| Asphalt mixtures are widely used in water conservancy and pavement engineering as typical composite materials,which are prone to a large number of micro-cracks under changing environmental conditions such as temperature and humidity,coupled with long-term repetitive loading.Microwave heating can repair these microcracks promptly and quickly.However,due to the low microwave absorption efficiency of conventional asphalt mixtures,replacing aggregates with equal volume of steel slag can improve the microwave absorption capacity of asphalt mixtures.For microwave heating induced self-healing of steel slag asphalt mixtures as a technique,neither indoor tests nor macroscopic homogeneous models can reflect the effect of each component within the specimen on microwave heating,so the behavior of each component of steel slag asphalt mixes in the case of multi-physical field coupling is investigated in this paper from a meso-scale.Firstly,for the complex mesostructure of steel slag asphalt mixtures,a three-dimensional spherical aggregate and polyhedral aggregate random growth and placement algorithm was written to generate random aggregate models with high volume ratios according to the given gradation with high efficiency.A three-phase(steel slag,aggregate and asphalt mortar)asphalt mixture three-dimensional mesoscopic numerical model under the coupling of electromagnetic,temperature and moisture fields were developed,and the microwave heating analysis was performed on the asphalt mixture mesoscopic model.The reliability of the numerical model was verified by comparing the numerical simulation results with the experimental results in the literature.The model can well characterize the heat transfer process,evolution of electromagnetic field and moisture diffusion behavior of each component inside the asphalt mixture.Then,the optimum particle size and optimum replacement content of steel slag were investigated in order to achieve the best healing effect of steel slag asphalt mixtures under microwave heating.The results of both volumetric mean temperature and temperature distribution uniformity showed that it was optimal when both 4.75-9.5 mm steel slag replacement rate and 9.5-13.2 mm steel slag replacement rate were 60%.Steel slag can significantly increase the heating rate of asphalt mixtures and exhibit better microwave absorption performance.The dielectric constant,permeability and particle size of steel slag affect the microwave reflection ability of the specimen,and the microwave heating performance of asphalt mixture increases with the amount of steel slag added,and the resistance loss accounts for most of the total loss.However,the addition of excessive steel slag will not only prevent the self-healing asphalt mixture will also reduce the efficiency of microwave absorption.Finally,the moisture diffusion behavior of the steel slag asphalt mixtures under microwave heating was investigated.The moisture concentration distribution of the specimens showed a circular concentration gradient distribution and decreasing to the outside,and the peak moisture diffusion fluxes were distributed in the asphalt mortar and pores.The results of the homogeneous and meso-scale models indicate that the aggregate and pores affect the distribution and evolution of moisture concentration and diffusion flux during microwave heating of the specimens.The moisture in the asphalt mixture enters into the interior of the aggregate and steel slag by diffusion after heating,which inhibits the diffusion of moisture outward.The temperature accelerates the rate of moisture diffusion in the steel slag asphalt mixture,while the pore structure reduces the rate of moisture diffusion to the outside of the specimen during heating. |
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