Research On Permeability Of Microcapsule Based Self-healing Cementitious Composites

The cracking of concrete has a serious effect on the safety and durability of the structure, with the function of the intelligent perception and self-healing location for micro-crack and damage in cement matrix materials, micro-capsulation technology has become a new trend in the study of self-healing concrete. Permeability is an important performance evaluation of material self-healing effect, and depends on the microstructure of the material generally. The influence of the amount of microcapsules and their diameter on the permeability of cement composites was discussed, and by recovery rate and repair rate, that the amount of microcapsules and their diameter have the effect on healing function was found. And the nitrogen adsorption test and the mercury intrusion test were also used to detect the distribution of the pore configuration of material. Then, a model was analyzed and established considering the critical pore size, capillary porosity and the amount of microcapsule and their diameter, and capillary porosity and repair rate of critical pore size were characterized by healing action. According to the model of pore structure and permeability, combining with impermeability and the parameter of pore structure tested by MIP, the model of pore structure and permeability and the relationship of impermeability repair rate and pore parameter repair rate before and after restoration was established. That also indirectly indicated that the amount of microcapsules and the size of microcapsules could be used to analyze permeability of cement-based materials qualitatively. The performance prediction model was established the influences of microcapsule on permeability of cement-based materials were analyzed quantitatively. Conclusions are as follows:(1)The results of previous four experiments indicated that the impermeability of cement composites, for the same size sample, improved obviously when the content of microcapsules ranges from 0% to 3%. However, the impermeability of the sample reduced when the content increased. The impermeability of cement composites decreased, for the same content and size of the sample, when the average size of microcapsule ranged from 150.05μm, 205.62μm and 243.16μm respect. For the same dosage of microcapsules specimen, as the particle size increases gradually, its impermeability is reduce. Furthermore, the repair rate of the impermeability of cement composites and its recovery rate are characterized by the healing function of the sample. That the more microcapsules and the larger microcapsule are able to help improve the healing performance were found. For the natural immersion test and carbonization test, the permeation depth of samples increased with time.(2) BET and MIP measured the pore structure parameter with the different content and size of microcapsules, taking the degree of influence on permeability into account. In this paper, the volume of pore, the critical pore size and capillary porosity are selected to analyze. Studying microcapsule content and size changes on self- healing cement-based material parameters of the initial pore, the relationship was determined by the appropriate method of testing the pore structure, initial pore parameters with microcapsule content and particle size increased. Determine the laws between initial parameter of the measuring pore method and micro-capsule dosage and increasing of particle size. The relationship of the recovery rate and amount of microcapsules and particle size was established closely. Improvement in samples pore structure was found after repair through qualitative analysis.(3) According to the previous model of permeability and pore structure, combining with impermeability detected by permeability test and the parameter of pore structure tested by MIP, the paper established a self-healing material initial permeability and pore structure of the relationship model. Therefore, the quantitative influence of amount and size of self-healing cement-based materials on permeability resistance of cement-based materials was known indirectly. And the content of microcapsule, size of microcapsule and time quantitatively were analyzed, and they had an effect on impermeability of cement composites. Then the repair rate of the impermeability of cement composites and the repair rate of pore structure parameters were simulated. The effect of pore structure on macroproperty of ECC was predicted.