Experimental Study Of Microcapsule Based Self-healing Concrete On Impacting Mechanical Properties And The Self-healing Performance

For concrete structure,the formation and propagation of cracks in concrete is a common occurrence.When harmful substances spread to a concrete structure that serves with cracks,it will increase the risk of structural damage and degradation,posing a threat to safety and durability.Self-healing concrete is a type of functional material in civil engineering developed in recent years.Self-healing systems have the built-in capability to repair cracks without major intervention on the structure,and can repair the structure damages autogenously.Compared with the traditional method,the technology based on self-healing concrete can provide solutions of improving the durability of the engineering structure and prolong the service life.Self-healing systems meet the requirements of the“functional-intelligent”integration proposed by the building materials and structures,and thus the development of using self-healing concrete in engineering structure is very promising.As an important part of the self-healing research,the healing effect of microcapsule based self-healing concrete on mechanical properties has been confirmed by the experimental research under quasi-static loading.However,the behavior and healing effect of microcapsule based self-healing concrete under dynamic loading is not clear,and there is a lack of investigation on the microscopic mechanism which affects its macroscopic performance.In this study,the dynamic mechanical properties of microcapsule based self-healing concrete under impact loading are investigated firstly.The self-healing mechanism of a microcapsule self-healing system is studied by both the macroscopic and microscopic experimental methods.In addition,based on the practical engineering,this study also explores the feasibility of using the self-healing system to improve the durability of concrete structure in engineering application.Firstly,on the basis of the existing technology,organic microcapsules were synthesized by in-situ polymerization,which using urea-formaldehyde resin as the shell and the epoxy resin mixture as the core material.In order to achieve the healing effect,the concrete sample with self-healing function should be prepared by introducing damage first.Three test conditions of virgin,damaged and healed were designed to compare and analyze the healing effect of the self-healing concrete.Ultrasonic testing was used to acoustically characterize the damage introduced in self-healing concrete,visualizing the damage process.The healing effect of microcapsule based self-healing system was investigated by testing the acoustic parameters under different conditions.The results show that the sound velocity of the healed condition is significantly improved compared to the damage condition,while there is still a certain gap compared to the virgin condition.Secondly,the dynamic mechanical properties of microcapsule based self-healing concrete under impact loading were studied by using a split Hopkinson pressure bar（SHPB）test device.Impacting tests at strain rates ranging from 1s^-1 to 100s^-1 were conducted with different microcapsule addition and different condition,revealing the effect of microcapsule content on the dynamic properties and the strain rate effect.The healing efficiency of microcapsule based self-healing system on the dynamic mechanical properties of self-healing concrete were also studied.The results show that the dynamic compressive strength decreases gradually with the increase of 0%,2%,5%and 8%microcapsules,while the dynamic split tensile strength increases with the increase of microcapsule content.Concerning the“strain rate”effect,the strain rate has a significant effect on the dynamic compressive strength and dynamic split tensile strength of self-healing concrete.The dynamic increase factor（DIF）increases with the increase of strain rate,regardless of the content of microcapsules.By comparing the virgin,damaged and healed condition,it is found that the healing function of microcapsule based self-healing system on dynamic compressive strength and dynamic split tensile strength is not significant.The self-healing ability of dynamic strength is different from that of static strength.The healing effect of microcapsule on dynamic performance of self-healing concrete under dynamic loads deserves further tests to verify.Finally,the healing effect and healing mechanism of microcapsule based self-healing system on the mechanical properties and impermeability of self-healing concrete has been studied by combining the macroscopic test and microscopic mechanism analysis,according to the practical engineering.The results show that the microcapsule based self-healing system has significant healing effect on the strength and impermeability of damaged samples.Although the incorporation of microcapsule has a certain negative effect on the compressive strength and shrinkage properties of self-healing concrete,however,these modifications are still within acceptable standards in the practical engineering.Besides,the performance of self-healing concrete can also be compensated by adding some supplementary cementitious material,as well as the fiber materials.Furthermore,the results of healing effects of microcapsule based self-healing system and the field test show that microcapsule based self-healing concrete is an environmentally friendly self-healing material,which has good applicability in practical engineering and has great application potential especially in the underground engineering and coastal engineering.