• Title/Summary/Keyword: Engineering Properties of concrete

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A Study on Controlled Blasting Design in Construction Field (건설현장에서의 제조 발파 설계에 관한 고찰)

  • 이화창
    • Explosives and Blasting
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    • v.14 no.1
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    • pp.49-63
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    • 1996
  • Blasting is a work that destruct an object by use of explosive. Its use covers a wid range, and it is applicable to blast the rocks, minerals, coal, steel and concrete structures, bridges, etc. To execute the blast plan most effectively, the properties of the object and the explosives should be well understood, and all the other conditions must ve incorporated in its design and plan. A safe blasting pattern and procedure should be selected considering the envirinmental effects and dther conditions. At the same time, a protective protective pricedures should be utilized to prevent the safety hazards such as the excessive blast vubration, air pressure, and the flying fragments. This study reviews the controlled blasting techniques in these regards.

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Evaluation of the Mechanical Properties of Field-Cast Shotcrete and Long-Term Durability by Combined Deterioration Test (현장타설 숏크리트의 역학적 성능 평가 및 복합열화시험을 통한 장기내구성 평가)

  • Ma, Sang-Joon;Jang, Phil-Sung;Kim, Dong-Min;Choi, Jae-Seok
    • Journal of the Korea Concrete Institute
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    • v.19 no.1
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    • pp.47-56
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    • 2007
  • Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcrete is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcrete practice. The purpose of the study is, therefore, to explore the trobles in the current shotcreting practice, and to develop high-quality silica fume shotcrete. For the purpose of security a long-term durability of shotcrete, this study conducted combined deterioration tests. In this study, a combined deterioration test in consideration of a variety of deterioration factors were proceeded. Especially, micro-silica fume that was used frequently in overseas because of a outstanding strength-promotion effect was applied to combined deterioration test, and a long-term durability of shotcrete was investigated according to additions mixing. As a result of test, the shotcrete mixed Micro-silica fume showed a good deterioration quality compared with the other mixes. And is shows that the Micro-silica fume has an outstanding strength-promotion effect and is effective to secure a long-term durability of shotcrete by means of decreasing a deterioration caused by steel fiber mixed.

Review of Steel ratio Specifications in Korean Highway Bridge Design Code (Limit States Design) for the Design of RC Flexural Members (철근콘크리트 휨부재 설계를 위한 도로교설계기준(한계상태설계법)의 철근비 규정 검토)

  • Lee, Ki-Yeol;Kim, Woo;Lee, Jun-Seok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.37 no.2
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    • pp.277-287
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    • 2017
  • This paper describes the specifications on balanced steel ratio and maximum reinforcement for the design of RC flexural members by the Korean Highway Bridge Design Code based on limit states design. The Korean Highway Bridge Design Code (Limit States Design) is not provide for the balanced steel ratio specification for the calculation of required steel area of RC flexural members design. The maximum steel area limited the depth of the neutral axis at the ultimate limit states after redistribution of the moment, and also recommended the maximum steel area should not exceed 4 percent of the cross sectional area. However, from the maximum neutral axis depth provisions should increase the cross section is calculated to be less the maximum reinforcement area, and according to the 4% of the cross sectional area of the concrete, the tensile strain of the reinforcement is calculated to be greater than double the yielding strain, so can not guarantee a ductile behavior. This study developed a balanced reinforcement ratio that is basis for the required reinforcement calculation for tension-controlled RC flexural members design in the ultimate limit states verification provisons and material properties and applied the ultimate strain of the concrete compressive strength with a simple formular to be applied to design practice induced. And assumed the minimum allowable tensile strain of reinforcement double the yielding strain, and applying correction coefficient up to the ratio of maximum neutral axis depth, proposed maximum steel ratio that can be applied irrespective of the reinforcement yield strength and concrete compressive strength.

The Fire Resistant Performance of RC Column with Confined Lateral Reinforcement According to Fire Exposure Condition (횡방향 철근으로 구속된 철근콘크리트 기둥의 화재 노출조건에 따른 내화성능)

  • Choi, Kwang Ho
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.4
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    • pp.311-318
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    • 2018
  • When reinforced concrete structures are exposed to fire, their mechanical properties such as compressive strength, elasticity coefficient and rebar yield strength, are degraded. Therefore, the structure's damage assessment is essential in determining whether to dismantle or augment the structure after a fire. In this study, the confinement effect of lateral reinforcement of RC column according to the numbers of fire exposure face and stirrup was verified by fire resistant test with the heating temperatures of 400C400C, 600C600C and 800C800C. The test results showed that the peak stress decreases and peak strain increases as the temperature is getting higher, also transverse ties are helpful in improving the compressive resistance of concrete subjected to high temperature. Based on the results of this study, the residual stress of confined concrete under thermal damage is higher at the condition of more lateral reinforcement ratio and less fire exposure faces. The decreasing ratio of elastic modulus of more confined and less exposure faces from the relationship of load and displacement was also smaller than that of opposite conditions.

A Study on the Method of Eye Tracking Analysis Based on the Properties in Visual Perception of User -With Emphasis on the Development of Analysis-Framework for Product Design- (사용자의 시각적 인지 특성에 기초한 시선추적 분석 방법에 대한 연구 -제품 디자인을 위한 분석 프레임 개발을 중심으로-)

  • 최민영
    • Archives of design research
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    • v.16 no.4
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    • pp.197-206
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    • 2003
  • Nowadays, the studies on interface and cognition-engineering has become issues of general interest as newly design-methods which analyze the behavior of user on products. However existing studies were mainly done with verbal-centered method which made it difficult for the designer to apply for visual realization. Moreover many mistakes and noises are taken place whenever the designer converts verbal statements and needs of user into visual factors. Therefore the designer needs to analyze visual perception on user and product as visual-centered methods. This study applies the eye tracking method as analysing-instrument and aims to develop the analysis-framework, the concrete techniques of measurement and the application for the product design. At first the nature and the process of visual perception on products are reviewed for developing analysis method. Then the technique of eye tracking and the meaning of fixation and movement are discussed to specify the concrete method. The basic experiment of product can reveal general analysis process, advantage and guideline for the application of eye tracking method. The Study is peformed through the following 4 steps ; to pre-research into product design and visual perception theory ; to identify the concrete experiment method, to measure the fixation/movement data and analyze the raw data, to convert the result of analysis to the visual framework. Finally the major findings and the limits of the study are suggested and summarized.

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Experimental Study on Properties of Temperature History Using Heating Sheet and Insulation Form at Low Temperature (발열시트 및 단열재를 사용한 거푸집 내부 콘크리트의 저온환경하 온도이력 특성에 관한 실험적 연구)

  • Choi, Si-Hyun;Lee, Han-Seung;Choi, Hyun-Kuk
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.4
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    • pp.132-139
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    • 2017
  • In this study, in order to prevent the frost damage of the concrete, the characteristics of the form using heating sheet utilizing the chemical reaction of quicklime and the insulation were evaluated through experiments at low temperature. In the case of form at 10C10C, the form with attached heating sheet showed a temperature history of more than 10C10C higher than that of wood form at the early of concreting due to heat of the quicklime in the heating sheet. In the case of the insulated form, the concrete was kept at a high temperature by preserving the hydration heat. When the heating sheet and the isopink(extruded polystyrene) were attached together on the form, the effect was the same as that of the vacuum insulation. The compressive strength of the form with vacuum insulation and form with isopink, heating sheet as measured about 5 MPa at age 3. The experimental in Mongolia, as with the pervious results, the form with the heating sheet and the insulation showed the highest temperature history over 25C25C for 48 hours. Therefore, it was confirmed that the heating sheet and insulation are attached to the form, which helps the concrete strength development at low temperature by heat generation and the insulation effect.

Material Properties of Ultra Rapid Hardening Mortar for Repairing Sewage Treatment Concrete Pipes (콘크리트 하수관거 보수용 초속경 수중불분리 모르타르의 재료적 특성)

  • Lee, Byungjae;Lee, Sunmok;Bang, Jin-wook;Kim, Yun-yong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.3
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    • pp.57-62
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    • 2020
  • Among the sewage pipes installed in Korea, the length of concrete pipes exceeding 20 years is 66,334 km (42.5%). Deteriorated concrete sewer pipes need to be repaired due to the leakage of internal sewage, which causes problems such as sink holes by expanding the cavity around the pipeline. In this study, we tried to apply anti-washout underwater mortar with ultra rapid hardening cement and segregation reducing agent to sewage pipe repair. As a result of the setting time test, the final set time was delayed by up to 172% by incorporating segregation reducing agent. In the test for measuring the degree of mortar segregation in water, it was measured at pH 12 or less under all mixing conditions. In addition, the suspension amount was measured to be 50 mg / l or less to satisfy the KCI-AD102 standard by incorporating a segregation reducing agent. In terms of the average value of mortar compressive strength, by incorporating segregation reducing agent, the strength of the specimens produced in air was more than 80% of that of the specimens produced in water. Conversely, the bond strengths of the specimens produced in water were measured to be higher than those of the specimens produced in air. Water resistance was evaluated by measuring water absorption and water permeability. Water absorption and water permeability were reduced by 42.6% and 36.6%, respectively, by mixing segregation reducing agent.

A Study of Blasting Demolition by Scaled Model Test and PEC2D Analysis (축소모형실험 및 PFC2D해석에 따른 발파해체 거동분석)

  • 채희문;전석원
    • Tunnel and Underground Space
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    • v.14 no.1
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    • pp.54-68
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    • 2004
  • In this study, scaled model tests were performed on blasting demolition of reinforced concrete structures and the experimental results were analyzed in comparison with the results of numerical analysis. The tests were designed to induce a progressive collapse, and physical properties of the scaled model were determined using scale factors obtained ken dimension analysis. The scaled model structure was made of a mixture of plaster, sand and water at the ratio determined to yield the best scaled-down strength. Lead wire was used as a substitute for reinforcing bars. The scaled length was at the ratio of 1/10. Selecting the material and scaled factors was aimed at obtaining appropriately scaled-down strength. PFC2D (Particle Flow Code 2-Dimension) employing DEM (Distinct Element Method) was used for the numerical analysis. Blasting demolition of scaled 3-D plain concrete laymen structure was filmed and compared to results of numerical simulation. Despite the limits of 2-D simulation the resulting demolition behaviors were similar to each other. Based on the above experimental results in combination with bending test results of RC beam, numerical analysis was carried out to determine the blasting sequence and delay times. Scaled model test of RC structure resulted in remarkably similar collapse with the numerical results up to 900㎳ (mili-second).

Interaction Experiment on Chloride Ion Adsorption Behavior of C-S-H Phases (C-S-H 상의 염소이온 흡착 메커니즘 규명을 위한 반응 작용 실험)

  • Yoon, In-Seok
    • Journal of the Korea Concrete Institute
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    • v.29 no.1
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    • pp.65-75
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    • 2017
  • C-S-H phase is the most abundant reaction product, occupying about 50~60% of cement paste volume. The phase is also responsible for most of engineering properties of cement paste. This is not because it is intrinsically strong or stable, but because it forms a continuous layer that binds together the original cement particles into a cohesive whole. The binding ability of C-S-H phase arises from its nanometer-level structure. In terms of chloride penetration in concrete, C-S-H phase is known to adsorb chloride ions, however, its mechanism is very complicated and still not clear. The purpose of this study is to examine the interaction between chloride ions and C-S-H phase with various Ca/Si ratios and identify the adsorption mechanism. C-S-H phase can absorb chloride ions with 3 steps. In the C-S-H phase with low Ca/Si ratios, momentary physical adsorption could not be expected. Physical adsorption is strongly dependent on electro-kinetic interaction between surface area of C-S-H phase and chloride ions. For C-S-H phase with high Ca/Si ratio, electrical kinetic interaction was strongly activated and the amount of surface complexation increased. However, chemical adsorption could not be activated for C-S-H phase with high Ca/Si ratio. The reason can be explained in such a speculation that chloride ions cannot be penetrated and adsorbed chemically. Thus, the maximum chloride adsorption capacity was obtained from the C-S-H phase with a 1.50 Ca/Si ratio.

Analytical Behavior of Concrete Derailment Containment Provision(DCP) according to Train Impact Loading (열차 충돌하중에 대한 콘크리트 일탈방호시설물(DCP)의 해석적 거동 검토)

  • Yi, Na-Hyun;Kim, Ji-Hwan;Kang, Yun-Suk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.11
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    • pp.604-613
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    • 2018
  • In recent years, numerous train derailment accidents caused by deterioration and high speed technology of railways have increased. Guardrails or barriers of railway bridges are installed to restrain and prevent the derailment of the train body level. On the other hand, it can result in a high casualties and secondary damage. Therefore, a Derailment Containment Provision (DCP) within the track at the wheel/bogie level was developed. DCP is designed for rapid installation because it reduces the impact load on the barrier and inertia force on the steep curve to minimize turnover, fall, and trespass on the other side track of the bridge. In this paper, DCP was analyzed using LS-Dyna with a parameter study as the impact loading location and interface contact condition. The contact conditions were analyzed using the Tiebreak contact simulating breakage of material properties and Perfect bond contact assuming fully attached. As a result, the Tiebreak contact behaved similarly with the actual behavior. In addition, the maximum displacement and flexural failure was generated on the interface and DCP center, respectively. The impact analysis was carried out in advance to confirm the DCP design due to the difficulties of performing the actual impact test, and it could change the DCP anchor design as the analysis results.