Design Me thods f o r Hot-Mixed Asphalt­Rubbe r Conc rete Paving Materials

James G. Chehovits

I NTRODUCTION

The properties and use of a s phalt-rubber materials for various paving and maintenance activit i es have been well documented in the lite r a ture. The majority o f thi s li terature r eports on properties of asphalt-rubber mater ial s (1-12), and use of asphalt -rubber in s tress absor bing membranes ( SAM) and inter l aye r s (SAMI) (13-25). Research s tudies have shown that a s phalt -rubber mater ial s have significantly modified phys i ca l prope rties when compared to asphalt cement. These mod i fi cations inc lude inc reased high t emperature modulus , viscosity, and toughness ; increased elasti c ity , r educed temperature suscept i bi lity , and less age hardeni ng. In several states and countries abroad , use o f asphalt - rubber in S~~ and SAMI appl i cat i o ns has become r out ine construction prac ti ce for r ehabilitat ing dete riora ted pavements and extending overlay life .

In the United St8tes, asphalt-rubber material s have been used on a limi ted basis as the b inder f o r ho t-mixed asphalt concrete pavements. A r ecent survey by the Asphalt-Rubbe r Producers Group (ARPG) i ndicated that at l east 35 projects which used asphalt-rubber b inde r were placed between 1975 and 1987 in 12 s t ates. Several research studies have been completed whic h investigated use of aspha lt-rubber as an asphalt concrete paving binder (26, 27) . Addit i ona lly, there have been several we ll documen t ed fi e ld t est projects placed by several states (28 , 29, 30 , 31). The li terature indi cates that several o the r countries have used a sphal t-rubber binders f o r ho t-mixed paving (32, 33 , 34) .

Limited information i s currently avai l abl e o n methods to be used f or deSigning hot-mixed a spha lt concrete mixtures whe n using asphalt - rubber binder s. vallerga (35) has suggested several s pec ifi ca ti on changes whi ch should be made when using aSPhalt-rubber. Hoy t and lytton (27) r epor ted o n a mixture design procedure f or a spha lt-rubber paving mixtures which wa s used in a lab research program that studied the feasibility of us ing asphalt-rubber binder in de nse graded airfield pavements.

The purpose of thi s paper is to describe design procedures which have been developed since 1984 as the result of approx imate ly 30 ho t-mixed paving pro jects which used a sphalt-rubber binde r. Procedures f or selecting the asphalt-rubber materia l proportions and r esul ting desired properties , mixture aggregates, and binder cont en t s f or dense , open , and gap graded mixture types a r e prese nted al ong with s uggested cons truction guidelines and spec ifi cations .

FACTORS WHICH INFtUENCE ASPHALT-RUBBER PROPERTIES

The interaction whi ch occurs between asphalt and recycled rubber has been snown to be dependent on a variety of factors:

• Asphalt physical and chemi cal properties • Rubber physical and chemical properties • Time • Temperature • Mixing conditions (high shear or low shear) • Use of add.i ti ves

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

Asphalt Cement

Chemical and physical properties of the asphalt influence several properties of the asphalt-rubber. Stiffness (asphalt grade) and tempe rature suscept i bility will influence high t emperature and low temperature performance of the asphalt- rubber. Chemi ca l make-up o f the asphalt will influence the degree of interacti on which occurs bet~en the a sphalt and the rubber. Asphalts which have higher degrees of aromaticity tend to dissolve and interact with rubber to a greater degree than asphalts with lower aromatic contents .

Rubber

Several character is tics of the rubber influence properties of the asphalt-rubber blend. Physical rubber c haracteristics including particle size (gradation) , shape (angular or elongated) , · surface texture (as influenced by grinding method) , and contaminant presence (fibers, etc.) influence properties of the asphalt-rubber. Chemical compositional character isti cs also influence blend properties. These characteristics include rubber hydrocarbon content , specific type of rubber polymer or blends (amount of SBR and natural), plastic izer content , and reinforcement type and content (carbon black and other materials).

Time and Temperature

Various research projects have shown that the time exposure and temperature of the asphalt-rubber blend influence physical properties . Increased time results in greater inte raction. Increased temperature results in quicker interaction.

When physical properties of asphalt-rubber are monitored, the material will thicken (increase in viscosity) as the rubber particles swell in the asphalt. After a period of time, depending on temperature and materials properties . the rubber will begin to break down (devulcanize and melt), and viscos ity will reduce.

Rate of devul canization will also be influenced by the mixi ng conditions. Because of these influences , it is important that asphalt-rubber blend s be checked for appropriate properties at a variety of time periods which can occur during actual use .

Mixing Condi ti ons

The amount of s hear . or intens ity o f mi xi ng . will influe nce the properties o f the aspha lt-rubber. Produc ti on mixing ~ys tems

are designed t o ' i nsure uniform wett ing and suspension of the rubbe r particles in the asphalt.

It is important that lab mixing procedures do not s ubjec t the a sphalt-rubber t o excessive amount s of s hear whi c h could quic ke n the rubber devul canization process.

Additives Extending oils can be used t o soften the mate ri a l f o r

improved low t emperatur e performance a nd f or improving the degree of interact i on between the aspha lt a nd rubbe r . Adhes i on agents commonl y used in asphalt paving (heat stable anti-stripping agents) can be used t o imp r ove film stripping r es istance . Diluents whi c h are used in asphalt-rubber chip sea l appli cati o n must no t be used in hot -mixed applications .

TEST METHODS FOR ASPHALT RUBBER

The physica l prope rti es of asphalt-rubber have been shown in a vari e ty o f studi es t o be substantially different tha n f o r unmodified asphalt cement (1-12). Many o f these s tudies have used common a sphalt tes t procedures as well a s non-s tandard procedur es t o attempt t o quantify the modified physical properti es o f a sphalt-rubber . The non-standard procedures inc lude Schweyer Rheomete r (2 . 3) . s liding plate v iscometer (1.3). force ductility (2.3 . 8.10). torque f ork viscosity (2,3.8.10), mechani cal spect rogra ph (1) , and several o thers.

Physical attributes o f a s phalt-rubbe r whi c h should considered for ho t-mixed applications inc lude :

e Viscosity at hi g h t e mperatures f or appropriate mixing and compactio n characteristics.

• Consistency at high pavement experienced during the summer.

s urface tempe ratures

• Cons istency at moderate temperatures.

• Elast i c ity

• Low temperature characteristi cs

Testing me thods whi c h can be used t o eva luate these attributes are 8 5 f o ll ows:

Vi scos ity

The viscosity of asphalt-rubber materia l s tempe ratures (250-4000 F) can easily be monitored using type viscome ters such as a Haake hand he ld portable (10 ) or a Brookfi e ld viscometer (ASTM 03236)(36).

at high r otati ona l viscometer

High Tempera ture Cons i stenc y

The cons i stency of- asphalt-rubber at high pavement surface t emperatur es can be indi cated by severa l procedures inc luding Ring and Ball Softeni ng Point (ASTM 036) . Modi fi ed Fl ow (ASTM 03407). or a cone penetra t ion et 1220F (ASTM 03407 end 05)(37).

Moderate Temperature Consistency

Moderat e ea s ily by using

Elasticity

t emperature (770F) the ASTM 03407 Cone

consis t en cy can be eva luat ed Penet ration test at 770F (37),

The e last i c ity of asphal t rubber can simpl y be evaluated u s ing the ASTM D~407 r esilience test whi ch indicates the amount of r ebound unde r a 75 gram l oad at 770F (37).

Low Temperatur e Characteristics

Several t es t me thod types can be used to provide an indication of l ow temperature prope rties. These inc lude Cone Pe netrat i on (ASTM 03407) at 32 or 39.2o F ; Ductility at 39.2o F (ASTM 0113) and Low Tempera t ure Fl exibi lity (Modif i ed ASTM C 711 . sec ti on 7.2 u s ing a 900 bend in 10 seconds at l ower and lowe r t emperatures until fra c ture occur s) (37,38).

SELECTION OF ASPHALT RUBBER FORMULA

The physica l properties of asphal t-rubber depend on the ingredients and interac ti on conditions . The refore. to obtain the desired properti es . appropr i ate ingredients and interacti on cond i t i ons must be chosen . These choices wh i ch must b e made are:

e Selecting the asphalt cement source and type. • Se lec ting the rubber source and t ype. • Selec ting the rubber con t ent. • Selecting the interacti on conditions.

Additionally, it i s important that the asphalt-rubber material have appropriate s t abi lity of properties . since properties vary with interacti on time and time of interaction can vary during ac tual use . Therefore, t est ing o f an a spha lt-rubbe r blend of ingr edient s during projec t formulation studi es should be performed no t j ust at a single interaction period, but at a vari ety of interacti on pe riods t o evaluate stability and retenti on o f properties. A procedure f or interac ting the asphalt-rubber f or 24 hours during formulation s tudies i s contained in Append ix 1 . Physical properties can be evaluated from samples poured at 3D , 60 . 90 . and 120 minutes of inte raction t o identify property retention during nor mal usage periods after comp l etion of field mi xi ng. Tests at 6 hour s Can iden tify properties of the blend if

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 lower temperature to simulate overnight unheated storage) can indicate stability o f properties if the asphalt-rubber i s to be used the next day.

Suggested physica l property limits for asphalt-rubber materials for hot-mixed asphalt-concrete applications are listed in Table 1 for hot, moderate , and cold c limates.

Asphalt-Cement

The grade of asphalt cement used major influence on blend properties over range.

in asphalt-rubber, is a the entire temperature

Asphalt cement for asphalt-rubber should meet appropriate specifications for paving use such as ASTM 03381 or 0946. Typical grades used range from AC-2.5 t o AC-20, o r 200-300 penetration to 60-70 penetration. It is important that the specific asphalt cement be compatible , or capable of interacting with the specific rubber being used. This is indicated by appropriate increases in viSCOSity during the interact ion period. Since the interaction with rubber results is an increase in high temperature modulus, asphalt cements used are typically somewhat softer than usual unmodified asphalts used for similar applications.

Figures 1,2, and 3 , show results of constant load creep tests performed on asphalt-rubber materials which contained a variety of asphalt-cement grades each with 17% by total weight of a minus 20 mesh tire rubber. Testing was performed using a procedure reported by Cotzee and Monismith (24). Data shown in these figures indicates that addition of rubber produces a stiffening effect at moderate temperatures (740F) which i s approximately equivalent t o using an asphalt which is 2 to 3 grades harder . At lOOoF, the effect is even greater. At low temperature (390 F) however, the effects of stiffening are much less. For the asphalts which were approaching the brittle point (the AC-20 and AC-7.5) at 390F. creep with rubber was very similar to creep of the unmodified asphalt. Thi s data therefore indicates that asphalt-rubber materials and unmodified asphalt creep at similar rates at low temperatures near the base asphalt brittle paint. However, as temperature increases , the a sphalt cement reduces in st iffness to a greater degree than the asphalt-rubber as indicated by reduced creep of the asphalt-rubber . The effect becomes greater as temperatures increase. The data suggests that it is pOSsible to use asphalt cements in asphalt-rubber which are softer than the normal unmodified paving grade used for the specific application to provide reduced stiffness (higher degrees of creep) at low temperatures and increased stiffness (reduced creep) at high temperatures.

Base asphalt grades asphalt-rubber material a climate property limits of

wh i ch ha ve meeting the

Table 1 are as

been found to hot, moderate, follows:

produce and cold

Climate Type

Hot

Moderate

Cold

Base Asphalt for Asphalt -Rubber AR Grade AC Gr ade Penetration Grade

AR-4000,AR- 2000 AC- 20 , AC-IO

AR-IOOO AC- 5 , AC- 2.S

AR-1000 with 3% to 6% extender

AC 2 . 5 with 0-3% extender

60-70, 85-100

120-150,200-300

200- 300 with 0-3% extender

Var i ous extending oi l s can be used in asphalt-rubber materials t o inc r ease the interac ti on between the asphalt and rubbe r, and to improve l ow t empe rature performance by decreasing the stiffness of the asphalt - rubber when softer asphalt grades are not a vailable. Extender types used are generally napthenic or aromat i c petrol eum oi l s whi ch have a minimum flash point of 400°F.

For most common o il s with viscosities between 500 and 3000 SUS at 1000F, approximately 3X by asphalt weight is requi r ed to soften an asphalt an equ ivalent of 1 grade . Typi ca ll y , each percent of extender oil l owers ring and ball softening point (ASTM 0 36) r esults by 1 . 5 to 2.0 degrees Farenheit.

Rubber

Rubbe r used for aspha lt-rubber should be primarily made from r ecyc l ed pneumatic tires . The rubber s hould be ground on appropriate systems, a nd s hould be free from con t aminants inc luding mineral matter , fiber and metal . The rubber should be sufficiently dry to prevent foaming when added to hot asphal t. Generally this means a moisture content o f les s than 0.75%. Mine ral contaminants shou ld no t exceed 0.25%. The rubber may be produced from buffings . whole tire, or stampi ngs. The rubber hydrocarbon content s hould be between 40 and 50% and should be r e l a tive l y uniform throughout the rubber shipment.

If low degrees of interaction occur as ind i cated by insuffi c ient viscosity increase or l ow elongation, use of rubber with a smaller particle size , r ougher surface texture or higher rubber hydrocarbon or na tural rubber content can inc r ease the degr ee o f interact i on.

The gradation of the rubber i s very important when us ing a spha lt-rubber in ho t·mixe d paving mixtures. If the rubbe r particle size i s too large f or the vo id spaces within the aggregate, compaction difficultie s can occur and mixes can a c t • spongy · after compaction. Since the voids in the aggregate depend on the spec i fic mix type, different rubber gradations are suited for different mix types. For open- gr aded mixtures , l arge rubber particles can be used wi thout problems. Dense-graded mix tures , however; requi r e use of fine r rubber to produce mixes which compact appropriately. Sugges t ed gradations are as follows:

Sieve Size

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

Rubber Content

Percent Open-graded mix

100 75- 100 25-60 0-20 0-5

Passing Dense- graded mix

100 95-100 70-100 0-20 0-5

The maximum amount of rubber which can be used in asphalt-rubber for hot-mixed paving applications is limited b~' the requirement that the asphalt - rubber must be capable of being pumped, and mixed appropriately with the aggregate. Asphalt-rubber materials with viscosities of up t o 4000cp at 3500F (as indicated by a Haake Rotational viscometer) have been found to be acceptable for use in dense-graded mixtures . If viscosities significantly exceed 4000cp at 3500 • aggregate coa ting problems during mixing can result. Higher v i scositi es (up to 6000cp) have been used with open-graded mixtures without aggregate coating problems. Generally. with most asphalts and typical rubber types appropriate for hot-mixed paving, maximum rubber contents based on viscosity are approximately 18 to 20% by total weight of the asphalt-rubber mixture.

The minimum rubber content r equired is based on producing appropriate consistency at high service temperatures (softening point) and elasticity (resilience). Increasing the rubber content provides both incr.eased elasticity and increased high temperature reinforcement of the asphalt-rubber . Generally , rubber contents of at least 15% by total asphalt-rubber mixture weight are r equired to meet reqUirements of Table 1.

Table 2 shows properties of blends of asphalt-rubber at several rubber percentages. Figure 4 i s a plot of the test data versus rubber content. Note that f or these combinations. hot climate properties are met at rubber contents of between approximately 16 and 19% rubber. Also note that the mixture viSCOSity increases rather linearly up to a rubber content of 15% and then begins to more rapidl y increase with increasing rubber contents. Figure 4 indicates that a 1500cp viscosity is achieved with 15% rubber, and that 4000cp is achieved at 19% rubber , a 4% range . An appropriate se lec ti on for rubber content for this mixture would be 17% to provide a mixture in the center of the viscosity range while meeting other properties for a hot climate asphalt-rubber. Testing would then be required during the additional heating periods as previously discussed.

Interaction Conditions

The time and temperature cond iti ons for the inter action between the ~sph~ lt and the rubber need to be spec ifi ed because of the influence on resulting properties. As previously di scussed, en i mportant con s i derat i on for an asphalt-rubbe r materia l is stability o f pro perties over time per i ods experienced during construction. Appropriate temperatures f or asph~lt-rubber inte rac ti on ere 350 + /- 250F. In this temper~ture range , the inte raction generally proceeds quick enough t o r each desi red properti es within 30 minutes to 1 hour after blending the rubber with the a s phalt while prov iding adequate property r e t ent i on during ex t ended heat ing . At temperatures lower than 3250 F, int e ra ction periods whi ch are generally greater than 1 hour are required t o achieve d es ired properties . Thi s can cause low prod uction rates . . Temperatures in the range of 3750 t o 42SoF qui ckly produce desired properties , but may lack in property stability d ur ing extended heating periods. Table 3 shows test data during a 24 hour laboratory . interaction pe riod f o r a typi cal asphalt-rubber blend . These data indi cate a uniform vi scos ity from 30 minu t es of interac ti on to 24 hours, and adequate s tability of phys i ca l properties to me et moderate c limate property limits of Tabl e 1 throughout the 24 hou r interaction peri od.

DESIGN OF DENSE- GRADED ASPHALT-RUBBER CONCR ETE

Bo th Marshall and Hveem methods (39) with sl i ght · modi fications can be used f or design of dense-graded asphalt -rubber concre t es. Both procedures e s sentially cons i st of' selecting aggregates and binder, compac ting mixes at varying binder contents , ana lyzing compacted spec imen voids, mechanical t est ing , and then select ing the binder con t ent based on data obtai ned. The follo\1'ing discuss i ons when us ing a spha lt-rubber, can be applied to both Marshall and Hveem procedures .

Aggregate

Dense-graded asphalt-rubber concrete paveme nt s are composed of typi ca l dense -graded type aggregates and appropriate aspha lt-rubber binder . Aggregate should meet the same quality requirement s as f or conv.enUonal asphalt concrete which would be used in similar applications . Due to the presence of the rubbe r parti c l es in the asphalt-rubber binder, the aggregate gradation for dense-graded mixtures should be maintained on the coarse side of the gradation band. Gradations which plot between the maximum densi ty line and the uppe r limit of the band should be avoided (Figure 5). Mai nt ai ning the gradation on the middl e to coarse side of typi cal dense-graded bands i s important t o provide sufficient void spaces in the aggregate for the rubber particles. If the gradation i s too fine, or the rubber particles ere t oo large , compaction problems resulting from rubber interference between aggregate parti c les can r esult . Thi s effect i s indicated b~' t wo

observations during the mixture design procedure. First , immediately ~fter compaction and while hot, the mixture will appear to have a somewhat unstable and • spongy ' characteristic if coarse aggregate particles are pressed into the mix. second ", a r elatively level trend in mixture air voids data will be noticed with increasing . asphalt-rubber contents , instead of the typical decrease in air voids. Both of these effects can generally be reduced and eliminated by coarsening the gradation or by reducing rubber particle size used. Suggested gradation limits for 3/8 inch, 1/2 inch, and 3/4 inch maximum sized dense-graded mixtures f or use with asphalt-rubber binder are li sted in Table 4 .

Asphalt-Rubber

The asphalt-rubber for use in dense-graded paving mixtures should be composed of rubber meeting the previously stated gradat i on 1 imi t s ' for use in dense-graded mixes, and the appropriate asphal t cement or b l end with extenders to meet desired physical parameters such as those listed in Table 1.

Tri al Asphalt-Rubber Contents

Due to the replacement of a portion of the asphalt by r ubber in the asphalt-rubber (15 t o 20~), generally. asphalt - rubber contents to be investigated during dense-grade d mixture designs are 15 to 25X higher than asphalt cement contents which would be used for the same aggregate type. During the des ign procedure . the rubber in the aspha lt should be considered as an integral part of the overall binder.

During specimen evaluation and analysis , the rubber is accounted f or blio' measuring the asphalt - rubber specific gravity or by calculating the combined specific gravity of the asphalt and rubber blio' proportion. With typical asphalt cements (specific gravity of 1.00 to 1 .02) and granulated tire rubber (spec ific gravity of 1 . 15-1. 20), the combined specific gravity of the asphalt-rubber is between 1.02 and 1.05 at 600F.

Specimen Mixing

Prior to mixing, it i s recommended that the asphalt - rubber be heated to 350 +/- 100 F t and the aggregate to 300 +/- SOF. The 3500 F temperature for the asphalt - rubber is recommended for each asphal t-rubber grade in Table I, regardless o f base asphalt grade due t o the specified viscosity of between 1500 and 4000 cpo The a sphalt-rubber s hould be heated in an oven us ing the procedure contained in Appendix 2 and should be stirred to assure uniformi ty (approximately 15 seconds) immediately before adding t o the 3000

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

performed using standard types of mechanical mixers u s ing whips or paddles. Mixing should be performed immediately after addition of the asphalt-rubber to the aggregate. Mixing should continue for at least 30 seconds beyond the time required to obtain complet e aggregate coating. Total mix time should not exceed 2 minutes. If complete aggregate coating i s not achieved in 2 minutes (whiCh may be due to very fine or dusty mixes) either the asphalt-rubber content shou ld be increased or a liquid anti-stripping agent

~hould be added t o the asphalt - rubber t o assist aggregate coating. · Fo ll owi ng compl et i on of mixing, the mixture should be split into appropr iat e po rti ons (approx . 1100 t o 1200 gms ) f or compaction of spec i me n s . If Hveem compaction will be used , the spec imens should be sub jec ted to the standa rd 1400 F curing procedure for 15 hours .

SpeCimen Compact ion

When using Marshall compaction , the indi v idua l spec imens s hould be placed in a forced draft oven maintained at 280 + /- 50 F f or between 1 and 2 hours prior to compaction. Ins ure that the mixture has r eached the compacti on temperature by checking the a c tual mix temperature with a thermometer.

SpeC imen compaction cons i s t s of r emoving the specimen from the oven , plac ing into heated Marsha ll molds , spading for 1 5 times , and compacting us ing standard Marsha ll procedures. Compact i on l evel can be 35 , 50 , or 15 blows per side as dictated f or the anti c ipated tra ffic leve l . Compacti on should be completed within 3 minutes f o llowing removal of spec i mens from the oven.

When using the Hveem procedure , the mix shoul d be heated t o a compac ti on t empe r a ture o f 280 +/- 50F aft er the curing period. Compaction the n procedes using the standard Hveem kneading procedure . Some agencies use a compa cti on t emperat ure of 3000F. Immediate l y f o llowing completion o f compact i on , the specimens can be eval ua t ed f or ins tability and ' spongyness ' as p revi ous l y discussed. For both procedures, specimens should be a llowed t o cool off f or a min i mum o f 4 hours pri or t o r emov ing from the mo lds. The reason f o r this is that if specimens are r emoved whi l e still warm, d e f ormati on due to rebound from t he rubbe r particles may occur, which cou l d distort r esult s.

Specimen Testi ng

For bo th Marshall and Hveem procedures , f o llowing r emoval from the molds , s pec i mens are tes t ed using stand a rd procedures to evaluate stabi lity , fl ow , stabilome t er value, density, voids , e t c.

Marsha ll Procedure: Tes t r esult s should be r eported USing s tanda rd procedures and me thods. The design asphalt-rubber binder con t en t s hould be selected to provide a mix ture with a n appr opr iate l eve l of air voids while providing appropriate stability fl ow , and V. M. A. a s indi cated f o r conventi onal mixture s in the MS-2 manual (40). TWo modifications in d es ign c riteri a should be used f or aspha lt-rubbe r dense-graded concr e t e . First, due to the inc reased viscosity , elasticity, and soften ing point o f the a sphalt-rubb'er , asphalt- r ubber concr ete mixtures tend to experience less compac tion and dens ifi cati on from traffi c after construction. Therefor e , f o r dense-graded mixtures containing asphalt-rubber binder , the desi gn air void leve l can be set at the l owe r end of the 3 t o 5% range. The target theref or e for air void l eve l s hould be 3 to 4%.

The second modification in ana lYSis of r esult s f or d e t e rmining design binder content i s that maximum fl ow values can be rai sed t o 24 f or light traffic , 22 f or med ium traffiC, and 20 for h e avy traffic due t o the higher binde r contents which are typically r equired . An e xample of a mix design which shows data and r esu lt s for a de nse - graded hot mi x u s ing asphalt - rubber is

contained in Appendix 3 , Typi c al d es ign a s phalt - rubber binde r contents f or dense- graded mixture s range between 6.5 and 7 . 5% b~1 total mixture weight, (7.0 t o B.Il by agg regate weight).

Hveern Procedure: As with the Marshall procedure . test results should be reported usi ng standard procedures and methods. Aspahlt-rubber mixtures generally yield stabilometer values whi ch are significantly lower than those obtained for convential asphalt concrete (31). This may be due to the more elastic behavior of the compacted mixtures. Typical stabilometer res ul ts wi th asphal t-rubber dense - graded mixes are 20 to 30 wh en using aggregate whi c h produces 35 to 40 stabilities with asphalt cement.

For specification purposes lit is suggested that the aggregate to be u sed be verified t o be capable of providing a minimum Hveem stability which mee t s standard specifications when using asphalt cement (35 or 37 minimum) . The suggested value f o r stability when using the same aggregate and asphalt-rubber i s 20 minimum. During specimen evaluation , as with the Marshall procedure, it i s suggested that air voids f or the design be targeted at 3 to 4 percent instead o f the 4% minimum. As with the Ma r s hall procedure , t ypi cal binder contents are 6 . 5 t o 7.5% by total mix weight .

. Mo isture Res i stance: After the asphalt - rubber binder content of the mix has been determined , the moisture resistance of the mix should be checked. Conventional procedures such as Irrrnersion Compression (ASTM 01075) (37), Lottman (40). or Tunnicliff-Root (41) can be used. Additives whi ch are used t o improve moisture r esistance ( l iquid additives , hydrated lime , or cement). of conventiona l asphalt concretes can be used f o r asphalt-rubber mixtures. Ac ceptance criteria should be the same a s for conventional asphalt concrete .

DESIGN OF OPEN-.GRADED ASPHALT- RUBBER CONCRETE

The modified physical properties of asphalt - rubber binder permit its use . in a variety of manners with open-graded aggregates. Due to the higher viscosity of the asphalt-rubber, very high binder contents (up to 10 or 11%) can be used effectively without experiencing excessive drain off which occurs with asphalt cement . Use of a higher binder content results in mixes with thicker binder films, improved aging resistance and better durability . When using asphalt-rubber binder, high mix temperatures can be used, again without the drain off problem, to permit construction in cooler temperatures or at longer haul distances than with conventional open-graded mixtures. High binder contents produce mixtures which have crack reflection reduction characteristics similar to spray applied and chipped stress-absorbing-membranes (SAM's) (42) . The design procedures which follow generally use methods outlined in the Federal Highway Administration Report No. FHWA-RD 74-2 titled "Design of Open Graded Asphalt Friction Courses· (43) with several modifications to account for the unique properties of asphalt-rubber materials . The procedures describe methods for determining the asphalt-rubber content for three different types of open-graded mixture applications. 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 concrete should meet the same quality requirements as for conventional asphalt concrete which would be used in similar applications. Recommended aggregate gradations are listed in Table 5. These gradations are typical of many 3/8 and 1/2 inch open-graded mixtures used throughout the United States. For the 3/8 inch gradation, overly thickness should not exceed 1 inch . For the 1/2 inch gradation, maximum thickness should be 1 1/2 inches.

Asphalt-Rubber

The asphalt-rubber for use in open- graded paving mixtures should be composed of r ubber meeting the previously stated gradation limits for use in open- graded mixtures and the appropriate asphalt cement or blend with extenders to meet desired physical parameters such as those listed in Table 1. Due to the large void spaces which exist between aggregate particles in open- graded mixtures , larger rubber particles can be used in the asphalt-rubber than with dense - graded mixtures.

Asphalt - Rubber Content

The suggested method for determining content consists of three basic steps followed for mix type.

the by

asphalt-rubber an adjustment

Step 1. Determine the surface constant Kc using the FHWA RD-14-2 procedure (oil soaking (43). This procedure is also contained Institute t-1S-2 manual.

of the aggregate and drain off) in the Asphalt

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

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

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

Open- Graded Asphalt-Rubber Concrete Types

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

Free Draining Friction Coarse: This type of mixture is constructed using the base asphalt-rubber content with no modifications. This provides a friction coarse which has skid resistance and draining characteristics similar to a conventional open-graded friction coarse constructed using asphalt-cement. Use of the asphalt-rubber binder provides improved durability and permits use of higher mix temperatures for cool climates. Typical asphalt-rubber binder contents are between 6.5 and 8.0% by aggregate weight. This mix type generally has between 15 and 18% air voids when compacted using 50 blows per side with a Marshall Hammer at 2750F. An example design is shown in Appendix 4.

Durable Friction Course: The binder content for the durable friction course is determined by multiplying the previously determined base asphalt - rubber by a factor of 1 . 2. Typical asphalt - rubber binder contents are 8.0 to 9.5 percent by aggregate weight. This mix type has somewhat thicker binder film thickness which results in increased durability, but with a somewhat lessened drainage capacity. This mix type generally has 12 to 15% air voids when compacted using 50 blows per side with a Marshall Hammer at 2150F.

Plant Mix Seal: The binder content for the plant mix seal type of open graded asphalt - rubber concrete is determined by multiplying the previously determined base asphalt- rubber content by a factor of 1.4. Typical asphalt-rubber binder contents for this mix type are 9 to 11% by aggregate weight . When compacted at 2750F using 50 blows of the Marshall Hammer per side, this mix type generally has 8 to 12% air voids. The high binder content produces a mix with improved aging resistance , durability and resistance to reflective cracking. When this mix type is placed to

a thickness of 3/4 inch, there will be between 0 . 65 and O.B gallons of asphalt-rubber per square yard on the pavement which is typical of 8 stress absorbing membrane type application.

Specimen Mixing .

Following determining the asphalt-rubber content for the application , mixtures of the open-graded a spha lt-rubber concrete are made . The asphalt-rubber should be heated in an oven to 3500F + / - 100F and be stirred immed iately proir to addition to aggrega t e in order to insure that the mixture is homogeneous and rubber particles are not segregated . Proportioned aggregate should be heated to 3000F prior to mixing with the heated asphalt-rubber.

Mixing of the asphalt - rubber with the aggregate should be performed using appropriate types of mechanical mixers using whips or paddles. Mixing should be performed immediately after addition of the asphalt-rubber to the aggregate. Mixing should continue for at least 30 seconds beyond the time required to obtain complete asgregate coating. Total mix time should not exceed 2 minutes.

Following completion of the mixing , the mix should be split into 1000gr. portions for drainage testing and appropriate sized specimens for moisture r eis i stance testing .

Mixture Production Temperature Determination

Testing should be performed in accordance with the FHWA RO-74-2 drainage procedure (Section 6 . 11 . A temperature of 2900F is recommended for starting the drainage eva luation . If drainage at 2900F after both 15 and 60 minutes is acceptable. a mix production temperature of 2900 F + / - l OoF can be used. If excessive drainage occur s . lower temperatures should be investigated unti l , appropriate drainage levels are obtained . The appropriate drainage l e ve l i s defined as no more than a s li ght puddle (l ess than 1/4 inch diameter at points of contact between aggregate and the glass plate.

Moisture Resistance Testing

MoistUre r esistance of the mixture s hould accordance wi th standard t est ing methods used mix tures such as Immersion Compression or 24 Immersi on.

be determined in f or open-graded hour Marshall

Immersion Compress i on: Testing u s ing ASTM D 1075 procedures (371 . Mix should be the previously determined mix pressure should be 2000 psi instead of 3000

should be compaction

t emperature, psi (4 31 .

pe rformed temperature and molding

Marshall Immersion: For Marshall Immersion testing, specimens should be compacted after conditi oning at the mixing t emperature f or 1 to 2 hours. Specimen compact i on should be 50 blows per side of the Marshall hammer and compaction should be compl eted within 3 minutes after r emoval from the oven .

DESIGN OF GAP-GRADED ASPHALT-RUBBER CONCRETE

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

The inceased voids permi t use of an increased asphalt-rubber content to provide increased mixture durability . Suggested aggreg~te grading limits are shown in Table 6. Aggregate should meet normal other quality requirements f or asphalt concrete aggregates . Asphalt - rubbe r should be of the appropriate type listed in Table 1 and should use the dense-graded type of rubber.

The Marshall des ign procedure for dense -graded mixtures whi ch was di scussed previous ly can be used for the design of gap-graded asphalt-rubber concretes. During the deSign. it is suggested that air void levels of 3 to 5 percent be achieved . Additi ona l criteria li sted in the dense-graded design procedure should be met except that flows can be raised to 26. 24. 22 f or light. medium and heavy traf.fic.

Gap-graded mixtures which have a mor e open gradation which approaches an open-graded mix can also be used. As the gradation is opened , greater amounts of asphalt-rubber binder are required t o produce 3 t o 5 percent air voids, and the mix will take on characteristics closer t o an open-graded mixture.

Typical binder contents for gap-graded mixture gradations listed in Table 6 are between 7 . 0 and 8.5% by total mix weight. Suggested thickness limits f or 3/8 inch gap-graded asphalt - rubber mixtures are 3/4 to 1 1/2 inches, for 1/2 inch mixtures, are 1 to 2 inches , and f or 3/4 inch mixtures . 1 3/4 to 3 inches. If gap-graded mixtUres with more open gradations are used , maximum thi ckness should be reduced.

ASPHALT-RUBBER CONCRETE MIX PRODUCTION

Equipment

Asphalt -rubber concrete can be mixed in either batch or drum. type producti on plants. It i s suggested that in order to prevent contamination of the storage tanks, and to prevent segregation of the asphal t-rubber, that a seperate asphal t-rubber storage tank with a ppropriate 8gitation be used. Additionally. it is sugges ted that a seperate asphalt-rubber supply system equiped with a pump and metering system capable of adding binder t o the aggregate at the correct percentage tbe used. Asphalt-rubber binder content should be maintained within plus or minus 0.5 percent of the · design value f or ~ingle test values.

Mixture Production Temperatures

suggested asphalt-rubber temperatures when being added to the aggregate f or all mi x types are between 325 and 3750F. For dense and gap-graded mixtures it is recommended that the aggregate temperature be 290 t o 3250F . For open-graded mixtures, aggregate temperatures should be appropriate to r esult in the lob determined mix temperature.

CONSTRUCTION TECHNIQUES AND GUIDELINES

Asphalt-rubber mixtures are hauled, placed, and compacted using convent i onal equipment and s lightly modified techniques. When hauling asphalt-rubber mixtures , truck beds should be sprayed with a water-soap, solution or dilute silicone emulsion instead of kerosene or diesel fuel. Kerosene or diesel fuel shou ld not be used because of an affinity f or absorption into the rubber particles which can result in mix tenderness.

Mixture laydown temperatures should not be be low 2500F for open-graded mixtures or 2750 F for dens e-graded or gap-graded mixtures.

Asphalt-rubber mixtures should be compacted using steel-wheeled rollers. Pneumatic rollers should not be used due to an inc reased adhesiveness of the asphalt-rubber binder, which can stick t o the rubber tires . Compaction should proceed quickly 8S soon as the mixture is capable of supporting the r ollers without excessive shoving. Delays should be avoided because 8 S asphalt-rubber mixtures cool , they become mor e difficult t o compact due t o the reinforcement provided by the rubber. Figure 6 shows lab dens ity data obtained f o r dense-graded mixtures made with 120 and 60 pene tration asphalt-cement, and asphalt-rubber made from the 120 penetration asphalt and 18% minus 20 mesh rubber . Note the reduced dens iti es of the asphalt-rubber mixture in comparrison to the aspha lt cement mixtures as temperature drops fr om 2750F to 2000F.

Open-graded asphalt-rubber mixtures should be compacted us ing a minimum of 3 full r o ller coverages. Dense and gap-graded mixtures should br compac ted to provide a minimum of 95% of the lab compacted density. Vibratory r ol lers can be used with dense and gop-graded mixtures, but shou ld not be used for open- graded mixtures .

With some asphalt - rubber the compacted mix may exhibit construction. If this occurs , application (approximately 4 l bs. be use to alleviate the problem.

concretes at high binder contents, excessive stickiness just after it is recommended that a light per square yard) of blotter sand

S~~RY

This paper covers design methods which can be used f or hot-mixed asphalt- rubber concrete pavements . Properties of asphalt-rubber binders appropriate for use in hot- mixed paving mixtures are discus sed along with factors which influence asphalt-rubber properties . Criteria for selecting the specific asphalt-rubbe r formula and specifications for use in hot, moderate, and cold cli~tes are presented .

Mixture design methods for asphalt-rubber dense, open, and gap-graded mixtures are discussed . Each method foll ows conventional Marshall, Hveem, or FHWA procedures with sugsested mod ifications to incorportate asphalt-rubber binder. The methods presented can easily be performed by most l aboratories profi c ient at asphalt-concrete mix designs with aquisition of mino r pieces of additional equipment. Evaluation c riteria and suggested property limit s for both the asphalt~rubber and asphalt-rubber concrete mixes could possibly be used as a basis for establishment of uniform construct i on specificat i ons.

Property

Table 1 Suggested Phys ical Prope rty Limits f o r Asphalt-Rubber Materials f o r

Use in Hot-Mixed Asphalt Concrete Appli cati ons

Property Limits1ll ... ~~,-_ Hot (2) Moderate - Cold

Climate Climtlte Climate

Viscosity . Haake , 3500 F Softening Point, (ASTM 036) Cone Penetrati on , 77 0 F

1500- 4000 130°F min

l500-4000Cp 120°F min

1500-4000cp llOoF min

(ASTM 03407) Resilience , 770F (ASTM 03407) Ductility , 770 F (ASTM 0113) Low Temperature Flexibility 3

(ASTM C711 modified)

Notes :

20-60 20% min 15 cm/min

50-100 10% min 15 cm/min

80-150 0% min 15 cm/min

15° max

1) . Property peri od such as

limit s should be s tipulated at a spec ifi c 60, 90 , and 120 minutes.

int e r ac tion

2). Make c limate se l c tion based on the following tempe rature ranges from the U. S . Department of Comme r ce Enviromental Data Servi ce . Ho t c limate - average July max - 1100F-; average Jan. l ow 300 F+ . Moderate Climate average July max - 1000F- ; average Jan. low - IS-30°F . Cold Climate - average July max - 800F-; average Jan. low 150 F- . Make the selec ti on based on January low, the n check Jul y t emperatures . If July temperatures exceed those o f the grade selected based on Janua r y temperatures , use the next stiffer grade.

3). As be u sed. moderat e

an alternate, Cone Pe netration at 39 . 2o F . 200g. 5 sec . Limits would be 10 min. for hot c limate, 25 min. c limate , and 40 min . for cold c limate.

can for

Table 2 Physical Properties of Asphalt Rubber Blends with

Differing Rubber Contents

Percent Rubbe r (Mix BASis) Prope rty ~ _6_ .L ...JL ...ll.. ...ll.. Viscosity, 350o F, .c p 60 550 aoo 900 1500 2500

Cone Penetration,77o F 4a 40 43 .. 40 30

Resilience , 77°F - 1 -1 12 19 23 .0

Softening Point . F 122 126 136 140 142 146

Notes:

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

2). Intera c tion period is 90 minutes at 3500F.

--.l.L

6000

27

47

162

Table 3 Asphalt Rubber Test Data During B 24 hr

Interaction Per i od

Interaction Period TE ST PERFORMED 30 60 90 120

min min min min 6 hrs 24 hrs

Vi scosi t~" Haake @ 350°F in centipoise 2000 2000 2200 2200 2200 2200

Penetration, Cone @ 77°F in 1/10 Illll 72 69 67 65

Resil ience 0 77°F in % rebound 17 20 20 23

Duct ility, 77°F 5 cm/min;cm 2. 21 25 32

Softening Point in of 122 127 128 128 128 129

Frac ture Temperature

OF LOUIest Passing ,. 12 12

of Fracture 12 10 10

Notes :

1). Asphalt cement is AC - 5 , Penetration (05) Point • llOo F.

198, Softening

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

3). Interaction temperature is 350° F.

4). 6 hour to 22 hour holdover temperature is 300°F.

Table 4 Suggested Gradation Specifications f o r De nse-Gr aded Asphalt

Rubbe r Co ncrete (Percent Passing)

Mix Desi gnation Sieve S i ze 318" 1/2" 3/4"

1 • 125 . 0 1lIJl) 100 100 100

3/4 119.0 IlIJl ) 100 100 90-100

1/2" (12.5 IlIJl ) 100 90-100 70-90

3 /8 " (9.5 rrm) 90-100 75-95 60-80

•• (4.75 rnn) 60- 80 50-70 40 -60

# 8 12.36 1lIJl) 4 0 - 60 35-50 30-4 5

# 30 ( 600-um) 18-30 15 -25 12-22

#50 (300- um) 8-18 6 -1 6 5-14

#200 175-um ) 2-8 2- 8 2-6

· Table 5 Suggested Gradations for Open- Graded Asphalt-Rubber Concrete

Mixtures (Percent Passing)

Mix Desisnation Sieve Size 3/B" 1/2"

3/4 " (19 . 0 om) 100 100

112" (12.5 ITJlll 100 95-100

3/8 " (9 . 5 nm) 85-100 75-95

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

# 8 12.36 nrn) 5-15 5-1 5

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

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

Table 6 Suggested Gradation Specifications for Gap- Graded

Asphalt-Rubber Concrete (Percent Passing)

Mixture Designation Sieve Size 3/S" 1/2" 3/4"

l' (25 .0 lIlll ) 100 100 100

3/4" (19.0 lIlll ) 100 100 90-100

1 /2" ( 12. 5 mm) 100 90-100 65 - S5

3/S" (9.5 JJJTl) 90-100 70-90 50- 70

#. (4.75 mm) 50-65 35-50 30-45

#8 (2.36 lIlll ) 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 wn) 3-7 2-6 2- 6

z 0

" < 0 z

~

• 0 0 • w •

.,

" " 30

" 20

" " s

, ,

J.~-l'- Ae-7.S .. HI> in I:lounder and 111 ... bh ..

r-. .... r--...,I- AC-7.S of u% u.t.

2 . J , s , • TIME, HUWT£S

, "

AC-l.S "lIh7: b,endc r and 111 a"bb,..

AC 1.S

IIC-7.S -+ lI..bber

AC-20 + lubber

AC-20

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

FlGURE 2. Constant Load Creep Plots For Asphalt Cement And Asphalt-Rubber At 74F With A 25 g. Load

" " " " • " 0

;: ~ • " ~

" " -u ~ . 0 • ,

0

0

FIGURE 3.

.>0 •

" " .60 § ,

... !So ~ s • E

~ i! o l: 140

• - l

~

" " -.. 130 ~ ~

, -g -< • ~ 120 ~

§ • >

110 0

, , • , • Tna::, KIh11Tts

'\C-20

, • , .0

AC- ',) v 1th 14% l>tundcr a nd 11% ."bbu

AC7.5 Wi th 7% l>tt~nder

and 171 Rubber

Constant Load Creep Plots FOT Asphalt Cement And Asphalt-Rubber At IOCF With A 1 g . Load

k£!iILItHCt

SOF'TENINC POIHT

0 l • , ., . , VISCOSITl

•• , .

"

" "

-~

o " < •

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

o • ;;; • •

C!V.DATlON AREA TO AVOlD

SIEVE SlI [ 0 .4) POWER

..

FIGURE 5. I l lustration Of Gradat i on Area To Avoid With A Typical Dense-Graded Gradation When Using Asphalt- Rubber Bi nder

AC-1.~ (120 pell.)

'"

AC-20 (60 pell.)

'"

E § lJ~ Collpaotin Illort • B/l~ 11..., ~nhdl

" ' +---------.---------r--------r-------:~ 2H )DO '" m '"

COKPACnO); TD!Pf:lATtlll , t

Figure 6. Variation Of Density Of A Dense-Graded 1/2 " Mix With Asphalt Cement And Asphal t-Rubber When Compacted At Temperatures Ranging From From 200F To 300F

D • • • •

APPENDIX 1 Procedure For Lab Interaction or Asphalt-Rubber Materials

The r ecommended procedure for preparing a spha lt-rubber materials in the laboratory consists of subjecting the asphalt-rubber to temperatures and times which will occur in actual use. The mixture is then tested at several specifi c points in the interaction period to evaluate the properties of the mixture during norma l application periods . The procedure for preparing a spha lt- rubber is a s follOlJ!s :

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

2) . Selection of the proportions of each material to be tes ted.

3). The asphalt cement.extender (if used) and adhesion agent (if used) ar,e placed in a standard 1 gallon open top metal can. Approximately 2,000 grams of the blended materials should be used. The materials are then heated us ing any convenient met hod to 50 +/- 10F above the desired temperature to be used during the interac tion period. During heating, the materials should be stirred to insure uniformity.

4). All of the granulated rubber to be used in the mix is then added to the heated esphalt cement end stirred in using an appropriate hand stirring devi ce (spatula) for·opproximately 30 seconds or until ell of the added rubber is wetted into the asphal t.

5). The mixed material is then placed in a forced draft oven maintained at an appropriate temperature to ~intain the desired interaction tempera ture (typically approximate ly 25F above the interacti on temperature). The container should be loosely covered .

6). After 15 minutes has elapsed, after the rubbe r has been added, the container is removed from the oven, then stirred b!.' hand for 15 seconds, and then replaced in the oven.

7). The sample is then sUrred for 15 seconds . aiter an additional 15 minutes, and then is stirred at 30 minutes intervals until 2 hours has elapsed. During this time period, while stirring, the temperature should be checked and recorded so that adjustments in oven temperature can be made, if required to keep the sample temperature within plus or minus lOF from the desired interaction temperature.

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

9) . After 6 hours of interaction. the oven temperature is reduced to 300F Bnd the asphalt rubber sample exposed to the 300F temperature until 22 +/- 1 hours have elapsed since the rubber was added to the ftsphal t. The asphalt rubber is then stirred by hand for 15 6econds, replaced in the oven, and then the oven temperature is raised to raise the temperature of the asphalt-rubber to the interaction temperature within 2 hours. This completes the interaction period.

Intrpductjon ;

APPENDIX 2

ReCOIflmendf'd Procedure for Preparing Samp]M pf AfiDbalt Rllbber fpr Testing

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

Asphalt Rllbber Preparation for Testing;

Heating ; The sample of asphalt rubber should be placed in an appropriate metal container, no larger than 1 gallon (a standard one gallon round open top paint can ie suitable). The can i6 then placed in an oven . (preferrably forced draft) maintained at 25 F above the temperature the asphalt rubber is to be 'heated to. For example if the asphalt rubber i8 to be heated to 350 F, the oven temperature shou ld be 375 F. Higher temperatures should not be used due to the possibility of over reacting the rubber components. The can containing the asphalt rubber should be covered while heating in ' the oven, After the material has been in the oven approximately 1 hour, the can should be rem o ved and the sample stirred for 15 seconds, At this time, the sample will not be totally melted . The can is then replaced in the oven, covered, heated for an additional 3 0 minutes, removed and stirred for 15 seconds again. Temperature is then checked with an appropr iate thermometer. This procedure 16 then repeated until the sample is uniformly melted and has reached the mixing or application temperature . For a 1 gallon sample it will take approximately 2 1/2 hours to reach 350 F.

APPENDIX 3 Example Dense-Graded Aspha l t-Rubber Concrete Mix Design Marshall Method

1. Aggregate - Crushed Limestone 25% 1/2". 30% 1/1. -3/8" . 1.5% crushed sand

ilLom , '" '" ." ". Kll sneIrI tA'II OI\ to~'U. "'" " ... 'IrRIAl. I , , •

l/< ~ lJlo.o I ~.O H".O 100.0' 1 0~ \

I ,. 93.0 1 0~ . 0 100.0 U . l\ !'S~lO~ 1

JIB" ~ 0. 1 l OO . ~ 100.0 e5.] ~ f:>-~~ '

• ,"0. '" , .. ~~. ] 1 00.0 U.l1 ~~-n \

• • ~o . • ' .0 !.l 8 B.] U.l I l ~-S~ \

" t ,"0. " U ] .~ ~l. ] ](. " If-!!\

" No.. 2~ ", 1.1 ... 1 0.S S.B' 4- f'

.

l! ~"1.1t ,. " . " .

~. f.3 9;> : .t " ' .~'H ...,,, AA.! I> 1 ". " '.1H.4 ~ .,~ , <;>

, -- '-' " , .uS~ tJ·'IIOl> l.J ., ] .O~ \ l.~;lI

2 . Asphalt Cemen t AR- I.000 . Penet r ation .77F (D5) - 1.9; Softening point (036) - 120F

3 . Gr ound Rubber Gradation

S j .. ,,~ Siu Rubbu Cudot1on

100

,,, 100

,,, ,,, 1100 11.6

1100 I , ,

'1 .. ,. ~· 'u L .p.1. I

'.0

,., T ,S!

'.'

4. Phys i ca l Pr operties of As phalt- Rubber (1 6% r ubber , ." a s phal t ) 350F interac tion

'n51 PDU'O~ " .. !!' l1Q !.l!.! ~

Vi.c~. J ty . HI.ke . t ) )00

,

i n c ltntipo i u " '" .,00 '" '' "oo " OO .\1 00

Pennrn i on , Cone , "of 1n 1/ 10 mo. " " "

bl11h nce • 71"'1 '" 1 u bovnd " " " Du< ~ 111t y f 11°, i n ca , ulled , f.ll ur l , ) <:.'.In. "

Sohltnl n,. ' Ol M i n " , '" '" '" '" '" '" fr , cl ure Te_pltT, luTe

" r l.o~~H Pu~ln, " " " 0, , ,,nUT,. " " " 5. Aspha l t. -Rubber Concr e t e Mix t ure Results

Mix Temp . - 300F . . ' Compac t i on Temp • - 275F 50/50 Blow Marshall

~ I J I D !! AI Sl e l DATI SQKKIBI

l ult 3D Or

iii •• • A.fl t! tr .., ~rr. " t.l ... ShUlIt, rl . ..

Sp g t. . ' uCl hid. I t . M ' t lin " " · I (PPll n", ) 11IIQ Q ' U",

2 . ~. ~ .. 1."" u~., .. ,. U.O' ••• 'M l .-1 . ~"H 2 . ' H ~ 1 ' '1 . 5 1 .1 ' 15 . 1\ ,. , 2. ~~ " -1 , " 1" 1 • • ' . '-1 n"' . ~ J. n IS .D' , .. '0"", " , • • n .. , 1 • • .., .. I ~n . J J . : , n . ~ ' .. , 21 H "

Recommended asphalt -rubber binder con tent i s 6.5%

6 . Mois t ure Res i s tance Results (r efe r ance 41 procedure)

'u. l1 ~ U~ :oo;D "' ''''tn U t e • •. "" ' '' . .~h 51: ~" hl"~ ,,,,,,,,h. p.I ,.,

j .1' I . • I. )

n o Itf n . D u. I

" D 'J1 U ~t eOHI>JT JOn D SPEC' MtH , . Id h . ' ~ h I L A" Ii.,., u lo. , . ~ <

I ;.lt1J 1.6 )0.) ,-~ 1.1 1/.1 "-"""""""T.77:1 I. i It. , h . ~ I.)

l U:,U ",u~Th " ,1<. n .

, U ! d ru. lI. s .. ~ r. '!c~ St ,. nq,~. p. j

~S.I " IP . ' lu, !l •• 10. II .1 I X. ,

APPENDIX 4 Exampl e Open-Graded Asphalt- Rubbe r Concrete Mixture Des i gn f or Free- Draining Friction Course

1. Aggregate Crus hed siliceous gravel

• • ' . "

,-

· .. t I t ,., I .l O

.:-.~ n. <0 .

101 11J~'' S;.. ... , .u. 1C>)JI I O~

2 . Asphalt Cement

"

" ,

...

. 00

".0 t6.J

11 . 1

•••

AR- 2000

» ,

.~

n.7

29.'

•• • ••• , ..

I

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

,

' l . l

ll. J

••• •• • , ..

66 11 7F

,

n .'

•• • ...

.00

n .' ".6

'0.0

U . I

•••

J. tl"

J.111l

'-'

3 . Ground Rubber Gradation % Pa.ssing

.10 ... II .. IH OC

.. , . 00

.n ". J

.~ )l . t-... ll .' ... .., .~ '-'

.. 00 .., .. ~ •••

u- 7~

u- 20

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

nSf n U'OIUI!:D l!! ~ " m ib : !' h ..

'fnmsllY . IlAAA1: .u »0 0, ,- ,- ~~ ,,,. - -IN CU1'lr01U

pn .. tTu.TI~, COQ:' nO, " .. " a Illo _

kl.IiIUUCl , n"T U » » " ,~-

1lUcrl1.1lY • n"T U ... " PlAUD • fA1LllU • ) ... / .. , ..

IOno;1': 1VlIrt n or '" '" '" '" '" '" n,t,quu. nWIUTUJJ:

0, l,.(lI.·tST 'M5 1~ C " " " Clf nAt'f\/J:[ ." " "

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

0. .. Dr'd ~h ""'~'

OU SOh •• , •• eD<I Drd .... _I",

"""HU' S.I'. oJ "" ......

' .... .... 1 .... h « ... (l.71Il/l.Io5 )

h.f .. o """.10.' (Le)

100.0,

101.0

1 . 711)

1.01

,.~

, ., 7.U

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)

lOOn, 0011. VCI'J .lI,h, _, "f ... Ifto,~ .... 010 .... "" ... U . ft. '0 .10 . 11 .. 1_ ,lou _"h, .... I ... <_'oc' , .. 1ft' .1 ....... f 10 ... boft ~ hth. .

7.

8.

Density .nd Air Voids of Compacted Mix

'1:!<I ... n JI~. l un I.C . HoU ..... s.c. ... • • 1Iy I." ".14. , 1.'141 1.UU 11,,4

• l.''l~ 1.24H Ill. l

---" ..... p 1.9190 2.1414 110.4

I . tulk ' 1'«111< , •• vit1 duen.h .. d ... 1. , p ... nth .... Id spul_ •••

1 . til> too.;. • • )O(IT, c~.C<!Oft ' "'I'_ - 11~r.

) , Coopo<tlcn. ) O/~O blo,' )'~nh.ll.

4 . '"phal< r.bb~ r <_.u • • 1.01 ( .. .I> ••• 10).

14 ••

n.'

14.'

Mois ture Resistance Evaluation, Marshall Immersion Procedur e

5pecl ...

' " , IIn.boli

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33.

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