Types of modifiers!

Highway agencies have recognized the benefits of using modified asphalts to reduce the amount and severity of pavement distresses and to increase service life.

Modified asphalts are often generically called “polymer modified asphalts.” Polymers are probably the most common type of modification, but today’s modified asphalts may be produced in several ways. According to the Asphalt Institute’s “(MS-4) Asphalt Handbook”, modifiers and additives being used to boost performance include polymers, chemical modifiers, extenders, oxidants and antioxidants, hydrocarbons and anti-stripping additives.

“Polymers” cover a broad range of modifiers, with elastomers (rubbers or elastics) and plastomers (plastics) being the most commonly used types. Styrene-butadiene rubber (SBR) and styrene-butadiene-styrene (SBS) are frequently used elastomers. Research conducted as part of the National Cooperative Highway Research Program found that SBS is the most often used modifier. These modifiers are used to reduce rutting and to improve fatigue and thermal cracking resistance.

Crumb rubber is an elastomer made from ground tires. Several technologies are in place for using ground tire rubber. This material is used primarily to address rutting.Plastomers are used to improve the high temperature (rutting) properties of modified materials. Low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) are examples of plastomers used in asphalt modification.

The most commonly used chemical modifier is polyphosphoric acid (PPA). This modifier may be used in combination with polymers to increase the high-temperature stiffness.

Other modifiers that may be used include asphalt binder extenders (primarily sulfur) and hydrocarbon materials. Hydrocarbons can produce either hardening or softening effects. Materials can be added to increase rutting resistance. Softening agents or rejuvenators are used to lower the viscosity of aged asphalt binders in mixes containing recycled asphalt pavement (RAP).