Kinetics and toxicological potential of heavy metal leaching from asphalt pavements.

The leaching of heavy metals from asphalt pavement has attracted increasing attention due to its associated environmental risks. Comprehending the leaching process is crucial for ensuring the safe utilization of asphalt pavement. This study investigates heavy metal leaching kinetics from asphalt pavements using tank-leaching tests and dynamic simulations employing both first and second-order kinetic models. Furthermore, this study reveals the toxicological potential of heavy metal leaching from asphalt pavement by assessing its temporal metal accessibility based on the obtained kinetic attributes. Six distinct asphalt mixtures were prepared and tested, each exhibiting two different gradations. The findings demonstrated that both kinetic models effectively elucidated the leaching process. Notably, the relatively stable final leaching stages primarily adhered to first-order kinetics, while the second-order kinetics provided a superior description of the more intricate initial leaching stages. In terms of toxicological potential, the results indicated that recycled waste-incorporated asphalt pavements, specifically bottom ash-incorporated asphalt and asphalt rubber, exhibited excessive heavy metal leaching for varying durations, ranging from several days to months under specific conditions. This study has provided valuable insights into the metal leaching kinetics of asphalt pavements and their associated toxicological impact, significantly advancing the current understanding of the consequences of heavy metal leaching from asphalt pavements.

Investigation on the Micro Deformation Mechanism of Asphalt Mixtures under High Temperatures Based on a Self-Developed Laboratory Test.

Rutting has always been considered the main disease in asphalt pavement. Dealing with rutting disease would be benefitted by understanding the formation of rutting and testing the rutting performance of mixtures more reasonably. The objective of this paper is to systematically investigate the rutting mechanism by employing a self-designed rutting tester along with the corresponding numerical simulations. The deformation of different positions of the existing tracking tester was found to be inconsistent, and the loading was not in line with reality. Accordingly, a more practical tester was proposed: the reduced scale circular tracking (RSCT) tester integrates the functions of asphalt mixture fabrication and rutting monitoring. The results demonstrated that the loading of the new tester is closer to the actual situation. In addition, determining the stress and displacement characteristics of particles in the asphalt mixture was found to be difficult due to the limitations of the testing methods. Therefore, a two-dimensional virtual rutting test based on the RSCT was built using PFC2D (Particle Flow Code 2 Dimension) to investigate the mechanism of formation in rutting and to obtain the corresponding guidance. The numerical simulation showed that all particles of the specimen tended to move away from the load location. The main cause of rutting formation was the eddy current flow of asphalt mastic driven by coarse aggregates. The aggregates with diameters ranging from 9.5 to 4.75 mm were observed to have the greatest contribution to rutting deformation. Therefore, the aggregate amount of these spans should be focused on in the design of mixture grading.

Preparation of Octadecyl Amine Grafted over Waste Rubber Powder (ODA-WRP) and Properties of Its Incorporation in SBS-Modified Asphalt.

Through a covalent grafting reaction, octadecyl amine (ODA) was grafted on the surface of waste rubber powder (WRP) to obtain an ODA-WRP modifier, which was in turn compounded with a styrene-butadiene-styrene block copolymer (SBS) to prepare ODA-WRP/SBS-modified asphalt. The three major indicators (i.e., dynamic shear rheometer (DSR), multi-stress creep recovery (MSCR), and separation tests) showed that 1-ODA-WRP effectively improved the complex shear modulus (G*), elastic Modulus (G'), and loss modulus (G″) by 36.47%, 40.57%, and 34.77% (64 °C and 10 Hz), respectively, as compared to pristine SBS-modified asphalt. Fluorescence microscopy (FM) results concluded that the enhancement in mechanical properties was accredited to the better compatibility of various components in asphalt and establishment of network structure between ODA-WRP and SBS in ODA-WRP/SBS-modified asphalt. Fourier infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analyses confirmed the successful synthesis of ODA-WRP. This study could be of great help in synthesizing ODA-WRP asphalt modified with SBS for highways and construction applications.

Preparation and Properties of SBS-g-GOs-Modified Asphalt Based on a Thiol-ene Click Reaction in a Bituminous Environment.

Styrene-butadiene styrene graphene oxide nanoplatelets (SBS-g-GOs)-modified asphalt was prepared by reacting thiolated GOs (GOs-SH) with SBS in asphalt using a thiol-ene click reaction. The temperature resistance and mechanical properties of asphalts were analyzed by dynamic shear rheology (DSR) and multiple-stress creep-recovery (MSCR) tests, which revealed that an optimum amount of GOs-SH (0.02%) can effectively improve the low temperature and anti-rutting performance of SBS asphalt. Segregation experiments showed that SBS-g-GOs possessed good stability and dispersion in base asphalt. Fluorescence microscopy results revealed that the addition of GOs-SH promoted the formation of SBS network structure. Textural and morphological characterization of GOs-SH and SBS were achieved by Fourier transform infra-red (FT-IR) spectroscopy, energy-dispersive X-ray spectroscopy (EDX), atomic-force microscopy (AFM), X-ray diffraction (XRD), and scanning electron microscopy (SEM), while surface chemical composition was tested by X-ray photoelectron spectroscopy (XPS). Based on textural characterization data, a suitable reaction mechanism was proposed that involved the preferential reaction between GOs-SH and 1,2 C=C of SBS. The currently designed GOs-SH incorporated asphalt via thiol-ene click reaction provides new ideas for the preparation of modified asphalt with enhanced mechanical properties for target-oriented applications.