One of the main benefits advertised about the use of warm-mix asphalt is the increased workability at conventional and lower compaction temperatures. From a field perspective, “workability” is commonly defined as the asphalt mixture property that describes the ease with which the asphalt mixture can be placed, worked by hand, and compacted to the desired mat density. Unfortunately, a laboratory property and test condition have yet to be developed to quantify these field characteristics. A research effort to evaluate the workability and compactability of different warm-mix additives preblended in a polymer-modified asphalt binder at varying percentages is summarized. Different test procedures, both asphalt binder related and asphalt mixture related, were evaluated and compared. Test results indicated that conventional mixing and compaction temperature asphalt binder tests were insensitive to the different warm-mix additives and dosage rates. Compaction data obtained with the gyratory compactor also indicated the device was generally insensitive to workability and compactability. Meanwhile, the University of Massachusetts workability device and the Marshall compaction hammer were found to rank the general workability and compactability of the mixtures in a rational order and compared favorably with one another. Not only was a promising new asphalt binder test, the lubricity test, sensitive to dosage rate and warm-mix additive, but the ranking compared favorably with mixture tests. The hope is that the information in this research effort can help in the selection and validation of warm-mix additives as a compaction aid.

This study, part of the NCHRP 9–45 Project, analyzed the effect of mineral filler properties on asphalt mastic and the rutting potential of asphaltic mixture. The mineral filler properties were characterized by four tests: Rigden voids (RV), fineness modulus (FM), calcium oxide (CaO) content, and methylene blue value. The rheological properties of asphalt binder and mastic were characterized with the use of apparent viscosity and multiple stress creep recovery tests. Dynamic modulus and flow number tests were conducted to examine the asphaltic mixture rutting potential. The tested mixtures included several variables: four asphalt binder types, including virgin and polymer modified; two aggregate gradations; and a selected group of fillers. The study concluded that asphalt mastic performance was significantly affected by the fractional voids in the filler and possibly by the CaO content and FM. This effect, however, depended on binder type. On the one hand, the styrene–butadiene–styrene modified binder showed the strongest effect as a result of the mineral filler inclusion when tested as mastic. On the other hand, RV and CaO content showed relatively greater correlation with the mixture rutting potential, as compared with other filler properties. Addition of RV improved the prediction models for dynamic modulus and flow number. The effect of RV on the mixture rutting potential was more pronounced for the coarse mixture than for the fine mixture.

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