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최하진(Choi, Ha-Jin),최경규(Choi, Kyung-Kyu),최완철(Choi, Oan-Chul),황용재(Hwang, Yong-Jae) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.6
On the basis of dry shrinkage tests of fiber reinforced concrete performed in the previous study, an analytical model was developed to predict the cracking time of concrete in ring test. Due to the geometrical characteristics of the ring type restrained shrinkage test, differential shrinkage causes complex tensile stress in concrete ring. For simplicity in application, the ring test specimens were idealized as linear specimens and the degree of restraint was defined considering displacement compatibility between steel and concrete rings. The tensile stress in ring test specimens was also defined using elastic modulus of concrete and free dry shrinkage strain. The tensile strength of concrete was derived from CEB-FIP model based on flexural test results. In the proposed model, cracking development tine is determined at the intersection between tensile stress and tensile strength curves of concrete ring. Compared with existing test results the proposed model shows reliable prediction of the crack development time.
누설 표면파 계측을 통한 시멘트계 재료의 응결에 대한 기계적 특성 평가
최하진(Choi, Hajin),박주혜(Park, Joohye),홍진영(Hong, Jinyoung) 한국콘크리트학회 2021 한국콘크리트학회 학술대회 논문집 Vol.33 No.2
본 연구는 시멘트계 재료의 기계적 특성을 예측하기 위해 비접촉 초음파를 활용하여 누설 표면파를 계측하고 이를 이론적으로 입증하는데에 목적을 두고 있다. 탄성파 이론에 따르면 유체-고체의 반 무한체 공간의 계면에서는 누설 표면파가 발생되며, 탄성계수가 증가할수록 그 속도는 증가한다. 비접촉 초음파를 활용하여 누설 표면파의 속도 계측 및 분석 결과, 시멘트계 재료의 종결 이후에 발현되는 탄성계수의 예측이 가능하였다. The purpose of this study is to measure Leakage-Ralyeigh waves using air-coupled ultrasonics to predict the mechanical properties of cementitious materials and to prove them theoretically. Leaky-Rayleigh waves occur at the interface of the fluid-solid joint-half space, and its velocity increases as the elastic modulus increases. As the results, it was possible to predict the elastic modulus developed after final setting of cementitious materials using air-coupled ultrasonics.