Study On The Resistance Of UHTCC To Chloride Ion Attack Under Load And Dry-wet Cycle

The Ultra High Tough-ness Cementitious Composites(UHTCC)is a new type of fiber reinforced cement based material.UHTCC has broad application prospects in engineering with its excellent tensile properties and crack controllability,and its mechanical properties and durability can be further studied before it is put into use.Therefore,based on the study of the basic mechanical properties of UHTCC,this paper makes a related experimental study on its resistance to chloride ion erosion.In this paper,the internal chloride ion corrosion of UHTCC under the coupling of dry-wet cycle and chloride salt is analyzed.The resistance of chloride-ion corrosion of UHTCC under the action of load-chlorine salt coupling is studied.The microscopic products and pore structure changes of UHTCC before and after corrosion by chloride were also described.The conclusions obtained are as follows:(1)PVA fiber greatly improves the tensile and flexural properties of UHTCC,and the greater the volume of PVA fiber,the greater the strength and ductility of UHTCC.In general,as the water-to-binder ratio increases,the strength of UHTCC decreases and the ductility increases.When the mass ratio of fly ash to cement is 1.2,the strength of UHTCC reaches the maximum.(2)The depth of chloride ion erosion of UHTCC gradually increases with the increase of water-to-binder ratio,and the growth rate is also increasing.The greater the concentration of the chloride salt solution,the greater the depth of chloride ion erosion of the test piece.The chloride ion erosion depth of the specimen under the coupling of dry-wet cycle-chlorine salt is obviously larger than that under the full immersion test condition.The larger the water-to-binder ratio,the larger the free chloride ion content of the test piece.The effect of the water-to-gel ratio on the free chloride ion content is more obvious with the increase of the chloride salt concentration.The wet and dry cycle promotes the transport of chloride ions,which has higher chloride ion content than the full immersion test.(3)The chloride ion erosion depth of the specimen under load increased with the increase of the load rate.The self-healing phenomenon occurs after the preloaded test piece is unloaded,and the chloride ion erosion depth is reduced to some extent compared with the continuously loaded test piece.The free chloride ion content of the specimen increased with the increase of the load rate,and the free chloride ion content of the specimen under continuous loading was significantly larger than that of the preloaded specimen.At the same time,the free chloride ion at the crack is higher than the crack-free content,and gradually increases with the depth extension.(4)After the corrosion of the chloride salt,the main product Friedel salt was formed,resulting in a decrease in the porosity of the material.As the concentration of chloride increases,the porosity of the material decreases in turn.Dry and wet circulation promotes the production of CaC03,making the material more compact.The chloride ion content in the crack of the loaded test piece is higher,and the porosity is much lower than that before corrosion.