Abstract
The purpose of this study is to evaluate the performance on the compressive bonding shear strength of ultra-high strength steel fiber reinforced cementitous composites(UHSCC). As a result of compressive bonding shear strength through Direct shear test, It was found that the specimen($150{\times}150{\times}150mm$) of NC(Normal concrete) + NC showed similar compressive bonding shear strength at whole experimental level. On the other hand, the specimen of UHSCC + UHSCC showed decrease of compressive bonding shear strength from after 30 minutes of the retarded placement than 0 minute. As a result of analyzing failure mode of bonding interface, It was found that the specimen of NC + NC showed mixed failure at whole experimental level. In case of the specimen of UHSCC + UHSCC, it showed interface failure from the specimen that are 30 minutes, 60 minutes and 90 minutes of delay of concrete placing. As a result of analyzing XRD test in terms of the placement interface on the specimen of NC and UHSCC, relatively much amount of $SiO_2$ was detected from the specimen of UHSCC than that of NC. It is judged that the most of main components of coating film shown in the specimen of UHSCC is $SiO_2$. In conclusion, it is judged that UHSCC which is made from after 30 minutes of delay of concrete placing is unable to be used as structural member because of deterioration of bonding performance. From later study, it is judged that the improvement of bonding performance from the part of cold joint occurrence is necessary through the interface preparation method.
본 연구는 고강도 섬유보강 시멘트 복합체(UHSCC) 접착성능을 평가하는 것이 목적이다. Direct shear test를 통해 압축전단접착강도를 측정한 결과 NC(보통강도콘크리트)+NC 실험체($150{\times}150{\times}150mm$)에서는 모든 수준에서 유사한 압축전당접착강도를 나타내었고, 반면 UHSCC+UHSCC에서는 지연타설 30분 후부터 0분에 비해 압축전단접착강도가 낮아지는 것을 확인할 수 있었다. 이를 통한 접착면의 파괴모드를 분석한 결과 NC+NC 에서는 모든 수준에서 비계면 파괴를 보였고 UHSCC+UHSCC에서는 30분, 60분, 90분 시험체에서 계면파괴가 일어났다. NC 및 UHSCC의 타설면을 XRD 시험을 통해 분석한 결과 NC 시험체에 비해 UHSCC의 시험체 에서 많은량의 $SiO_2$의 성분이 검출되는 것을 알 수 있었고 UHSCC에서 나타난 코팅막의 주성분의 대부분은 $SiO_2$로 사료된다. 따라서 본 연구에서 사용된 UHSCC는 지연타설 30분 후 부터는 접착성능의 저하로 구조체로서의 사용이 어렵다고 판단된다. 금후 연구에서는 콜드조인트 발생 부위의 면처리 방법을 통한 접착성능 향상이 필요하다고 사료된다.
