 Uses of asphalt rubber? What's asphalt rubber? I'll tell you, 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. About 70% of a scrap tire is still rubber. This high quality rubber can be recycled into an improved method of building roads and other surfaces. The 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 15-25% crumb rubber at 350-450 degrees Fahrenheit. This mixture reacts and forms a gel called asphalt rubber. Additives may then be incorporated to adjust the viscosity of the mixture. There are many uses of asphalt rubber. They include asphalt rubber concrete, A-R-C. Asphalt rubber open graded friction courses. Stress-absorbing membranes or SAMs. Stress-absorbing membrane interlayers. Sammies. SAMs with cape seals to provide a smoother surface, a three-layer system, and as a waterproof membrane. Asphalt rubber has many applications. Asphalt rubber concrete is essentially a dense or open grade asphalt concrete mixture, except the binder is a reacted asphalt rubber blend instead of conventional asphalt cement. It provides a more durable asphalt concrete with better stability and is highly resistant to oxidation and cracking. Using asphalt rubber as the binder for asphalt concrete mixtures increases pavement life because of the film thickness and resistance to binder oxidation from the antioxidants and carbon black in the rubber. The higher viscosity of the asphalt rubber binder increases resistance to permanent deformation while the elastic characteristics provide increased resistance to reflective and thermal cracking. Asphalt rubber is also used as a binder for asphalt concrete open graded friction courses to solve many of the durability problems associated with open graded mixtures due to the higher viscosities. Higher binder percentages can be used to obtain thicker films on the aggregate. Thicker films relate to increased durability and when considering all the other improved properties of the asphalt rubber binder, the mixes are improved substantially. In a stress-absorbing membrane or SAM as they are called, asphalt rubber is spray applied to the pavement surface at 5 to 7 tenths of a gallon per square yard and then covered with aggregate. The application rate is adjusted for various aggregate sizes and road surface conditions. Attack code of diluted emulsified asphalt may be needed if the pavement is extremely raveled or when applying on a concrete surface to produce adequate adhesion between the asphalt rubber membrane and the pavement. Double SAM chip seals are applied when pavement surfaces are extremely rough. A large cover aggregate is placed on the bottom layer and a smaller cover aggregate on the top course. SAMs provide a lasting, waterproof, skid resistant, durable surface which thwarts oxidation and flexes to conform with movements of the surface. Using asphalt rubber in a SAM improves and extends the serviceability of asphalt pavements which are experiencing extensive cracking. Why? Because asphalt rubber waterproofs the base and keeps surface water out of the subgrade. Its adhesive and elastic characteristics binds the old surface together to eventually eliminate pavement deterioration. The encapsulation characteristics of asphalt rubber SAMs virtually stop the aging of underlying asphalt concrete. A stress absorbing membrane interlayer or SAMI for short is similar to a SAM but followed by placement of a 1 to 3 inch asphalt concrete surface layer. Stage construction may be used with the overlay placed later. SAMIs are used on both asphalt and concrete pavements to retard reflective cracking of thin overlays by reducing crack tip stresses. The encapsulating characteristics of a SAMI also reduce age hardening of asphalt concrete extending the serviceable life of overlays. To provide a smoother surface on parking lots and airfields a cape seal is often placed over an asphalt rubber SAM. Generally a type 2 slurry seal is used which provides a treatment of about 1 quarter inch which eliminates the potential of loose chips. A three layer system consists of a thin asphalt concrete leveling course followed by application of an asphalt rubber SAMI which is overlaid with asphalt concrete or asphalt rubber concrete. It provides a means of restoring rideability and smoothness to distressed concrete pavements as an alternative to expensive grinding, cracking and seeding or thick overlay sections. The stress absorbing characteristics of the sandwiched asphalt rubber interlayer retards reflection of cracks through the system. It's an effective means of rehabilitating concrete pavements at less than half the cost of grinding. Both SAMs and SAMIs are ideal to control entrance of moisture into sub grades. They can be applied directly on the sub grade of new construction. On top of pavement and shoulders of existing roadways and to seal ponds and landfills. Asphalt rubber membranes prevent entrance of surface moisture or moisture caused by hydrogenesis in the base course from entering the sub grade. The use of asphalt rubber membranes provides long term effectiveness in reducing detrimental sub grade swelling and distortion on existing roadways and new construction. Additional advantages of using asphalt rubber include construction time is shortened. Projects can be opened to traffic almost immediately and inconvenience to the motoring public is substantially reduced. The asphalt rubber producers group appreciates you taking the time to learn about the many uses of asphalt rubber.