膨張・収縮低減コンクリートの収縮ひび割れ評価  [in Japanese] EVALUATION ON SHRINKAGE CRACKS OF EXPANSIVE/SHRINKAGE REDUCING CONCRETE  [in Japanese]

Access this Article

Author(s)

Abstract

ひび割れの分散性を評価できる拘束ひび割れ試験により、収縮低減剤および膨張材を単独使用あるいは併用したコンクリートと普通コンクリートのひび割れ性状を比較し、各材料の収縮ひび割れ低減効果を定量化するための検討を行った。その結果、収縮低減剤や膨張材にはひび割れ本数・ひび割れ係数を明確に低減する効果があること、各材料のひび割れ低減効果を無拘束試験体で測定する乾燥収縮ひずみに対応させると、収縮低減剤は普通コンクリートの乾燥収縮ひずみに対する低減量、膨張材は普通コンクリートの乾燥収縮ひずみに対する低減量に初期の膨張ひずみ分として100~150×10<sup>-6</sup>程度の低減量を加味すること、併用した場合には各材料を単独で使用した場合の効果を足し合わせること、で概ね評価できる可能性があることを示した。

It is empirically known that using shrinkage reducing agent(SRA)and/or expansive additive(EX)is effective in reducing shrinkage cracks in concrete structures. However, in order to control cracks more rationally, it is necessary that reduction effect of SRA and EX in shrinkage cracks are quantitatively evaluated for design values. In this paper, shrinkage crack characteristics were compared between concrete using SRA or EX solely, or in combination SRA and EX, and plain concrete by investigating crack distribution in uniaxially restrained specimens in which a deformed steel bar embedded. Furthermore, shrinkage crack control effects of SRA and EX were evaluated by determining relationship of drying shrinkage strain measured in the unrestrained specimens with the cracking coefficient calculated from the number of cracks and crack width. As a result, compressive strength and modulus of elasticity of concrete using SRA and EX cured under temperature of 20℃ and relative humidity of 60% after wet curing at 7 days were equal to or greater than those of plain concrete. The drying shrinkage strain of concrete using SRA or EX was found approximately 10-20% less than that in plain concrete. SRA and EX were obviously effective in reducing the number of shrinkage cracks and the cracking coefficient. It were also suggested that the crack control effect of SRA could be approximated quantitatively as the decrease in drying shrinkage strain, and that of EX could be as the sum of the decrease in drying shrinkage strain and the amount of expansion-induced strain of about 100-150×10<sup>-6</sup>. Further the effect of combined use of SRA and EX could be evaluated as the sum of their individual effects.

Journal

  • Cement Science and Concrete Technology

    Cement Science and Concrete Technology 69(1), 341-348, 2015

    Japan Cement Association

Codes

  • NII Article ID (NAID)
    130005140615
  • Text Lang
    JPN
  • ISSN
    0916-3182
  • Data Source
    J-STAGE 
Page Top