# Preparation and Properties of Waterborne Polyurethane and SBS Composite-Modified Emulsified Asphalt
## 1 Introduction
prepared waterborne epoxy resin emulsified asphalt (WEREA) adhesive coatings using polyurethane epoxy resin, finding high early and late strength, ensuring effective bonding of road structural layers and enhancing durability [21]. [PERSON] et al. studied waterborne epoxy resin (WER) and styrene-butadiene rubber (SBR) composite modified emulsified asphalt (WER-SCMEA) fog seal material, demonstrating good water stability and wear resistance [22]. To address the poor low-temperature performance of waterborne epoxy emulsified asphalt (W-EA), [PERSON] et al. used waterborne polyurethane (WPU) as a modifier, finding that adding 10% WPU significantly improved low-temperature crack resistance [23]. Waterborne polyurethane (WPU), abbreviated as PU in this text, uses water as a solvent, offering advantages such as pollution-free production, safety, reliability, good compatibility, and easy modification. Its molecular chain contains numerous amino ester bonds and polyurethane segments, providing excellent physical properties such as high hardness, toughness, wear resistance, and chemical resistance. PU is widely used in coatings, adhesives, leather finishing, and other fields. With stringent global environmental protection requirements, PU, as an environmentally friendly polymer material, has promising development prospects. This study utilizes cationic waterborne polyurethane (WPU+), abbreviated as PU+ in the following text. Despite its diverse applications, PU is seldom used for preparing composite modified emulsified asphalt. The preparation method for PU and the impact of this material on emulsified asphalt's performance require further investigation to meet engineering standards. [PERSON] et al. examined the feasibility of using water-based acrylate (WA) and PU as modifiers to enhance the performance of SBR/SBS-modified emulsified asphalt. They found that water cationic acrylate (WCA) provided the best modification for SBS-modified asphalt emulsion, balancing storage stability and high-temperature performance [24]. However, mixing PU with SBS-modified emulsified asphalt caused emulsion breaking, indicating poor storage stability, and no further performance tests were conducted [24]. Given the ease of preparing composite modified asphalt emulsions, SBS-modified emulsified asphalt and PU can be stored separately and mixed on-site. This study posits that despite the poor storage stability of SBS-modified emulsified asphalt with PU emulsion, the potential benefits of PU modification warrant further analysis. In this study, SBS-modified emulsified asphalt and PU+ emulsion were mixed and stirred according to a dosage gradient. All the content is calculated based on the quality of SBS-modified emulsified asphalt. The emulsion was evaporated immediately after stirring to obtain the residue, which was then analyzed using routine performance tests. Advanced rheological tests, including temperature sweep (TS), frequency sweep (FS), linear amplitude sweep (LAS), and multi-stress creep recovery (MSCR) tests, were performed using a dynamic shear rheometer (DSR). Surface free energy (SFE) tests were conducted using a fully automated surface tension meter (STM). Comprehensive evaluations of the high-temperature rheological properties, fatigue performance, adhesion performance, and water damage resistance of the asphalt were performed. Chemical changes during the modification process were characterized using Fourier transform infrared spectroscopy (FTIR), and polymer distribution in the evaporated residue was observed using fluorescence microscopy (FM). This study aims to explore the feasibility of incorporating cationic water-borne polyurethane (PU+) to enhance the performance of SBS-modified emulsified asphalt, providing an effective modification method for preparing high-performance cold binders.