アルカリシリカ反応による鉄筋の破断機構 [in Japanese] Fracture Mechanism of Steel Bar by Alkali Silica Reaction [in Japanese]
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In order to clarify the fracture mechanism of steel bars through an alkali-silica reaction (ASR), the mechanical properties and fracture observation of steel bars ruptured by ASR and the delayed fracture resistance was investigated in detail, and a stress analysis during the bending process of steel bars was also performed. The macroscopic fracture morphology of steel bars was as follows : the first crack was initiated near the ridge of the steel bar in the inner side of the bending area. Then, the second and third cracks were generated and propagated in the direction of the outer side of the bend. The first crack was a kind of ductile fracture, and the second and third cracks were cleavage fractures ; quasi-cleavage fractures were not observed anywhere on the entire fractured surface. In addition, surface seams, large non-metallic inclusions and voids were observed with some frequency in the fractured steel bar. As a result, low Charpy absorbed energy in the unbent portions was obtained, and surface hardness in the bent portions remarkably increased through strain aging. Residual tensile stress existed in the inner surface after bending; in particular, the existence of high residual tensile stress near the ridge was confirmed by FEM analysis. Furthermore, delayed fractures did not occur in the constant loaded test using the notched specimen with diffusible hydrogen of 0.97 ppm. Thus, it was concluded that the fracture of steel bars through ASR produced brittle fractures. Such fractures were caused by the deterioration of fracture toughness, which resulted in strain aging due to bending; the existence of large non-metallic inclusions and voids; the existence of residual tensile stress after bending; and the increase in applied stress to the steel bar through ASR. Initiation and the propagation behavior of the second and third cracks in the steel bar were also consistently explained by the brittle fracture mechanism.
Zairyo-to-Kankyo 59(4), 143-150, 2010
Japan Society of Corrosion Engineering