Effect of Mixing and Compaction Temperature on Dynamic Modulus of Modified Binder Bituminous Mixtures

Abstract

Modified binders are increasingly used to cater to the high tire pressure and frequency of loading. The use of modified binders poses considerable challenges in terms of material characterization and distress prediction. However, one area which is least explored is related to the mixing and compaction temperature to be used for mix production using modified binders.In this investigation, the influence of mixing and compaction temperature on the dynamic modulus of bituminous mixtures produced using two modified binders is studied. A polymer modified binder (PG70-16) and an improved crumb rubber modified binder (CRMB-IMP) was used with Bituminous Concrete Grade 2 of the Indian Specification. Samples were fabricated with two sets of mixing and compaction temperature. In the first set, the samples were produced with the mixing and compaction temperature used in the current field practice (20°C higher than that of unmodified binder). In the second set, samples were mixed at a temperature corresponding to the non- Newtonian to Newtonian transition regime. To establish such regime, a shear rate sweep was carried out on the binder using a rotational viscometer. The AASHTO protocol was followed for fabricating the samples of bituminous mixtures and dynamic modulus was determined as a function of frequency and temperature. The collected dynamic modulus values were used to fit a master curve and it was found that considerable differences exist in the master curve between the dynamic modulus values of mixtures produced using these two protocols though the volumetric properties of these mixtures were identical. It is clearly seen from this exercise that when it comes to modified binders, even rudimentary issues related to mixing and compaction temperature are not resolved.