材料分離が構造体コンクリートの各種品質に及ぼす影響

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タイトル別名
  • EFFECTS OF SEGREGATION ON VARIOUS PROPERTIES OF CONCRETE IN STRUCTURES
  • ザイリョウ ブンリ ガ コウゾウタイ コンクリート ノ カクシュ ヒンシツ ニ オヨボス エイキョウ

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 It is not clear how much the blocking of coarse aggregate while passing between reinforcing bars and the settling of coarse aggregate during compaction with vibration are prevented in present concrete works. In case these types of segregation phenomenon occur, the distribution of ratio of coarse aggregate to matrix mortar becomes non-uniform in a concrete structure. In addition, it is considered that various properties of concrete also become non-uniform in a member due to this. However, the variation of these properties can not be observed from surface of members and is not recognized as the object of quality control and inspection.<br> We consider that the method of mix design, construction, quality control and inspection to prevent the quality degradation of concrete in structures due to segregation need to be improved, in order to further upgrade concrete structures in the future.<br> In this study, various types of concrete with different workability were placed into wall specimen with reinforcing bars to impede concrete flow, and the degree of segregation such as the blocking and the settling of coarse aggregate was examined. Furthermore, the effects of segregation on the distribution state of various properties of concrete in a structure were investigated. The following findings were obtained as the results.<br> (1) Even if ordinary concrete has low segregation resistance, the ability that concrete can just pass between reinforcing bars does not always decreased.<br> (2) In case ordinary concrete has low segregation resistance, the resistance to the blocking of coarse aggregate in concrete passing narrow space between reinforcing bars, whose clearance is approximately 35 to 40 mm or less, is significantly decreased. In addition, the resistance to settling of coarse aggregate is also decreased.<br> (3) Even if the result of slump flow test does not shows the state of segregation, powder type and thickener type of high fluidity concrete do not always have enough resistance to the blocking of coarse aggregate while passing narrow space between reinforcing bars and to the settling of coarse aggregate.<br> (4) The segregation between coarse aggregate and mortar makes much difference in amount of rise in temperature caused by heat of hydration, Young’s modulus and drying shrinkage strain of concrete in a member. By contrast, it makes little difference in compressive strength and surface quality.<br> (5) The segregation state of coarse aggregate in concrete structures can be potentially grasped by non-destructive method such as the measurement of surface temperature distribution by infrared thermographic camera and the measurement of distribution of ultrasonic propagation velocity. Moreover, the on-peak surface temperature of concrete decreases averagely 0.14 °C and the ultrasonic propagation velocity increases averagely 0.020 km/s with 10 L/m3 increase of coarse aggregate content under the condition of this experiment.

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