• Magazine of the Korea Concrete Institute
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• v.7 no.4
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• pp.129-136
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• 1995

Thls research Includes est~mat~ons of the relat~on ktween the strength of concrete and the fracture energy for river sand concrete and crushed sand concrete using the wedge sphtting test method. Furthermore the fracture energy and the characteristic length of two types of concrete were compared and d~scussed. Fracture behaviors of crushed sand concrete and natural sand concrete had the similar trend in fracture characteristics. The fracture energy was increased with the increase of compressive strength in the strength range of 20-60MPa, but was not increased for the concrete more than 6OM.Pa of compressive strength.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.273-281
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• 2015

In this paper, the performance of alkali-activated slag cement (AASC) is assessed in terms of compressive strength and drying shrinkage, using three different types of silica sand and river sand. The sand type has an important influence on the properties of AASC mortar. Three silica sands (SS1, SS2 and SS3) and river sand (RS) were considered. Three series of blended sands have been tested. A first series (S1) with RS and SS1, a second series (S2) with RS and SS2 and third series (S3) with RS and SS3 with a different blended ratios. The result shows a very significant influence of the blended sand on the AASC mortar properties. The compressive strength and drying shrinkage related with the particle sizes and blended ratios of sands are investigated considering blended sand properties like fineness modulus (FM) and relative specific surface. The type and blended ratio of sand seems to have very significant and important consequences for the mix design of the AASC mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.178-184
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• 2017

This study was aimed to investigate the tensile behaviors of PE(Polyethylene) fiber-reinforced highly ductile cementitious composites with different combinations of micro silica sand and normal sand(river sand) with maximum particle size of 4.75 mm. Flow test result indicated the increase of flowability with higher replacement ratio of river sand. There was no noticeable difference in the mean compressive strength with different replacement ratio of river sand, but the variation in the compressive strength increased as higher amount of river sand was adopted for the replacement. The difference in the uniaxial tensile strength was negligible, but the tensile strain capacity was significantly influenced by the replacement ratio of river sand. It is thought that increased density of multiple cracks induced improved tensile strain capacity when higher percentage of river sand was adopted for fine aggregate. The deviation in the strain capacity increased as the replacement ratio of river sand was higher, as in the compressive strength. This study presented the feasibility of using normal sand instead of micro silica sand for highly ductile cementitious composites with equivalent or better uniaxial tensile performance, even though it might increase the deviation in the performance.

• Korean Journal of Agricultural Science
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• v.24 no.2
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• pp.194-206
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• 1997

This paper was performed to evaluate the properties of no-coarse lightweight concrete using perlite and expanded polystyrene bead on fine aggregate. The results were shown that w/c and unit weight was affected by absorption ratio and unit weight of using aggregate itself. The compressive strength of no-coarse lightweight concrete was showed $187kgf/cm^2$ by using natural sand, $170kgf/cm^2$ by using perlite. Tensile and bending strength were showed the same tendency of compressive strength, but when expanded polystyrene bead concrete dose not have strength nearly. The pulse velocity and static modulus of elasticity of no-coarse lightweight concrete were smaller than that of normal cement concrete. And stress-strain curves were shown that was increased with increase of stress, and when the stress-strain curve using expanded polystyrene bead was repeated at short intervals increase and decrease irregularly.

• The Journal of the Korean dental association
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• v.22 no.10 s.185
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• pp.855-860
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• 1984

국산 세치제와 잇솔이 갖추어야 할 기본요건과 개발방향이 제시된 세미나가 지난해에 이어, 지난 7월 14~15일 양일간에 걸쳐 속리산 관광호텔에서 구강보건학계와 럭키ㆍ부광ㆍ태평양등 국내 3대 세치제 제조회사의 52명이 참석한 가운데 서울치대 예방치학교실 주최로 개최되었다. 총 13개 연제가 발표된 이번 세미나에서는, 국민 복지를 빨리 증진시키기 위하여, 기업간의 건전한 경쟁을 유도하고, 기술개발을 촉진하며, 국산품의 품질 개선, 가격인하, 국제경쟁력의 신장등, 정부의 기본방향을 재확인하는 동시에 거시적이고 원시적인 안목으로 볼때 기술개발을 위한 산학활동과 선업간의 협력은 산업발전을 통하여 국민복지 증진에 분명히 기여할 수 있음을 강조한 서울치대 김종배교수의 주제 발표와 세치제의 주요작용, 세치제의 abrasiveness 및 polishing 효과와 용어의 정의, 개인에 적합한 세치제의 선택방법, Monofluorophosphate와 plaque 및 타액의 상호작용, 세치제의 선호변인 분석, 세치제 광고문안상의 문제점, 세치제의 전망, 세치제의 전망, 세치제 개발의 제요소, 세치제의 검정 기준과 과정, 잇솔의 기본요건과 시판잇솔의 규격, 잇솔의 강모형태와 탄력성에 관한 이론적 고찰, 개인에 적합한 강모강도를 가진 잇솔의 선택방법, 「A study on the F'ion concentration of commercial dentifrices」에 대해 폭넓고 진지한 토의가 있었다. 다음은 이날 발표된 내용을 요약정리한 것이다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.168-176
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• 2017

This study, as a research for using crushed sand as a fine aggregate of concrete for nuclear structures, we improved the performance of impact crusher in the existing crushed sand production process and adjusted grain size to conform to ASTM C 33 The shape and grain size characteristics of a crushed sand were examined and concrete was prepared according to the substitution ratio of the sand to investigate the properties of fresh concrete and hardened concrete. The experimental results show that most of the concrete characteristics are equivalent to those of concrete using only heavy sand. However, when the substitution rate of steel sand exceeds 50%, the amount of air, compressive strength and tensile strength are somewhat reduced.

• Journal of Korean society of Dental Hygiene
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• v.2 no.2
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• pp.159-173
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• 2002

The 180 toothbrushes out of 18 models( ten brushes for each model) were used for this examination among the toothbrushes for adults which were sold in the domestic markets. After three-month brushings through a roll ing method and Bass method were practiced with Toothbrush Stroke Tester which reproduced brushing methods outside the mouth, I investigated the morphology bristle tips of using scanning electron microscope(SEM). The conclusions are as follows. 1. Soft bristle toothbrushes(of 8 models out of 9 models) were badly damaged at the bristles end after 3 month toothbrushing. 2. Medium bristle toothbrushes(of four models out of five models) were irregularly worn at the bristles end after 3 month toothbrushing. 3. Hard bristle toothbrushes(of three models out of four models) were chisel-shapedly worn at the bristles end after 3 month toothbrushing. 4. Taper-shaped toothbrushes were very irregularly bent at the bristles end after 3 month toothbrushing. 5. It was examined in the bristle stiffness that soft bristle toothbrushes were found in 9 models(50.00%), medium bristle toothbrushes in 5 models(27.78%), and hard-bristle toothbrushes in 4 models(22.22%).

• Resources Recycling
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• v.10 no.2
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• pp.41-49
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• 2001

In this study, the properties of cement mortar and concrete using ceramic wastes as fine aggregates and coarse aggregates are considered experimentally. Flow value of mortar using ceramic waste as fine aggregates is increased more or less, and the com- pressive strength of mortar using ceramic wastes as fine aggregates is increased with elapsed age. The slump value of concrete using ceramic wastes fine aggregates and coarse aggregates is somewhat decreased. The compressive strength of concrete using ceramic wastes as fine aggregates and coarse aggregates is lower than that of OPC concrete in early age, but has gradually increased in long ages.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.459-467
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• 2006

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river as to grow construction demand and the low grade of nature sand like sea sand. Following, need is to diversify the supply sources of fine aggregates which are excessively relying on sea sand and urgency is to find as soon as possible aggregate resources that can substitute sea sand. On the other hand, various fine aggregates are utilized to produce concrete in the domestic construction fields. However, few studies have been systematically investigated on the effects of such fine aggregates on concrete properties. Therefore, this study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the quality of concrete through the analysis of the effects of such fine aggregates on the physical properties of fresh concrete and strength of hardened concrete. Results revealed that crushed sand degraded the fluidity and air entraining of concrete compared to natural aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting bad grain shape and grade was larger adverse effect on the physical properties of concrete. The type of fine aggregates appeared to have negligible influence on the strength for W/C of 55%, 45% while crushed sand decreased the strength for W/C of 35% compared to natural aggregates. It analyzed that the combination of crushed sand exhibiting bad grain shape and grade with natural aggregates improved the characteristics of fresh concrete and had negligible influence on the strength.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.83-87
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• 2002

종강도 위주의 일반 상선의 LMC 의 경우는 단지 선박을 l 차원 Beam Model 로 단순화하여 선미로부터 선수까지의 Weight Distribution 과 Buoyancy Distribution 을 계산하여 두 값의 차이를 Shear Force 로 계산하고 Shear Force 적분값을 Bending Moment 로 계산한다. 횡강도가 중요시되는 Barge 선의 경우 Global Transverse Strength 같은 경우에는 위의 식을 적용할 수 있으나 복수의 바지선을 Hinge Type 이 아닌 Fixed Type 으로 고정시켜 사용할 경우 각각의 Connector 에 작용하는 Strength 값이 횡강도의 큰 비중을 차지한다. 일반적인 Load Master Computer 의 경우 이와 같은 계산이 불가능하며 NAPA 와 같은 전용 계산 프로그램의 경우 하나의 Condition 을 계산하는데 소요되는 시간이 많아 실질적인 Monitoring 은 불가능하다. 이에 특수목적의 Load Master Computer(ShipManager-88) 를 제작하게 되었고 이 Program 을 이용하여 Loadout 과 Floatoff 의 Simulation 을 수행하고 Monitoring 하였다. ShipManager-88 은 Barge 선의 종강도 횡강도, Stability, Trim & Draft 등을 계산하며 Sequence 기능으로 실제 LOADOUT 과 FLOATOFF 시의 모의시뮬레이션을 수행해 볼 수 있으며 Online Interlace 제공으로 Tank 에 설치된 센서에서 Level 값을 받아 실시간으로 현재 선박의 상태를 정확하게 계산할 수 있다. 실제 LOADOUT and FLOATOFF 를 수행하면서 Check 한 부분은 종강도, 횡강모 Stability, Deform, Connector Strength, Level 등을 Check 하였고 종방향의 LOADOUT 이 불가능한 Project 를 위해 Transverse LOADOUT 을 이용할 계획이다.