• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.425-428
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• 2006

In order to estimate the reduction of laodbearing capacity, followed by the attributive change of heat while high strength concrete structure is revealed on fire it is necessary to evaluate, it is necessary to evaluate the property of material under high temperature such as thermal conductivity, specific heat, compressive strength, modulus of rigidity and diminution figure. Therefore, this study is for the purpose of presenting evaluation data for the analysis of thermal behavior about the high strength concrete material under high temperature, through the experiment by manufacturing concrete(40, 50, 60, 80, 100 MPa) commonly used in the construction field. As a result of the study, in the case of physical attribute, it demonstrates a greater fluctuation of change than the one of 30 MPa concrete. In case of specific heat, the high strength concrete, shown the serious diminution between $500{\sim}600^{\circ}C$, presents the thermal change area corresponding to the change of high strength concrete. In compressive strength, regardless of intensity of concrete, all of them show the first intensity loss between normal temperature and $100^{\circ}C$, the dramatic loss beyond $400^{\circ}C$. The concrete weighing above 50 MPa shows a twice lower dramatic intensity loss than the one weighing $30{\sim}40MPa$. The concrete ranging from $60{\sim}80MPa$, shows the biggest diminution of modulus of elasticity under $400^{\circ}C$, which implies the structural unstability of temperature.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.51-57
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• 2018

The objective of the present study is to examine the feasibility on the development of high-insulation concrete using aerogels with hydrophilic surface treatment. To prevent the segregation and enhance the dispersibility of agerogels in the cement pastes, the substrate of aerogels was modified to be hydrophobic property using surfactant. The modified aerogels were added from 0% to 100% of the cement volume at the interval of 25% under the constant cement content. Some cement pastes showed segregation phenomenon and flocculation of aerogels during mixing phase. The addition of aerogels decreased the compressive strength of cement pastes but enhanced the thermal conductivity. The thermal conductivity of pastes with 100% aerogels was lower by 43% when compared with that measured in the conventional paste. To improve the compressive strength and insulation capacity of concrete containing aerogels, a reliable surface treatment method of aerogels needs to be further investigated.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.268-273
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• 2016

To improve mechanical strength of carbon foams, the carbon black (CB) added carbon foams were fabricated by impregnating different contents of carbon black (CB) and mesophase pitch using polyvinyl alcohol (PVA) solution into polyurethane foam and being followed by heat treatment. The cell wall-thicknesses of carbon foams were controlled by adding amounts of CB, and it was confirmed that the compressive strength of carbon foams was increased as increasing cell wall-thickness. The compressive strength had the highest value of $0.22{\pm}0.05MPa$ with the highest bulk density of $0.44g/cm^3$ when adding 5 wt% CB in carbon foam. However, the thermal conductivity was decreased by adding CB in carbon foam. The results indicated that the thermal conductivities of carbon foams were reduced by increased interlayer spacing ($d_{002}$) with the addition of CB in carbon foams.

• Journal of the Korean GEO-environmental Society
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• v.13 no.8
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• pp.45-55
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• 2012

This study is about the application of waste stone sludge as fill material. Waste stone sludge, weathered granite soil, and the mixture of the former and the latter strengthened with staple fiber are experimentally analyzed for measuring strength property. When staple fiber was mixed with waste stone sludge, weathered granite soil, and the mixture, there was a nearly linear relationship between the amount of the staple fiber and the increasing ratio of unconfined compressive strength. The increasing ratio of unconfined compressive strength was the largest in weathered granite soil. The increasing ratio of unconfined compressive strength of the mixture was similar to that of waste stone sludge. In the case of the mixture of weathered granite soil and waste stone sludge, an internal friction angle tended to increases rely on increasement of staple fiber content, whereas the change of cohesion was small. An internal friction angle was increased by 21 percent when staple fiber content is 0.75 percent. Comparing with weathered granite soil or waste stone sludge, strength parameters of the mixture were increased relatively. Thus strengthening effect of staple fiber in the mixture is expected.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.313-318
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• 2003

The development of new materials with light weight and high strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress(in this thesis). The compressive residual stress was imposed on the surface according to each shot velocity(57, 70, 83, 96 m/sec) based on Shot-peening, which is the method of improving fatigue lift: and strength. By using the methods mentioned above, I arrived at the following conclusions 1. The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. And in stage I, ${\Delta}K_{th}$, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts unlike the Un-peened material. Also m, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than that of the Un-peened material. That is concluded from effect of da/dN. 2. Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.518-521
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• 2005

We performed the mechanical test for obtaining properties of femoral head. Tested sample was male and 35 years old. We measured bone mineral density by dual X-ray absorption method(DEXA). Results of DEXA, he has normal condition of bone density. His BMD $1.159g/cm^2$ and T-Score is 1.6. Tested femurs were harvested by surgical method from donated cadaver. We made 9 specimens in femoral head, 8 specimens in neck used by diamond core drill. Then we performed compressive test in saline solution at $38^{\circ}C$. We obtained results that elastic modulus of femoral head was 0.439GPa, neck was 0.459GPa. Compressive strength of femoral head was 7.441 MPa, neck was 7.095MPa. There was no significant difference of mechanical properties between left and right femoral head & neck. Invested local properties of femoral head have more strength superior and anterior side, femoral neck has more strength in superior and inferior side but other side except for superior has more weakness along the lateral side.

• Fire Science and Engineering
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• v.18 no.1
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• pp.31-36
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• 2004

The purpose of this study is to present data for the reusing, rehabilitation and estimation of safety of RC structure damaged by fire, and for the prevention of explosive spatting by investigation the properties of explosive spalling, compressive strength and ultrasonic pulse velocity according to kinds of fine aggregate, admixture and water-cement ratios. In explosive spalling properties with kinds of aggregate, explosive spalling does not appear or little at surface in the case of used sea sand, but the case of using recycled sand or crushed sand is worse and worse. Property with the kind of admixture does not appear specially. And high strength concrete with W/C 30.5% was taken spalling, but 55% does not appear. It is found that residual compressive strength after exposed at high temperature showed 45％ in W/C 55%, and 64％ in W/C 30.5％ of its original strength averagely. Ultrasonic pulse velocity is different with kinds of aggregate. W/C. and heating time. When 3 month age after heating ultrasonic pulse velocity is recovered abut 1.3％～8.4％ of its 1 month age after heating.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.143-150
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• 2022

Geopolymers were made by mixing IGCC slag and aluminum smelted waste and their properties were compared with those of IGCC slag based geopolymers. When two raw materials were mixed, the highest compressive strength was obtained at 1.78 of Si/Al ratio. Because the change in compressive strength and density was not so sensitive by the change in Si/Al ratio; that is, the permissible range of Si/Al ratio mixing ratio is broad, it was speculated this broad permissible range would be advantageous for commercialization. The Compressive strength of geopolymers including red mud was higher than that of IGCC based ones and the safety was confirmed by TCLP test. Therefore, it was concluded that the making geopolymers by mixing red mud not only enhances the properties of geopolymers but also gives a recyclability as safe construction materials.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.115-124
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• 2022

Porous basalt aggregate is commonly used in roadbed engineering, but its application in concrete has rarely been studied. This paper studies the application of porous basalt in concrete. Porous basalt aggregate is assessed for its effects on mechanical strength and durability of prepared C50 concrete; because it has a hole structure, porous basalt aggregate is known for its porosity, and porous basalt aggregates can be made full of water through changing the content of saturated basalt; after full-water condition is achieved in porous basalt aggregate mixture of C50 concrete, we discuss its mechanical properties and durability. The effects of C50 concrete prepared with basalt aggregate on the compressive strength, water absorption, and electric flux of concrete specimens of different ages were studied through experiments, and the effects of different replacement rates of saturated porous basalt aggregate on the properties of concrete were also studied. The results show that porous basalt aggregate can be prepared as C50 concrete. For early saturated porous basalt aggregate concrete, its compressive strength decreases with the increase of the replacement rate of saturated aggregate; this occurs up to concrete curing at 28 d, when the replacement rate of saturated basalt aggregate is greater than or equal to 40 %. The compressive strength of concrete increases with the increase of the replacement rate of saturated aggregate. The 28 d electric flux decreases with the increase of the replacement rate of saturated aggregate, indicating that saturated porous basalt aggregate can improve the chloride ion permeability resistance of concrete in later stages.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.421-434
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• 2022

In the present study, reference samples were prepared using ore preparation facility tailings taken from the copper mine (Kure, Kastamonu), Portland cement (PC) in certain proportions (3 wt%, 5 wt%, 7 wt%, 9wt% and 11 wt%), and water. Then natural zeolite taken from the Bigadic Region was mixed in certain proportions (10 wt%, 20 wt%, 30 wt% and 40 wt%) for each cement ratio, instead of the PC, to prepare zeolite-substituted CPB samples. Thus, the effect of using Zeolite instead of PC on CPB's strength was investigated. The obtained CPB samples were kept in the curing cabinet at a temperature of 25℃ and at least 80% humidity, and they were subjected to the Uniaxial Compressive Strength (UCS) test at the end of the curing periods of 3, 7, 14, 28, 56, and 90 days. Except for the 3 wt% cement ratio, zeolite substitution was observed to increase the compressive strength in all mixtures. Also, the liquefaction risk limit for paste backfill was achieved for all mixtures, and the desired strength limit value (0.7 MPa) was achieved for all mixtures with 28 days of curing time and 7 wt%, 9 wt%, 11 wt% cement ratios and 5% cement - 10% zeolite substituted mixture. Moreover, the limit value (4 MPa) required for use as roof support was obtained only for mixtures with 11% cement - 10% and 20% zeolite content. Generally, zeolite substitution seems to be more effective in early strength (up to 28th day). It has been determined that the long-term strength losses of zeolite-substituted paste backfill mixtures were caused by the reaction of sulfate and hydration products to form secondary gypsum, ettringite, and iron sulfate.