Evaluation of Rigden fractional voids test method and the relation to mastic viscosity

Mineral filler fractional voids value has been used as an indicator of filler stiffening effect since the introduction of the test by Rigden in 1947. The objective of this study is to evaluate the potential of the Rigden voids test to predict the mastic viscosity for a wide range of fillers and binders used in North America. In this study a detailed literature review, conducted as part of the NCHRP 9-45 projects, identified a small set of filler physical and chemical properties that are expected to have the most important effects on mastic behavior. Rigden fractional voids, as well as these other important physical and chemical properties were measured for a set of 30 fillers selected from various sources in the United States. The properties of these fillers were analyzed and used to select 17 fillers that cover the wide range of properties measured for the larger set. These 17 fillers were blended with 4 binders and resulting mastics were tested to measure the increase in viscosity relative to the unfilled binders. The results showed that the Rigden factional voids values could not be used to successfully predict the stiffening effect of the fillers since different asphalt binders interact differently with the fillers. Detailed statistical analysis clearly showed that the mastic viscosity is significantly dependent on the filler and asphalt binder types. The analysis of the results shows that these properties in addition to their interactive effects with the binder type govern the viscosity increase of the Mastics. The results also revealed that one filler types demonstrate extreme interaction with a specific type of binder. The prediction model developed for the relative viscosity of mastics was able to closely estimate the stiffening effect of the fillers. These results confirm earlier studies conducted in Europe and resulted in the recent development of European Norms for fillers.