• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1507-1512
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• 1994

High strength cement hardened body was prepared by ordinary portland cement, silica-fume, super-plasticizer and the industrial by-product powder such as tailing, paper sludge ash and granulated slag. These raw materials were mixed and formed with w/c=0.18. The cement hardened body is cured in the autoclave at 18$0^{\circ}C$, 10atm. These admixtures made the compressive strength of all specimens develope by 170~230%. The highest compressive strength could be obtained by 236 MPa when mix composition was 14 wt% of silica-fume and 26 wt% of granulated slag. The compressive strength increased with decreasing the average pore size and the amount of the poe over the size of 50 nm by which the appearance of high compressive strength of the cement hardened body were mainly influenced. In the result, the hydration products were C-S-H, tobermorite and ettringite and it was realized that the reason why the cement hardened body became dense and revealed the higher strength was that those hydrates were formed inside of the pore and filled in it and the unhydrated materials played the role of an inner-filler.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.2
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• pp.66-73
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• 2022

Partial-hardened hot stamping has been well known to be very effective to absorb more energy in automotive lateral crash. Hardness distribution and dimensional change after partial-hardened hot stamping have been studied to find out effect of thermal deformation of the heated hot stamping die on dimensional accuracy of automotive center pillar. Soft zone of commercial center pillar showed 275~345 in Vickers hardness, indicating bigger non-uniformity which resulted from thermal deformation of heated die. Dimensional changes in soft zone of the commercial center pillar measured by three dimensional scanner were much bigger than that in hard zone. It has been found that hot stamping die compensation considering thermal deformation in soft zone causes a significant decrease in hardness deviation in the soft zone, corresponding to 20 percent of commercial center pillar and subsequently leads to much higher dimensional accuracy.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.734-738
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• 2008

Ettringite$(3CaO{\cdot}Al_2O_3{\cdot}3CaSO_4{\cdot}32H_2O)$, one of the hydrated phase of Portland cement is usually formed in the early stage of hydration by the reaction of tricalciumaluminate$(C_3A)$ and gypsum. The rapid and strong crystal growth of separated rod-shaped ettringite have been utilized for the preparation of special cements of rapid setting, high strength and non-shrinking properties. The ettringite also has been noticed as a promising materials for the immobilization of various waste ions because of its unique crystal structure which has abundant channels and exchangeable ionic compounds. In this study, the formation and growth behavior of the ettringite was investigated in the system $C_3A-CaSO_4-H_2O$ using $C_3A$ clinker and gypsum to obtain a microporous body for waste ion immobilization. Ettringite was revealed to form by the dissolution-precipitation mechanism and the bulk body was by the entangled growth of rod-shaped ettringite crystals. The hardened body was composed of nearly pure rod-shaped ettringite interlocked each other with adequate mechanical strength. The homogeneity of structure, pore size, specific surface area and porosity of the hardened body were influenced by reaction temperature, water/powder ratio and the curing time. The hardened body prepared with water/powder ratio of 1 at $24^{\circ}C$ for one day showed excellent morphological properties for the purposed materials.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.123-124
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• 2021

Recently, the danger of fine dust has emerged worldwide. In general, fine dust refers to particulate matter less than 10㎛ and ultrafine dust less than 2.5㎛, and according to the announcement by HEI (Health Impact Research Institute) in 2015, the concentration of ultrafine dust in Korea is the second highest among OECD member countries. It was investigated. In this study, an experiment was conducted to analyze how the diatomaceous earth substitution rate affects the strength characteristics of the permeable block. As the replacement rate of diatomaceous earth increased, the strength decreased. The reason why the strength decreases with the use of diatomaceous earth is that the strength of the hardened body decreases as the structure of the hardened body becomes less dense as the amount of diatomaceous earth increases, and the reason that the strength decreases as the replacement rate of diatomaceous earth increases is the reason for the absorption performance of diatomaceous earth. Therefore, it is judged that a void was generated inside the hardened body while water was absorbed and then evaporated or discharged in the matrix, and accordingly, the strength decreased.

• Journal of the Korean Ceramic Society
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• v.36 no.12
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• pp.1342-1349
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• 1999

In order to improve the density and the mechanical strength without change in chemical composition the hardened pastes of hydroxyapatite cement were reinforced with powders and/or whiskers of hydroxyapatite. The powders behaved as a seed of hydroxyapatite formation rather than a filler while the whiskers were mrerly dispersed in matrix and capillary pores of the hardened bodies leading to increase in mechanical strength. But the increase in strength But the increase in strength was nnt enough owing to the lack of homogeneous dispersion of the fibers. The highest diametral tensile strength of 18.5 MPa was measured at the hardened hydroxyapatite body in which well-dispersed whisker phase formed uniformly during hydro-thermal curing of power-added and dry-formed hydroxyapatite cement.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.873-874
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• 2006

PCBN tools are used worldwide for machining of hardened steel parts in automotive industries. But in heavy interrupted cutting of hardened steel, the tool life is not so stable by sudden breakage of the cutting edge, and total cost of cutting by PCBN is not so economical compared to the grinding. To solve this problem, new PCBN has been developed. New PCBN has very fine and homogeneous microstructure to increase the toughness of sintered body that it provides a reliable tool life for heavy interrupted cutting.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.44-51
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• 2012

In this study, hardened loess bodies, which did not compose of cement or any chemical binder, were made and tested to evaluate the physical properties such as slump, air content, and compressive strength. Addition of a natural binding material to mixture of loess and lime showed better performance in physical properties. However a lime among natural binding materials is considered as a superior binder to improve the properties of the hardened bodies. According to the experimental results, mixing proportion with 45% of W/B ratio, $285kg/m^3$ of water content, and 60% lime substitution ratio was recommended to acquire the good performance of physical properties for the hardened loess bodies.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.41-42
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• 2023

Test results for a total of four types of complex waterproofing methods were analyzed. In the case of the A method, the stress generated by high-viscosity compounds adhering to the base test body during the behavior of the test body was transferred to the sheet surface layer. In the case of the B method and the C method, the properties of the waterproof sheet consisting of a non-hardened seal based and a non-hardened seal are well reflected and stress absorption in the non-hardened seal layer acts strongly, rapidly reducing stress transfer to the surface of the waterproof sheet. In the case of the D method, slip occurs due to repeated behavior, and the stress on the attachment surface is reduced, and the stress transfer to the surface is greatly reduced. As a result, four types of composite waterproofing methods resulted in changing the stress transfer mechanism caused by behavior on the concrete surface due to the physical properties of the internal constituent material of the waterproof sheet.

• Journal of the Korean Ceramic Society
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• v.32 no.8
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• pp.873-880
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• 1995

In order to prepare the modified belite (C2S-C4A3S-C4AF-CS) cement with low energy, clinkers were synthesized by converter slag, limestone, gypsum and clay. The synthesized clinkers were characterized and the hydration processes were investigated by XRD, SEM and microconduction calorimetry. The hydrates were mainly C-S-H and ettringite. The needle-like ettringite formed by the hydration of C4A3S at the early stage of hydration was filled in the inner vacant spaces of the hardened body and it might contribute to the rapid-hardening phenomena. The hardened body became stronger due to the hydration of C2S at the later period. The compressive strengths of the cement-3 mortars hydrated for 3, 7 and 28 days were 115, 128 and 211 Kgf/$\textrm{cm}^2$, respectively.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.25.2-25.2
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• 2000