Experimental Study On The Durability Of Shotcrete In Drying-wetting Cycles And Saline Lake Brine Erosion

Shotcrete is widely used in underground engineering,slope engineering,foundation pit engineering and reinforcement engineering.With the increasing development of tunnel and underground engineering in recent years,the application of shotcrete lining is also increasing.The saline lake is widely distributed in China,and the sulfate,chlorine salt and magnesium salts are the main factors leading to the deterioration of concrete in saline lake.In the process of saline lake brine erosion of shotcrete,the corrosive ions by shotcrete initial pore and micro cracks into the interior,formed from the outside to the inside,from the light and heavy erosion mode,bring the swelling,peeling and cracking,resulting in failure of shotcrete.However,the concrete in the water level fluctuating zone of saline lake,shotcrete is subjected to the combined action of drying-wetting cycles and the saline lake brine,which will undoubtedly aggravate the deterioration.Therefore,to carry out the research of degradation and deterioration mechanism of shotcrete under the combined action of the drying-wetting cycles and saline lake brine erosion,it is of great significance to evaluate the durability of concrete structures under saline lake environment.This paper use the research methods of combining theoretical analysis and laboratory accelerated test,combining macro,meso and micro analysis,study on the rule of performance degradation and damage deterioration of shotcrete under the combined action of drying-wetting cycles and saline lake brine erosion,aimed at providing a theoretical basis for the evaluation of shotcrete structure durability under the saline lake environment.The main research contents are as follows:?1?To carry out the experimental study macro physical properties on shotcrete of saline lake brine erosion,analysis the influence of the construction technology and the steel fiber of the shotcrete of saline lake brine erosion in mass loss rate,relative dynamic elastic modulus,compressive strength and the relative damage layer thicknes.The changes rule of mass loss rate,relative dynamic elastic modulus,relative compressive strength and damage layer thickness of shotcrete under the combined action of drying-wetting cycles and the erosion of saline lake was studied,and comparative analysis of specimens of salt crystallization and surface crack width,volume change,comprehensive evaluation of multiple aspects of the deterioration process.?2?To carry out the experimental study on ions concentration of pore solution shotcrete of saline lake brine erosion,considering the influence of construction technology and steel fiber on ions concentration distribution and diffusion of pore solution shotcrete,The pH,Cl^-,SO_-4²,Ca²⁺ and Na+ were used as the analysis object in the pore solution of shotcrete,the concentrations of pH,Cl^-,Ca²⁺ and Na+ were measured by electrochemical analysis,and the concentrations of SO_-4² were measured by barium sulfate gravimetric method,under the combined action of drying-wetting cycles and saline lake brine erosion,research the changes rule of the pH,Cl^-,SO_-4²,Ca²⁺ and Na+ concentration with depth in pore solution at the same erosion age,at the same time,the Cl^-diffusion rule of shotcrete was studied,and the change of the Cl^-diffusion coefficient with erosion age was verified.?3?To carry out experimental study on meso pore structure in shotcrete of saline lake brine erosion,the influence of construction technology and steel fiber on the pore structure characteristics of the shotcrete in the erosion environment of saline lake brine was analyzed,use the pore structure analyzer,the change rule of surface air content and pore length frequency with pore chord of shotcrete under the combined action of dryingwetting cycles and saline lake brine erosion were studied,the pore structure parameters of shotcrete were tested,the air content,specific surface,pore spacing factor,void frequency,pore average chord length and paste to air ratio changes with the age of erosion were researched.?4?To carry out experimental study of microstructure on shotcrete of saline lake brine erosion,X-ray diffraction analysis?XRD?,comprehensive thermal analysis?TG-DSC?,Fourier transform infrared spectroscopy?FT-IR?and scanning electron microscopy?SEM-EDS?were used as the technique means of micro measurement,the evolution of the microstructure,the change of the internal mineral composition,the composition of the corrosion products and the change of the micro morphology of the shotcrete under the saline lake brine erosion are analyzed..In this paper,the variation of the phase composition and microstructure of the shotcrete with the age of erosion under the combined action of drying-wetting cycles and saline lake brine erosion is studied.