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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Author(s)

    • 鳥居 和之 Torii Kazuyuki
    • 金沢大学 理工研究域環境デザイン学系 College of Science and Engineering, Department of Environmental Design, Kanazawa University

Abstract

ASRによる鉄筋の破断機構を明確にするために,ASRによって破断した鉄筋の詳細な調査を行うとともに鉄筋の遅れ破壊特性,鉄筋の曲げ加工時の応力解析などを調査した.鉄筋のマクロ的な破断形態は,曲げ加工内面側の節付け根部から一次き裂が発生し,曲げ外面側に向かって二次,三次き裂が発生,伝ぱしていた.一次き裂は延性破面,二次,三次き裂はへき開破面であり,擬へき開破面は観察されなかった.また,鉄筋の表面疵,鉄筋内部には粗大な非金属介在物やボイドが散見され,鉄筋健全部のシャルピー吸収エネルギーは低かった.鉄筋曲げ加工部は,曲げ加工によるひずみ時効により表層部硬さが上昇していた.鉄筋の曲げ加工後の残留応力は曲げ加工内面側で引張残留応力であり,特に節付け根部の残留応力が高いことをFEM解析で確認した.定荷重の遅れ破壊試験では,切欠き試験片に0.97 ppmの水素をチャージしても,遅れ破壊が発生しなかった.ASRによる鉄筋破断は,鉄筋の曲げ加工によるひずみ時効硬化および粗大な非金属介在物やボイドに起因する破壊靭性値の低下と曲げ加工による引張残留応力およびASRによる鉄筋への引張応力の増加の要因によって,脆性破壊したものと考えられた.また,脆性破壊説で,二次,三次き裂の発生および伝ぱ挙動の説明が可能であった.

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.

Journal

  • Zairyo-to-Kankyo

    Zairyo-to-Kankyo 59(4), 143-150, 2010

    Japan Society of Corrosion Engineering

Codes

  • NII Article ID (NAID)
    130004503033
  • Text Lang
    JPN
  • ISSN
    0917-0480
  • Data Source
    J-STAGE 
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