시멘트의 수화기구모델에 관한 연구 ( Mathematical Modeling of Hydration Mechanism in Cement Paste )

현철 대한건축학회 1999 大韓建築學會論文集 : 構造系 Vol.15 No.6

시멘트페이스트의 自己收縮에 관한 연구

현철 慶星大學校 環境問題硏究所 1998 環境硏報 Vol.8 No.1

Autogenous shrinkage of concrete has been defined as decrease in volume duv to hydration of cement, not due to other causes such as evaporation, temperature change and external load and soon. For ordinary concretes, autogenous shrinkage is so little compared to the other deformations that it has been dignored. It has recently been proved, however, that autogenous shrinkage considerably increase with decrease in water to cement ratio. And it has been reported that cracking can be caused by autogenous shrinkage, when high-strength concretes were used. In this study, we propose an anlytical system to represent autogenous shrinkage in cement paste in order to control crack due to autogenous shrinkage. The system is composed with the hydration model and pore structure model. Contrary to the usual assumption of uniform properties in the hydration progress, the hydration medel to refine Tomosawa's represents the situation that inner and outer products are made in cement paste. As such, this tool can be used to study the effect of curing condition, mix-proportions etc. on early age development and related progblems. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste and chemical phenomenon of hydration in cement particle. The proposed model can predict the pore volume ratio and the pore structure in cement paste under variable enviromental conditions satisfactorily. The autogenous shrinkage prdiction system with regard to pore structure development and hydration at early ages for different mix-proportions shows a reasonable agreement with the experimental data.

현장용 시멘트페이스트 레올로지 측정기구 개발

현철 대한건축학회 2007 大韓建築學會論文集 : 構造系 Vol.23 No.6

Rheological tests on cement paste were necessary for evaluation of workability on field. The slump, mini cone, and marsh cone test are common methods for assessing the flow properties of fresh cement paste and concrete. Although these methods provide quantitative measures of workability, the relationship between these methods and more quantitative rheological parameters is not fully understood. Some appliances for more accurate measurement are recently proposed. However, these are too expensive to use in field. Therefore, the goal is to propose the simple, cheap and useful rheometer for measuring the rheological properties of cement paste and concrete. In this study, C-P Rheometer consisting of a cylinder and a pipe is proposed. Yield stress of cement paste is calculated by measuring the height of cement paste in cylinder when it finishes dropping. Plastic viscosity is also done by measuring the time for cement paste to drop and pass through the range between two fixed heights of cylinder. The new rheometer is in excellent agreement with the experimental yield stress and plastic viscosity data obtained using the authorized rheometer(Brookfield RVDVⅢ+). The conclusion is that this new simple rheometer is reliable for measuring the rheological properties of cement paste.

기산심해

현철 샘터사 2012 월간 샘터 Vol.504 No.-

高强度콘크리트의 自己收縮豫測에 관한 硏究

현철 대한건축학회 2005 大韓建築學會論文集 : 構造系 Vol.21 No.3

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration. For ordinary concretes, autogenous shrinkage is so little that it has been dignored. It has recently been reported, however, that cracking can be caused by autogenous shrinkage, when high-strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste and concrete in order to control crack due to autogenous shrinkage. The system composed of the hydration model and pore structure model. The hydration model which refined Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste. The proposed model can predict the pore volume ratio and the pore structure in cement paste under variable enviromental conditions satisfactorily. The fomula for elastic modulus change of cement paste according to hydration was made in order to calculate autogenous shrinkage. The model for predicting autogenous shrinkage of cement paste and high-strength concrete shows a reasonable agreement with the experimental data of various mix-proportions.

자율 수중 운동체에 대한 비연성 제어기 설계 및 시뮬레이션을 통한 성능 평가

현철,이동준 제어로봇시스템학회 2012 제어로봇시스템학회 국내학술대회 논문집 Vol.2012 No.4

콘크리트부재의 온도이역예측에 관한 연구 ( A Study on the Prediction of Thermal History in Concrete Structure Member )

현철 대한건축학회 1999 大韓建築學會論文集 : 構造系 Vol.15 No.11

고속 기동하는 수중 운동체의 발사 초기 불안정 구간에 대한 강인 자세 제어 기법

현철 한국정보기술학회 2014 한국정보기술학회논문지 Vol. No.

In this paper, robust controller scheme for underwater launched high-speed autonomous underwater vehicle(AUV) is proposed. The proposed controller scheme can stabilize the AUV rapidly in the unstable region after launch. Controlling the target AUV is not trivial, because it is not stable and is affected with large acceleration, deceleration and roll moment. We can obtained simple but robust control performance using the conventional controller for the normal running condition, by only adjusting the distribution of control fin. Three cases of control simulations have performed with different control fin distribution for AUV in unstable region. The simulation results show that the proposed control scheme is suitable for controlling AUV in initial unstable region after underwater launch. 본 논문에서는 수중에서 발사되는 고속 자율 수중 운동체에 대한 견실한 제어기법을 제안하였다. 제안된 제어기법은 발사 후 불안정 구간에서 빠른 속도로 수중 운동체를 안정화 할 수 있다. 대상 수중 운동체는 자체적인 안정성 확보가 어려운데다, 발사 직후 큰 가감속 입력과 롤 모멘트를 받기 때문에 이를 제어하는 것은 쉽지 않은 문제가 된다. 이를 위하여 기존의 정상 주행 상태에 대한 제어기를 그대로 이용하되, 가로축, 세로축, 롤축의 제어 타각 분배만을 조절함으로써, 단순하지만 강력한 성능을 보이는 제어로직을 구성하였다. 제어 타각 분배 유형을 세 가지 경우로 나누어 초기 불안정 구간에 대한 수중 운동체 제어 시뮬레이션을 수행하였다. 시뮬레이션 결과, 제안된 제어 기법을 사용하였을 때 발사 초기 불안정 구간 제어에 더욱 적합한 성능을 보였다.

시멘트페이스트의 細孔構造예측에 관한 연구

현철 慶星大學校 1998 論文集 Vol.19 No.2

In this paper, we propose an analytical model to represent the hysteresis behavior of pore production in cement paste. The proposed model is based upon the physical phenomenon of ion diffusion in cement paste and chemical phenomenon of hydration in cement particle. The proposed model can predict the hydration ratio, the pore volume ratio and the pore structure in cement paste under variable environmental conditions satisfactorily.

모르터의 자기수축예측에 관한 연구

현철 경성대학교 공학기술연구소 2003 공학기술연구지 Vol.S2 No.2

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration. For ordinary concretes, autogenous shrinkage is so little that it has been dignored. It has recently been reported, however, that cracking can be caused by autogenous shrinkage, when high-strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste and mortar in order to control crack due to autogenous shrinkage. The system composed of the hydration model and pore structure model. The hydration model which refined Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste. The proposed model can predict the hydration ratio and the cumulative pore volume in cement paste satisfactorily. Autogenous shrinkage was predicted by elastic modulus calculated from experiment data and former study. The model for predicting autogenous shrinkage of cement paste and mortar shows a reasonable agreement with the experimental data in case of different mix-proportions.