• Computers and Concrete
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• v.4 no.1
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• pp.33-47
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• 2007

Slipforming is a construction method in which the forms move continuously during concrete placement. This paper presents a numerical procedure based on the finite element method to simulate the thermal behavior of concrete during slipforming operations. The validity of the model was successfully tested by simulating a very complex but well documented field case of actual slipforming operations performed during the construction of an offshore concrete oil platform structure. The results obtained have been related to the shape of the concrete "hardened front" in the forms, which allows quick evaluation of the operation. The results of the numerical investigation have shown that the shape of the "hardened front" can be affected by the temperature of the fresh concrete and ambient conditions. For a given initial concrete temperature, there are limitations for the ambient temperature that, when exceeded, can create an unfavorable shape of the concrete "hardened front" in the forms. Similarly, for a given ambient temperature, the initial concrete temperature should not be fall below an established limit in order to avoid unfavorable shape of the "hardened front".

• Journal of applied mathematics & informatics
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• v.42 no.1
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• pp.49-64
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• 2024

When setting up a structure with an embedded shallow arch, there is a phenomenon where the end of the arch moves. To study the so-called moving domain problem, one try to transform a considered noncylindrical domain into the cylindrical domain using the transform operator, as well as utilizing the method of penalty and other approaches. However, challenges arise when calculating time derivatives of solutions in a domain depending on time, or when extending the initial conditions from the non-cylindrical domain to the cylindrical domain. In this paper, we employ the transform operator to prove the existence and uniqueness of weak solutions of the shallow arch equation on the moving domain as clarifying the time derivatives of solutions in the moving domain.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.135-148
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• 2014

This study was performed to evaluate the performance about Improved C12A7 based mineral accelerator (ICM) increased in initial and long-term strength. ICM was developed to overcome the long-term strength decrease in existing accelerator. To evaluate the performance of ICM according to addition rate, setting time, compressive strength, and flexural strength tests were conducted in laboratory. In results, initial setting time was slower, final setting time was faster than existing $C_{12}A_7$ based mineral accelerator (CM) when usage of ICM 6%. In compressive and flexural strength, existing CM was higher than ICM at 3hours and 1day. After 7days, strength of shotcrete using ICM was increased. Rebound test, compressive strength and flexural strength test with optimum addition rate through the laboratory test were conducted in field. Field experiment results were the same as laboratory test. Long-term strength performance of ICM was superior to existing accelerator.

• Journal of the Korea Institute of Building Construction
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• v.12 no.4
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• pp.393-400
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• 2012

The effect of ground granulated blast-furnace slag (GGBS) and alkaline activator on the properties of setting, compressive strength, drying shrinkage and resistance of carbonation was assessed to develop high volume slag concrete, the GGBS replacement rate of which was more than 80 percent. The changes in the concrete as the replacement rate of GGBS increases were as follows. Initial and final setting time was delayed by two and a half hours, and the compressive strength development properties of concrete in early and long term age were decreased. Drying shrinkage was satisfactory as below $6{\times}10^{-4}$ in every mixture, and yet showed a tangible trend by replacement rate. Carbonation was materially increased. Setting time and early strength development property, however, were extremely advanced by the addition of the alkaline activator. While drying shrinkage was improved by the alkaline activator, resistance to carbonation was not.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.550-554
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• 2007

A one-dimensional heat transfer model coupled with parameter estimation is developed in this study to predict the effective thermal conductivities of soil formation and borehole resistances from in situ field test data. In this application a new method of using initial ignoring time(IIT) obtained from error estimation is tried and turned out to be successful in determining soil thermal conductivities. The validity of this model is accomplished through comparison of the predicted temperature profiles of the model with the data from laboratory scale experimental setting. Eleven test boreholes were constructed in Ochang, Chungcheong Buk Do, and thermal response test was carried out with each borehole. The results of the in situ tests were analyzed with our 1-D numerical model and compared with the results of line source method. The comparison shows that the thermal properties from line source method is a little lower (${\sim}95%$)than those from numerical method. The reason of such result seems to be the lower thermal conductivity of grout material, which is not counted in line source method.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.7
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• pp.323-327
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• 2005

This paper presents an operator training simulator for power system restoration against massive black-out. The system is designed especially focused on the generality and convenient setting up for initial condition of simulation. The former is accomplished by using power flow calculation methodology, and PSS/E data is used to define the initial situation. The proposed simulator consists of three major components - the power flow(PF) module, data conversion(COW) module and GU subsystem. PF module calculates power flow, and then checks overvoltage of buses and overflow of lines. COW module composes an Y-Bus array and a data base at each restoration action. The initial Y-Bus array is constructed from PSS/E data. The user friendly GUI subsystem is developed including graphic editor and built-in operation manual. As a result, the maximum processing time for one step operation is 15 seconds, which is adequate for training purpose. Comparison with PSS/E simulation proves the accuracy and reliability of the training system.

• Journal of The Korean Digital Architecture Interior Association
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• v.13 no.3
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• pp.51-58
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• 2013

The projects are becoming more complicated and amplified as the design and development technology is advancing. Thus, existing architectural processes and methods are revealing limitations. The technology of BIM is an IT applied to construction, that provides the state-of-the-art tools to overcome these limitations to improve on architectural designing, technology, cost, etc. Therefore, it it necessary to converge the advises and collaboration from the various experts at the initial step in a common processing platform. In this research project with Korean Education Development Institute, configuration and utilization of EDU BIM template is studied because setting an anchor point from the initial phase is necessary for such processes at the perspective of the operator. The purpose of this study is to prevent time consumptions at the initial phase of BIM foundation, to ensure accurate information inputs within the repetitive tasks, and for effective information management that will produce consistent results through utilization of BIM technology.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.181-183
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• 2003

This paper presents an operator training simulator for power system restoration against massive black-out. The system is designed especially focused on the generality and convenient setting up for initial condition of simulation. The former is accomplished by using on line calculation methodology, and PSS/E data is used to define the initial situation. The proposed simulator consists of three major components - the Power flow(PF) module, data conversion(CONV) module and CUI subsystem. PF module calculates power flow, and then checks overvoltage of buses and overflow of lines. CONV module composes an Y-Bus array and a data base at each restoration action. The initial Y-Bus array is constructed from PSS/E data. The user friendly GUI module is developed including graphic editor and built-in operation manual. As a result, the maximum processing time for one step operation is 15 seconds, which is adequate for training purpose. Comparison with PSS/E simulation proves the accuracy and reliability of the training system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.117-124
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• 2017

In this study, to evaluate the setting time, compressive strength and drying shrinkage of ordinary Portland cement and Portland blast-furnace slag cement mortar with 0, 10, 20, 30 wt.% alpha-calcium sulfate hemihydrate. As a results, as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the initial setting time of ordinary Portland cement and Portland blast-furnace slag cement mortar was faster. In addition, the compressive strength decreased with increasing replacement ratio of alpha-calcium sulfate hemihydrate in both ordinary Portland cement mortar and Portland blast-furnace slag cement mortar. The strength development of Portland blast-furnace slag cement mortar with alpha-calcium sulfate hemihydrate was effective than that of ordinary Portland cement mortar. On the other hand, in the case of the mortar with alpha-calcium sulfate hemihydrate, it was confirmed that shrinkage deformation was reduced at the early age by growth pressure of needle-shaped ettringite crystals produced by incorporation of alpha-calcium sulfate hemihydrate. However, the effect of inhibiting shrinkage deformation of mortar with alpha-calcium sulfate hemihydrate was not significant as the age passed. Therefore, it is considered that the alpha-calcium sulfate hemihydrate is useful as a construction material.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.275-281
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• 2017

This study examined the effect of water-to-binder ratio (W/B) and phosphate-to-binder ratio (P/B) on the flow, setting time, compressive strength development, and pH variation of magnesium-potassium phosphate composites, MKPC mortars. Ten mortars mixtures were prepared with the W/B varying from 20% to 40% at each P/B of 0.3 or 0.5. The hydration products and microstructural pore distribution of the MKPC pastes were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP). The initial flow and setting time of MKPC mortars tended to decrease with an increase of P/B, indicating that the final setting time was shortened by approximately 24% when P/B increased from 0.3 to 0.5. The slope of the early-strength development measured in the MKPC mortars was considerably higher than that of cement concrete specified in code provisions. For obtaining a relatively good 28-day strength (above 30 MPa) and a near neutral pH (below 9.0) in MKPC mortars, the P/B and W/B need to be selected as 0.5 and 30%, respectively. The strubite-K crystal increased with the increases of P/B and W/B, which leads to the decrease of the macro-capillary pores.