Study On The Corrosion Process And Strength Degradation Characteristics Of Acidic Wet And Wet Cycle

For a long time,water-rock interaction has been a hot research topic in the field of geotechnical engineering.The formation of geological disasters such as rock and soil collapse and landslides are closely related to the long-term effect of water.In recent years,the rapidly developing industry has brought about problems such as environmental degradation.Acid rain is one of the effects.Natural sunlight and rainfall often alternate,and this cyclic effect will exacerbate the deterioration of rock physical and mechanical properties,leading to frequent geological disasters.In order to study the effect of sunshine and rainfall alternation on rock degradation in depth,a dry-wet cycle test of limestone was designed and conducted,and the physical and chemical indexes of the test piece were tracked by means of nuclear magnetic resonance and ion concentration detection.Through the analysis of the results of the uniaxial compression test and the Brazilian split test after the dry-wet cycle,the relationship between each physical mechanical parameter and the number of dry-wet cycles and the action environment is obtained.The specific research work and results are as follows:1.Wet and dry cycle tests of limestone specimens of two specifications were carried out.Under the environment of sulfuric acid-nitric acid mixture with pH 3 and 5 and distilled water(pH=7),carry out 0(natural drying),1,5 and 10 dry-wet cycle tests on limestone specimens with the specifications of ?×H=48mm × 30mm and 48mm × 100mm.The relationship between the mass loss of limestone,saturation water absorption and porosity and the number of dry and wet cycles n,pH was analyzed by weighing the mass of each dry and wet cycle node sample and conducting a nuclear magnetic resonance test.The results show that the acidic environment can significantly change the quality and water absorption capacity of the specimen.It is reflected that the lower the pH of the acidic environment,the higher the loss rate and water absorption rate in the quality stage,and as the number of dry and wet cycles increases n,both The magnitude of the phase change has been reduced.The NMR T2 spectrum shifted to the right with increasing n,and the T2 spectrum area also increased significantly.The lateral relaxation time and the porosity characterized by the T2 spectrum area are positively correlated with n,and numerically negatively correlated with pH.2.Uniaxial compression test after wet-dry cycle was carried out.The specimens dried after the wet-dry cycle were subjected to uniaxial compression tests in batches to form stress-strain curves,calculate the elastic modulus and uniaxial compressive strength of each specimen,and describe the distortion process of the limestone specimen under load and the final destruction form.The stress-strain curve of most limestone specimens rises in a tooth shape.At the same dry-wet circulation node,the smaller the pH of the solution,the smaller the elastic modulus and uniaxial compressive strength.At the same pH,the greater the number of dry and wet cycles,the greater the decrease in elastic modulus and uniaxial compressive strength.It shows that the acidic environment has obvious influence on the elastic modulus and uniaxial compressive strength.The elastic modulus and uniaxial compressive strength of the specimens have a logarithmic relationship with the number of dry and wet cycles n,and a positive correlation with pH.3.The Brazilian split test after the dry and wet cycles was carried out.The tensile strength of limestone specimens is obtained by collecting test data.For the limestone,which is a brittle rock,its uniaxial tensile strength decreases with the number of wet and dry cycles n,and its decrease gradually decreases.Fitting the curve between the tensile strength and the pH of the working environment shows that there is a positive correlation between the tensile strength and the pH of the working environment,and it also reflects that the greater the n,the lower the tensile strength.4.After the dry and wet cycle of the solution element mass concentration detection test.Dilute the solution after soaking in wet and dry cycle 100 times and then check the element mass concentration.Among the detected elements,Ca element has the highest mass concentration,followed by Fe element and Mg element.The analysis of the relationship between the Ca element mass concentration and the number of dry and wet cycles n and pH shows that the Ca element mass concentration basically increases by multiples with the increase rate of n.It shows that the Ca element precipitation rate is relatively stable when the solution pH is maintained continuously.In addition,the mass concentration of Ca element has a negative correlation with the uniaxial compressive strength and tensile strength of the specimen.5.The degradation effects of physical and mechanical parameters of each test piece were compared.By normalizing and deriving the deterioration function of physical and mechanical parameters with n in each action environment,the degree of deterioration of each physical and mechanical parameter with the number of dry and wet cycles is compared.Under different action environments,the deterioration effect of each parameter is:when pH=3,uniaxial compressive strength>elastic modulus>porosity>uniaxial tensile strength>water absorption;when pH=5,uniaxial compressive strength>Elastic modulus>Uniaxial tensile strength>Porosity>Water absorption;when pH=7,uniaxial compressive strength>Elastic modulus>Water absorption>Porosity>Uniaxial tensile strength.6.The dry-wet cycle is an important condition for the loss of rock mass,the increase of pores,the increase in the mass concentration of each element,and the deterioration of physical and mechanical properties.The acidic environment further accelerate the deterioration of each index.However,the loss of mass during dry-wet cycle,the increase of porosity,the increase of element mass concentration have a corresponding relationship with the physical and mechanical indicators after the corrosion stage of the rock sample:the loss of the mass of the specimen during the immersion chemical reaction process causes the increase of the pores and precipitation With the increase of ions,the skeleton support of the entire surface layer of the rock sample weakens,plus the softening effect caused by the dry-wet cycle,and eventually the physical and mechanical indicators deteriorate.In the change trend of the above indicators,the stronger the acidity,the more obvious each indicator changes with the number of dry and wet cycles.