Study On The Preparation Of Compartmented Fiber And Its Influence On Self-healing Of Asphalt Concrete

Asphalt concrete is the main pavement form of high-grade highway in China.Due to the influence of driving load,climate and environment,asphalt pavements are prone to diseases such as cracks,looseness,and potholes,advanced pavement maintenance technologies are urgently needed.Asphalt has a certain self-healing performance.It has become a research hotspot in the field of asphalt pavement maintenance to enhance the self-healing ability of asphalt concrete by using microcapsules encapsulated with healing agent in order to repair the microcracks in the asphalt pavement in the bud state,and avoid them developing into macro diseases.However,there are some technical bottlenecks in the application of self-healing microcapsules in asphalt pavement,such as the rupture of microcapsules is difficult to control,the healing efficiency is limited,and the healing period is too long.Therefore,based on the idea of bionics and inspired by the special compartmented structure of toad eggs,this work synthesized the compartmented fiber encapsulating healing agent by microfluidic technology,in which the healing agent is distributed in different compartments and the release time is different,which is expected to give asphalt concrete long-term and multiple crack selfhealing performance.The main research results are as follows:(1)Based on the synthesis mechanism of compartmented fiber by microfluidic technology and the stress state of sunflower oil droplet in microfluidic chip,the technological parameters of the synthesis of compartmented fiber were determined.The calcium alginate compartmented fiber(AF),calcium alginate/silica compartmented fiber(CF)and calcium alginate/graphene oxide compartmented fiber(MRF)were synthesized to encapsulate sunflower oil.The morphology,structure,thermal stability,mechanical properties and microwave heating characteristics of the three kinds of compartmented fibers were studied by fluorescence microanalysis,scanning electron microscopy,infrared spectroscopy,thermogravimetry and nano indentation.The results show that sunflower oil is uniformly distributed in different compartments in the form of droplets,and the thermal stability and mechanical properties of the three compartmented fibers meet the requirements of asphalt concrete forming;MRF has excellent microwave heating effect,and the heating rate of asphalt containing 5% MRF can reach 3.4 °C/s.(2)Through the modified tensile test,the effect of three kinds of compartmented fibers on the self-healing performance of asphalt was studied by using the recovery rate of tensile strength.The results show that the self-healing performance of asphalt can be improved by more than 30% by three kinds of compartmented fibers.The selfhealing rate of MRF asphalt with 5% MRF is 73.8% higher than that of virgin asphalt after 10 s of microwave heating action,which shows that the self-healing performance of asphalt can be significantly improved by the synergistic effect of microwave heating and healing agent.(3)The AC-13 asphalt concrete containing 0.235% of compartmented fiber was prepared.The distribution of compartmented fiber in asphalt mortar was studied by CT scanning test.The influences of compartmented fiber on concrete volume performance,high temperature rutting performance,low temperature crack resistance,water sensitivity and four-point bending fatigue performance were also studied.The results show that the fiber distribution in the mortar is uniform and the fiber structure is complete.The three kinds of compartmented fiber have little effect on the volume performance of asphalt concrete.The three kinds of compartmented fiber improve the high temperature performance and fatigue performance of asphalt concrete,and slightly reduce the low temperature performance and water loss resistance of asphalt concrete.(4)The effects of CF and MRF on the self-healing performance of asphalt concrete with and without water conditions were studied by three-point bending strength recovery test and fatigue life recovery test.The action mechanism of different aqueous solutions was studied by infrared spectrum and scanning electron microscope.The results show that the recovery rate of the fracture strength of CF asphalt concrete is up to 65%.After microwave heating for 30 seconds,the recovery rate of fracture strength of MRF asphalt concrete is 24.7% higher than that of CF asphalt concrete.The internal cracks of MRF asphalt concrete can be repaired many times by microwave heating;sodium ion can corrode the compartmented fiber wall at the fracture surface and promote the release of the healing agent,so the salt alkali environment containing sodium ion can promote the self-healing of the asphalt concrete containing compartment fiber.(5)The fluorescence microscopy was used to study the healing effect and mechanism of compartmented fiber on asphalt concrete.Molecular dynamics was used to simulate the diffusion process of sunflower oil in asphalt molecular level.Based on the action mechanism of healing agent in compartmented fiber,healing efficiency of three healing agents,namely sunflower oil,engineer oil and waste cooking oil was compared studied.The results show that the healing process by compartmented fibers includes compartments rupture,capillary flow filling cracks of sunflower oil,sunflower oil wetting asphalt,sunflower oil rapidly diffuses in asphalt,asphalt viscosity decreases sharply,and asphalt flow to crack,crack disappearance and asphalt performance is restored.The structure of the adjacent compartments of the ruptured compartment is complete,which makes it possible to repair cracks for many times.MRF has excellent microwave heating ability,which can make asphalt flow rapidly and repair cracks quickly.The diffusion of sunflower oil in asphalt can be divided into two stages: rapid contact diffusion and stable diffusion.The diffusion coefficient of sunflower oil molecules in asphalt increases with the increase of temperature and asphalt aging.Sunflower oil has the best capillary flow ability,the fastest wetting speed and the strongest viscosity reducing effect,the engineer oil has the largest wetting work and fatigue performance recovery ability to the asphalt.The three kinds of healing agents have different healing effects,and the compartmented fibers encapsulated with different healing agents are suitable for asphalt road surface in different traffic environments.