Experimental Study On Strength And Chloride Diffusion Of Fiber-reinforced Concrete Under Compound Chloride Environment

Marine engineering has high requirements for the durability of concrete.Seawater and sea sand are rich in various inorganic salts,which can accelerate the corrosion of steel bars when used in reinforced concrete structures.Systematic study on antichloride behavior of fiber-reinforced concrete(FRC)is expected to provide research basis for improving the durability of concrete structures,which is of great significance to reduce the economic loss caused by the insufficient durability of concrete structures.Due to the complicated deterioration mechanism of various inorganic salts on concrete,it is difficult to accurately reveal the deterioration mechanism of a certain type of salt ion on concrete by accelerated aging tests using seawater or simulated seawater containing multiple salts.To reveal the deterioration mechanism of chloride salts on concrete and explore the influence of chloride salts on the strength of FRC,a rapid aging test of seawater sea-sand concrete in a compound chloride environment simulating the marine environment was carried out in this paper.The seawater sea-sand concrete was simulated by concrete mixed with saltwater(Na Cl solution),and the chloride ion erosion environment of concrete at the dry-wet alternating region and underwater in marine engineering were respectively simulated by chloride salt(7%Na Cl solution)dry-wet cycle effect and immersion effect.The effects of erosion age,fiber type and content on the strength and chloride ion diffusion coefficient of FRC with different strength grades are studied.The main conclusions are as follows:(1)The strength of steel fiber-reinforced concrete(SFRC)at an erosion age of120 days was slightly lower than that at 60 days but was still greater than that at the initial uneroded age.The changing pattern of imitation steel fiber-reinforced concrete(ISFRC)was similar to that of SFRC.Both steel fiber and imitation steel fiber could improve the splitting tensile strength of concrete,but the increment of the former was larger than that of the latter.(2)During the entire erosion age,the compressive strength of concrete increased first and then decreased with the increase in the steel fiber content,but increased continuously with the increase in the imitation steel fiber content.With the increase in the fiber content,the splitting tensile strength of both SFRC and ISFRC increased accordingly.The influence of different erosion conditions(long-term soaking and drywet cycle)on SFRC reduced continuously with the increase in steel fiber content.The strength of ISFRC was less affected by the erosion conditions.(3)During the entire erosion age,the early strength of SFRC mixed with saltwater was higher than that of SFRC mixed with fresh water.With the increase in erosion age,SFRC using different mixing water had little difference in the compressive strength.The compressive strength of concrete immersed in chloride salt was higher than that of concrete subjected to chloride salt dry-wet cycles.The compressive strength of concrete mixed with chloride salt was higher than that of concrete mixed with freshwater when subjected to erosion environment.The splitting tensile strength at an early age was similar to the compressive strength of the concrete mixed with different types of water.After 60-day chloride salt erosion,the splitting tensile strength of SFRC mixed with chloride salt began to decrease,while the splitting tensile strength of the control group using freshwater had little change.(4)During the entire erosion age,the compressive strength and splitting tensile strength of SFRC increased linearly with the strength of the concrete matrix.The strength grade of concrete had a significant influence on the chloride diffusion coefficient.Concrete with a higher strength level had better chloride resistance.(5)The chloride diffusion coefficient of SFRC under different erosion conditions WAS lower than that of plain concrete,indicating that the incorporation of steel fiber restrained the penetration of chloride ions in concrete.(6)During the entire erosion age,the chloride diffusion coefficients of the two concrete groups mixed with saltwater were lower than that of concrete mixed with fresh water.