• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.35-38
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• 1993

Although bonding material content of the high strength flowing concrete is very important in engineering properties, in rich mix concrete increasing the bonding material content may not follow more good properties. This study is to investigate the influence of the bonding material content affecting on the engineering properties of high strength flowing concrete, and this paper is to analyze the properties of hardened concrete. The results reveal that the strength of concrete having loss bonding material content is higher than that of concrete having more bonding material content, and that in proportion to increasing of concrete strength brittleness factors decrease, and that the static modulus of elasticity in this study is less than that in specification.

• Fire Science and Engineering
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• v.12 no.4
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• pp.31-40
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• 1998

Very often, whether accidentally or intentionally set fire, according as building are elevated, varied or complicated day by day. It is of primary importance that we have a treatment of fire damaged structure. In general, strength and elasticity modulus of heated concrete are reduced. Product background of cement, sand and coarse aggregate differ from country to country, so that thermal behaviour of concrete make a difference in high temperature. To cope with demand, this paper is a study on relation to microstructure and strength reduction. In consequence of experiments, concrete exposed to high temperature are estimating the reduction of mechanical properties in comparison with microstructure characteristics which are abtained from the SEM/EDX, XRD and DSC-TG analysis of heated specimens under various temperature.

• Steel and Composite Structures
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• v.21 no.4
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• pp.755-773
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• 2016

In the present paper, a new high-order simple-input analytical method is used to study thick laminated composite straight tubes subjected to combined axial force, torque and bending moment. The most general displacement field of elasticity for an arbitrary laminated composite straight tube is obtained to analytically calculate stresses under combined loadings based on a layerwise method. The accuracy of the proposed method is subsequently verified by comparing the numerical results obtained using the proposed method with finite element method (FEM) and experimental data. The results show good corresponded. The proposed method provides advantages in terms of computational time compared to FEM.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.416-421
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• 1997

This study was conducted to evaluate durability of high-strength light-weight aggregate concretes which are increasingly demanded recently. Two different artificial light-weight aggregates were used and two levels of high-strength concretes were made using w/c of 33% and 37% for target strength of 500kg/$\textrm{cm}^2$ and 400kg/$\textrm{cm}^2$, respectively. Cylinder specimens($\phi$=10cm and h=20cm) were made and treated with freezing-and-thawing(F/T) cycle at $-18^{\cire}C$ and $4^{\cire}C$. Dynamic modulus of elasticity and surface condition were evaluated with F/T cycle increase. The results showed that durability of the light-weight aggregate concretes was worse than that of conventional concrete, and the light-weight high-strength concrete with w/c=37% had the better durability than the one with w/c=33%.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.265-268
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• 2005

Thermoplastic elastormer (TPE) has many advantages such as high flexibility, high elasticity and high elongation, etc. TPE is easily molded such as plastic materials, therefore, many TPE parts are applied as home appliances and mechanical parts. However, if TPE is once molded, its mechanical properties are changed by injection molding conditions such as melt temperature, mold temperature, injection pressure and holding pressure, etc. In this study, the influences of the injection molding condition on the mechanical properties of thermoplastic vulcanizates(TPVs), which is one of the TPE, were investigated. By the injection molding experiment, as increasing the melt temperature, the tensile strength, shrinkage and hardness decreased. By the scanning electron microscope (SEM) analyzing the TPVs' crystallization, the morphology was affected by the melt temperature.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.59-67
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• 1998

The object of this study is to investigate the strength characteristics and the freeze-thaw resistance of high strength concrete incorporating fine blast furnace slag. Major experimental variables were the water/cement ratio, maximum size of coarse aggregate, and cement types such as ordinary portland and slag cement. The results were as follows ; The workability of fresh concrete incorporating fine blast furnace slag was better than that of OPC(ordinary Portland cement) in terms of slump. The freeze-thaw resistance showed better than that of OPC, keeping more than 90% of relative modules of elasticity after 506 cycles and showing only a hair crack at surface without serious damage. Thus, the fine blast furnace slag might be recycled at concrete to make high strength concrete at fields.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.2
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• pp.59-66
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• 2004

This study was performed to evaluate the freezing and thawing properties of the high strength concrete using recycled coarse aggregate. The recycled coarse aggregate replaced natural crushed aggregate by 0%, 25%, 50%, 75% and 100%. The compressive strength of the concrete using recycled coarse aggregate showed more than 300 kgf/$cm^2$ at the curing age 28 days. The mass loss ratio by freezing and thawing was less than 1% at all mix type. The relative dynamic modulus of elasticity was decreased with increasing the freezing and thawing cycles. Also, the durability factor by the freezing and thawing was decreased with increasing the content of recycled coarse aggregate. But, the recycled concrete except 100% recycled coarse aggregate showed 60 or more durability factor in the freezing and thawing 300 cycles. Accordingly, these recycled coarse aggregate can be used for high strength concrete.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.11
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• pp.1050-1054
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• 2006

There have been intensive and continuous efforts in the field of DLC coating process because of their feature, like high hardness, high elasticity, abrasion resistance and chemical stability and have been applied widely the industrial areas. In this research, optimal grinding condition was investigated using Microlens Process Machine for the development of aspheric glass lens which is to be used for mobile phone module with 3 mega pixel and 2.5X optical zoom, and tungsten carbide(WC) mold cote was manufactured using high performance ultra precision machining and the effects of DLC coating on the form accuracy(PV) and surface roughness(Ra) of WC mold core was evaluated.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.315-325
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• 2017

The purpose of the paper is to determine the influence of two widely used steel fibers and polypropylene fibers on the sulphate crystallization resistance, freeze-thaw resistance and surface wettability of ultra-high performance concrete (UHPC). Tests were carried out on cubes and cylinders of plain UHPC and fiber reinforced UHPC with varying contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Extensive data from the salt resistance test, frost resistance test, dynamic modulus of elasticity test before and after freezing-thawing, as well as the contact angle test were recorded and analyzed. Fiber hybridization relatively increased the resistance to salt crystallization and freeze-thaw resistance of UHPC in comparison with a single type of fiber in UHPC at the same fiber volume fraction. The experimental results indicate that hybrid fibers can significantly improve the adhesion properties and reduce the wettability of the UHPC surface.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.65-67
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• 2011

This research analyzed the mechanical properties of high strength concrete produced by limestone aggregate, and summarized the result as follows: Due to the property of unhardened concrete, slump flow value increased more or less according to the increase in LG replacement, but didn't show a big difference while clear tendency of air content couldn't be found. Due to the property of hardened concrete, there appeared an increase in the rate of compressive strength the more LG replacement increased, and the modulus of elasticity also showed a tendency similar to the increase rate of compressive strength.