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• GC was synthesized by the ball milling method and employed for asphalt modification. • GC improved the mechanical properties and rutting resistance of asphalt binders. • GC promoted the thermal-activated healing potential of the two asphalt binders. • GC uniformly dispersed in asphalt binders by physical and chemical reactions. Graphene, featuring excellent mechanical, electrical, thermal, and optical properties, has received increasing attention in asphalt modification. However, high production costs and poor dispersibility used in asphalt binders have limited its large-scale application. Therefore, in the present work, a high-quality and inexpensive carbon black, a typical carbon-based material and tire processing by-product, was selected to compound graphene to improve its dispersion in the base and crumb rubber (CR) modified asphalt matrix well as reducing the cost of utilization. This modifier is ultimately expected to enhance the performances of both the base and CR modified asphalt. First, the graphene/carbon black composite (GC) was prepared by the ball milling method and used to modify the asphalt binders. Then, the dynamic viscoelastic mechanical tests, i.e., multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and fatigue-healing cycle test, have been conducted to comprehensively evaluate the rheological and healing properties of the base and crumb rubber (CR) modified asphalt binder. Subsequently, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were adopted to reveal the morphology and interaction between GC and asphalt binders. The test results indicated that the incorporation of GC significantly improved the high-temperature rutting resistance and heat-activated healing performance of the two asphalt binders. Moreover, the introduction of GC enhanced the fatigue damage tolerance and low-temperature ductility of the CR modified asphalt. Meanwhile, the loose GC interacted with the asphalt molecules to form tight connections through physical and chemical reactions. This may cast some light on the application of GC in asphalt modification. [ABSTRACT FROM AUTHOR]

• SBS modified asphalt binder incorporated with PVP-GNPs was prepared. • PVP-GNPs was successfully synthesized by non-covalent interactions. • Rutting resistance of PVP-GNPs/SBS modified asphalt was significantly improved. • Fatigue damage tolerance of PVP-GNPs/SBS modified asphalt was enhanced. With the rapid development and application of nanomaterials in recent years, graphene nanoplatelets (GNPs) compounded styrene–butadienestyrene (SBS) to prepare novel asphalt binders with superior high-temperature performance and outstanding mechanical property, have gradually become a hot topic. However, this approach may result in poor compatibility of GNPs with SBS modified asphalt. In this work, the loosely layered composite, polyvinylpyrrolidone stabilized graphene nanoplatelets (PVP-GNPs), has been prepared with a polymer, polyvinylpyrrolidone (PVP), adsorbed onto the surface of graphene nanoplatelets through non-covalent interactions. Subsequently, the prepared PVP-GNPs as a modifier was added into SBS modified asphalt to increase the compatibility with the asphalt binder. The conventional experiment results revealed that the addition of a certain amount of PVP-GNPs improved the softening point and temperature sensitivity. Meanwhile, dynamic rheological tests (Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), Linear Amplitude Sweep (LAS), and Bending Beam Rheometer (BBR)) showed an enhancement of the viscoelastic properties, high-temperature rutting resistance, medium-temperature fatigue damage tolerance, and low-temperature thermal cracking resistance. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) techniques demonstrated the successful attaching of PVP onto the surface of GNPs, which expanded the spatial distance of GNPs and facilitated the intercalation of asphalt molecules. Moreover, 1.0%–1.5% was recommended as the optimal dosage of PVP-GNPs for modification. This study may shed light on the application of GNPs to asphalt pavements. [ABSTRACT FROM AUTHOR]

• Alkali leaching on dense-graded asphalt paved on a concrete bridge deck. • Investigated the static water transport inside asphalt mixtures for various modes. • Examined the distinction between the alkali and non-alkali leaching cores by Computed Tomography (CT). • Revealed the major driving mechanism for alkali leaching on as-built concrete bridge deck pavements. Recently, a new distress type in as-built dense-graded asphalt concrete (DGAC) paved on concrete bridge decks, namely alkali leaching, has been detected in China. The water carries dissolved alkali ions from the cement concrete deck to the pavement surface and reacts with CO 2 in the air to form whitish carbonate deposits. The "bottom-up" water transportation process in the presence of the natural environment without vehicle loading effect is a complicated problem. Thereby, scrutiny of the driving force of the "bottom-up" water transportation process in cement concrete bridge deck pavements (CCBDPs) plays a vital role in realizing the mechanism of alkali leaching. In the present study, three potential driving mechanisms that may cause this process are proposed and simulated in the laboratory, including water vapor diffusion under action of multiple temperatures and relative humidity (RH), capillary rise, and leaching water caused by variation of atmospheric pressure. The microstructure of alkali leaching samples cored from distress pavement is also carefully examined by X-ray CT. The obtained results show that the diffusion mass of water vapor demonstrates a rapid lessening with the reduction of the relative humidity differences. A highly linear correlation between the RH difference and the diffusion flux of the water vapor for different temperatures is also identified, indicating that the DGAC with various air voids follows Fick's first law of diffusion. Further, capillary rise indeed occurs in the DGAC but does not contribute to the alkali leaching process. The pressure difference could continuously drive the leaching water to the surface of DGAC samples, and the critical pressure difference (0.3–0.7 kPa) would be generally less than the daily variation of the atmospheric pressure (approximately 0.8 kPa in weather alternate days). The quantitative analysis of the internal structure for alkali leaching cores also reveals that the distressed cores present relatively higher void ratios, especially for small volume and narrow pores. The entrapped air within unsaturated pores provides the precondition for water transport subjected to the atmospheric pressure differences. These findings contribute to the understanding of static moisture transportation in the dense-graded asphalt mixtures and clarify the main driving mechanism of moisture-induced alkali leaching on CCBDPs. [ABSTRACT FROM AUTHOR]

• Efflorescence of dense-graded asphalt paved on a cement concrete bridge deck. • Calcium Carbonate was found to be the main efflorescence material. • Cement concrete bridge deck provide the alkaline source for efflorescence materials. • Carbonation is the result of Ca(OH) 2 transformation in the presence of H 2 O and CO 2. • Migration model of the efflorescence material was established. A new distress type, namely alkali leaching, was recently observed to have developed on an as-built dense-graded asphalt concrete (DGAC) paved on a cement concrete bridge deck in China. Not only does alkali leaching affect the aesthetic appearance of the cement concrete bridge deck pavement (CCBDP) due to the distinctive color contrast, it also creates a potential threat to the service life of the bridge. In this paper, an alkali leaching distressed section of a CCBDP in Shaanxi Province (China) was studied. The study results indicated that whitish spots cannot be removed by natural water. In situ pH measurements indicated highly alkalinine materials appear on the surface of pavement layers. Based on these findings, the formation mechanism of alkali leaching on CCBDP was analyzed. The corresponding results showed that the main mineral of alkali leaching was Calcium Carbonate (CaCO 3). Under wet conditions, rainwater infiltrates into the cement bridge deck from the sides of the pavement. Continuous exposure to moisture or humid environments facilitates the subsequent hydration to generate Ca(OH) 2 , which is the alkaline source for alkali leaching. The generated Ca(OH) 2 migrates with rainwater to the pavement surface through capillary action. With the repeated circles of wet and dry conditions, the in-situ carbonation products lead to formation of alkali leaching on the pavement surface. [ABSTRACT FROM AUTHOR]