• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.6
• /
• pp.9-15
• /
• 2018

According to the development and use of self-consolidating concrete in field, interest in material properties of early-age concrete is rising. Setting time with hydration process of cement is one of significant indicator to evaluate the early-age material properties of concrete, various nondestructive methods including penetration resistance measurement have been proposed to estimate setting time. This study performed an experimental approach to evaluate setting time delay in mortar adding superplasticizer using electrical resistivity measurement. For this purpose, total nine types of mortar samples were prepared, and its electrical resistivity was monitoring during 24h after mixing. From the experimental result, rising time of electrical resistivity was used to evaluate setting delay of mortar, and penetration resistance was also measured for comparison. In addition, dynamic elastic modulus and compressive strength of 1day mortar were measured to investigate a possibility the use of electrical resistivity measurement for evaluation of early-age material properties.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.1
• /
• pp.87-94
• /
• 2003

Recently, LPLi(Liquied-Phase LPG injection) system is studied for the new stringent emission regulations. But , there are some problems to be solved such as injector tip icing and fuel leakage for LPLi system development. In this paper, the icing problem near injector tip which leads to difficulty of accurate A/F control was studied and reported. Icing of injector tip and port wall was observed at all the cases in this study regardless of injection duration and angle, air humidity change. The spray angle of LPLi was observed approximately two times wider than that of Gasoline injection. This makes the LPLi spray collide with intake port around injector tip. Temperature of the wetted area was decreased and icing of water vapor contained in intake air because of evaporation of the fuel film. The ice of the injector tip and port wall is also affected by the materials related to heat transfer.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.4
• /
• pp.48-56
• /
• 2022

Controlling the setting time of cementitious materials is one of the most important factors in securing early-age performance of concrete structures. Recently, the use of retarding admixtures, which enable the inhibition of some hydration products to control the securing time due to average temperature rise is suggested. Although various non-destructive evaluation methods have been proposed to evaluate cement hydration and hardening of cement-based materials to overcome the limitations of Vicat needle test, experimental research is still required to use the non-destructive evaluation method with added retarding admixtures. In this study, measurements of electrical resistivity and ultrasonic wave velocity in early-aged cement pastes were performed according to the addition of retarding admixture(tartaric acid). The setting time of the cement pastes was evaluated by obtained rising time of the both non-destructive measurements. As a result, the possibility of evaluating the setting delay in cement pastes was confirmed through comparative analysis with the initial and final setting times by Vicat test. In addition, X-ray diffraction results at the rising time of electrical resistivity showed a key hydration product affecting the setting delay.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2001.11a
• /
• pp.87-88
• /
• 2001

대기오염물질 제거에 중요한 역할을 하는 침적 현상은 크게 건성침적(dry deposition)과 습성침적(wet deposition)으로 구분된다. 건성침적은 오염물질이 중력이나 분자 확산에 의해 지면이나 그 부근에 침강ㆍ흡착하는 현상이며, 습성침적은 구름 속의 에어로졸이 응결핵으로 제거되는 성우제거(rainout)와 구름 이하의 고도에서 강수에 의해 제거되는 세척제거(washout)와 같은 현상을 일컫는다. 습성침적은 강수 및 구름 물리와 관련하여 대기 중 오염물질 제거에 큰 비중을 차지함에도 불구하고 건성침적에 비해 그 연구가 미흡한 실정이며, 침적 모형을 이용한 연구는 더욱 찾아보기 어렵다. (중략)

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5A
• /
• pp.307-315
• /
• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
• /
• 2002.11a
• /
• pp.85-88
• /
• 2002

기상학적으로 안개는 지상에서 발생하는 응결 현상으로, 시정이 1km 이하일 때로 정의된다. 안개 발생은 기후 인자의 영향을 많이 받는다. 따라서 각 지역마다의 발생 특성을 따로 통계해야 할 필요가 있다. 특히 항공 교통의 장애가 되는 위험 요소로서의 역할이 중시되어 각 비행장마다 발생 특성이 따로 통계 분석되고 이용되어 왔다.(중략)

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.2
• /
• pp.39-44
• /
• 2004

As air pollution has become an important issue across the world, studies of clean fuel are on going to reduce combustion emissions. One example is development of the LPLi(Liquefied Phase LPG injection) engine. Some problems are occurred during development. One of the problems is icing phenomenon at injector tip due to evaporation potential heat when liquid LPG is injected. If the Icing is raised at injector tip or injector inserting hole, it disturbs fuel injection. And if the ice particles are inducted into cylinder, it brings problems associated with control of emission and air/fuel ratio. In order to solve the problems, a rig system was set up and observed Icing of injector tip. Engine test was carried out for visualization of injector tip icing and its effects on combustion and emissions.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2001.11a
• /
• pp.338-339
• /
• 2001

본 연구에서는 대기 중의 오존농도 증기에 크게 기여하는 오존전구물질인 탄화수소계 휘발성유기화합물 중 가장 휘발성이 큰 $C_2$-C$_3$계열의 오존전구물질을 분석하기 위하여 흡착농축 분석법을 이용한 효율적인 분석법을 확립하고자 하였다. $C_2$계열의 탄화수소류의 경우 휘발성이 매우 커서 일반적으로 -3$0^{\circ}C$의 저온에서 강한 흡착제를 이용하여 재농축하는 과정을 거쳐서 분석하는 방법을 사용하고 있다. 그러나, 공기 중 상대습도가 높을 경우 수분에 의한 흡착제의 응결현상으로 인해 농축트랩이 막히는 등의 여러 가지 문제점을 유발할 수 있으므로 철저히 수분을 제거하여야 하는 것으로 알려져 있다. (중략)

• Journal of the Korean earth science society
• /
• v.24 no.4
• /
• pp.250-257
• /
• 2003

The purpose of this study was to test the hypotheses that student's abductive reasoning ability plays an important role in hypothesis-generating about vapor condensation, and student's hypothesis-generating requires their causal explicans as well as experience. To test the hypotheses, the instruments of hypothesis-generation, prior knowledge, and experience with vapor condensation were developed and administered to 6th grade students. This study found that 72 subjects among 89 students who had prior knowledge about vapor condensation failed to apply their prior knowledge to hypothesis-generating about the vapor condensation. This result showed that the students' failure in hypothesis-generating was related to their deficiency in abductive reasoning ability. In addition, this study showed that 54 subjects among 56 students who had experience with vapor condensation also failed to generate hypotheses. This result supported that student's causal explanations were separated from their experience. Therefore, this study suggests that science education should include the teaching of abductive reasoning skills for developing student's hypothesis-generating skills.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
• /
• 2002.11a
• /
• pp.97-100
• /
• 2002

산업사회로의 급속한 발전에 따른 인위적인 환경오염 중에서 산성강우에 의한 자연환경 및 생태계의 심각한 문제로 대두되고 있다. 이러한 대기오염물질은 대기 중에 부유하면서 직접적인 피해를 주기도 하지만, 비, 눈 등의 강수현상에 의해 응결ㆍ낙하(rainout)되거나, 세정작용(washout)으로써 강수 내 화학성분의 변화를 초래한다고 하였다(박종길과 황용식, 1997).(중략)