Polyurethane as a modifier for road asphalt: A literature review

Abstract

During its service life, ordinary asphalt pavement frequently develops rutting, cracking, spalling, and other ailments. Polyurethanes (PUs) are frequently utilized in the construction, transportation, and furniture industries as soft and stiff foam, elastomers, and adhesives. Over the past five years, research on the use of PU and its raw materials as modifiers for road asphalt has increased annually. Thus, this paper primarily reviews the following topics: 1) First, the necessity of modified asphalt, the limitations of SBS-modified asphalt and Rubber powder modified asphalt, and the benefits of polyurethane-modified asphalt (PUMA) are discussed; 2) Second, the relevant background of PU, including common raw materials, synthesis methods, structures, and primary application scenarios, is presented. 3) Bitumen’s chemical composition and typical functional groups are summarized. Based on this, the mechanism of PUMA was analyzed from four different perspectives: chemical reaction, Fourier Transform Infrared Spectroscopy (FTIR), change in the proportion of SARA, and Fluorescence Microscopy (FM). 4) Four processes of preparing PUMA are reviewed: one-shot process, prepolymer process, semi-prepolymer process, and direct injection process. The most prevalent process is the prepolymer process; 5) The road performance of PUMA with different preparation processes was systematically analyzed. In general, PU can significantly increase the high-temperature performance, water stability, fatigue resistance, anti-aging qualities, and adhesion of asphalt, but their low-temperature performance and temperature sensitivity remain debatable; 6) Five research directions for PU as an asphalt modifier for roads are summarized: PU modified emulsified asphalt, Bio-based polyol PUMA, PU and other materials composite modified asphalt, waste PU modified asphalt, and PU foam asphalt; 7) Finally, the existing problems and development trend of PUMA are reviewed.