• 레미콘
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• no.4 s.71
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• pp.44-56
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• 2002

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.3-9
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• 2013

In ultra high strength concrete, when electric arc furnace oxidizing slag is substituted for sea sand as fine aggregate, compressive strength was improved about 15 MPa. To figure out the cause of the improvement in compressive strength, this study considered the dissolution characteristics of Ca component in fine aggregate and examined the microstructure, porosity, microhardness, and Ca/Si mole ratio on the interface of fine aggregate and paste. And to examine the mechanism of strength improvement resulted from the shape of fine aggregate, this study measured the surface roughness of fine aggregate with AFM. According to the result of this experiment, the mechanisms of strength improvement in ultra high strength concrete resulted from the use of electric arc furnace oxidizing slag as fine aggregate can be divided into chemical and physical mechanisms. In the chemical mechanism, the soluble Ca component contained in electric arc furnace oxidizing slag is dissolved and forms a hydrate between fine aggregate and paste to improve the interlocking strength of fine aggregate-paste. Also, it makes the microstructure around the fine aggregate. And in the physical mechanism, electric arc furnace oxidizing slag has a twice greater surface roughness than sea sand, so the interlocking strength between fine aggregate and paste increases, which contributes to the development of compressive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.11-18
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• 1992

프리텐션방식 원심력 고강도콘크리트 말뚝(KS F4306) 콘크리트의 압축강도가 800kg/$\textrm{cm}^2$이상인 고강도콘크리트를 요구하고 있으나 국내에서는 500kg/$\textrm{cm}^2$ 이상의 콘크리트 말뚝제조가 불가한 실정이므로 본 연구에서는 고황산염시멘트를 이용한 고강도콘크리트 말뚝제조에 관한 공학적 특성 연구의 일환으로써 고황산염시멘트의 수화특성 및 고강도 발현기구 구명과 공학적 특성중에서 압축.휨강도의 내동해성, 건조수축 특성 및 화학저항성등을 비교 고찰하여 보통 시멘트보다 품질 특성이 우수함을 확인하였다. 또한 고강도 콘크리트 말뚝의 시제품 제조를 위하여 2개 공장에서 현장 실험한 결과 94.7kg/$\textrm{cm}^2$의 양호한고강도콘크리트를 얻었다. 향후 고강도콘크리트 말뚝 제조의 공업화 및 양산회가 기대된다.

• Magazine of the Korea Concrete Institute
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• v.5 no.1
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• pp.129-138
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• 1993

프리텐션 방식 원심력 고강도 콘크리트 말뚝[KS F 4306]제조에 관한 실험적 연구로써 고황산염시멘트를 이용한 800kg/$ extrm{cm}^2$이상의 고강도콘크리트 제조시 수화 특성검토와 콘크르트 조직내의 기공율과 압축강도간의 상관식을 도출하여 고강도 발현기구를 규명하였으며 콘크리트 압축 및 휨강도간의 상관식 유도와 내구성 측면에서의 내동해성, 건조수축, 화학저항성등을 보통 포틀랜드 시멘트와 비교 고찰한 결과, 고황상염시멘트의 내구성이 우수함을 확인하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.113-123
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcements and the ratio of shear rebars. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. The increase of plastic deformation after yielding transforms the shear transfer by arch action into by truss action. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The strain distribution model of shear reinforcements and flexural reinforcements based on test results is presented. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The flexural-shear failure mechanism determines the ultimate state of RC coupling beams. It is expected that this model can be applied to displacement-based design methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.407-419
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• 2006

Situations where support is provided solely in shaft resistance of drilled shafts are where the base of the drilled hole cannot be cleaned so that it is uncertain that any end bearing support will be developed. Alternatively, where sound bed rock underlies low strength overburden material, it may be possible to achieve the required support in end bearing on the rock only, and assume that no support is developed in the overburden. However, where the drilled shaft is drilled some depth into sound rock, a combination of side wall resistance and end bearing can be assumed. Both theoretical and field studies of the performance of rock socketed drilled shafts show that the major portion of applied load is usually carried in side wall resistance. Normal stress at the rock-concrete interface is induced by two mechanisms. First, application of a compressive load on the top of the pile results in elastic dilation of the concrete, and second, shear displacement at the rough surface of the drilled hole results in mechanical dilation of the interface. If the stiffness of the material surrounding the socket with respect to normal displacement is constant, then the normal stress will increase with increasing applied load, and there will be a corresponding increase in the shear strength. In this study, the numerical analyses are carried out to investigate the behavioral characteristics of side of rock socketed drilled shafts. The cause of non-linear head load-settlement relationship and failure mechanism at side are also investigated properly and the design charts are suggested and verified for the leading to greater efficiency and reliability in the pile design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.395-406
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• 2006

Drilled shafts are a common foundation solution for large concentrated loads. Such piles are generally constructed by drilling through softer soils into rock and the section of the shaft which is drilled through rock contributes most of the load bearing capacity. Drilled shafts derive their bearing capacity from both shaft and base resistance components. The length and diameter of the rock socket must be sufficient to carry the loads imposed on the pile safely without excessive settlements. The base resistance component can contribute significantly to the ultimate capacity of the pile. However, the shaft resistance is typically mobilized at considerably smaller pile movements than that of the base. In addition, the base response can be adversely affected by any debris that is left in the bottom of the socket. The reliability of base response therefore depends on the use of a construction and inspection technique which leaves the socket free of debris. This may be difficult and costly to achieve, particularly in deep sockets, which are often drilled under water or drilling slurry. As a consequence of these factors, shaft resistance generally dominates pile performance at working loads. The efforts to improve the prediction of drilled shaft performance are therefore primarily concerned with the complex mechanisms of shaft resistance development. The shaft resistance only is concerned in this study. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by the construction practices. In this study, the influences of asperity characteristics such as the heights and angles, the strength characteristics and elastic constants of surrounding rock masses and the depth and length of rock socket, et. al. on the shaft resistance of drilled shafts are investigated from elasto-plastic analyses( FLAC). Through the parametric studies, among the parameters, the vertical stress on the top layer of socket, the height of asperity and cohesion and poison's ratio of rock masses are major influence factors on the unit peak shaft resistance.