Study On Mechanical Properties Of Concrete Under Coupling Of Load And Simulated Acid Rain Corrosion

Striped distribution,open-air service,long-term load bearing,etc.,are the salient features of railway engineering structures.In the context of open-air service in harsh environments,concrete structures in high-speed railways require superior durability properties,including resistance to corrosion,carbonation,and freeze-thaw cycles.As a result of prolonged loading and exposure to severe environmental conditions,the load-bearing capacity of these concrete structures progressively diminishes over time.When the concrete is out of service prematurely,it may even cause traffic accidents and cause adverse effects.China’s economy has undergone rapid development since the implementation of reform and opening up policies.However,the consequent increase in industrialization has resulted in increasingly severe pollution levels.The pernicious presence of acid rain pollution,being a primary component of atmospheric contamination,results in incessant corrosion of concrete structures exposed to the elements.Concrete,as a multiphase composite alkaline material,has certain fine cracks and holes inside the concrete at the early stage of cement hydration,and new cracks will gradually develop and expand during the service period of concrete under fatigue load,making concrete more susceptible to acid rain erosion.As a result of the combined effects of acid rain erosion and loading,the production of expansion products persists within the concrete.When the expansion stress of these products surpasses the ultimate tensile stress of the concrete,the internal structure undergoes continuous expansion until ultimately fracturing.As the damage continues,the process of acid rain erosion→ concrete cracking→ acid rain erosion is repeated and the deterioration rate is accelerating,and the concrete will lose its service ability prematurely and cause safety hazards.In this paper,the performance test of concrete under the coupling of load and simulated acid rain corrosion is carried out to study the influence of load stress ratio,corrosion time and coupling period on the mechanical properties of concrete.Through the combination of test and numerical simulation,the degradation law of concrete mechanical properties was analyzed,and the durability damage model and constitutive model of concrete under load and simulated acid rain corrosion were established,and the model was verified by combining the test data and the performance of concrete was predicted.The work content and achievements are as follows:(1)Based on the research of the research group,high-strength concrete is configured and the concrete damage is given by the cyclic loading method.In this manner,the load in the service process is borne by the concrete,and the extent of strength deterioration of the concrete defines the magnitude of damage.Based on the precipitation data in Jiangxi Province,ascertain the proportion between the simulated acid rain corrosion solution and the acid-base level.Establish a dry-wet cycle spraying location and configure a spraying regimen,while periodically fine-tuning the p H value of the solution and replacing it as necessary.(2)A comprehensive investigation was conducted on the deterioration and degradation mechanism of concrete exposed to simulated acid rain corrosion.Test data were used to systematically analyze the impact of corrosion age on various parameters,including the visual appearance of concrete,failure morphology,quality,compressive strength,elastic modulus,and stress-strain behavior.The law of deterioration of concrete performance by corrosion cycle is obtained.The results show that simulated acid rain corroded concrete will have two processes of strength increase and decrease.During the initial stages of corrosion,the presence of erosive byproducts leads to a filling and compacting effect which enhances the quality,compressive strength,and elastic modulus of concrete.However,as the corrosion progresses and excessive expansion byproducts accumulate,the concrete experiences continued cracking and a significant acceleration in the rate of deterioration.As a result,the quality,compressive strength,and elastic modulus of the concrete continue to deteriorate and the rate of decline intensifies.(3)The investigation of the deterioration mechanism of concrete subjected to the combined effects of loading and simulated acid rain was conducted,and a comprehensive analysis was carried out to determine the impact of the load-stress ratio and the coupling cycle on the concrete’s performance.By subjecting concrete to the synergistic effect of loading and simulated acid rain corrosion,the law governing the deterioration of its performance was deduced.Consequently,a model to assess the damage to the durability of concrete was established,which relied on the compressive strength as a fundamental indicator.The results show that the 10% and 25% low stress level loads have a certain slowing effect on the corrosion process of concrete,and the 25% stress level has the best effect on resisting simulated acid rain corrosion.40%,55%,70% high stress level loading will accelerate the concrete corrosion process,the higher the stress level,the faster the concrete corrosion process.The gathered empirical data underwent analysis in order to formulate a damage model that accounts for the lasting effects of load and simulated acid rain corrosion on concrete.Through the analysis of the concrete durability damage model,it is found that the enhancement effect of the low stress level load on the filling and dense cracks of concrete is greater than the degradation effect of simulated acid rain corrosion.The damage rate of concrete is small in the early stage of corrosion,and the damage rate continues to increase as the coupling cycle advances.When subjected to the combined impact of elevated stress levels and simulated acid rain corrosion,concrete experiences a higher rate of deterioration in its initial corrosion stage,followed by an accelerated growth rate in subsequent testing cycles.(4)The Abaqus software has successfully replicated the three cyclic loading cycles in the testing regimen,thereby yielding the stress-strain profile of concrete under uniaxial compression after said loading cycle.Remarkably,the numerical simulation findings are in congruence with the experimental results.On the basis of the three cyclic loading cycles and the three corrosion cycles,the fourth loading cycle is simulated,and the uniaxial compression test is carried out to obtain the stress-strain curve and other results.Using the segmental formula of concrete stress-strain full curve proposed by Guo Zhenhai,the experimental and simulated data pertaining to the stress-strain behavior of concrete subjected to load and simulated acid rain corrosion were subjected to regression analysis,thereby yielding fitting outcomes for the stress-strain response of high-performance concrete at varying levels of damage.The results show that under the joint action of load and simulated acid rain corrosion,the concrete exhibits brittleness strengthening in the early stage of the test,and the concrete shows brittleness weakening in the later stage of the experiment due to stiffness degradation.Based on the peak stress,peak strain,and constitutive model of concrete,it is of certain reference value to predict the strength,stress-strain curve and other data of concrete in the subsequent test process.