Chemical modification of asphalt by acid has been known for quite some time. Chemically modified asphalts can extend the upper application temperature limit and prevent rutting of asphalt mixture by increasing asphalt stiffness. During the past two decades, many studies focused on polymer modification have indicated that polymer additives can successfully improve asphalt pavement performance. The low cost of acid modification, relative to polymer and other modifiers, makes the acid modification alternative important and competitive. Unlike the situation with other modifiers, information about chemically modified asphalts is limited, and performance data are almost nonexistent. During the past few years, major advancement in characterization of load-related damage resistance behavior of asphalts has been achieved. A new protocol for measuring resistance of binders to rutting and fatigue has been introduced by the NCHRP 9-10 project. In addition, new protocols to measure construction-related properties, such as zero shear viscosity for mixing and compaction temperatures and storage stability, are proposed. The effectiveness of chemical treatments with acid and polymer modifier in improving performance-related properties of paving asphalt were evaluated. The results indicated that chemically modified asphalts show significant improvement in rutting and fatigue resistance. However, the effect of aging on rheological properties of chemically modified asphalts was significantly different from its effect on polymer-modified asphalt. There are also indications that resistance to moisture damage of mixtures produced with the chemically modified asphalts is not as good as that for mixtures made with polymer-modified asphalts.
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