ベントナイト液中のコンクリートの鉄筋の付着強度に関する研究 : 其の一・モデル実験

Abstract

These experiment have been performed to investigate the bond strength of reinforcement in concrete cast into the bentonite suspension and the compressive strenght of that concrete. In this method, the bentonite suspension is always in jected, as the drilling proceeds, to prevent the wall surface from falling and then concrete is poured into the bentonite suspension using tremie pipe. It is feared that the compreesive strength of concrete and the bond strength of the reinforcement may decrease as the result of the in perfect replacement of bentonite suspension with concrete. These expreiments were performed to clarify there points and they consisted of the two experments, one of which was the model experiment in the laboratory and the other was the experiment performed at job sites, The results of the experments show that the compressive strength of the concrete cast into the bentonite suspension about 13% concentration is lower than that of the concrete cast in ordinary way, and in the concrete cast into the bentonite suspension below the value, it does not decrease so much. However, at the top end and the both side ends of the concrete wall cast into the bentonite suspension, consiclerable decrase of the compressive streugth is observed. As to the bond strength in the concrete cast into the bentonite suspension, it is found to be lower than that of the ordinatry concrete and the following formula for the relation between the concentration of bentonite suspension and the bond strength is suggested. ^τx=α・τ_c(1-βX^2) where; X=concentration of bentonite suspension (%) τ_x=bond strength (kg/<cm>^2) for concrte poured into bentonite suspension with concrete of × % τ_c=bond strength (kg/<cm>^2) of ordinary concrete. α, β=coustants Further, it is shown that the bond strength of concrete decreases considerably when the bentonte suspension is gelatinized by Ca^++ ion of the cement. And the bond strength of ths concrete at the top and the both side ends of the wall is also found to decrease.