Study On Self-healing Properties Of Modified Asphalt Based On Microcapsules Encapsulating Rejuvenator

The traditional method of directly using asphalt rejuvenator to repair asphalt microcrack had disadvantages such as poor permeability,complex construction,and environmental pollution.Microencapsulation of asphalt rejuvenator is a new method to solve microcracks in asphalt materials.When microcracks appear inside the asphalt,they will penetrate through the microcapsules under the action of tip stress.The microcapsules break and release the rejuvenator,which mixes the components of the aged asphalt to restore self-healing performance of asphalt,thereby accelerating the self-healing efficiency of the aged asphalt microcracks.In this paper,the rejuvenator was microencapsulated,and the prepared rejuvenator microcapsules were incorporated into the aged asphalt material to enhance the self-healing properties of microcracks in aged asphalt.In order to study the self-healing properties and mechanism of asphalt modified by microcapsules of rejuvenator,this paper used asphalt rejuvenator as the core material and urea formaldehyde resin（UF）as the shell material to prepare rejuvenator microcapsules through in-situ polymerization method.Firstly,environmental scanning electron microscope（ESEM）,laser particle size analyzer（LPSA）,Fourier transform infrared spectrometer（FT-IR）and thermogravimetric analyzer（TGA）were used to evaluate the microscopic morphology,particle characteristics,chemical structure,thermal stability and salt tolerance of the rejuvenator microcapsules.Then,the rejuvenator microcapsules were added to the aged asphalt,and the microstructure,conventional performance,self-healing efficiency,and self-healing behavior of the microcapsule modified asphalt were evaluated by using asphalt penetrometer,softening point meter,ductility meter,and laser scanning confocal microscope（LSCM）.Finally,the synthesis mechanism of microcapsules and the self-healing mechanism of rejuvenator microcapsule modified asphalt were discussed.The main results are as follows.ⅠPreparation and characterization of r rejuvenator microcapsules（1）Microcapsules of asphalt rejuvenator were prepared by in-situ polymerization method.The surface of microcapsules were rough and spherical,which was beneficial for increasing the adhesion between the microcapsules and asphalt.As the temperature increases,the overall color of microcapsules become deepen.When the temperature exceeds 200℃,a small amount of aggregation occurs in the microcapsules,accompanied by the rupture of some microcapsules.The particle size of microcapsules showed a normal distribution,which was between 50 and 300μm.With the increase of temperature,the particle size of microcapsules increased slightly,which may be caused by the agglomeration of microcapsules at high temperature.（2）The characteristic peaks of asphalt rejuvenator(3021.4cm^-1、2923cm^-1、2849.4cm^-1)and UF(3328cm^-1、1633cm^-1、1540cm^-1)can be found in rejuvenator microcapsules.With the increase of temperature,the characteristic peak intensity of urea-formaldehyde resin（UF）gradually weakened.This indicated that the rejuvenator microcapsules are successfully prepared and can withstand higher temperatures without rupture.（3）The mass loss rate of rejuvenator microcapsules reached 82.9%at 226-372.6℃,while the mass of microcapsules remained basically unchanged at 372-500℃.This indicated that microcapsules have good thermal stability and can meet the temperature requirements of asphalt mixing（160-180℃）.（4）When the concentration of Na Cl was less than 15wt%,the rejuvenator microcapsules were evenly distributed,uniform in size and no rupture.When the Na Cl concentration is greater than 15wt%,a small number of microcapsules were broken.This shows that the microcapsules have excellent salt resistance.II Self-healing properties of rejuvenator microcapsule modified asphalt（5）The rejuvenator microcapsules were incorporated into the aged asphalt.It was found by ESEM that the microcapsules were well bonded to asphalt.With the aging of the asphalt,the surface of asphalt changed from smooth to wrinkled,which hindered the diffusion of rejuvenator.（6）Add different amounts of microcapsules into aged asphalt to prepare rejuvenator microcapsules modified aged asphalt.With the increase of microcapsule content,the penetration and ductility of unaged,short-term aged and long-term aged asphalt showed an increasing trend,and the softening point showed a decreasing trend.This shows that the incorporation of microcapsules can improve conventional performance of aged asphalt.（7）When the dosage of microcapsules was 3wt%,the self-healing efficiency of unaged asphalt reached the maximum value of 75.6%,which increased by 35.2%;When the dosage of microcapsules was 2wt%,the self-healing efficiency of short-term aged asphalt reached the maximum value of 69.0%,which increased by 32.1%;When the dosage of microcapsules was 4wt%,the self-healing efficiency of long-term aged asphalt reached the maximum value of 64.0%,which increased by 46.2%.This indicated that microcapsules can significantly enhance the self-healing efficiency of aged asphalt.（8）The self-healing time of unaged asphalt was about 50 minutes,the self-healing time of short-term aged asphalt was about 70 minutes,and the self-healing time of long-term aged asphalt was much longer than 70 minutes.This showed that microcapsule incorporation can shorten the self-healing time of aged asphalt,and with the aging of asphalt,the self-healing time would increase.III Mechanism of action of r rejuvenator microcapsule modified asphalt（9）A certain molar ratio of urea,formaldehyde in the appropriate temperature and weak alkaline environment will generate water-soluble prepolymer,emulsified asphalt rejuvenator is evenly dispersed in water,forming a stable emulsion.After the prepolymer is added to the emulsion,the water soluble prepolymer is adsorbed on the asphalt rejuvenator under acidic conditions and gradually deposited.After the resorcinol is added,the prepolymer is solidified and finally the microcapsules with certain mechanical strength are formed.（10）From the molecular point of view,the rejuvenator is basically formed by small molecules with faster diffusion rate to both sides of the microcrack,while the small and medium molecules of the aged asphalt gradually form large molecules and the diffusion rate decreases dramatically.Rejuvenator molecules diffuse into the asphalt molecules,accelerating the diffusion rate of asphalt molecules and making the asphalt molecules on both sides close to each other as well as winding,lastly shortening the self-healing time of microcrack.