• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.397-400
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• 2005

This study is a result that, in order to improve the early stage strength of fly ash, the calciumsulfoaluminate in which the generation of ettringite was very active in the early stage was substituted by some amount, and then the effect on the early stage was analyzed. when fly ash was substituted by 30$\%$, the strength dropped by maximum 54 $\%$ in the 3rd day of aging, compared to the cement mixture, but when CSA was substituted by 8 $\%$ in the fly ash amount, the strength improved at the 86 percent level of cement, it is suggested as an economical and effective method to improve the early-stage strength that CSA should be mixed by 8$\%$ compared to the fly ash amount used

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.52-57
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• 2009

The effect of aging treatment on the microstructure and mechanical properties of super duplex stainless steel with W was investigated. The phase was precipitated mainly at the early stage of aging and a lower aging temperature under $750^{\circ}C$, but the phase was formed after long-term aging treatment between $600^{\circ}C$ and $900^{\circ}C$. The volume fraction of the phase increased with aging temperature up to $750^{\circ}C$ and then decreased up to $900^{\circ}C$. With an increase in the aging time, the volume fraction phase at the early stage of aging increased slightly, and then increased rapidly beyond a certain time. The rapid increase in the tensile strength and hardness and decrease in the elongation and impact toughness were measured with aging temperatures up to $750^{\circ}C$. On the other hand, the tensile strength and hardness decreased slightly, and the elongation and Charpy impact toughness were unchanged with aging temperatures over $750^{\circ}C$. The tensile strength and hardness increased rapidly at the early stage of aging, and then increased slowly beyond a certain time. The elongation and Charpy impact toughness decreased rapidly at the early stage of aging, and then remained unchanged beyond a certain time. The phase that formed at the early stage of aging and the lower aging temperature had a considerable effect on the elongation and Charpy impact toughness of the super duplex stainless steel with W.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.1-7
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• 2003

In this study, CT specimens were prepared from spring steel(SPS5) processed shot peening. The fatigue crack growth tests were carried out in the environment of the room temperature md low temperature at $25^{\circ}C$, $-30^{\circ}C$, $-50^{\circ}C$, $-70^{\circ}C$ $-100^{\circ}C$ and $-150^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth (Region II) were decreased in proportion to descend temperature. It was shown that the fatigue resistance characteristics and fracture strength at low temperature are considerable higher than those of mom temperature in the early stage and stable of fatigue crack growth region.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.175-181
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• 2009

In this research, experiments were conducted to find out whether polycarboxylate could be used as a crude steel admixture for practical work, depending on the change in the replacement level of the compound mixed into polycarboxylate. Its fluidity was satisfactory, its airspace was a bit smaller than the KS standard, and its unit volume weight was proven to meet the standard. The amount of bleeding was smallest in B2, and in terms of the solidification time, the first and the last solidification was faster in A1, B1, and C1. With regard to the compressive strength in early days as acharacteristic of hardened concrete, all addition rates of 7-day C2 displayed the highest strength value, among which the addition rate of 1.3% had the biggest strength performance tendency. The seal strength also showed the strength performance rate which was about one tenth as big as that of the compressive strength. The length change rate resulting from dryness and contraction was proven to be good, and once the appropriate AE air entraining agent is used, it is evaluated to be a very useful and practical compound out in the field.

• Applied Microscopy
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• v.43 no.4
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• pp.155-163
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• 2013

Meta-kaolin (MK) and blast furnace slag (BS) were used as raw materials with NaOH and sodium silicate as alkali activators for making geo-polymers. The compressive strength with respect to the various pre-curing conditions was investigated. In order to improve the recycling rate of BS while still obtaining high compressive strength of the geo-polymers, it was necessary to provide additional CaO to the MK by adding BS. The specimens containing greater amounts of BS can be applied to fields that require high initial compressive strength. Alkali activator(s) are inevitably required to make geo-polymers useful. High temperature pre-curing plays an important role in improving compressive strength in geo-polymers at the early stage of curing. On the other hand, long-term curing produced little to no positive effects and may have even worsened the compressive strength of the geo-polymers because of micro-structural defects through volume expansion by high temperature pre-curing. Therefore, a pre-curing process at a medium range temperature of $50^{\circ}C$ is recommended because a continuous increase in compressive strength during the entire curing period as well as good compressive strength at the early stages can be obtained.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.628-631
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• 2004

In this paper, mechanical properties of concrete incorporating CKD are discussed with W/B and fluidity. For setting properties, an increase in W/B retarded setting time greatly in $5^{\circ}C$, while accelerated in $20^{\circ}C$. For fluidity, an increase in slump delayed the setting time with dosage of SP agent. The presence of CKD has little influence on setting time compared with plain concrete. For compressive strength, an increase in maturity enhanced compressive strength. Fluidity had no relation to compressive strength. At low curing temperature, concrete with CKD has slight strength loss compared with plain concrete. However, remarkable strength loss at low curing temperature in early stage was not found, which can be applicable to low temperature environment concrete placing.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.575-580
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• 2012

Geopolymers were synthesized using raw materials produced from two different areas: one was from Indonesia and the other was from Habcheon, Korea. The constituting phases of the Indonesian raw material were quartz and kaolinite, while those of the Habcheon sample were quartz, halloysite and albite. They were both calcined at $750^{\circ}C$ for 6 hours, and solution of NaOH and water glass was added to activate the geopolymeric reaction. The compressive strength of geopolymer synthesized from the Indonesian raw material showed a low value of $151\;kgf/cm^2$ after curing for 28 days. However, it could be greatly increased by adding blast furnace slag powders of $1188\;kgf/cm^2$ and $1969\;kgf/cm^2$ at 20 wt% and 40 wt% additions, respectively. The compressive strength of the geopolymer synthesized from the Habcheon raw material was high, at $557\;kgf/cm^2$, after 28 days, and the very high early-stage (3 days) strength of $556\;kgf/cm^2$ for this sample was remarkable. Commercially available Habcheon metastate raw material, of which composition showed low CaO and $Na_2O$ contents compared to the calcined Habcheon raw material, was also examined. It was found that the compressive strength of the commercial metastate type was nearly identical to that of the calcined Habcheon raw material except for the relatively low value at an early curing stage and at a high curing temperature of $60^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.6
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• pp.614-620
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• 2009

A fuel tank of a vehicle is an important part due to its flammable contents ant its importance during crash conditions. Therefore, the fuel tank's design should be assessed for durability and robustness to ensure safety during the early development phase. Previously, evaluation for the durability was done by testing in physical driving conditions which could only be done after the completion of the vehicle. Computation simulation is a more effective method to evaluate the strength and durability of the fuel tank during the early stage. In this paper, two outstanding computational simulation methods are studied. One evaluates PV cycle fatigue due to build up pressure in the fuel tank and the other evaluates the PSD vibration fatigue from modal characteristics. The results show that computational methods agree with physical tests and are thus suitable to analyze the strength and durability of the fuel tank at early development phase.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.83-90
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• 2004

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature and low temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, $-30^{\circ}C$, $-50^{\circ}C$, $-70^{\circ}C$,$-100^{\circ}C$, and $-150^{\circ}C$, in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I)was increased but stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to decrease temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerably higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.106-111
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• 2003

This study made an experiment On fatigue crack propagation da/dn, stress intensity factor range ${\Delta}K$ respectively in room temperature and in low temperature. And we got the following characteristics from fatigue crack growth test carried Out in the environment of room temperature and law temperature at $25^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, and $-100^{\circ}C$ in the range of stress ratio of 0.3 by means of opening made displacement. The threshold stress intensity factor range ${\Delta}Kth$ in the early stage of fatigue crack growth (Mode I) and stress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Made II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at law temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.