Study On Self-healing Performance Of Microwave-absorbing Asphalt Mixture By Microwave Heating

Cracks are one of the major diseases of asphalt concrete pavement.If not repaired in a timely manner,it will seriously affect the service life of the asphalt pavement.Microwave heating is an advanced,environmentally friendly,and efficient way of maintaining asphalt pavement.However,ordinary asphalt mixtures have weak microwave radiation reflection ability.To further enhance the microwave absorption ability of ordinary asphalt mixtures,absorbing agents can be added to the asphalt mixture to improve the self-healing performance of the asphalt material.The thesis focuses on three types of microwave-absorbing materials,namely carbon black powder,carbonyl iron powder,and nickel-zinc ferrite powder.By replacing part of the mineral powder with microwave-absorbing materials,microwave-absorbing asphalt mixtures were prepared,and research was conducted on the self-healing performance of microwave-absorbing asphalt mixtures under microwave heating.The physical and chemical properties and microwave heat-induced performance of carbon black powder,carbonyl iron powder,and nickel-zinc ferrite powder were tested.The particle size distributions of the three microwave-absorbing materials were concentrated between 0.06～141.60μm,1.42～89.34μm and 0.18～502.38μm,respectively,and they exhibited good thermal stability.These materials contain conductive compounds and metal oxides,resulting in a high complex permittivity,demonstrating excellent microwave heat-induced performance.The optimum proportion of the microwave-absorbing asphalt mixture was determined through the Marshall stability test.The microwave-absorbing asphalt mixture containing carbon black powder,carbonyl iron powder,and nickel-zinc ferrite powder showed good road performance,such as high-temperature stability,low-temperature performance,and water stability.The microwave heat transfer performance of the microwave-absorbing asphalt mixture was studied using microwave heating experiments and COMSOL Multiphysics software numerical simulation.The results showed that after 120 seconds of microwave heating,the surface and internal temperature rising rates of the microwave-absorbing asphalt mixture containing 30%carbon black powder,carbonyl iron powder,and nickel-zinc ferrite powder were0.66℃/s,0.67℃/s,0.54℃/s and 0.67℃/s,0.68℃/s,and 0.57℃/s,respectively,which were more than 1.1 times that of ordinary asphalt mixture.Through volume integral calculation of the model,the energy dissipation of carbon black powder,carbonyl iron powder,and nickel-zinc ferrite powder asphalt mixtures decreased by 21.6%,33.6%,and 16.5%,respectively,compared to ordinary asphalt mixtures.At the same time,the numerical simulation results of the temperature distribution of microwave-heated absorbing asphalt mixtures were consistent with the experimental results.The microwave heating self-healing properties of microwave-absorbing asphalt mixtures were quantitatively studied using the peak load ratio(HI_F)and fracture energy ratio(HI_U)of specimens after microwave heating and healing in SCB(Semi-Circular Bending)tests.The effects of microwave-absorbing material type and dosage,microwave heating power,heating time,healing time,and degree of damage on the self-healing properties of absorptive asphalt mixtures were investigated.The results showed that under the same microwave-absorbing material dosage,the carbonyl iron powder asphalt mixture had the highest self-healing rate,followed by the carbon black powder asphalt mixture,and the nickel-zinc ferrite powder asphalt mixture had the lowest self-healing rate due to the differences in their electromagnetic properties.Under the same microwave heating conditions,as the absorbent material dosage increases from10%to 30%,the healing rate of the microwave-absorbing asphalt mixture gradually increases.When the microwave heating time is 120 seconds and the microwave power is 700 W,and the dosage is 30%,the three types of microwave-absorbing asphalt mixtures achieve the best healing effect,and their healing rates are HI_Fand HI_U,respectively:71.16%,67.62%,61.32%and 48.8%,52.05%,39.17%The healing time was an important factor affecting the self-healing ability of the microwave-absorbing asphalt mixture.When the healing time increased from 4 h to 16h,the microwave heating self-healing rate of the microwave-absorbing asphalt mixture gradually increased,indicating better self-healing ability.The more severe the damage to the microwave-absorbing asphalt mixture,the worse the self-healing effect.When the crack depth was 15 mm,the self-healing rate of the microwave-absorbing asphalt mixture was lower,indicating that the crack repair was more difficult.