ABSTRACT
Polymers are used in asphalt to increase the range of temperature in which the asphalt mix can be used without any distress and to improve bonding of asphalt binder and aggregates. Elastomers and plastomers are the two major types of polymers used in asphalt. Block copolymers, random polymer, and natural and synthetic latex are examples of elastomers, which are used primarily for decreasing temperature susceptibility, increasing tensile strength at high strain, and improving the cohesion and adhesion of asphalt binder. For example, styrene butadiene rubber (SBR) is used for reducing the rutting potential of asphalt mixes at high temperatures. Plastomers consist of polyethylene and ethylene copolymers, and are used primarily to decrease temperature susceptibility, increase modulus, or increase tensile strength. For example, ethyl vinyl acetate (EVA) is used for modifying the strength, stiffness, and workability of the asphalt mix. Polymers can be either preblended with the liquid asphalt binders or blended with the mix at the HMA plant. A growing use of polymer-modified asphalt is in chip seal coats and other thin-layer maintenance applications, as an interlayer for resisting reflective cracking, as well as in other specialty mixes such as the open graded friction course (OGFC) and stone matrix asphalt (SMA). The use of polymers has become almost routine in many applications, and this has necessitated the development of special characterization tests (such as the direct tension test and the multiple stress creep and recovery test, or MSCR) and conditioning tests (such as the modified rotating German flask, or MGRF) for polymer-modified asphalt binders. Two issues that are specifically important for the good performance of polymer-modified asphalt mixes are storage stability and degradation. Storage stability involves the compatibility of the polymer and asphalt binder when stored for long time periods at elevated temperatures, and degradation refers to the deterioration of the properties of the polymer due to the presence of oxygen at high temperatures. For information on modified asphalts, the reader is advised to see the Association of Modified Asphalt Producers (AMAP) Web site (www.modifiedasphalt.org).
