盐碱区桥梁墩柱混凝土表层离子扩散规律研究OA北大核心

To study the diffusion law of ions in bridge pier concrete in saline area,laboratory accelerated corrosion tests of pier concrete under the combined action of axial compressive stress,freeze-thaw cycles,and salt attacks were conducted based on field investigations of the composition of saline soil and concrete corrosion of piers in a certain project.The contents of layered Cl-and S2-4 in the surface of concrete were measured.The diffusion coefficient of ions was calculated to analyze the macroscopic diffusion laws of ions in concrete under multifactorial impacts.Employing X-ray Diffraction(XRD)product analysis and Scanning Electron Microscopy(SEM)techniques,the microstructural performance evolution of concrete under multifactorial coupling was further discussed.The accuracy of the macroscopic ion diffusion patterns was validated.The results show that the diffusion coefficients of Cl-and S2-4 decrease in power function with the process of coupling corrosion.The existence of load does not change the time-varying diffusion law of Cl-sand S2-4.However,there exists distinct thresholds of load influence,quantified as 0.3fck and 0.5fck,respectively.The effect of S2-4 on the diffusion of Cl-under freeze-thaw cycle is dual,which promotes in the early stage and restrains in the later stage.The existence of load will make the characteristic of'S2-4 promoting the diffusion of Cl-'show earlier.The existence of Cl-can restrain the diffusion of S2-4 under freeze-thaw cycles.The main corrosion product of sulfate is ettringite,which accumulates in the pores of concrete.The chloride salt reacts with the hydration product of cement to form Friedel's salt,which adheres to the pores of concrete in needle shape.Furthermore,ettringite and Friedel's salt may transform into each other in the mixed environment of chlorine and sulfur.Ettringite is more stable than Friedel's salt based on the solubility product theory.The research results can provide important references for further studying the corrosion mechanism,protection technology,and improving the service life of bridge in saline area.