Storage stability of modified binders using the newly developed LAST procedure

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Abstract
The Laboratory Asphalt Stability Test (LAST) was introduced as part of the NCHRP 9–10 project to evaluate storage stability of asphalt binders. The unique design allows varying the temperature, time of storage, and level of agitation during storage and allows sampling of the material continuously throughout the test. The test design is based on scaling down one of the commonly used storage tanks used for modified asphalts in the field. The test results can be used to guide the production of the modified binders and determine the performance of these binders during the construction process. This paper discusses the design and introduces the details of the testing protocol proposed to evaluate thermal stability of binders. The protocol follows a systematic procedure for detailed evaluation of effects of phase separation and possible degradation during storage. A set of parameters is proposed for use as indices to reflect the potential of binders for phase separation and/or thermal degradation. A large number of binders have been tested with the LAST and the results are summarized and discussed in this paper. The results indicate that binders can vary significantly in their thermal stability characteristics and thus their stability characteristics need to be measured and considered in selection of binders for different applications. The LAST results indicate that some binders are very stable for extended times, others can be kept homogeneous only with minor agitation while others require more rigorous agitation. Time for separation is an important factor that should be considered. The results also indicate that agitation can result in degradation of modifier and/or significant additive hardening. The rheological measurements conducted indicate that phase separation and/or degradation appear to have influences on rheological type of binders, such that frequency dependency of temperature dependency changes with storage.

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