PVA 섬유보강 시멘트 혼합토의 휨강도 특성에 관한 연구

Abstract

This study analyzed the effects of the cement content (200kg/㎥, 250kg/㎥and 300kg/㎥), the content ratio of PVA fiber (0.0%, 0.25%, 0.50%, 0.75%), and the length of PVA fiber (6mm, 12mm) on the bending strength characteristics of un-reinforced cement mixed soil (clay-cement) and clay-cement-PVA fiber mixed soil (hereinafter, PVA fiber reinforced cement mixed soil) according to the curing period. For analyzing the deflection of specimen when measuring the bending strength, a supporter was attached to the central part of specimen and LVDT was connected to measure the deflection at the mid-point of specimen depending on loading patterns, and the flexural toughness was evaluated through the load-deflection curve. As a result, in case of un-reinforced cement mixed soil, as the cement content increases, the bending strength is increased. But it is indicated that a brittle failure has been occurred after the bending stress reaches the peak value. On the other hand, in case of PVA fiber reinforced cement mixed soil, it was found that as the cement content and the content ratio of PVA fiber increase, the bending strength is increased. And also, it is indicated that a type of ductile fracture has been occurred. This may be attributed to "bridging" effect offered by PVA fibers in the mixture. In addition, 12mm-long PVA fiber reinforced cement mixed soil exhibited a greater bending strength and a larger residual strength than 6-mm long PVA fiber reinforced cement mixed soil. It is also indicated that the longer PVA fiber showed a better resistance to cracking compared to the shorter PVA fiber. The longer PVA fiber provided a larger surface area and thereby providing a greater surface friction force between soil particle and PVA fiber. Accordingly, it is concluded that the PVA fiber content ratio and its length significantly affect on the bending strength and fracture behavior of PVA fiber reinforced cement mixed soil. Also, it was found that as the mixing amount of fiber increases, its equivalent bending tensile strength and bending flexural toughness index (I5) is increased.