Effect of processing on the rheological properties of poly-urethane/urea bituminous products

In this work, bitumen modification, by “in situ” formation of poly-urethane/urea-based polymers in the bituminous matrix, has been studied. This procedure consisted of a first modification by the addition of MDI-PPG reactive prepolymer (polypropylene-glycol, PPG, functionalized by polymeric MDI, 4,4′-diphenylmethane diisocyanate), in a first stage, and a further modification of the new bitumen-MDI-PPG molecules as water was added, in a second stage. Thin layer chromatography, TLC–FID, and infrared spectroscopy, FTIR, techniques have been used to follow the reactions occurring in four different types of bitumen. Rheological measurements have demonstrated that the resulting bitumen modification strongly depends on the processing conditions selected during the first stage. Thus, bitumen modification degree after water addition increases as processing time does. Furthermore, water addition has been found to promote bitumen foaming at low processing temperatures, which could be used in novel applications where a foamed binder is required. As a result, a reactive bitumen modification mechanism, involving a set of three chemical reactions, has been proposed.