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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.

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The effect of warm-mix asphalt (WMA) technologies on the moisture susceptibility of a mixture and the adhesion characteristics of the asphalt binder used in it was evaluated. A 9.5-mm Superpave® mixture designed with performance-grade asphalt PG 64-22 was used as the control mixture. Four types of WMA technologies were evaluated: Advera, Evotherm, Sasobit, and SonneWarmix. The Hamburg wheel-tracking device (HWTD) was used to evaluate the effect of each WMA technology on the moisture susceptibility of the mixture at three aging times and three aging temperatures. A liquid antistrip and hydrated lime were added to any mixture that failed the HWTD to determine if they could correct the failure. Because the moisture susceptibility of a mixture is related to failure in the adhesive bond between the binder and the aggregate, a pulloff test, the bitumen bond strength (BBS) test, was used to evaluate the impact of the WMA technologies on the adhesion characteristics of the asphalt binder. The HWTD test results indicated that the moisture resistances of all mixtures improved significantly with an increase in aging time or temperature. Mixtures aged at longer times and at higher aging temperatures exhibited the best performance. The addition of the antistrip agents improved the HWTD results. The BBS test showed that only Sasobit had a significant effect on the pull-off tensile strength of the binder, although only under dry conditions. Overall, no correlation between the BBS and the HWTD was found.

A high-performance thin asphalt overlay (HPThinOL) is specified as having a thickness of 1 in. or less and is used in applications requiring high levels of rutting and fatigue resistance. HPThinOLs are used as a pavement preservation strategy and are placed on pavements that have remaining structural capacity that is expected to outlive that strategy. Current specifications for HPThinOLs generally call for a polymer-modified asphalt (PMA). However, PMA binders are more expensive than unmodified asphalt binders. This expense, coupled with the higher binder content requirement generally associated with HPThinOL, could lead to an initial higher cost in relation to other pavement preservation strategies. Although the higher initial cost can be offset by incorporating high amounts of reclaimed asphalt pavement (RAP), the use of high amounts of RAP in PMA mixtures might adversely affect the mixture performance (stiffness, cracking, or workability). Warm-mix asphalt (WMA) technology may improve the workability of HPThinOL that incorporates high RAP content and PMA binders. This study evaluated the effect of PMA binders, high RAP content, and WMA technology on the stiffness, resistance to reflective cracking, moisture susceptibility, and workability of HPThinOL mixtures. PMA binders and high RAP content increased the stiffness of HPThinOL significantly; however, the use of WMA technology lowered mixture stiffness and improved workability. PMA may improve the cracking resistance, moisture susceptibility, and rutting resistance of high-RAP HPThinOL mixtures, depending on whether a WMA technology is used.