Cold Road Pavement Modified with Polyurethane Dispersion Nanocomposite

Today, the importance of asphalt pavement is clear to all, and researchers are always working to improve its quality and sustainability against weathering and traffic load. The main part of asphalt pavement is bitumen that polymeric modification of bitumen plays an important role in increasing asphalt performance. In recent years, due to the importance of environmental problems, instead of old methods of asphalt preparation due to dispersing harmful particles into the atmosphere when bitumen melts, emulsion bitumen is been used. The polymer modification of emulsion bitumen has been less studied due to need of dispersed polymer in water. This research is aimed at modifying emulsion bitumen with polyurethane dispersion (PUD) and its effect on bitumen performance. For this purpose, different polyurethanes were prepared using diisocyanate, polyethylene glycol (PEG) with different molecular masses (200, 400, 600 and 1000 gr/mol) and N-methyl diethanol amine (MDEA). Particle size distribution of PUD s in aqueous phase is presented in Figure 1. In this research nanoclay was also used to further enhance bitumen. For this purpose, at first nanocomposites with PUD synthesized with PEG600 and different percentages of nanoclay (1, 3 and 5% w/w) were prepared and used for modifying emulsion bitumen (from Jouybar Green Star Industries Co., Iran). Evaluation results showed that with increasing nanoclay content penetration degree decreased from 64.7 to 35 and softening point increased from 49.4 to 63. Based on average of these results, 3% w/w of nanoclay was considered as the optimum amount for bitumen modification. At last nanocomposites of all synthesized polyurethane samples with different polyethylene glycols molecular weight, and 3% w/w nanoclay were made and used for the modification of emulsion bitumen. Results are presented in Table 1. As we can see in Table 1, when the PEG molecular weight increases, the softening point increases too. It can be explain for its flexibility due to the increase in the elasticity of polyurethane by increasing in the length of soft segment in it. Increasing the molecular weight also reduces the penetration degree of the emulsion bitumen.