Asphalt-Rubber It all starts with scrap tires, a serious

solid waste problem everywhere. One of the most economically sound ways of solving this problem is to put them to use improving our roads. This high quality rubber can be recycled into an improved method of building roads and other sur- faces. The Asphalt Rubber Producers Group's mission, which is to develop increased use of Asphalt-Rubber, has a direct impact on reducing the amount of scrap tires stockpiled.

Scrap rubber is ground or granulated into crumb rubber, shipped to a project site and blended with asphalt cement. The blending process consists of mixing asphalt cement and 15-to-25-percent crumb rubber at 350" to 450" Fahrenheit. This mixture reacts and forms a gel called Asphalt- Rubber. Additives may then be incorpo- rated t o adjust the viscosity of the mixture.

Asphalt-Rubber Concrete (ARC)

1. Description -A conventional asphalt concrete mixture for dense or open graded surfaces or base course layers, except the binder used is a reacted Asphalt-Rubber material instead of as- phalt cement.

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Function -To provide a more durable asphalt concrete which increases stability, reduces oxidation, and im- proves crack resistent characteristics.

Significance -Use of Asphalt-Rubber as the binder for asphalt concrete mixtures provides increased durability due to binder oxidation resistance and resulting thicker films which retards oxidation. The antioxidants and carbon black contained in the rubber also contributes to aging resistance. The higher viscosity of the Asphalt-Rubber binder results in increased resistance to permanent deformation, while the elastic characteristics impart increased resistance to reflective and thermal cracking.

Three Layer System 1.

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Description - Construction of a thin asphalt concrete leveling course, fol- lowed by application of an Asphalt- Rubber SAM, which is then covered with asphalt concrete, which results in a SAMI.

Function - To provide a means of re- storing rideability and smoothness to deteriorating concrete pavements as an alternative to grinding, seating, and thick overlays.

Significance - Asphalt-Rubber three layer systems have provided an effec- tive means of rehabilitating deterio- rated concrete pavements at less than me-half the cest d grinding. The stress absorbing characteristics of the sand-

reflection of cracks and joints through the system.

wiched Asphalt-Rubber layer retards ~ ~~ ~~~~

Stress Absorbing Membrane (SAM)

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Description- Asphalt-Rubber is spray applied to pavement surfaces at 0.5 to 0.7 gal. per s.Y., and then covered with 1/4- to 3/8-inch chips. The applica- tion rate is adjusted for various chip sizes and road surface characteristics. A tack coat of diluted emulsified as- phalt may be needed if the pavement surface is extremely oxidized, in order to produce adequate adhesion between the membrane and the pavement surface. A double SAM is used where pavement surfaces are extremely rough, with 3/8" bottom chips and l/4" top course.

Function - Provides a lasting water- proof and durable surface which resists oxidation and flexes to conform with movements of the surface. Provides a skid resistant surface.

Significance - Aspkrdt-hbbei SAM's improve and extend the serv- iceability of asphalt pavements which are experiencing extensive cracking. The life extension results from the

lasting waterproofing characteristics provided by the Asphalt-Rubber, as base and subgrade weakening, due to surface water intrusion, is eliminated. The adhesive and elastic characteris- tics bind the deteriorated surface together to eventually eliminate this pavement deterioration. The encapsu- lation characteristics of Asphalt- Rubber SAM's also have been shown to virtually stop aging of underlying asphalt concrete.

Stress Absorbing Membrane Interlayer (SAMI)

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Description - Similar to a SAM, but followed by the construction of an asphalt concrete surfacing layer which is 3/4 to 3 inches in thickness. Stage construction may be used with overlay construction up to several years later. The Asphalt-Rubber binder may be softer than when used as a S A M because the membrane is not exposed to traffic.

Function - Provides an effective method of reducing and retarding

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reflective cracking of thin overlays by reducing crack tip stresses. Used for both asphalt and concrete pavements.

Significance - The use of Asphalt- Rubber SAMI's extends the serviceable life of overlays by retarding the rate of reflective crack formation. The SAMI also waterproofs the underlying pavement and reduces age hardening of asphalt concrete as a result of encapsulation characteristics.

3. Significance - Same as a SAM, but used in areas where the coarse surface texture of the SAM is not desirable. Eliminates potential for loose chips. Particularly applicable for airfields and parking lots.

Waterproof Membrane

1. Description - Either a SAM or SAMI designed t o control entrance of mois- ture into subgrades. May be applied directly to subgrade on new construc- tion or on top of pavement and shoul- ders on existing highways.

Cape Seal

2. Function - To prevent entrance of surface moisture and/or moisture generated by hydro-genesis in the base course entering the subgrade.

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Description - Same as a SAM, but followed by application of a slurry seal. Stage construction may be used. Generally a Type I1 slurry seal is recommended. This provides a treat- ment which is approximately 1/2" in thickness.

Function - Same as a SAM, but with a smoother surface texture.

3. Significance - Use of Asphalt- Rubber membranes has demonstrated long term effectiveness in reducing detrimental subgrade swelling and distortion. Has shown t o be effective in both new construction and on existing roadways.

If you have further questions, contact the ARPG or your local applicator.

The Asphalt Rubber Producers Group 3336 N. 32nd Street, Suite 106

Phoenix, Arizona 85018 (602) 955-1141

~ ~ ~~ fiu Asphalt Rubber Producers Group 1: 3336 North 32nd Street, Suite 106 Phoenix,Arizona 850180 (602) 955-1141