Monitoring The Corrosion Of The Inner Wall Of The Grouting Sleeve Through Piezoelectric Ceramics And The Research On The Connection Performance Of The Grouting Sleeve

Grouting sleeve joint is an important connection method for fabricated concrete structures,and its performance directly affects the safety of the structure.During the long-term service of the prefabricated structure,the grouting sleeve is at the junction of the prefabricated structure.The outer protection of the grouting sleeve is relatively weak.In the process of long-term service,the grouting sleeve is the first to be corroded.However,the connection of the stressed steel bars of the fabricated structure is mainly connected by the grouting sleeve,so the problem of the connection performance after corrosion is studied necessary.From the experimental point of view,this paper firstly identifies the corrosion degree of the inner wall of the grouting sleeve through piezoelectric ceramics,then studies the influence of the inner wall corrosion on the connection performance of the grouting sleeve,and finally studies the influence of the corrosion of steel bars on the bonding performance of the grouting sleeve joint.The main work and research results are as follows:(1)In order to identify the different corrosion degrees of the inner wall of the grouting sleeve due to chloride ion erosion,the time required for the grouting sleeve to reach different rust rates is derived by formulating.Electrochemical methods are used to accelerate corrosion of the inner wall of the sleeve.Piezoelectric ceramic sheets are pasted on the inner wall of the grouting sleeve and the outer wall of the steel bar before corrosion.The corrosion monitoring system is used to monitor 5 groups of test pieces with different corrosion rates to obtain different frequencies of each test piece.Time domain signal under.The time domain signal is analyzed by signal peak-to-peak value and wavelet packet energy value respectively.The results show that the signal peak-topeak value and wavelet packet energy value are more sensitive to the measured signal.Based on these two methods,two different corrosion identification indicators are proposed.These two corrosion indicators can better identify the corrosion state of the inner wall of the sleeve and provide a reference for the corrosion monitoring method.(2)In order to study the effect of corrosion on the inner wall of the grouting sleeve in the fabricated concrete structure on its mechanical properties after long-term service,10 grouting sleeve connection specimens were made.The theoretical corrosion rate is0%,3%,6%,9%,12%.Accelerated corrosion of the inner wall of the grouting sleeve was carried out by electrochemical methods,and a pull test of the corroded components was carried out.The results are as follows: when the corrosion rate is 0% and 3%,the failure form of the grouting sleeve connection test piece is shown as steel fracture failure,the relative slip between the grouting material and the inner wall of the sleeve is very small,The connection performance is determined by the tensile performance of the steel bar.When the theoretical corrosion rate reaches 6% and above,the failure form of the grouting sleeve connection test piece is shown as the grout pullout,and the limit pullout force and the limit slip amount decrease with the increase of the corrosion rate.Compared with the non-corroded sleeve,when the measured corrosion rate reaches12.74%,the rust causes a loss of nearly 50% of the ultimate drawing force of the grouting sleeve connected to the specimen.In view of the situation that the grout is pulled out after the sleeve is corroded,a fracture bond slip model for the corrosion of the inner wall of the grout sleeve is proposed.The theoretical model is mainly divided into four sections,namely,the micro-slip section,the fracture section,the strengthened slip section and Flat segment.It provides a theoretical reference for the numerically refined modeling of the grouting sleeve connecting specimens with corrosion on the inner wall.(3)In order to study the bond-slip constitutive relationship between the corroded steel bar and the grouting material,considering the influence of steel bars of different diameters,strain gauges were attached to the steel bar in the slot,and 20 grouting sleeve connecting members were poured.Electrochemical methods are used to make the corrosion rates of steel bars reach 0%,3%,6%,9%,and 12% respectively.Pull-out tests were carried out on 20 components,and the load-slip curves of each component under different corrosion degrees and the strains of steel bars at different anchor positions were obtained.Through experimental results and theoretical analysis,the bond stress and relative slippage at different anchor positions of each component are obtained,the bond anchor position function before and after corrosion is determined,and the bond degradation mechanism is analyzed.Finally,a constitutive model of the bond-slip between the corroded steel bar and the grouting material is established considering the position function,which provides a basis for the finite element analysis of the corroded grout and steel bar.