Study On The Corrosion And Deterioration Characteristics And Mechanism Of Concrete Of Vertical Shaft Lining In Sulfate Environment

With the exploitation and development of underground resources in our country,as an important route for mine production vertical shaft should meet the requirements in safety.Nevertheless,the serious durability problems are becoming increasingly apparent during the shaft service.Especially for the shaft,which was constructed in the 1980s and 90s and currently in service,C30～C40 concrete was widely adopted.Due to the low strength of concrete the durability of shaft lining has become a very severe problem as serving time going on.The shafts are even deformed and ruptured,threatening seriously on the mine safety and regular production in the worse cases.The concrete of shafts is always in service in a complex environment for decades.The service performance and service life of shafts is defined by the diverse geologic conditions such as ground pressure,dynamic disturbance and so on.At the same time,there is a close relationship between the performance and the long-term effects of environmental factors such as mine groundwater and microorganisms.Therefore,the concrete of shafts usually suffers from the mechanical and chemical damage processes,which will cause deterioration of the service state and performance.Mine groundwater is often rich in soluble salts,especially sulfates is quite common.Sulfates makes the shaft lining easily to suffer from chemical corrosion.Ground water table variation and the movement of mine water will lead to accelerated erosion process of the shafts as well.So it is necessary to study the deterioration characteristics and mechanism of concrete of shafts in sulfate corrosion environment taking into account shafts service conditions,which will help to evaluate the service state and performance of concrete of shafts and forecast the service life,and also help to provide references for repair and reinforcement.In this paper,the conventional C30 concrete of shafts is adopted.Based on the rapid simulated experimental for sulfate corrosion,the physical-mechanical and microcosmic properties testing were done to study the performance deterioration characteristics and mechanism of the concrete of shafts caused by sulfate attack under the mine service conditions considering initial damage,triaxial pressure,loading and unloading disturbance and different composition of cations.Based on the corrosion mechanism a effective way was studied to improve the properties of the concrete of shafts under the sulfate environment by using chemistry to control the sulfate attack process.The main contents and conclusions are as follows.(1)Through the experimental study on the concrete of shafts under the sulfate corrosion environment,the degradation factors were established to quantitatively evaluate the performance change of the concrete of shafts under the sulfate environment based on the parameters including compressive strength,splitting tensile strength,flexural strength and ultrasonic velocity.And the function relationships were obtained between the degradation factors and sulfate corrosion time.Based on the stress-strain relationship and the acoustic emission ringing counts,the load and corrosion damage models of the concrete of shafts were established,thus the sulfate corrosion damage and load damage were unified with the mathematical models.(2)Through the experimental study on the concrete with different degree of initial damage of shafts in the sulfate corrosion environment,the performance changes of the concrete with different degree of initial damage were described and analyzed in detail from the aspects of apparent morphology,mass,ultrasonic velocity,compressive strength,stress-strain curves,and the activities of acoustic emission under sulfate attack.The degradation factors were established to quantitati-vely evaluate and predict the performance change of the concrete of shafts in the sulfate corrosion environment.Based on the stress-strain relationship and the acoustic emission ringing counts,the load and corrosion damage models of the concrete with initial damage were established.Furthermore,the microstructures,minerals and corrosion products of concretes with initial damage was analyzed to reveal the deterioration mechanism.(3)Through the triaxial compression test on the corroded concrete of shafts under different confining pressure,the effect of corrosion time and confining pressure on the failure mode,deformation and strength of the concrete were analyzed and studied.The degradation factors were established to quantitatively evaluate the performance change of the concrete caused by sulfate attack under triaxial compression based on the elastic modulus and cohesion.And the strength failure criterion,damage evolvement model and constitutive relationship of the concrete under triaxial compression were established considering the sulfate corrosion effects,which provided references to evaluate the performance degradation degree of the concrete of shafts under the triaxial compression and sulfate environment.(4)Through the cyclic loading and unloading test on the corroded concrete of shafts under the triaxial compression,the performance degradation of the corroded concrete under the dynamic disturbance were studied.Based on the analysis of the energy dissipations,energy ratio was used to quantitatively evaluate the deterioration of the corroded concrete of shafts under loading-unloading disturbance,which provided references to evaluate the performance degradation degree of the corroded concrete of shafts taking into account disturbance factors.(5)Through the experiment the effect of three common cations including Na+、Mg2+、NH4+ on the performance degradation of materials of shaft lining caused by sulfate attack was studied.The performance changes of the materials of shaft lining in sodium sulfate,magnesium sulfate and ammonium sulfate corrosive environments were described and analyzed in detail from the aspects of apparent morphology,mass,ultrasonic velocity,compressive strength and flexural strength.The degradation factors were established to quantitatively evaluate the performance change of the materials of shaft lining.Furthermore,in sulfate corrosive environment the effect of three common cations including Na+、Mg2+、NH4+ on the microstructures,minerals and corrosion products components of materials of shaft lining were analyzed and researched to reveal the deterioration mechanism of materials of shaft lining by microscopic testing means such as the environmental scanning electron microscopy(ESEM),energy-dispersive X-ray analysis(EDX)and X-ray diffraction(XRD)respectively.(6)Aiming at sulfate corrosive environment,barium hydroxide was added into the concrete to control and affect the corrosion process since Ba2+ can react with SO42-to generate BaSO4.And the macroscopic properties improvement of concrete of shafts attributed to barium hydroxide were described and analyzed in detail from the aspects of apparent morphology,mass,ultrasonic velocity and mechanics characteristics under the condition of uniaxial compression.The effect of barium hydroxide on the microstructures and corrosion products of concrete of shaft lining were analyzed to reveal the effect mechanism of barium hydroxide by means of the environmental scanning electron microscopy(ESEM),energy-dispersive X-ray analysis(EDX),X-ray diffraction(XRD)and thermogravimetry-differential thermal analysis respectively.