• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.269-272
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• 2008

This paper reports on the cracking mitigation and flexural behavior experimentally observed in concrete prisms layered with strain-hardening cement composites (SHCCs) which is micro-mechanically designed cement composite and exhibits pseudo tensile strain-hardening behavior accompanied by multiple cracking while using a moderate amount of fiber, typically less than 2 percent in term of fiber volume fraction. In this study, SHCC is reinforced with 1.3 percent polyvinyl alcohol (PVA) and 0.20 percent polyethylene (PE) in volume fraction. Tests were conducted using $100{\times}100{\times}400mm$ long prisms supported over a simply supported span of 350mm. The four point load was applied using MTS servo control machine. The thickness patched with SHCC is the main variable for this study. Experimental study shows that when subject to monotonic flexural loading, the SHCC layered repair system showed 2.7 - 4.2 times increased load carrying capacity, and mitigated cracking damage of concrete beams layered with SHCC compared with plain concrete beams.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.369-374
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• 2008

Two types of conductive materials are selected and their applicable properties are investigated so as to give the capability of self-diagnosis of fracture in composite mortar, concrete and reinforced concrete. In this study, for giving selfdiagnosis capability, the powder of cokes and milled carbon fiber as conductive materials are selected and intermixed with mortar, concrete and reinforced concrete. After examining change in the value of electric resistance before and after the occurrence of cracks at each flexural load-stage in composite mortar, concrete or reinforced concrete, the relationships of each factors (electric resistance, crack and flexural load) are analyzed. As the results, it can be recognized that conductive materials with powder of cokes and milled carbon fiber can be applied for self-diagnosis of flexural fracture in composite mortar, concrete and reinforced concrete specimen.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.795-800
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• 2001

Two evaluation techniques of the tunnel lining concrete using ultra sonic velocity method are developed. Modified linear regression technique is proposed to enhance the corelation between the pulse velocity and the compressive strength of core specimens. And bivariate normal distribution is assumed to evaluate the quality of concrete as a terms of compressive strength. A simple corelation table between the pulse velocity and the compressive strength of core specimens are proposed.

• Journal of Korean Association for Spatial Structures
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• v.12 no.3
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• pp.79-87
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• 2012

In this study, static displacement sensors using lead switches are bonded on concrete beams and RC beams, and monitoring systems to crack damages are studied using radio frequency. If load is received on the center of flexible specimens, bonded static displacement sensors will be destroyed, and these become to send signals of damages at radio frequency system connected with static displacement sensors. Study of these functional building elements will be protected from external factors by unusual weather, earthquake, etc, in RC buildings and structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.40-47
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• 2014

Recently the use of concrete post-installed set anchors has been increasing because this constructing method is flexible and easy to attach or fix structural members when we repair, reinforce, or remodel structures. Accordingly, designers and builders of Korea depend on foreign design codes since there are no exact domestic anchor design codes that they could credit. The anchor in plain concrete loaded in tensile exhibits various failure modes such as concrete breakout, splitting, steel failure, pull-out and side-face blowout, that depending on the tensile strength of the steel, the strength of concrete, embedment depth, interval, the edge distance and the presence of adjacent anchor. The objective is to investigate the effects of the variations like anchor embedment depth, interval and edge distance on pull-out fracture behavior of post-installed concrete set anchor embedded in plain concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.809-816
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• 2006

More than effectively judging the existence of reinforcing bars under multi boundary layers and void shapes in concrete, this study aims to develop the analysis algorithm of radar response on multi boundary layers in reinforced concrete and radar capable of estimation of the shape of specific voids in plain concrete. To detect or estimate reinforcing bars and void shapes in these conditions, the simulation analysis model of transmission and reflection wave of electromagnetic radar is used. This radar simulation model is carried out with reinforced or non reinforced concrete of various boundary conditions and void shapes. And, the output signals (images) of radar simulation results are calculated and represented by convolution method. As the results, it is clarified that this simulation analysis technique can be used to analyze radar response on multi boundary layers in reinforced concrete and void shapes in concrete.

• Magazine of the Korea Concrete Institute
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• v.4 no.4
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• pp.149-160
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• 1992

콘크리트 압축강도가 설계의 규준이 될 경우 배합비를 결정하는 방법은 여러 가지가 있으나, 파괴에너지 및 탄성계수와 같은 규준이 주어질 경우 배합비 결정에 적용하는 방법은 거의 없다. 이를 위하여 본 연구는 콘크리트 재료성질의 관계에 관한 배합설계도(Mix design diagram)를 제안하였다. 이 방법은 시멘트량, 물-시멘트 비가 콘크리트의 압축강도, 탄성계수, 할렬인장강도, 파괴에너지 그리고 콘크리트 특성길이(Characteristic length)에 주는 영향을 실험에 의하여 규명하였다. 시편제작을 위하여 각기 다른 물-시멘트비와 워커빌리티를 갖는 6종류의 무근콘크리트 배합이 사용되었다.

• Magazine of the Korea Concrete Institute
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• v.8 no.1
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• pp.130-137
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• 1996

본 연구는 정적 및 동적하중 재하상태에서 배합조건을 달리한 콘크리트의 파괴특성을 조사하고자 3점 휨 실험을 실시하였다. 실험은 물-시멘트비를 일정하게 유지한 상태에서 슬럼프 값을 변화시키는 경우와 슬럼프 값을 일정하게 유지하면서 물-시멘트비를 변화시키는 경우로 구분하여 배합비를 달리한 6가지 배합형태의 무근콘크리트 시편 54개를 제작하였다. 실험결과에 의하여 콘크리트의 파괴에너지(Gf)와 특성길이(lch)를 구한 수 이를 강도특성(f'c, fsp , Ec, ff)과의 상관관계를 규명하고 파괴에너지(Gf)를 이용한 배합설계의 타당성을 검토하였다.

• Journal of the Korea Institute of Building Construction
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• v.11 no.5
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• pp.419-425
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• 2011

Topping concrete that is not reinforced with rebar to prevent poor tensile performance is vulnerable to cracking. In this study, jute, which is known to be an excellent natural fiber material for strengthening concrete performance, was compared with other cellulose fibers in terms of its capacity to reduce the cracking of concrete. As a result, it was found that compared with concrete using other fibers, concrete using jute fiber showed more than a 50 % reduction of plastic shrinkage crack resistance with the contents of 0.9 kg/$m^3$ and 1.2 kg/$m^3$ for. For impact strength tests, the final destruction of WF and PULP fibers took up to 5 times the number of falls, while jute has 10-18 circuitry, showing excellent ductility properties.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.107-115
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• 1998

반복하중을 받는 무근 및 철근 콘크리트 부재는 하중의 반복작용에 의해 과도한 균열 및 처짐을 유발하고 결과적으로 전체 구조요소의 파괴를 일으킨다. 따라서 하중반복에 의한 누적손상의 진행과정을 정량적으로 평가하여 철근콘크리트 보의 사용성과 안전성을 평가하는 것이 중요하고 특히 취성적 거동 특성을 갖는 전단거동의 경우에 더욱 의미가 있다. 본 연구에서는 반복전단하중에 의한 누적손상의 정량적 분석을 위하여 평균변형도 및 평균응력개념에 기초한 수정압축장이론(modified compression field theory)에 의하여 누적손상 모델을 제안하였다. 본 연구에서 제안된 모델을 통하여 반복전단하중에 의한 처짐과 변형도의 변화를 평가하는데 유용하게 이용될 것으로 사료된다.