Research On The Corrosion Regularity And Durability Of Prestressed Anchor

In recent years,prestressed anchors have been widely used in tunnels,high slopes,deep foundation ditches and dam foundation and other construction.Influenced by the complex geological circumstance,prestressed anchors are prone to corrosion,resulting in properties degradation or even failure,which will affect the safety of projects.This paper is devoted to researching the corrosion regularity and durability of prestressed anchor.Based on the corrosion damage theory of anchor,the corrosion regularity of anchor under different influence factors is studied by indoor accelerated corrosion test.According to the system for health assessment of prestressed anchor,in-situ excavated experiment and detecting test are conducted to evaluate the health statue of the anchors synthetically.Some results beneficial to theory and practice are as follows.(1)By referring to a large number of literatures,the influencing factors causing corrosion of anchors are analyzed and divided into internal factors and external factors.The internal factors are mainly related to material and anti-corrosion measures of prestressed anchors and the external factors are mainly environmental factors(2)According to corrosion characteristics of anchor,combining with its environmental characteristics,structural characteristics and stress characteristics,the main types of corrosion of prestressed anchor are divided into stress corrosion,hydrogen embrittlement,pitting corrosion,crevice corrosion,corrosion fatigue,etc.and some theories are used to explain the different corrosion.According to the different corrosion principle corresponding to the different types of corrosion,some corrosion control measures are put forward.(3)The corrosion morphological features of strands are studied by the accelerated corrosion test with different medium factors.The corrosion mechanism of strands is analyzed based on the features.The results show that different types of corrosion occur in different pH solutions,where the strand undergoes different stages of corrosion.When the solution pH=2,the pitting corrosion occurs;when the solution pH=7,the uniform corrosion occurs;when the solution pH=12,the crevice corrosion occurs.The corrosion types and morphology features of strands are related to that whether the solution contains Cl~-and what the Cl~-concentration is in it.(4)The influence of Cl~-concentration,pH value and time on the corrosion of strand and the mutual coupling relationship among different influencing factors are analyzed according to the change rule of corrosion amount per unit length of strand under different influence factors.The results show that the corrosion amount per unit length of strand increases at first and then decreases with the increase of Cl~-concentration,which increases with the increase of time and decreases with the increase of pH value.The coupling effect of pH value and Cl~-concentration on the corrosion of strand is significant,while the coupling effect of time and Cl~-concentration is less significant,and the coupling effect of time factor and Cl~-concentration factor is relatively weak.(5)According to the health assessment system of prestressed anchors,the environmental index,corrosion status,chemical and mechanical properties changes,deformable features and operating time are investigated in both macro and micro perspectives using chemical and mechanical tests to evaluate the health statue of the anchors synthetically.The results show that the different parts of the anchors are in different corrosion degree because of the varied corrosion prevention measures.The prevention methods of the free and fixed part of the anchors are better than the one of the anchor head.The study results also indicate that the undamaged cement grout has positive effects on anchoring and steel strand corrosion prevention.It can be concluded that the anchors from the experiment are in good working condition,and there are no noticeable chemical and mechanical properties changes that were detected in the tests.The research methods and results could be used as reference for health assessment of similar prestressed anchors.