Evaluating the test protocols to determine the mixing and compaction temperatures of modified bitumen

摘要

This paper investigates the feasibility of estimating the mixing and compaction temperatures of modified bituminous mixes using various viscosity-temperature relationships of bitumen. In this study, three methods were employed to determine the appropriate production temperatures for bituminous mixes, without compromising the mix properties: the equiviscous method, high shear rate (HSR) method, and zero shear viscosity (ZSV) method. The equiviscous method is generally adopted when the binders are supposed to follow the Newtonian law of fluids, whereas in HSR and ZSV methods, it is assumed that binders possess non-Newtonian characteristics. For all three methods, a rotational viscometer was used to determine the binder viscosity at variable shear rates and different testing temperatures. The VG40 grade of bitumen was modified using four types of modifiers, namely waste plastics such as low-density polyethylene (LDPE) and polypropylene (PP); polyethylene wax (PEW); and waste cooking oil (WCO). Bituminous concrete grading-II mix properties were evaluated using Marshall parameters, tensile strength, and moisture susceptibility of the samples to observe the effects of multiple production temperatures. The results indicated that, in plastic-modified binders, both HSR and ZSV methods yielded lower mixing and compaction temperatures compared to the equiviscous method. However, the ZSV method yielded substantially lower temperatures which significantly impacted the mixture properties. In unmodified, PEW-modified, and WCO-modified binders, it was observed that similar production temperatures were obtained using equiviscous and HSR methods. The study concluded that, for plastic-modified binders, the HSR method can be recommended since it lowers the mixing and compaction temperatures by about 2-15 degrees C without impacting the mixture properties significantly, whereas for unmodified, PEW-modified, and WCO-modified binders, the traditional equiviscous method seemed to be the most suitable option.