| How to intelligently realize automatic percepts location of microcrack and damage in cement matrix and instantly self-heal is one of novel capacities of cement concrete repair, which is very important to improve durability of concrete and service life of concrete structure.Based on concrete material science, organic chemistry, physical chemistry and others relative theory, created microcapsule based technique for cementitious composites in the paper, and analysised relate theory, proposed evalution method of self-healing efficiency.Urea-formaldehyde/epoxy resin microcapsule synthesized for self-healing cementitious composite by in situ polymerization method, which is micro size spherical particle that urea formaldehyde resin as shell encapsulates core of epoxy resin glue solution, Through orthogonal test, and based on microscopic tests and kinetic, analized main effect factors of characterization parameters of UF/E microcapsule, such as particle size, shell thickness, surface morphology and envelopment rate, etc, and concluded optimal synthesis proce ss route and parameters, urea reacts with formaldehyde for1hour at70℃with molar ratio is1.5:1.0for obtaining pre-polymer, mass ratio of core material of epoxy resin glue solution/shell materal of urea-formaldehyde pre-polymer is (1.0～1.2):1.0, suitable temperature of acidification phase is50℃, and pH value of forming the wall material is2-3. The suitable temperature of enhanced stage of solidifying wall material is60℃.A kind of epoxy resin based crack repairing agent is developed that can be cured in cement based material with higher bonding capacitiy, which composited by epoxy resin E-51, Butyl Glycidyl Ether (BGE) and imidazole solidified agent (MC120D). Based on Kissinger equation and Arrhenius euquation, analized curing reaction kinetics of E-51/BGE/MC120D, when BGE is17.5%, MC120D is20%of E-51by mass, the activation energy of curing reaction of healing agent reach to lowst, which is favorable to curing at normal temperature in cement based material. By the differential ghermal analysis and FTIR analysis, explored mechanism of curing reaction, the test results show that when the content of MC120D is from10%to30%, the healing agent system is cured in two steps. However, when the content of MC120D exceeds30%, the curing reaction is completed in only one step. The capillary kinetics and siphon theory is used to analyze the performance requirements for microcapsule ruptured in the matrix, healing agent outflow from microcapsule and into microcrack for healing microcrack, and obtained the optimal composition of epoxy resin healing agent.The self-healing mechanism of cementitious materials with microcapsules is analyzed in this paper. When the cement-based materials cracked, the microcapsules next to the cracks ruptures, then the epoxy resin in the microcapsules react with the curing agent in the wall of cracks. The reacted materials form a kind of material with a strong plastic viscosity, filled in the cracks, which can decrease the porosity and block the continuous cracks, further repairing the strength and impermeability of cement-based materials, make the function of self-healing come true.Designed and prepared a microcapsule technique based self-healing cementitious composites, which constituted by PVA fiber, Portland cement, quratz sand, microcapsule and catalyst, etc. The evaluation method for self-healing of cementitious materials is also built in this paper. The percolation structure, pore structure and adsorption-desorption characteristics of crack controllable cementitious composites with different damage degree are investigated by the methods of electrochemical impedance spectroscopy (EIS), mercury intrusion poremetry (MIP) and nitrogen adsorption method (BET). The experimental results show that when the external load reaches to40-50%σmax, there is obvious cracks/damage in the matrix. The strength and Chloride ion permeability of damaged cementitious materials is considered as the evaluation index of self-healing. The factors influencing the self-healing rate of cementitious materials with microcapsules are also discussed. The sequence of influencing the self-healing rate is microcapsule dosage, followed by microcapsule diameter, damage degree and self-healing age. The condition for obtaining the maximum self-healing rate is that microcapsule dosage and diameter is6.0%and230μm, respectively, the damage degree is60%σmax, and the self-healing age is7days.Based on the above research, a kind of self-healing method is founded, named UF/E microcapsule technology. It is proved that the microcapsule technology makes cement-based material has certain self-healing function. Meanwhile, the main factors influencing self-healing rate of microcapsule is also analyzed. However, in order to achieve the technical engineering application, some problems are still needed further research. |
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