM 03236)(36).

at highrotationalviscometer

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High Temperature Consistency

The consistency of- asphalt-rubber at high pavement surfacetemperatures can be indicated by several procedures including Ringand Ball Softening Point (ASTM 036), Modified Flow (ASTM 03407),or a cone penetration at 1220 F (ASTM 03407 and 05)(37).

Moderate Temperature Consistency

Moderate temperature (770 F) consistency can be evaluatedeasily by using the ASTM 03407 Cone Penetration test at 77 0 F (37).

Elasticity

The elasticity of asphalt rubber can simply be evaluatedusing the ASTM 0~407 resilience test which indicates the amount ofrebound under a 75 gram load at 77 0 F (37).

Low Temperature Characteristics

Several test method types can be used to provide anindication of low temperature properties. These include ConePenetration (ASTM 03407) at 32 or 39.20 F; Ductility at 39.20 F(ASTM 0113) and Low Temperature Flexibility (Modified ASTM C 711,section 7.2 using a 900 bend in 10 seconds at lower and lowertemperatures until fracture occurs) (37,38).

SELECTION OF ASPHALT RUBBER FORMULA

The physical properties of asphalt-rubber depend on theingredients and interaction conditions. Therefore, to obtain thedesired properties, appropriate ingredients and interactionconditions must be chosen. These choices which must be made are:

e Selecting the asphalt cement source and type.• Selecting the rubber source and type.• Selecting the rubber content.• Selecting the interaction conditions.

Additionally, it is important that the asphalt-rubber materialhave appropriate stability of properties, since properties varywith interaction time and time of interaction can vary duringactual use. Therefore, testing of an asphalt-rubber blend ofingredients during project formulation studies should be performednot just at a single interaction period, but at a variety ofinteraction periods to evaluate stability and retention ofproperties. A procedure for interacting the asphalt-rubber for 24hours during formulation studies is contained in Appendix 1.Physical properties can be evaluated from samples poured at 30,60, 90, and 120 minutes of interaction to identify propertyretention during normal usage periods after completion of fieldmixing. Tests at 6 hours can identify properties of the blend if

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a job delay occurs and the asphalt-rubber is used the same day.Tests at 24 hours (with e~posure from 6 to 22 hours at a lowertemperature to simulate overnight unheated storage) can indicatestability of properties if the asphalt-rubber is to be used thenext day.

Suggested physical property limits for asphalt-rubbermaterials for hot-mixed asphalt-concrete applications are listedin Table 1 for hot, moderate, and cold climates.

Asphalt-Cement

The grade of asphalt cement used in asphalt-rubber, is amajor influence on blend properties over the entire temperaturerange.

Asphalt cement for asphalt-rubber should meet appropriatespecifications for paving use such as ASTM 03381 or 0946. Typicalgrades used range from AC-2.5 to AC-20, or 200-300 penetration to60-70 penetration. It is important that the specific asphaltcement be compatible, or capable of interacting with the specificrubber being used. This is indicated by appropriate increases inviscosity during the interaction period. Since the interactionwith rubber results is an increase in high temperature modulus,asphalt cements used are typically somewhat softer than usualunmodified asphalts used for similar applications.

Figures 1,2, and, 3, show results of constant load creeptests performed on asphalt-rubber materials which contained avariety of asphalt-cement grades each with 17% by total weight ofa minus 20 mesh tire rubber. Testing was performed using aprocedure reported by Cotzee and Monismith (24). Data shown inthese figures indicates that addition of rubber produces astiffening effect at moderate temperatures (740 F) which isapproximately equivalent to using an asphalt which is 2 to 3grades harder. At 100oF, the effect is even greater. At lowtemperature (390 F) however, the effects of stiffening are muchless. For the asphalts which were approaching the brittle point(the AC-20 and AC-7.5) at 390 F, creep with rubber was very similarto creep of the unmodified asphalt. This data therefore indicatesthat asphalt-rubber materials and unmodified asphalt creep atsimilar rates at low temperatures near the base asphalt brittlepoint. However, as temperature increases, the asphalt cementreduces in stiffness to a greater degree than the asphalt-rubberas indicated by reduced creep of the asphalt-rubber. The effectbecomes greater as temperatures increase. The data suggests thatit is possible to use asphalt cements in asphalt-rubber which aresofter than the normal unmodified paving grade used for thespecific application to provide reduced stiffness (higher degreesof creep) at low temperatures and increased stiffness (reducedcreep) at high temperatures.

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Base asphalt grades which have been found to produceasphalt-rubber materiala meeting the hot, moderate, and coldclimate property limits of Table 1 are as follows:

Climate TypeBase Asphalt for Asphalt-Rubber

AR Grade AC Grade Penetration Grade

Hot

Moderate

Cold

AR-4000,AR-2000

AR-1000

AR-1000 with 3%to 6% extender

AC-20,AC-10

AC-5,AC-2.5

AC 2.5 with0-3% extender

60-70, 85-100

120-150,200-300

200-300 with 0-3%extender

Various extending oils can be used in asphalt-rubbermaterials to increase the interaction between the asphalt andrubber, and to improve low temperature performance by decreasingthe stiffness of the asphalt-rubber when softer asphalt grades arenot available. Extender types used are generally napthenic oraromatic petroleum oils which have a minimum flash point of 4000 F.

For most common oils with viscosities between 500 and 3000SUS at 1000 F, approximately 3% by asphalt weight is required tosoften an asphalt an equivalent of 1 grade. Typically, eachpercent of extender oil lowers ring and ball softening point (ASTM036) results by 1.5 to 2.0 degrees Farenheit.

Rubber

Rubber used for asphalt-rubber should be primarily made fromrecycled pneumatic tires. The rubber should be ground onappropriate systems, and should be free from contaminantsincluding mineral matter, fiber and metal. The rubber should besufficiently dry to prevent foaming when added to hot asphalt.Generally this means a moisture content of less than 0.75%.Mineral contaminants should not exceed 0.25%. The rubber may beproduced from buffings, whole tire, or stampings. The rubberhydrocarbon content should be between 40 and 50% and should berelatively uniform throughout the rubber shipment.

If low degrees of interaction occur as indicated byinsufficient viscosity increase or low elongation, use of rubberwith a smaller particle size, rougher surface texture or higherrubber hydrocarbon or natural rubber content can increase thedegree of interaction.

The gradation of the rubber is very important when usingasphalt-rubber in hot-mixed paving mixtures. If the rubber particlesize is too large for the void spaces within the aggregate,compaction difficulties can occur and mixes can act • spongy· aftercompaction. Since the voids in the aggregate depend on thespecific mix type, different rubber gradations are suited fordifferent mix types. For open-graded mixtures, large rubberparticles can be used without problems. Dense-graded mixtures,however; require use of finer rubber to produce mixes whichcompact appropriately. Suggested gradations are as follows:

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Sieve SizePercent Passing

Open-graded mix Dense-graded mix

No. 10No. 16No. 30No. 80No. 200

Rubber Content

10075-10025-600-200-5

10095-10070-1000-200-5

The maximum amount of rubber which can be used inasphalt-rubber for hot-mixed paving applications is limited by therequirement that the asphalt-rubber must be capable of beingpumped, and mixed appropriately with the aggregate. Asphalt-rubbermaterials with viscosities of up to 4000cp at 3500 F (as indicatedby a Haake Rotational viscometer) have been found to be acceptablefor use in dense-graded mixtures. If viscosities significantlyexceed 4000cp at 3500 , aggregate coating problems during mixingcan result. Higher viscosities (up to 6000cp) have been used withopen-graded mixtures without aggregate coating problems.Generally, with most asphalts and typical rubber types appropriatefor hot-mixed paving, maximum rubber contents based on viscosityare approximately 18 to 20% by total weight of the asphalt-rubbermixture.

The minimum rubber content required is based on producingappropriate consistency at high service temperatures (softeningpoint) and elasticity (resilience). Increasing the rubber contentprovides both incr.eased elasticity and increased high temperaturereinforcement of the asphalt-rubber. Generally, rubber contents ofat least 15% by total asphalt-rubber mixture weight are requiredto meet requirements of Table 1.

Table 2 shows properties of blends of asphalt-rubber atseveral rubber percentages. Figure 4 is a plot of the test dataversus rubber content. Note that for these combinations, hotclimate properties are met at rubber contents of betweenapproximately 16 and 19% rubber. Also note that the mixtureviscosity increases rather linearly up to a rubber content of 15%and then begins to more rapidly increase with increasing rubbercontents. Figure 4 indicates that a 1500cp viscosity is achievedwith 15% rubber, and that 4000cp is achieved at 19% rubber, a 4%range. An appropriate selection for rubber content for thismixture would be 17% to provide a mixture in the center of theviscosity range while meeting other properties for a hot climateasphalt-rubber. Testing would then be required during theadditional heating periods as previously discussed.

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Interaction Conditions

The time and temperature conditions for the interactionbetween the asphalt and the rubber need to be specified because ofthe influence on resulting properties. As previously discussed, animportant consideration for an asphalt-rubber material is.stability of properties over time periods experienced duringconstruction. Appropriate temperatures for asphalt-rubberinteraction are 350 +/- 250 F. In this temperature range, theinteraction generally proceeds quick enough to reach desiredproperties within 30 minutes to 1 hour after blending the rubberwith the asphalt while providing adequate property retentionduring extended heating. At temperatures lower than 3250 F,interaction periods which are generally greater than 1 hour arerequired to achieve desired properties. This can cause lowproduction rates .. Temperatures in the range of 3750 to 4250 Fquickly produce desired properties, but may lack in propertystability during extended heating periods. Table 3 shows test dataduring a 24 hour laboratory. interaction period for a typicalasphalt-rUbber blend. These data indicate a uniform viscosity from30 minutes of interaction to 24 hours, and adequate stability ofphysical properties to meet moderate climate property limits ofTable 1 throughout the 24 hour interaction period.

DESIGN OF DENSE-GRADED ASPHALT-RUBBER CONCRETE

Both Marshall and Hveem methods (39) with slight·modifications can be used for design of dense-gradedasphalt-rubber concretes. Both procedures essentially consist of'selecting aggregates and binder, compacting mixes at varyingbinder contents, analyzing compacted specimen voids, mechanicaltesting, and then selecting the binder content based on dataobtained. The follouring discussions when using asphalt-rubber, canbe applied to both Marshall and Hveem procedures.

Aggregate

Dense-graded asphalt-rubber concrete pavements are composedof typical dense-graded type aggregates and appropriateasphalt-rUbber binder. Aggregate should meet the same qualityrequirements as for conv~ntional asphalt concrete which would beused in similar applications. Due to the presence of the rubberparticles in the asphalt-rubber binder, the aggregate gradationfor dense-graded mixtures should be maintained on the coarse sideof the gradation band. Gradations which plot between the maximumdensity line and the upper limit of the band should be avoided(Figure 5). Maintaining the gradation on the middle to coarse sideof typical dense-graded bands is important to provide sufficientvoid spaces in the aggregate for the rubber particles. If thegradation is too fine, or the rubber particles are too large,compaction problems resulting from rubber interference betweenaggregate particles can result. This effect is indicated by two

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observations during the mixture design procedure. First,immediately after compaction and while hot, the mixture willappear to have a somewhat unstable and • spongy· characteristic ifcoarse aggregate particies are pressed into the mix. Second~ arelatively level trend in mixture air voids data will be noticedwith increasing, asphalt-rubber contents, instead of the typicaldecrease in air voids. Both of these effects can generally bereduced and eliminated by coarsening the gradation or by reducingrubber particle size used. Suggested gradation limits for 3/8inch, 1/2 inch, and 3/4 inch maximum sized dense-graded mixturesfor use with asphalt-rubber binder are listed in Table 4.

Asphalt-Rubber

The asphalt-rubber for use in dense-graded paving mixturesshould be composed of rubber meeting the previously statedgradation limits' for use in dense-graded mixes, and theappropriate asphalt cement or blend with extenders to meet desiredphysical parameters such as those listed in Table 1.

Trial Asphalt-Rubber Contents

Due to the replacement of a portion of the asphalt by rubberin the asphalt-rubber (15 to 20%), generally, asphalt-rubbercontents to be investigated during dense-graded mixture designsare 15 to 25% higher than asphalt cement contents which would beused for the same aggregate type. During the design procedure, therubber in the asphalt should be considered as an integral part ofthe overall binder.

During specimen evaluation and analysis, the rubber is accountedfor by measuring the asphalt-rubber specific gravity or bycalculating the combined specific gravity of the asphalt andrubber by proportion. With typical asphalt cements (specificgravity of 1.00 to 1.02) and granulated tire rubber (specificgravity of 1.15-1.20), the combined specific gravity of theasphalt-rUbber is between 1.02 and 1.05 at 600 F.

Specimen Mixing

Prior to mIXIng, it is recommended that the asphalt-rubber beheated to 350 +1- 100 F, and the aggregate to 300 +1- 50 F. The350°F temperature for the asphalt-rubber is recommended for eachasphalt-rubber grade in Table I, regardless of base asphalt gradedue to the specified viscosity of between 1500 and 4000 cpo Theasphalt-rubber should be heated in an oven using the procedurecontained in Appendix 2 and should be stirred to assure uniformity(approximately 15 seconds) immediately before adding to the 3000

aggregate.Mixing of the asphalt-rubber with the aggregate should be

performed using standard types of mechanical mixers using whips orpaddles. Mixing should be performed. immediately after addition ofthe asphalt-rUbber to the aggregate. Mixing should continue for atleast 30 seconds beyond the time required to obtain completeaggregate coating. Total mix time should not exceed 2 minutes. Ifcomplete aggregate coating is not achieved in 2 minutes (which maybe due to very fine or dusty mixes) either the asphalt-rubbercontent should be increased or a liquid anti-stripping agent

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6hould be added to the asphalt-rubber to assist aggregate coating.'Following completion of mixing, the mixture should be split intoappropriate portions (approx. 1100 to 1200 gms) for compaction ofspecimens. If Hveem compaction will be used, the specimens shouldbe subjected to the standard 1400 F curing procedure for 15 hours.

Specimen Compaction

When using Marshall compaction, the individual specimensshould be placed in a forced draft oven maintained at 280 +/- 50 Ffor between 1 and 2 hours prior to compaction. Insure that themixture has reached the compaction temperature by checking theactual mix temperature with a thermometer.

Specimen compaction consists of removing the specimen fromthe oven, placing into heated Marshall molds, spading for 15times, and compacting using standard Marshall procedures.Compaction level can be 35, 50, or 75 blows per side as dictatedfor the anticipated traffic level. Compaction should be completedwithin 3 minutes following removal of specimens from the oven.

When using the Hveem procedure, the mix should be heated toa compaction temperature of 280 +/- 50 F after the curing period.Compaction then procedes using the standard Hveem kneadingprocedure. Some agencies use a compaction temperature of 3000 F.Immediately following completion of compaction, the specimens canbe evaluated for instability and ·spongyness· as previouslydiscussed. For both procedures, specimens should be allowed tocool off for a minimum of 4 hours prior to removing from themolds. The reason for this is that if specimens are removed whilestill warm, deformation due to rebound from the rubber particlesmay occur, which could distort results.

Specimen Testing

For both Marshall and Hveem procedures, following removalfrom the molds, specimens are tested using standard procedures toevaluate stability, flow, stabilometer value, density, voids, etc.

Marshall Procedure: Test results should be reportedusing standard procedures and methods. The design asphalt-rubberbinder content should be selected to provide a mixture with anappropriate level of air voids while providing appropriatestability flow, and V.M.A. as indicated for conventional mixturesin the MS-2 manual (40). Two modifications in design criteriashould be used for asphalt-rubber dense-graded concrete. First,due to the increased viscosity, elasticity, and softening point ofthe asphalt-rubber, asphalt-rubber concrete mixtures tend toexperience less compaction and densification from traffic afterconstruction. Therefore, for dense-graded mixtures containingasphalt-rubber binder, the design air void level can be set at thelower end of the 3 to 5% range. The target therefore for air voidlevel should be 3 to 4%.

The second modification in analysis of results fordetermining design binder content is that maximum flow values canbe raised to 24 for light traffic, 22 for medium traffic, and 20for heavy traffic due to the higher binder contents which aretypically required. An example of a mix design which shows dataand results for a dense-graded hot mix using asphalt-rubber is

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contained in Appendix 3. Typical design asphalt-rubber bindercontents for dense-graded mixtures range between 6.5 and 7.5% bytotal mixture weight, (7.0 to 8.1% by aggregate weight).

Hveem Procedure: As with the Marshall procedure, testresults should be reported using standard procedures and methods.Aspahlt-rubber mixtures generally yield stabilometer values whichare significantly lower than those obtained for conventia1 asphaltconcrete (31). This may be due to the more elastic behavior of thecompacted mixtures. Typical stabilometer results withasphalt-rubber dense-graded mixes are 20 to 30 when usingaggregate which produces 35 to 40 stabilities with asphalt cement.

For specification purposes, it is suggested that theaggregate to be used be verified to be capable of providing aminimum Hveem stability which meets standard specifications whenusing asphalt cement (35 or 37 minimum). The suggested value forstability when using the same aggregate and asphalt-rubber is 20minimum. During specimen evaluation, as with the Marshallprocedure, it is suggested that air voids for the design betargeted at 3 to 4 percent instead of the 4% minimum. As with theMarshall procedure, typical binder contents are 6.5 to 7.5% bytotal mix weight .

.Moisture Resistance: After the asphalt-rubber bindercontent of the mix has been determined, the moisture resistance ofthe mix should be checked. Conventional procedures such asImmersion Compression (ASTM D1075)(37), Lottman (40), orTunnic1iff-Root (41) can be used. Additives which are used toimprove moisture resistance (liquid additives, hydrated lime, orcement), of conventional asphalt concretes can be used for'asphalt-rubber mixtures. Acceptance criteria should be the same asfor conventional asphalt concrete.

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DESIGN OF OPEN~GRADED ASPHALT-RUBBER CONCRETE

The modified physical properties of asphalt-rubber binderpermit its use, in a variety of manners with open-gradedaggregates. Due to the higher viscosity of the asphalt-rubber,very high binder contents (up to 10 or 11%) can be usedeffectively without experiencing excessive drain off which occurswith asphalt cement. Use of a higher binder content results inmixes with thicker binder films, improved aging resistance andbetter durability. When using asphalt-rubber binder, high mixtemperatures can be used, again without the drain off problem, topermit construction in cooler temperatures or at longer hauldistances than with conventional open-graded mixtures. High bindercontents produce mixtures which have crack reflection reductioncharacteristics . similar to spray applied and chippedstress-absorbing-membranes (SAM's) (42). The design procedureswhich follow generally use methods outlined in the Federal HighwayAdministration Report No. FHWA-RD 74-2 titled 'Design of OpenGraded Asphalt Friction Courses' (43) with several modificationsto account for the unique properties of asphalt-rubber materials.The procedures describe methods for determining the asphalt-rubbercontent for three different types of open-graded mixtureapplications. These applications are:

• Normal free draining friction courses at low binder content• Durable friction courses at a medium binder content• Plant mix seals at a high binder content

Aggregate

Aggregate used for open-graded asphalt-rubber concreteshould meet the same quality requirements as for conventionalasphalt concrete which would be used in similar applications.Recommended aggregate gradations are listed in Table 5. Thesegradations are typical of many 3/8 and 1/2 inch open-gradedmixtures used throughout the United States. For the 3/8 inchgradation, overly thickness should not exceed 1 inch. For the 1/2inch gradation, maximum thickness should be 1 1/2 inches.

Asphalt-Rubber

The asphalt-rubber for use in open-graded paving mixturesshould be composed of rubber meeting the previously statedgradation limits for use in open-graded mixtures and theappropriate asphalt cement or blend with extenders to meet desiredphysical parameters such as those listed in Table 1. Due to thelarge void spaces which exist between aggregate particles inopen-graded mixtures, larger rubber particles can be used in theasphalt-rubber than with dense-graded mixtures.

Asphalt-Rubber Content

The suggested method for determiningcontent consists of three basic steps followedfor mix type.

theby

asphalt-rubberan adjustment

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Step 1. Determine the surface constant Kc of the aggregateusing the FHWA RD-74-2 procedure (oil soaking and drain off)(43). This procedure is also contained in the AsphaltInstitute MS-2 manual.

Step 2. Calculate the required asphalt cement content usingthe following formula: (43)

Percent Asphalt (agg. wt.) K 2.0 Kc + 4.0.

Step 3. Determine the base asphalt-rubber content bydividing the percent asphalt from step 2 by the asphaltcement (and extender if used) content of the asphalt-rubber.This provides an asphalt-cement content in the asphalt­rubber mix which is equivalent to that determined in Step 2.

Open-Graded Asphalt-Rubber Concrete Types

Open-graded mixes using asphalt-rubber can be classifiedinto three basic types depending on the binder content used.

Free Draining Friction Coarse: This type of mixture isconstructed using the base asphalt-rubber content with nomodifications. This provides a friction coarse which has skidresistance and draining characteristics similar to a conventionalopen-graded friction coarse constructed using asphalt-cement. Useof the asphalt-rubber binder provides improved durability andpermits use of higher mix temperatures for cool climates. Typicalasphalt-rubber binder contents are between 6.5 and 8.0% byaggregate weight. This mix type generally has between 15 and 18%air voids when compacted using 50 blows per side with a MarshallHammer at 2750 F. An example design is shown in Appendix 4.

Durable Friction Course: The binder content for thedurable friction course is determined by multiplying thepreviously determined base asphalt-rubber by a factor of 1.2.Typical asphalt-rubber binder contents are 8.0 to 9.5 percent byaggregate weight. This mix type has somewhat thicker binder filmthickness which results in increased durability, but with asomewhat lessened drainage capacity. This mix type generally has12 to 15% air voids when compacted using 50 blows per side with aMarshall Hammer at 2750 F.

Plant Mix Seal: The binder content for the plant mixseal type of open-graded asphalt-rubber concrete is determined bymultiplying the previously determined base asphalt-rubber contentby a factor of 1.4. Typical asphalt-rubber binder contents forthis mix type are 9 to 11% by aggregate weight. When compacted at2750 F using 50 blows of the Marshall Hammer per side, this mixtype generally has 8 to 12% air voids. The high binder contentproduces a mix with improved aging resistance, durability andresistance to reflective cracking. When this mix type is placed to

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a thickness of 3/4 inch, there will be between 0.65 and 0.8gallons of asphalt-rubber per square yard on the pavement which istypical of a stress absorbing membrane type application.

Specimen Mixing ,

Following determining the asphalt-rubber content for theapplication, mixtures of the open-graded asphalt-rubber concreteare made. The asphalt-rubber should be heated in an oven to 3500F+/- 100F and be stirred immediately proir to addition to aggregatein order to insure that the mixture is homogeneous and rubberparticles are not segregated. Proportioned aggregate should beheated to 300oFprior to mixing with the heated asphalt-rubber.

Mixing of the asphalt-rubber with the aggregate should beperformed using appropriate types of mechanical mixers using whipsor paddles. Mixing should be performed immediately after additionof the asphalt-rubber to the aggregate. Mixing should continue forat least 30 seconds beyond the time required to obtain completeaggregate coating. Total mix time should not exceed 2 minutes.

Following completion of the mixing, the mix should be splitinto 1000gr. portions for drainage testing and appropriate sizedspecimens for moisture reisistance testing.

Mixture Production Temperature Determination

Testing should be performed in accordance with the FHWARD-74-2 drainage procedure (Section 6.1). A temperature of 290°Fis recommended for starting the drainage evaluation. If drainageat 2900F after both 15 and 60 minutes is acceptable, a mixproduction temperature of 2900F +/- 100F can be used. If excessivedrainage occurs, lower temperatures should be investigated until.appropriate drainage levels are obtained. The appropriate drainagelevel is defined as no more than a slight puddle (less than 1/4inch diameter at points of contact between aggregate and the glassplate.

Moisture Resistance Testing

Moisture resistance of the mixture should be determined inaccordance with standard testing methods used for open-gradedmixtures such as Immersion Compression or 24 hour MarshallImmersion.

Immersion Compression: Testingusing ASTM D 1075 procedures (37). Mixshould be the previously determined mixpressure should be 2000 psi instead of 3000

should be performedcompaction temperature

temperature, and moldingpsi (43).

Marshall Immersion: For Marshall Immersion testing, specimensshould be compacted after conditioning at the mixing temperaturefor 1 to 2 hours. Specimen compaction should be 50 blows per sideof the Marshall hammer and compaction should be completed within 3minutes after removal from the oven.

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DESIGN OF GAP-GRADED ASPHALT-RUBBER CONCRETE

Gap-graded asphalt-rubber concrete mixtures are a variationof dense-graded 'mixtures in which the aggregate gradation iscoarsened to provide a greater amount of mixture voids.

The inceased voids permit use of an increased asphalt-rubbercontent to provide increased mixture durability. Suggestedaggregnte grading limits are shown in Table 6. Aggregate shouldmeet normal other quality requirements for asphalt concreteaggregates. Asphalt-rubber should be of the appropriate typelisted in Table 1 and should use the dense-graded type of rubber.

The Marshall design procedure for dense-graded mixtureswhich was discussed previously can be used for the design ofgap-graded asphalt-rubber concretes. During the design, it issuggested that air void levels of 3 to 5 percent be achieved.Additional criteria listed in the dense-graded design procedureshould be met except that flows can be raised to 26, 24, 22 forlight, medium and heavy traffic..

Gap-graded mixtures which have a more open gradation whichapproaches' an open-graded mix can also be used. As the gradationis opened, greater amounts of asphalt-rubber binder are requiredto produce 3 to 5 percent air voids, and the mix will take oncharacteristics closer to an open-graded mixture.

Typical binder contents for gap-graded mixture gradationslisted in Table 6 are between 7.0 and 8.5% by total mix weight.Suggested thickness limits for 3/8 inch gap-graded asphalt-rubbermixtures are 3/4 to 1 1/2 inches, for 1/2 inch mixtures, are 1 to2 inches, and for 3/4 inch mixtures, 1 3/4 to 3 inches. Ifgap-graded mixtures with more open gradations are used, maximumthickness should be reduced.

ASPHALT-RUBBER CONCRETE MIX PRODUCTION

Equipment

Asphalt-rubber concrete can be mixed in either batch or drum.type production plants. It is suggested that in order to preventcontamination of the storage tanks, and to prevent segregation ofthe asphalt-rubber. that a seperate asphalt-rubber storage tankwith appropriate agitation be used. Additionally, it is suggestedthat a seperate asphalt-rubber supply system equiped with a pumpand metering system capable of adding binder to the aggregate atthe correct percentage tbe used. Asphalt-rubber binder contentshould be maintained within plus or minus 0.5 percent of the'design value for ~ingle test values.

Mixture Production Temperatures

Suggested asphalt-rubber temperatures when being added tothe aggregate for all mix types are between 325 and 3750 F. Fordense and gap-graded mixtures it is recommended that the aggregatetemperature be 290 to 3250 F. For open-graded mixtures, aggregatetemperatures should be appropriate to result in the lab determinedmix temperature.

16

CONSTRUCTION TECHNIQUES AND GUIDELINES

Asphalt-rubber mixtures are hauled, placed, and compactedusing conventional equipment and slightly modified techniques.When hauling asphalt-rubber mixtures, truck beds should be sprayedwith a water-soap solution or dilute silicone emulsion instead ofkerosene or diesel fuel. Kerosene or diesel fuel should not beused because of an affinity for absorption into the rubberparticles which can result in mix tenderness.

Mixture laydown temperatures should not be below 2500 F foropen-graded mixtures or 2750 F for dense-graded or gap-gradedmixtures.

Asphalt-rubber mixtures should be compacted usingsteel-wheeled rollers. Pneumatic rollers should not be used due toan increased adhesiveness of the asphalt-rubber binder, which canstick to the rubber tires. Compaction should proceed quickly assoon as the mixture is capable of supporting the rollers withoutexcessive shoving. Delays should be avoided because asasphalt-rubber mixtures cool, they become more difficult tocompact due to the reinforcement provided by the rubber. Figure 6shows lab density data obtained for dense-graded mixtures madewith 120 and 60 penetration asphalt-cement, and asphalt-rubbermade from the 120 penetration asphalt and 18% minus 20 meshrubber. Note the reduced densities of the asphalt-rubber mixturein comparrison to the asphalt cement mixtures as temperature dropsfrom 2750 F to 200o F.

Open-graded asphalt-rubber mixtures should be compactedusing a minimum of 3 full roller coverages. Dense and gap-gradedmixtures should br compacted to provide a minimum of 95% of thelab compacted density. Vibratory rollers can be used with denseand gap-graded mixtures, but should not be used for open-gradedmixtures.

With some asphalt-rubberthe compacted mix may exhibitconstruction. If this occurs,application (approximately 4 lbs.be use to alleviate the problem.

concretes at high binder contents,excessive stickiness just afterit is recommended that a lightper square yard) of blotter sand

SUMMARY

This paper covers design methods which can be used forhot-mixed asphalt-rubber concrete pavements. Properties of.asphalt-rubber binders appropriate for use in hot- mixed pavingmixtures are discussed along with factors which influenceasphalt-rubber properties. Criteria for selecting the specificasphalt-rubber formula and specifications for use in hot,moderate, and cold climates are presented.

Mixture design methods for asphalt-rubber dense, open, andgap-graded mixtures are discussed. Each method followsconventional Marshall, Hveem, or FHWA procedures with suggestedmodifications to ipcorportate asphalt-rubber binder. The methodspresented can easily be performed by most laboratories proficientat asphalt-concrete mix designs with aquisition of minor pieces ofadditional equipment. Evaluation criteria and suggested propertylimits for both the asphalt~rubber and asphalt-rubber concretemixes could possibly be used as a basis for establishment ofuniform construction specifications.

17

Property

Table 1 Suggested Physical PropertyLimits for Asphalt-Rubber Materials for

Use in Hot-Mixed Asphalt Concrete Applications

Property LimitslllHot(2) Moderate ---C-o-l-d--

Climate Climate Climate

Viscosity, Haake, 3500FSoftening Point, (ASTM D36)Cone Penetration, 770F

(ASTM D3407)Resilience, 770F (ASTM D3407)Ductility, 770F (ASTM D113)Low Temperature Flexibility3

(ASTM C711 modified)

Notes:

1500-4000130°F min

20-6020% min15 ern/min

35° max

1500-4000cp120°F min

50-10010% min15 ern/min

1500-4000cp110°F min

80-1500% min15 ern/min

150 max

1). Property limits should be stipulated at a specific interactionperiod such as 60, 90, and 120 minutes.

2). Make climate selction based on the following temperatureranges from the U.S. Department of Commerce Enviromental DataService. Hot climate - average July max - 1100F-; average Jan. low ­30oF+. Moderate Climate average July max - 1000F-; average Jan.low - 15-300F. Cold Climate - average July max - 800F-; average Jan.low = 150 F-. Make the selection based on January low, then checkJuly temperatures. If July temperatures exceed those of the gradeselected based on January temperatures, use the next stiffer grade.

3). As an alternate, Cone Penetration at 39.20F, 200g, 5 sec. canbe used. Limits would be 10 min. for hot climate, 25 min. formoderate climate, and 40 min. for cold climate.

18

Table 2 Physical Properties of AsphaltRubber Blends with

Differing Rubber Contents

Percent Rubber (Mix Basis)Property 0 6 9 --11.- ~ ....l1L

Viscosity, 350°F, .cp 60 550 800 900 1500 2500

Cone Penetration,77o F 48 40 43 44 40 30

Resilience, 77°F -1 -1 12 19 23 40

Softening Point, F 122 126 136 140 142 146

Notes:

1). Asphalt is AC-20, rubber is minus No. 16 mesh.

2). Interaction period is 90 minutes at 350°F.

~

6000

27

47

162

19

Table 3 Asphalt RubberTest Data During a 24 hr

Interaction Period

Interaction PeriodTEST PERFORMED 30 60 90 120

min min min min 6 hrs 24 hrs

Viscosity. Haake @ 350°Fin centipoise 2000 2000 2200 2200 2200 2200

Penetration. Cone @ 77°Fin 1/10 mm 72 69 67 65

Resilience @ 77°F in% rebound 17 20 20 23

Ductility. 77°F 5 cm/min;cm 24 21 25 32

Softening Point in of 122 127 128 128 128 129

Fracture Temperature

of Lowest Passing 14 12 12

of Fracture 12 10 10

Notes:

1). Asphalt cement is AC-5. Penetration (D5) = 198. SofteningPoint = 1100F.

2). Asphalt Rubber Blend is 83% AC-5; 17% 20 mesh rubber.

3). Interaction temperature is 3500F.

4). 6 hour to 22 hour holdover temperature is 3000F.

20

Table 4 Suggested GradationSpecifications for Dense-Graded Asphalt

Rubber Concrete (Percent Passing)

Mix DesignationSieve Size 3/S- 1/2· 3/4·

1 1 (25.0 nm) 100 100 100

3/4 (19.0 nm) 100 100 90-100

1/2 11 (12.5 nm) 100 90-100 70-90

3/S- (9.5 nm) 90-100 75-95 60-S0

#4 (4.75 nm) 60-S0 50-70 40-60

#S (2.36 om) 40-60 35-50 30-45

#30 (600-urn) lS-30 15-25 12-22

#50 (300-urn) S-IS 6-16 5-14

#200 (75-urn) 2-S 2-S 2-6

21

, Table 5 Suggested Gradations forOpen-Graded Asphalt-Rubber Concrete

Mixtures (Percent Passing)

Mix DesignationSieve Size 3/8- 1/2-

3/4- (19.0 mm) 100 . 100

1/2- (12.5 1lJIl) 100 95-100

3/8- (9.5 om) 85-100 75-95

#4 (4.75 mm) 25-55 20-45

#8 (2.36 mm) 5-15 5-15

#30 (600 urn) 0-10 0-10

#200 (75 urn) 0-5 0-5

22

Table 6 Suggested GradationSpecifications for Gap-Graded

Asphalt-Rubber Concrete (Percent Passing)

Mixture DesignationSieve Size 3/8· 1/2· 3/4·

1· (25.0 mm) 100 100 100

3/4· (19.0 om) 100 100 90-100

1/2· (12.5 rom) 100 90-100 65-85

3/8 1 (9.5 nm) 90-100 70-90 50-70

#4 (4.75 rom) 50-65 35-50 30-45

#8 (2.36 mm) 28-40 20-32 16-28

#30 (600 urn) 12-22 8-18 6-16

#50 (300 urn) 6-16 5-14 4-12

#200 (75 urn) 3-7 2-6 2-6

23

AC-7.5 + Rubber

AC 7.5

AC-20 + Rubber

AC-20

AC-7.5 with7: Extenderand 17% Rubber

109876542 . 3

~~~.. AC-7.5 with 14% Extenderand 17% Rubber

45

40

35

z0....

30to<<l:>:z;0 25&:l~ 20IolU~Iol....

15

10

5

0

0

TIME, MINUTES

FIGURE 1. Constant Load Creep Plots For Asphalt CementAnd Asphalt-Rubber At 39F With A 500 g. Load

AC-7.5 + Rubber

AC-40

AC-20 + Rubber

AC7.5 with 7% Extenderand 17% Rubber

45

40

35

z0 30....to<<l:>Z0 25&:l£ 20IolU~Iol.... 15

10

5

0

0 2 3 4 5 6 7 8 9 10

TIME,MINUTES

FIGURE 2. Constant Load Creep Plots For Asphalt CementAnd Asphalt-Rubber At 74F With A 25 g. Load

24

AC-20

AC7.5 with 7% Extenderand 17% Rubber

AC-40

AC-7.5 with 14% Extenderand 17% Rubber

9 108765432

J~~:_;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;~AC-7 .5+RubberAC-20+Rubber

45

40

35

30

z 250....l-<<to'Z 200,..ll&l

Ii: 15\&luti 10Il.

5

0

0

TIKE. MINUTES

FIGURE 3. Constant Load Creep Plots For Asphalt CementAnd Asphalt-Rubber At lOaF With A 1 g. Load

170 6 50

c.lJ

160 0 50 400...,....~ to-!

"" 150 z 40 30....l-< ,....< ....,.... l-< 0

\0 0 -:r.., l>:: ..,~ ~

~ 140 l&l 3~

20 ~~ :r: SOFTENING POINT ~-- --Ii: "" ra-e; 130 10

....0 2 ....

14 .,.,..,to'

l&lZ l-<.... <~Z

lo.l~t: 120

........ 0 ,..l0 til ....til 0 til

u VISCOSITY ""til l>::....>

110-10

0

0 3 6 9 12 15 18 21

Rubber Content of Asphalt-Rubber (Total Weight)

FIGURE 4. Properties Of Asphalt-Rubber Blends At VariousRubber Contents (Data From Table 2)

25

.0

100

lOt.

70

to

o

40 0...z

$0 ;!...&

60 i!-

10

20

)0

f:=tI=t=1 +-1-~

~

-~

fL ..~ --- -LCRADATlON AREA -- TO AVOID.

~::L=.- .... - -~

-'-~ ~, - .- - - .. - f- . ~

~ f- - - .. _- :" '---~£'-- .--=-

ASTH 1/2" LIMITS- -.. .-

~.•.- MAXIMUM DENSITY-->--

- 1-- -~" I#-

.~

I.-f- P ._--

~'I..-. -- ,- /:I- .=-. -

I=L' 1/" -- _.

- ... --0 200 &0 )0 16 108 4 1/8 liZ ~." I.e 1.&

o

70

60

00

20

40

10

.e•

C>ZII)II)

:.

100 12SIEVE SIZEO.4~ POWER

FIGURE 5. Illustration Of Gradation Area To Avoid With ATypical Dense-Graded Gradation When UsingAsphalt-Rubber Binder

14S

140

...u~.

r::...E 135c:l

AC-7.S (120 pen.)

Compact1ve EffoTt • 15/15 Blow MaTshal1

30027S250

130 +- .... ..... ..... .....200

COMPACTION TDiP£RAnJRl. r

Figure 6. Variation Of Density Of A Dense-Graded 1/2"Mix With Asphalt Cement And Asphalt-RubberWhen Compacted At Temperatures Ranging FromFrom 200F To 300F

26

APPENDIX 1 Procedure For Lab Interaction Of Asphalt-Rubber Materials

The recommended procedure for preparing asphalt-rubber materialsin the laboratory consists of subjecting the asphalt-rubber totemperatures and times which will occur in actual use. The mixtureis then tested at several specific points in the interactionperiod to evaluate the properties of the mixture during normalapplication periods. The procedure for preparing asphalt-rubber.is as tolloo's:

1). Selection of asphalt cement, rubber, and additives for themixture.

2). Selection of the proportions of each material to be tested.

3). The asphalt cement,extender (if used) and adhesion agent (ifused) a~e placed in a standard 1 gallon open top metal can.Approximately 2,000 grams of the blended materials should beused. The materials are then heated using any convenientmethod to 50 +/- 10F above the desired temperature to be usedduring the interaction period. During heating, the materialsshould be stirred to insure uniformity. .

4). All of the granulated rubber to be used in the mix is thenadded to the heated asphalt cement and stirred in using anappropriate hand stirring device (spatula) for·approximately30 seconds or until all of the added rubber is wetted intothe asphalt.

5). The mixed material is then placed in a forced draft ovenmaintained at an appropriate temperature to maintain thedesired interaction temperature (typicallY approximately25F above the interaction temperature). The containershould be loosely covered.

6). After 15 minutes has elapsed, after the rubber has beenadded, the container is removed from the oven, then stirredby hand for 15 seconds, and then replaced in the oven.

7). The sample is then stirred for 15 seconds. after anadditional 15 minutes, and then is stirred at 30 minutesintervals until 2 hours has elapsed. During this timeperiod, while stirring, the temperature should be checkedand recorded so that adjustments in oven temperature canbe made, if required to keep the sample temperature withinplus or minus 10F from the desired interaction temperature.

8). From 2 hours to 6 hours of interaction the sample is stirredat 1 hour intervals.

9). After 6 hours of interaction, the oven temperature isreduced to 300F and the asphalt rubber sample exposed tothe 300F temperature until 22 +/- 1 hours have elapsed sincethe rubber was added to the asphalt. The asphalt rubber isthen stirred by hand for 15 seconds, replaced in the oven,and then the oven temperature is raised to raise the temperatureof the asphalt-rubber to the interaction temperature within2 hours. This completes the interaction period.

27

APPENDIX 2

Recommended Procedure for PreparingSampl~E of Asphalt Bubb~r for Testing

Introduction:

This procedure recommends methods which should be used for preparingmixed samples of asphalt rubber obtained from jobs or suppliers forlaboratory use in asphalt concrete mix design, chipseal evaluations,or other testing procedures.

Asphalt Rubber Preparation for Testing:

Heating: The sample of asphalt rubber should be placed in anappropriate metal container, no larger than 1 gallon (a standard onegallon round open top paint can is suitable). The can is then placedin an oven. (preferrably forced draft) maintained at 25 F above thetemperature the asphalt rubber is to be 'heated to. For example ifthe asphalt rubber is to be heated to 350 F, the oven temperatureshould be 375 F. Higher temperatures should not be used due to thepossibility of over reacting the rubber components. The can containingthe asphalt rubber should be covered while heating in'the oven. Afterthe material has been in the oven approximately 1 hour, the can shouldbe removed and the sample stirred for 15 seconds. At this time, thesample will not be totally melted. The can is then replaced in theoven, covered, heated for an additional 30 minutes, removed andstirred for 15 seconds again. Temperature is then checked with anappropriate thermometer. This procedure is then repeated until thesample is uniformly melted and has reached the mixing or applicationtemperature. For a 1 gallon sample it will take approximately 2 1/2hours to reach 350 F.

28

APPENDIX 3 Example Dense-Graded Asphalt-Rubber ConcreteMix Design Marshall Method

1. Aggregate - Crushed Limestone 25% 1/2", 30% 1/4-3/8", 45% crushed sand

CRADATIO~ ~~AlTSIS

jjLEND % 25\ 30\ 45\ JOB KU SPl:CIFICATIO)iFORHlTU lANGE

Jot',T£RIAL 1 2 3 ,3/"" 10(\.(' 10~ .0 10".0 100.0\ 10~'

1 '.,,, 93.0 100.0 100.0 96.3\ !'5-10C",~

"

3/B" 40.7 100.0 100.0 85.2\ e"-95'

"0. 4,. S.4 S~.2 100.0 64.1' 55-72\..:t..:- No. B ,LO S.3 88.2 '2.3\ 3E-5~\v-Iole ti~. 3" 3.5 2.7 51.2 2':.7\ If- ::\-v.

N". 2C'J 2.1 1.9 10.5 5.B\ '-f~ .

~~1.): 0::- CR .• I •:'. £.3992.f ~, 2.f2H

APPM.! !>''I SP. C~2.7f.64 ~.752~- -- 2.7 H

% A!SClf.nIOf' 1 .;> ., 2.00\ l.~iH

2. Asphalt Cement AR-4000, Penetration,77F (D5) = 49; Softening point (D36) = 120F

3. Ground Rubber Gradation

Sieve SiZE'

lID

1)6

'30

'''0'50

ISO

'100

'200

Rubber Cr8dation

100

100

!-9.9

34.5

17.4

11.6

1.4

29

4. Physical Properties of Asphalt-Rubber (16% rubber. 84% asphalt) • 350F interaction

US1 I'nFORHED 30 !Q 9(1 J20 6 hr !U!.!

°Viscos1ty, Haake .t 350 Fin centipoise 2200 4500 350(1 3800 3800 ;\JOO

Penetration, Cone E' 77°,in 1/10 Ill::, 49 51 55

Resilience E' 77°, in% rebound 26 23 20

Ductility @,,0, in empulled @f.ilure f~ em/min. 35

Softenlnt Point in 0, 144 147 145 145 144 147

fracture Temperature

0, Lo~est P.sslnt 30 28 28

0, 'racture 26 24 24

5. Asphalt-Rubber Concrete Mixture Results

Mix Temp. = 300F Compaction Temp. = 275F 50/50 Blow Marshall

.fUUORE DESIO" DATI SOKKIBI

Blnder e Bulk "elf. Denalty Air rrreou•• Stebll1ty rlowCQaleat I Sp. Or. Sp. Qr. r POC) Jptde I y. M. I. It odec I (Ppua'" ) (1I10g I DS b)

.... n 2. :"1/:;0 2.4912 14R.9 ".3' 15.0' ".6 21;11 If;

.... 5 2. :l"l',., 2 ... ,.,.., 14Q.S 3.2\ 15.1\ 5.1 2655 15

7.(1 ... .,11') 2. "r"" lSrJ.5 1.8' 15.0' 5.6 240:;', 17

7.'" '.40"12 2."~7q 150.3 1.2' 15.'" f;.1 2120; t'l

• lot.: Binder content 1. by total alature .ellht.

Recommended asphalt-rubber binder content is 6.5%

6. Moisture Resistance Results (referance 41 procedure)

U~~OND]T]ONrD SP[C]~rN

~ ~ Air Voids".ndl.

Stnnath. psi

.. ".2es? 7.7 llD---r-- ~ ,.r lot-,-~ 7.< llt;::y;- "T.79':r 1.3 DO. I

..O]STUH CONDITIONED Spr:C1~r~~ 'aid~ Bulk se; Air vo.ch '·olulll•• re) '.7tn 7.6 )().3~ ~ 1.1 2J.Lc-~ 1.1 2t./;:;;- ~ 1.3

Tt";!Hl S11<[";G7h U11C· 91 ,

, VoidSeturetion

"S.J

iI ....,2.(

T.nslh5t r.not t't p! j

IU;10".IX.I

30

APPENDIX 4 Example Open-Graded Asphalt-Rubber ConcreteMixture Design for Free-Draining Friction Course

1. Aggregate Crushed siliceous gravel

~ATJO~ ~~~'SJS

.1.0"Ill 13 32 50 5 JOI KU 5PlClnCAT1~

FDmJU IAJl(;I

K~Tn]A1. 1 :I J ,I" 100 100 100 100 10(\ 100

3/4" 100 100 100 98.5 99.9 100

112" 100 100 93.3 59.6 94.6 70-100

3/8" 100 97.7 31.2 2.' 60.0 u- 7~.,..20- 40- ,,, 99.0 29.5 4.4 1.8 24.6v-

10: o'12- 20t ,e 66.7 8.3 4.2 1.8 13.5

~

v-I 130 18.5 8.2 4.1 1.7 7.6 0- 14

1200 6.1 5-.7 2.0 1.0 3.7 0- 5

.~""K sr. CR. I 2.6119

AIJlJn>l St. CJ. i 2.71D---:I A!50;.FnOl' I 1.4

2. Asphalt Cement AR-2000

Penetration, 77F, (ASTM D5) =Softening Point, (ASTM D36) =

66117F

3. Ground Rubber Gradation% Passing

S1e..e Sbe lHOC

'10 100

'16 '9.2

')0 :J3.6-

'40 13.4

'50 4.2

'80 2.0

'100 1.2

1200 0.4

31

4. Physical Properties of Asphalt-Rubber (18% rubber. 82% asphalt).350F Interaction Temperature

TEST PUFORHI:D ~ 60 90 ill !l!!! .~

VlSCOSln. IIMKE AT 3:>0 0, 2000 2600 3400 3700 7000 (,000

IN C£I,7IPOIS£

Pn"tTRATlOl\. CONI: • 77°, 43 48 :>2II' 1/10 _

a£SlLJ£I'C[ • 77°, II' 3:> 38 33% llDom;D

DUCTILITY' 77°, 1" c:s J9Pm.UD • 'AJLUR£ •:> a/ldn.

SOl7£1'INC POINT II' 0, 137 J39 J38 142 1:>2 143

FRACTURI: TEMPIRATURI:22 240, ~"tsr PASSINC 24

of FRACTUR£ 22 20 22

5. Asphalt-Rubber Content Determination. FHWA Procedure (Reference 43)

Oven Dried Sample weilht

Oil Saturated and Drained wei&ht

Apparent S.r.. of Aggregate

Correction factor (2.7113/2.6:»

Corrected %Oil Retained

Surface Constant (~c)

.it~nous Content (2~(aubC) + 4.0) aI/A

JOO.O&

J02.0

2.7113

1.02

2.04

1.1

7.56

Base asphalt-rubber content = 7.56%(by aggregate, 7.0% by mix)

Binder Contents (Mix Basis)Free-Draining Friction Course =Durable Friction Course (7.0 x 1.2)Plant Mix Seal (7.0 x 1.4) =

7.0%= 8.4%9.8%

6. Drainage Evaluation at 275F, FHWA Procedure (Reference 43)

Asphalt Rubber Content

7.0%

15 .tnute reault

S11rht'

60 mnute naul t

S11Sht ,

NOTI: OnJy a very alight amount of drainage vas observed at 15 and 60 min.Maximum plate vetting va~ in a contact point diameter of less thanl. inch. .

32

7. Density and Air Voids of Compacted Mix

Sp~c1wn No. Bulk S.C. )laxisum S.C. knottv Mr Void~

~ 1.9141 2.2424 119.4 14.6

6 1.9439 2.2424 121.3 14.6

---Av~raf:~ 1.9290 2.2424 120.4 J4.6

IIOTE:

1. Bulk ap~cific Ir.vity d~t~radn~d USiD, parr. fin coat~d .p~Ci.eDS.

2. tux t~lllp•• 300r. COlllpacUon tellp•• 27ST.

3. Compaction. ~O/SO blo~ ~Arshall.

4. "phalt rubb~r cont~nt • 7.01 (atx ba.is).

8. Moisture Resistance Evaluation, Marshall Immersion Procedure

UNCO~~ITIOhLD SPECIMENS MOISTl~ CONDITIONED SPECIMENS

Sp~c1l11en Hershal) Hershal) Sp~ci_n ....rahell HerahallNo. !!.ill!!t.1: -~ ~'- S!!bU1ty Flow

3 960 27 900 24

, 880 22 2 700 31

----Av~rag~ 920 24.5 Awrage 800 27.~

Stability Ratio· 871

IIOTES:

J. Sp~ci_ns all contained 71 (atx basis) asphalt rubb~r.

2. tux t~mp•• 300r, compaction t~mp•• 27Sr.3. Compaction· SO/~O Harshall.,. Hoistur~ conditioning conaiated of a 24 bour aoak at J40F in .at~r.

33

REFERENCES

1. Green, E.L., and Tolonen, W.J., ·The Chemical and PhysicalProperties of Asphalt-Rubber Mixtures Basic MaterialBehavior· Report No. ADOT-R5-14 (162), Arizona Department ofTransportation, July. 1977.

2. Pavlovich, R.D., Shuler, T.S.and Physical Properties ofSpecifications and TestFHWA/AZ-79/121, ArizonaTransportation,November 1979.

and Rosner, J.C., ·ChemicalAsphalt-Rubber-Phase II-Product

Procedures·, Report No.Department of

3. Rosner, J.C., and Chehovits, J.C., ·Chemica1 andProperties of Asphalt-Rubber Mixtures-Phase IIIReport and Volumes 1-5, Report HPR 1-19 (159),Department of Transportation, July, 1981.

PhysicalSummaryArizona

4. Piggot, M.R., and Woodhams, R.T., IRecycling of Rubber Tiresin Asphalt Paving Materials· Department of ChemicalEngineering and Applied Chemistry, University of Toronto,Toronto, Ontario, March 1979.

5. Oliver, J.W.H., ·A Critical Review of the Use ofPolymers in Bitumen and Paving Materials·,1037-1, Australian Road Research Board, 1977.

RubbersReport

andAIR

6. Oliver, J.W.H., ·A Limited Laboratory Evaluation of aBituminous Plant Mix Material Containing Scrap Rubber·,Report AIR 178-8, Australian Road Research Board, 1976.

7. Oliver, J.W.H., ·Preliminary Investigation of the ElasticBehavior of Digestions or Comminuted Type Tread Rubber in aBitumen·, Australian Road Research Board, November, 1978.

8. Shuler, T.S., ·An Investigation of Asphalt-Rubber Bindersfor Use in Pavement Construction· Ph.D. Dissertation,Graduate School, Texas A&M University, College station,Texas, August, 1985.

9. Oliver, J.W.H., ·Modification of Paving Asphalts by Digestonwith Scrap Rubber·, T R R 821, Transportation ResearchBoard, Washington D.C., 1981, pp.37-44.

10. Schuler, S., Adams, C., and Lamborn, M., ·Asphalt-RubberBinder Laboratory Study·, Researsh Report FHWA A/TX-85-71 +347-1F, Texas A&M University, College Station, Texas,August, 1985.

11. Lalwani, S., Abushihada, A., and Halasa, A., IReclaimedRubber-Asphalt Blends Measurement of Rheological Propertiesto Asses Toughness, Resiliency, Consistency, and TemperatureSensitivityl, PROCEDINGS, AAPT, Volume 51, 1982, pp. 562-579.

34

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