Preparation And Microcrack Detection Of Fluorescently-labeled Self-Healing Microcapsule For Cementitious Materials

Cracks in cementitious materials have became a prominent problem in the field of engineering and a major problem in material research.And self-healing microcapsules can automatically repair the microcracks in materials by imitating the characteristics of the organism’s self-healing,combined with fluorescent probe which has the characteristics of high sensitivity,intuitive display,simple and efficient in detecting surface cracks of materials.Thus,it provides a sudden inspiration and a new perspective for solving the scientific problems of crack detection,monitoring and automatic repair of cement-based materials.In this paper,the fluorescent probe technology was introduced into self-healing microcapsules,which made the microcapsules core material repairing agent have fluorescence effect.By observing the distribution of fluorescence to achieve the purpose of microcrack detection,the crack detection method of cementitious materials was further enriched.In this paper,self-healing microcapsules(core material is epoxy resin E-51 and wall material is urea-formaldehyde resin)were prepared by two-step in-situ polymerization.The effects of the amount of modified ammonium chloride on the microstructure,particle size distribution,yield and core material content of self-healing microcapsules were studied,and the chemical structure and thermal stability of self-healing microcapsules were characterized.Then based on the optimal preparation process of self-healing microcapsules,fluorescently-labeled self-healing microcapsules were prepared by ultrasonic dispersion-in-situ polymerization with sodium fluorescein or rhodamine 6G labeled epoxy resin e-51 as the core material and urea-formaldehyde resin as the wall material.And the effects of fluorescent dyes on the microstructure of fluorescently-labeled self-healing microcapsules were studied.Meanwhile,the optical properties,chemical structure,thermal stability and curing reactivity of fluorescence labeled self-repairing microcapsules were studied.Lastly,The fluorescently-labeled self-healing microcapsules coating was applied on the surface of cement paste,and the fluorescently-labeled self-healing microcapsule was added into the cement paste to detect the surface and internal microcracks of the cement paste.The major work and harvest is as follows:1.With the increase of the ratio of the amount of ammonium chloride /urea-formaldehyde resin prepolymer from 6.90% to 16.20%,the yield of the mixture and the content of core material both increased first and then decreased,and the particle size of the microcapsules increased.When the ratio was 11.50%,the yield of the mixture and the content of microcapsules core material both reached the highest value,which were 79.05% and 68.40% respectively.And the particle size of self-healing microcapsules was mainly distributed in the range of 75-300 μm.At this time,self-healing microcapsules had good thermal stability and could be stored in the room temperature for a long time.2.The fluorescently-labeled self-healing microcapsules can be prepared by in-situ polymerization by using sodium fluorescein or rhodamine 6G to label epoxy resin E-51 as core material,urea-formaldehyde resin as wall material.The microcapsules have good surface morphology in the range of particle size 150-300 μm,and their fluorescence properties can be well maintained.3.The self-healing microcapsules labeled with sodium fluorescein and rhodamine 6G were used as fluorescent dyes respectively,the dosage of sodium fluorescein with E-51 epoxy resin is increased from 0.5% to 2.0%,the surface of the microcapsules are relatively rough and roughness has no obvious change,but the quantity and quality of the microcapsules decreased significantly,and the wall materials of urea-formaldehyde resin that were not fully utilized increased significantly.4.Sodium fluorescein on chemical structure and thermal stability of self-healing microcapsule,compared with self-healing microcapsules,fluorescently-labeled self-healing microcapsules under 250℃ also has good thermal stability,and has good activity of curing reaction.5.The fluorescently-labeled self-healing microcapsules core material has good fluorescence and fluidity properties.After 12 hours of placement,the core material of self-healing microcapsules after pre-pressing rupture basically loses.The width of fluorescence microcracks of double-sided adhesive microcapsule increases from 9 μm to 22 μm,which is basically consistent with the measured value.6.The fluorescently-labeled self-healing microcapsules can be made into self-repairing coatings and coated on the surface of cement paste.When microcracks occur on the surface of cement paste,the self-repairing coatings can not only detect the specific location of microcracks and repair them,but also calculate the width of microcracks by fluorescence intensity curve,which is about 40 μm,basically consistent with the actual width of microcracks.