Chloride Ion Transport Properties In Self-healing Concrete System

The durability of concrete structures is a hot issue in the field of engineering construction.The intrusion of chloride ions and sulfate ions are the two main factors that affect the durability of concrete.Recent years,self-healing concrete has gradually become a research hot-topic in civil engineering due to its properties of intelligent perception,real-time repair and designable function.Physically triggered self-healing concrete recovers the mechanical and impermeability properties through bonding the micro cracks.Besides,concrete structure is subjected to chemical environmental factors,which may affect the durability of concrete structures.In order to improve it,scholars have designed a microcapsule based self-healing system which is triggered by chloride ion.In this system,chloride ions may react with certain components in the microcapsule wall so that the microcapsule wall ruptures,afterwards,the healing agent flows out and recover the durability of concrete.In this study,the effect of lead sulfate and calcium nitrite on chloride transport was studied.The relationship between micro pore structure and chloride coefficient was investigated.The relation between porosity and mechanical properties was tested.A chloride ion transport model in a chloride-activated self-healing concrete system was proposed.The model was verified by experimental data.The time dependency of chloride coefficient and surface chloride content was considered in the model.The parameters in the model were identified.The effects of different boundary conditions and distribution conditions of microcapsule components on the chloride transport characteristics were analyzed.It was shown that when a small amount of lead sulfate was incorporated into cement-based materials,chloride could be bound by lead sulfate,however lager amount of lead sulfate could lead a micro expansion effect on the concrete materials.Therefore,the two opposite effects should be thoroughly taken into account when utilizing lead sulfate as a kind of shell material in microcapsule concrete.With the addition of calcium nitrite,the total porosity of cement-based materials would increase,and their compressive strength and impermeability are reduced.To this end,the application of calcium nitrite in the concrete field needs to consider these two effects.With the increase of the distribution thickness,distribution concentration and distribution width of lead sulfate,the chloride ion content showed a decreasing trend.However,with the deepening of its distribution position,the chloride ion content showed an increasing trend.