• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.256-261
• /
• 1995

Large-scaling recycling of demolished concrete will concrete will contribute not only to the solution of a growing waste disposal problem, it will also help to consweve natural resoures of sand and gravel and to secure future supply of reasonly priced aggregates for building and other construction purposes within large urban areas. Because recycled aggregate particles consits of substantial amount of relatively soft cement paste component, it is less resistant to mechanical actions. With this view in mind, to obtain a reference data for the development of recycling system and to a basic data the guiedline of recycled aggregate concrete construction and engineering properties of recycled aggregate concrete according to the factors, such as blending ratio of recyced aggregete with the natural aggregate, addition to the factors, such as blending ratio of recycled aggregete with the natural aggregate, addition of flyash, water coment ratio.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.455-456
• /
• 2010

For efficient quality control of cast-in-place concrete used in a large scaled construction field above 5,000 families, we completed the B/P test at 35 remicon plants with equal mixture design and investigated various properties such as fresh and hardened.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.47-51
• /
• 1997

The high speed machining which can improve the production and quality in machining has been adopted remarkably in dietmold industry. As the speed of machine tool spindle increases, the machinability evaluation and monitoring of high speed machining is necessary. In this study, the machinability of 30, 000rpm class spindle was evaluated by using the developed tool dynamometer and the machining properties of high hardened and toughness materials in high speed were examined. Finally, the in-process monitoring technologies of tool wear were presented through the prediction by the experimental formula and pattern recognition by the neural network.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.13 no.5
• /
• pp.67-74
• /
• 2004

Laser heat treatment is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching action to occur and the formation of matrensitic structure. In this investigation, the microstructrual features occurring in Nd:YAG laser hardening SM45C and $STD_11$ steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimisation of the processing parameters for maximum hardened depth of SM45C and $STD_11$ steel specimens of 10mm thickness by using CW:YAG laser.

• Journal of the Korean Society for Heat Treatment
• /
• v.9 no.2
• /
• pp.91-102
• /
• 1996

Microstructural control to produce multiphase structure has received much attention to improve the high temperature strength as well as low temperature ductility of intermetallics. Transmission electron microscopic investigation has been carried out concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 to 8 mol% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates took place homogeneously in the NiAl matrix and the alloys hardened appreciably. Selected area electron diffraction (SAED) patterns have not revealed any additional extra-spots during aging, because the Cr-particles show cube-cube orientation relationship and keep a perfect coherency with the ordered matrix lattice. Dislocations were confirmed to bypass the particles during deformation. Although the dispersion of Cr-particles increased the yield strength of NiAl at intermediate temperature, the strength decreased appreciably at higher temperatures.

• Transactions of Materials Processing
• /
• v.18 no.4
• /
• pp.304-309
• /
• 2009

Quenchable boron steel is a new type of high strength steel to reduce the weight of automobiles and maintain the safety conditions. Quenchable blanks can be hot-stamped and hardened in a water-cooled tool to achieve high strength. In this paper, new alloy for hot stamping is designed based on requirement of mechanical properties and two types of surface coating are investigated in viewpoints of oxidization and exfoliation. An automotive part of center pillar is manufactured by hot-stamping using Al-Si coated sheet. The performance of developed part is compared by static compression test and side impact crash test.

• Proceedings of the KWS Conference
• /
• 2004.05a
• /
• pp.203-205
• /
• 2004

Welding sometimes should be done inside-hull after launching. The opposite side is contacted sea-water In this case, it should be a concern that the cooling rate expected very rapid may deteriorate microstructures, and hence these microstructures are hardened, cracking happens, or toughness would be impaired. Therefore, a test program simulating the situation has been planned and welded using the ship class materials (AH32, EH36) with the related welding consumables (E71Tl-1, E81Tl-K2) and then carried out to investigate the effect of cooling rate on weldments quality. Based on the test results, it could be concluded that the welds of which the opposite side of arc is exposed to wet or flowing water are not affected by rapid cooling.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.04a
• /
• pp.700-703
• /
• 2000

With respect to durability, the impotance of carbonation lies in the fact that it reduces the pH on the pore water in hardened concrete. However, the carbonation velocity is effected by the water/cement ratio, materials, unit cement weight, porosity, kinds of finishing materials, accuracy of constructing, environmental factors and so on. And the air permeability is closely related to the carbonation velocity because it represents the properties of concrete. This paper presents an experimental investigation on the carbonation effected by air permeability n mortar and concrete. As a result, it was found that the carbonation velocity of concrete is faster than that of mortar and it is possible to predict the carbonation velocity using air permeability.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.10a
• /
• pp.190-195
• /
• 1997

The purpose of this study was to use daily waste incinerated ash, which was reclaimed worthlessly, as substitutes of fine aggregates in concrete. Various kinds of admixture was utilized to strengthen the cement mortar mixed with waste incinerated ash, and altered the curing condition to diminish the rate of expansion. By the results of this experiment, it was possible to produce the lightweight concrete, charactered with the gravity below 1.5 and over 160kg/$\textrm{cm}^2$ compressive strength by replacing all fine aggregates with waste incinerated ash. It was also observed that the low temperature curing condition, lessoned gas exhausts, was effective to increase the strength of cement mortar.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.339-342
• /
• 2003

This study is intended to investigate the influence of chemical admixture on bleeding of concrete. According to the results, the amount of bleeding with elapse of time does not make much difference in the case of naphthalene type water reducing agent(RN), Naphthalene type high performance water reducing agent(HN) and Melamine type high performance water reducing agent(HM), but it is largest in the case of Polycarbonic acid type high performance water reducing agent(HP). Bleeding speed also is highest in the case of HP in comparison with other chemical admixture. This prove that high performance water reducing agent like HP has little effect on fluidity of concrete, but influences the amount of bleeding more greatly, instead. As properties of hardened concrete, compressive strength makes no difference in the case of RN, HN and HM, but on the other hand, it increases in the case of HP due to a decrease of air content and the large amount of bleeding.