Research On Fiber Optic Monitoring Technique For Steel Corrosion And Freeze-Thaw Damage Of Concrete

The durability of concrete structures seriously affects the reliability and expected service life of existing structures,and steel corrosion and concrete freeze-thaw(F-T)damage are two of the most important issues in the durability of concrete.Under the constant action of these two effects,the structure will have major security risks,often causing major casualties,huge economic losses and adverse social impacts.Therefore,it is very urgent to effectively monitor the steel corrosion and concrete F-T damage suffered by the structures and evaluate the health status of the structures through data analysis.The existing monitoring method of steel corrosion damage can realize the monitoring of steel corrosion,which lays a good foundation for the steel corrosion monitoring field,but it cannot monitor the whole process of steel corrosion,and can only achieve qualitative analysis.In addition,there are few studies on the monitoring of concrete F-T damage,and they are all in the research stage of the laboratory.Therefore,at present,there is a lack of research on long-term monitoring of steel corrosion and concrete F-T damage in actual engineering environment.Based on this research background,based on white light interference(WLI)sensing technology and optical fiber coil monitoring methods,the long-term monitoring technology and evaluation of steel corrosion damage and concrete F-T damage were investigated,and for the actual engineering structure,the integration and application of fiber monitoring system for steel corrosion and concrete F-T damage were researched.The main contents of the full text are as follows:(1)Based on the WLI sensing technology and the fiber coil monitoring method,the steel corrosion sensor for monitoring the steel corrosion expansion strain(SCES)was designed and optimized.Through the accelerated corrosion test,the corrosion expansion strain of the steel bar and the surface strain of the concrete cover were monitored in real time.Under the same room temperature environment,the influence of the thickness of the concrete cover and the water-cement ratio on the strain of the fiber in the sensor was analyzed and compensation scheme was proposed.Then the influence of the thickness of the concrete cover and the concrete strength on the steel corrosion expansion strain was analyzed.By analyzing the development law between the SCES and the surface strain of the concrete cover,the corrosion expansion cracking strain of the concrete cover during the surface of cover cracking was determined.By analyzing the development law between crack width and SCES,the relationship between crack width and steel corrosion expansion strain was obtained,and the monitoring of crack propagation after cracking of concrete cover based on SCES was realized.(2)With the help of the finite element model,the effects of steel bar diameter,c/d and the effect of stirrups on the SCES when the interface concrete crack and corrosion expansion cracking strain when the cover surface crack were studied.Based on the deep division of the t1st stage,which refers to the stage before the surface of the concrete cover is cracked caused by corrosion expansion,combined with the steel corrosion expansion strain and finite element simulation results,the steel corrosion damage factor D,the evaluation index of the steel corrosion damage at the t1st stage,was proposed.The damage assessment of the stage before protective layer crack penetrates was achieved.(3)Based on the WLI sensing technology,two kinds of F-T sensors for monitoring the frost heave strain(FHS)of concrete were designed by using the fiber coil monitoring method.The stability of the two F-T sensors was discussed by comparing the monitoring results of the two F-T sensors.The F-T sensors used in subsequent studies were determined.Based on the analysis of the influence of temperature on fiber strain,a reasonable temperature compensation scheme was proposed.Then through the rapid freezing and thawing test of concrete,the variation law of FHS of different water-cement ratio in F-T cycles was studied.The mechanism of concrete F-T damage was discussed from the perspective of FHS.By comparing the frost heaving residual strain(FHRS)with the traditional evaluation index(mass loss rate and relative dynamic elastic modulus),the critical frost heave residual strain was proposed to characterize the accelerated deterioration of the concrete under the action of freezing and thawing cycles.(4)Based on the research results of(1),the steel corrosion monitoring system was proposed and designed for the service environment of Dalian Xinghai Bay Bridge.The concrete mix proportion of the corroded test piece and the thickness of the protective layer were determined according to the actual situation on site,and fiber monitoring system for the steel corrosion,which can collect data for a long-term and automatically is integrated,and the existing data is analyzed.Based on the research results of(3),according to the owner's requirements and the actual environment of the site,optical fiber monitoring system for the concrete freeze-thaw damage was designed and integrated at the water intake of the Hongyan River Nuclear Power Plant,and the temperature compensation scheme was improved according to the actual situation on site.The data that was monitored for a whole winter was analyzed.The integration and application of monitoring systems provide valuable data for studying steel corrosion damage and concrete freeze-thaw damage in real engineering environments.