A laboratory study of epoxy/polyurethane modified asphalt binders and mixtures suitable for flexible bridge deck pavement

Highlights

• The epoxy resin/polyurethane (EPU) modified asphalt binder was prepared.

• The optimal content of PU and EP are 8 wt% and 32 wt%, respectively.

• EPU modified asphalt binder has good mechanical properties and storage stability.

• The modification mechanism of EPU modified asphalt binder was explored.

• EPU modified asphalt mixture has good comprehensive pavement performance.

Abstract

Asphalt binder is prone to thermal cracking, which limits its application in flexible bridge deck pavement. Binders of rubbery characteristics, such as polyurethane (PU) and epoxy resin (EP), having high strength, modulus and toughness, could be applicable to resolve cracking issues at low temperatures. This research proposes a novel approach of using PU and EP to prepare an epoxy/polyurethane (EPU) modified asphalt binder. Properties and microstructure of the EPU modified asphalt binder were explored, and the appropriate formula was determined. Besides, the technical properties of the EPU asphalt mixture were also studied. The results show that EPU modified asphalt binder has satisfactory mechanical strength, flexibility and storage stability. 8 wt% PU and 32 wt% EP is determined as the optimal content. The results of Fourier transform infrared spectrum testing show that PU inserts into the three-dimensional network structure of EP, which plays a positive role in improving the flexibility and heat resistance of the modified asphalt binder. The growth of viscosity is greatly affected by temperature and modifier content, and the construction retention time is shorter than the specification requirements. Besides, the low-temperature cracking resistance of EPU modified asphalt mixture is significantly improved compared to epoxy asphalt mixture, which exhibits a good application prospect in flexible bridge deck pavement engineering.

Introduction

Deck pavement is one of the critical parts of the long-span steel box girder bridge. Bridge deck pavement materials with excellent performance play a positive role in improving the driving safety and structural durability of the bridge [1], [2]. At present, asphalt mastic mixture, pouring asphalt mixture and epoxy asphalt mixture are commonly used pavement materials in steel box girder bridge deck pavement [2], [3], [4], [5]. Among these, the epoxy asphalt mixture is more widely used because of its excellent anti-deformation ability, fatigue resistance, water stability and corrosion resistance [6]. In China, since the first successful use of epoxy asphalt concrete in the second Nanjing Yangtze River Bridge in 2000, epoxy asphalt concrete has been used in the construction of many large-span steel bridges, including Sutong Bridge and Xihoumen Bridge [7]. Numerous studies and practical applications have proven that epoxy resin (EP) can endow asphalt binder with excellent mechanical properties, making epoxy asphalt pavements several times stronger than ordinary asphalt pavements [6], [8], [9], [10], [11]. Unfortunately, pure epoxy asphalt binder has poor flexibility, and it is difficult to coordinate with the deformation of long-span bridge decks [4], [12] , resulting in brittle fracture at low temperatures. Consequently, thermal cracks become the most common defect in epoxy asphalt concrete bridge deck pavement, accounting for more than 90% of the total defects [13] , which affect the longevity of the surfacing layers on flexible bridges. Because of this, researchers have never stopped the research on epoxy asphalt binder. They used materials such as carbon nanotubes, organic montmorillonite, SBS and ethylene–vinyl acetate copolymers [14], [15], [16], [17] , together with EP, to prepare modified asphalt binders so as to obtain asphalt binders with improved performance. These studies have achieved positive results but mainly concentrated on high-temperature performance, thermal stability and mechanical properties, etc., and the effect of improving low-temperature performance is not ideal.

Polyurethane (PU) is a polymer material with urethane groups in its molecular structure formed by the reaction of isocyanate and polyol [18]. PU has excellent abrasion resistance, good damping performance, and heat resistance, so it is widely used in the fields of binders, building materials and packaging materials [19], [20]. In recent years, the application of PU in the modified asphalt binder has become increasingly popular, and researchers have also conducted a lot of research. Jin et al. [21] and Sheng et al. [22] used PU modified rock asphalt binder and emulsified asphalt binder, respectively, and the resulting modified asphalt binders have excellent low-temperature performance. Meanwhile, researchers also used the blends of PU and other materials, such as SBS, siloxane and organic montmorillonite to prepare modified asphalt binders, and the results obtained were satisfactory [23], [24], [25]. Besides, Zhang et al. [26] developed a thermoset polyurethane (TS-PU) modified asphalt binder. The addition of TS-PU improves the high-temperature and mechanical properties of virgin binder and is superior to epoxy asphalt binder in terms of flexibility and cost savings. These studies above have shown that PU modified asphalt binder has good comprehensive properties, and its low-temperature performance is particularly outstanding.

The preparation of EP-PU blends has been studied for a long time, and studies have shown that EP has good compatibility with PU, and the mechanical properties of both show a significant synergistic effect. Pure EP is prone to brittle fracture, while the blend exhibits a ductile fracture [27]. Besides, compared with pure EP, EP-PU blends have improved thermal stability and modulus, and they are mainly used in foam materials, coatings and concrete crack repair materials [28], [29], [30]. Although the waterborne epoxy resin-polyurethane-emulsified asphalt used for the waterproof bonding layer of the bridge deck has been studied [31] , there is no report about the simultaneous use of EP and PU to prepare modified asphalt binders for flexible bridge deck asphalt pavement.

Inspired by the research review above, this study uses PU instead of part of the EP to prepare EPU modified asphalt binder. The purpose is to obtain a kind of asphalt binder with excellent low-temperature cracking resistance, which can effectively reduce the cracks of the surfacing layers on flexible bridges. Firstly, the properties and microstructure of the EPU modified asphalt binder were studied by tensile test, scanning electron microscope (SEM), segregation test and laser scanning confocal microscope (LSCM) and its suitable formulation was determined. Secondly, Fourier transform infrared spectroscopy (FTIR) was used to analyze the modification mechanism, and the relationship between the viscosity and the temperature, as well as time of the EPU modified asphalt binder was explored through the viscosity test. Finally, EPU modified asphalt mixture was prepared and compared with epoxy asphalt mixture and PU modified asphalt mixture for pavement performance.