Issue 45

X. Z. Wang, Frattura ed Integrità Strutturale, 45 (2018) 100-107; DOI: 10.3221/IGF-ESIS.45.08 102 C ORROSION TEST OF ANCHOR STEEL orrosion is the most important factor affecting the service life of anchor steel. When the corrosion is slight, the tensile capacity of the steel bar is calculated according to the remaining cross-sectional area, without considering the strength reduction of the steel bar. When the steel bar is corroded to a certain extent, not only the sectional area of the steel bar is decreased, but also the strength and ductility of the steel bar have different rate reduce. When the steel corrosion is serious, the stress-strain curve of the steel bar has changed greatly. There is no obvious yield point on the curve, and the yield strength is very close to the tensile strength, it is very easy to cause the sudden brittle fracture of the structure [8-10]. Steel bar corrosion mechanism The chemical composition and mechanical properties of the steel used in the test are shown in Tab. 1. Chemical composition R el /MPa R m /MPa 20°C Impact en- ergy/A K /J C Si Mn S P V 0.26 0.56 1.57 0.011 0.024 0.107 705 875 35 Table 1 : The chemical composition and mechanical properties of the steel. The corrosion of anchor steel is an electrochemical corrosion process, mainly through the following four processes. (1) The process of anodic reaction. The iron atom in the anode region is transformed into cationic, and the electron is re- leased. The equation of reaction is: 2 2 2 Fe Fe e     (10) (2) The process of electron transport. The electrons which released from anode region are transferred through steel to the cathode region. (3) The process of cathode region. In the vicinity of the cathode region, the oxygen dissolved in the pore water absorbs electrons and occurs reduction reaction. The equation of reaction is: 2 2 2 4 4 O H O e OH      (11) The OH - produced at the cathode is sent to the anode through the liquid phase in the concrete pore, thus, a closed loop of corrosion current is formed [11-15]. (4) The formation process of corrosion products. The Fe 2+ generated in the anode region diffused and migrated in the aqueous solution, the OH - generated in the cathode zone diffuses through the pores in the concrete to the anode region. Near the anode, Fe 2+ and OH - form insoluble 2 ( ) Fe OH ,and oxidize to 3 ( ) Fe OH under oxygen enrichment. 2 2 2 ( ) Fe OH Fe OH     (12) 2 2 2 3 4 ( ) 2 4 ( ) Fe OH O H O Fe OH    (13) After Fe(OH) 3 dehydration, it becomes loose and porous red embroidered Fe 2 O 3 , that is: 3 2 3 2 2 ( ) 3 Fe OH Fe O H O   (14) Under the condition of less oxygen, Fe(OH) 2 oxidation is not complete, and part of Fe(OH) 2 forms Fe 3 O 4 , that is: 2 2 3 4 2 6 ( ) 2 6 Fe OH O Fe O H O    (15) Therefore, the final corrosion product depends on the oxygen supply. C