Study On Preparation And Strength Repair Of Self-healing Microcapsule For Cement-based Materials

Concrete is the most widely used building material in the world.Concrete will produce cracks and local damage that affected by its own factors and surrounding environment in the service process.The macroscopic crack of concrete is actually the expansion of micro-cracks.If such micro-cracks can be detected and fixed early,this will reduce and even avoid the occurrence of macroscopic fractures.In this paper,the microencapsulation technology is introduced to realize the automatic repair of micro-cracks in cement-based materials,so as to provide a new method for solving the problem that macroscopic crack healing in cement-based materials.In this paper,used epoxy resin E-51 as the core materials and urea-formaldehyde resin as the shell materials,microcapsule was synthesized by in-situ polymerization reaction.The influence of resorcinol dosage,emulsifier dosage and core material diluent dosage on the preparation of microcapsules were studied.The micromorphology,surface properties,size distribution,capsule indicators,chemical structure,thermal stability and curing activity of core material of microcapsules were characterized.Verify the compatibility of microcapsules with cement-based materials.The distributed situation and fracture behavior of microcapsules in cement paste were observed by ESEM.Subsequently,the self-healing microcapsules were applied to cement base materials.And recovery effect was verified by the restoration of compressive strength on cement-based materials.The way of microcapsules mixed with cement mortar specimens was optimized,the means of pre-loading of cement mortar specimens was perfected and the method of calculation formula of short age strength healing ratio of cement mortar specimens were improved.The influence of microcapsules dosage,microcapsules particle size,core material diluent dosage,core material curing agent dosage and the pre-damage degree on the healing ratio of cement-based materials were studied.At the same time,the effect of self-healing microcapsule on the strength of cement mortar specimens was studied under better repair conditions.The following conclusions are obtained from the above research:1 When the ratio of benzene resorcinol/urea was 12%and the ratio of emulsifier/core material was 5%,the preparation quality of microcapsules was better.Under the good preparation condition,microcapsules have good micromorphology,surface is rough that good for bonding with cement-based materials,uniform size and narrow particle size distribution.Also,the yield and core content are high which can reach 78.49%and 72.40%,respectively.2 The core material,core material diluent and shell material of microcapsule will not react with each other and can form a stable nuclear shell structure.Microcapsules can be stable at room temperature for a long period of time and more than 200℃ will be a large number of decomposition.The thermal stability of microcapsules is between core and shell materials.The microcapsule core material had good curing activity and possessed the ability to play the healing role in cement-based materials.Temperature and time have less impact on the curing reaction.3 Microcapsules could be kept good shape in cement paste and combined with the cement paste closely.Microcapsules also could rupture and had better dispersion in cement paste.And the mainly fracture behavior of microcapsules was based on small hole ruptured when cement paste specimen did not occur macro damage.4 Microcapsule is a kind of defect to cement-based materials,which can reduce the compressive strength.The determination of the healing rate of the short age needs to exclude the effect of initial strength and cement hydration.The minimum impact on cement mortar specimen’s strength was used microcapsules to replace the quality of sand.5 The minimum impact on cement mortar specimen’s strength was used microcapsules to replace the quality of sand.In the appropriate range,the particle size of microcapsule was smaller and particle size range of microcapsule was narrower the better for improvement of the short age healing ratio.When the pre-loading was 0.75σmax,the proportion of epoxy curing agent was 20%,the proportion of microcapsule was 6%and particle size range of microcapsule was 75-150μm,the short age strength healing ratio reached the highest was 24.1%.The addition of microcapsules could not only play the healing role but also increase the strength of cement mortar specimens.