Corrosion Characteristics Of Prestressed Concrete Strands Under Simulated Acid Rain Environment

After the 1980s,due to the their better durability,prestressed concrete structures have been widely used in China's industrial and civil buildings,bridge engineering,underwater construction,large-sized containers,etc.For example,the Hong Kong-Macao Bridge,Qinghai Sea-crossing Bridge,Seoul Bridge,Golden Gate Bridge,etc,which were built in recent years.With the development of China's industrialization process,the growth rate of fossil fuels and other fuels have grown rapidly,and the NO_X emissions of sulfur dioxide and industrial and automobile exhausts have gradually increased.These gases are washed by clouds and clouds under the clouds to form atmospheric precipitation with a pH value of<5.6,which was called"Acid rain".China's acid rain is mainly concentrated in the south of the Yangtze River,Central China,Southwest China,South China and East China,while the Central China region,which is dominated by Nanchang,Changsha,is a major acid rain pollution area in China.In the study of the durability of prestressed concrete,there are commonly used simulated liquid method,internal salt mixing method,immersion method,electric current acceleration method,spray method,artificial climate simulated corrosion,etc.Among them,the electric current accelerated corrosion method is the most applied.Although the corrosion of electric corrosion has a certain reference for the study of the corrosion performance of steel bars,with the deepening of the research,it is found that the method of accelerating corrosion of electricity is very different from the actual engineering in terms of mechanical properties of corrosion products,morphology and mechanism,while the corrosion components obtained by artificial climate simulation corrosion have certain similarities with the actual situation.Therefore,it is of great significance and important research value to study the corrosion mechanism and phenomenon of prestressed tendons after artificial accelerated corrosion and the durability of prestressed concrete members after corrosion.In order to study the corrosion characteristics of prestressed concrete steel strands under simulated acid rain environment,this paper relies on the research on seismic performance of corroded prestressed concrete structures under the acid rain environment of National Natural Science Foundation of China,project number(2014CB51468017),according to the acid rain frequency of our province for nearly ten years and the PH value,9 girders and 16 middle beam specimens were fabricated by accelerated corrosion in the inner salt.After fractured,the mathematical analysis and static tensile test were used to simulate the corrosion characteristics of prestressed concrete strands in acid rain environment,and finally draw conclusions.The main research work of this paper is as follows:(1)The loaded prestressed concrete beam specimens were subjected to shape-cutting treatment,and 6 steel strands were taken out to calculate the three-dimensional dimensions of the pit length,width and depth.According to the observation of a large number of pits,the geometry of the prestressed tendons was analyzed.The distribution law of the pits and the statistical analysis of the three-dimensional dimensions show that the length of the steel strands under the same corrosion rate obeys the lognormal distribution,the pit erosion width obeys the normal distribution,and the pit erosion depth obeys the normal distribution,but better obey the lognormal distribution.(2)The obtained 126 steel wires were subjected to the statistics of the pit corrosion shape of the most severely corroded parts,and the reasons for such a regular pit shape were observed from the macroscopic and microscopic directions,and combined with mathematical statistics,the steel strand specimens obtained under simulated acid rain environment were statistically analyzed in terms of maximum crater length,maximum width,maximum depth and width-depth ratio.The geometry of the prestressed tendons and the distribution of the pits are analyzed to establish the probability of corrosion of the steel etch pit geometry.Distribution function,and the variation law of corrosion rate and pit geometry parameters.(3)The 16 tensile steel strands obtained from the fracture of the prestressed concrete beam specimens after corrosion in simulated acid rain environment are subjected to static tensile test to analyze the degradation law of mechanical properties parameters of elastic modulus,yield strength and ultimate strength of the corroded steel strands,and analyze the causes of various types of fractures from macroscopic and microscopic perspectives combined with SEM scanning test,and construct the stress-strain constitutive model of corrosion prestressed tendons.The constitutive relation of the tendons and the stress-strain curves actually obtained by the test are used to verify the validity of the model.