Study on macroscopic properties and microstructure of thermosetting polyurethane asphalt binder (PAB) based on curing kinetics

Recently, novel thermosetting polyurethane asphalt binder (PAB) has been studied by more researchers. This paper investigated the curing mechanism, microstructure and macroscopic performance of PAB. The mechanical properties, rheological properties, and elastic recovery performance of PAB were evaluated. Fourier transform infrared spectroscopy (FTIR), fluorescence microscopy (FM) and gel permeation chromatography (GPC) were adopted to confirm the chemical reaction and microstructure, curing process was studied combined with kinetics. Results showed PAB was the first-order curing reaction system and slow curing progress was conducive to mixing application, polyurethane particles changed from granular to the reticular structure during curing. The ratio of large molecular weight showed an increasing trend as temperature/time up. Furthermore, multi-stress creep recovery demonstrated that elastic recovery performance of PAB-50 (0.1 kPa) can be improved to 2.2 times, 8.1 times approximately compared with styrene–butadienestyrene block copolymer asphalt binder (SBSMA) and unmodified asphalt binder (MA). The tensile strength of PAB-30 (cured at 4d-130 °C) was 3.1 times that of 2 h (130 °C). Viscosity temperature index (VTS) value gradually increased implied that temperature sensitivity was habited by curing time. Pearson correlation coefficient illustrated that the mechanical property of PAB was positively related to the large molecular weight and conversion rate of the isocyanate group. The non-recoverable creep compliance reduction positively relied on polyurethane content and microstructure.