• Title/Summary/Keyword: hardened concrete

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Numerical modeling of slipforming operations

  • Lachemi, M.;Elimov, R.
    • Computers and Concrete
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    • v.4 no.1
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    • pp.33-47
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    • 2007
  • Slipforming is a construction method in which the forms move continuously during concrete placement. This paper presents a numerical procedure based on the finite element method to simulate the thermal behavior of concrete during slipforming operations. The validity of the model was successfully tested by simulating a very complex but well documented field case of actual slipforming operations performed during the construction of an offshore concrete oil platform structure. The results obtained have been related to the shape of the concrete "hardened front" in the forms, which allows quick evaluation of the operation. The results of the numerical investigation have shown that the shape of the "hardened front" can be affected by the temperature of the fresh concrete and ambient conditions. For a given initial concrete temperature, there are limitations for the ambient temperature that, when exceeded, can create an unfavorable shape of the concrete "hardened front" in the forms. Similarly, for a given ambient temperature, the initial concrete temperature should not be fall below an established limit in order to avoid unfavorable shape of the "hardened front".

Development of Image Analysis Techniques for Measuring Air Void System in Hardened Concrete (콘크리트 내부 공극 분석을 위한 화상분석기법의 개발)

  • Jun In-Ku;Lee Bong-Hak;Yun Kyong-Ku;Jeong Won-Kyong
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.810-813
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    • 2004
  • Air void systems in hardened concrete has an important influence on concrete durability such as freeze-thaw resistance, water permeability, surface scaling resistance, and etc. Linear traverse method and point count method described at ASTM have been widely used to estimate the air void system in hardened concrete. These methods, however, are rarely used at present, because they require many efforts, are time consuming works, depend on each person's decision, and are not repeatable. Thus, new image analysis method using microscope and computer processes has been approached for analyzing air void system in hardened concrete. However, it is just in initial step. The purposes of this study were to develope an effective and reliable image analysis technique for estimating air void system in hardened concrete. The developed technique was proved to be accurate, reasonable and repeatable.

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A Fundamental Study on the Properties of High-Fluidity Concrete Using Viscosity Agent - Properties of Hardened Concrete - (증점제를 이용한 고유동콘크리트의 특성에 관한 기초적 연구 -경화상태의 특성-)

  • 김기철;박상준;조병영;윤기원;최응규;한천구
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.04a
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    • pp.198-201
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    • 1996
  • The purpose of this study is to analyze the properties of high fluidity concrete using the viscosity agent of a cellulose system with W/C of 35~50% in hardened state. It is proven that properties of high fluidity concrete in hardened state is nearly the same with normal concrete in the same W/C and no strength difference by tamping method do not appeared. Therefore, no tamping method is thought to be reguired in high fluidity concrete.

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Image analysis of an air void system in hardened concrete (경화콘크리트 내부의 기포분포상태 분석에 관한 연구)

  • 김기철;정재동
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.10b
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    • pp.791-796
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    • 1998
  • Air voids existed in hardened concrete have an important influence on concrete deterioration such as carbonation, freezing and thawing, and corrosion of embedded steel in concrete. Therefore it is very significant to investigate the pore structure of system(size, number and continuity of air voids) to solve the reason caused concrete deterioration. The purpose of this study is to develop the standard method of measuring air voids which affect properties in hardened concrete using image analyzing system. This paper presents the settlement of rapid and exact experimental method which extracts fine bubbles, calculates the number of air voids, and determines air-void distribution using image analyzing system with computer.

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Experimental investigation on hardened properties of recycled coarse aggregate concrete

  • Shohana, Shanjida A.;Hoque, Md. I.;Sobuz, Md. H.R.
    • Advances in concrete construction
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    • v.10 no.5
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    • pp.369-379
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    • 2020
  • Reduction of disposal of waste materials due to construction demolition has become a great concern in recent decades. The research work presents the hardened properties of concrete where the partial substitution of recycled coarse aggregate with natural aggregate in amount of 0%, 10%, 30% and 50%. By using different mixed proportions, fresh and hardened properties of concrete were conducted for this investigation. These properties were compared with control concrete. It can be seen that all of the hardened properties of concrete were decreased with the increasing percentage of recycled aggregate in concrete mixes. It was noticed that up to 30% recycled aggregate replacement can be yielded the optimum strength when it used in normal concrete. Finally, it can be said that disposed recycled concrete utilizing as a partial replacement in natural aggregate is a great way to reuse and reduce environmental hazards which achieve sustainability approach in the construction industry.

Performance of self-compacting concrete at room and after elevated temperature incorporating Silica fume

  • Ahmad, Subhan;Umar, Arshad;Masood, Amjad;Nayeem, Mohammad
    • Advances in concrete construction
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    • v.7 no.1
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    • pp.31-37
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    • 2019
  • This paper evaluates the workability and hardened properties of self-compacting concrete (SCC) containing silica fume as the partial replacement of cement. SCC mixtures with 0, 2, 4, 6, 8 and 10% silica fume were tested for fresh and hardened properties. Slump flow with $T_{500}$ time, L-box and V-funnel tests were performed for evaluating the workability properties of SCC mixtures. Compressive strength, splitting tensile strength and modulus of rupture were performed on hardened SCC mixtures. Experiments revealed that replacement of cement by silica fume equal to and more than 4% reduced the slump flow diameter and increased the $T_{500}$ and V-funnel time linearly. Compressive strength, splitting tensile strength and modulus of rupture increased with increasing the replacement level of cement by silica fume and were found to be maximum for SCC mixture with 10% silica fume. Further, residual hardened properties of SCC mixture yielding maximum strengths (i.e., SCC with 10% silica fume) were determined experimentally after heating the concrete samples up to 200, 400, 600 and $800^{\circ}C$. Reductions in hardened properties up to $200^{\circ}C$ were found to be very close to normal vibrated concrete (NVC). For 400 and $600^{\circ}C$ reductions in hardened properties of SCC were found to be more than NVC of the same strength. Explosive spalling occurred in concrete specimens before reaching $800^{\circ}C$.

A Fundamental Study on the Estimation of Unit Cement Content in Hardened Concrete (Test Method by Sodium Gluconate) (경화 콘크리트의 단위 시멘트량 추정 방법에 관한 기초적 연구)

  • 김광서;유영호;박도경
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.04a
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    • pp.24-29
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    • 1996
  • The purpose of this study is to propose new estimation method of unit cement content in hardened concrete. In general, the quantity of cement in hardened concrete is tested by hydrochlonic acid dissolving cement paste, however, hydrochloric acid dissolves sea shell contained in sea sand and lime stone in concrete. Therefore, the tested cement content is apt to estimate greater than actual cement content. The sodium gluconate solution dissolves only cement in concrete, it is hard to dissolve sea shell and lime stone as CaCo3. The effects of the quantity, concentration and temperature of sodium gluconate solution, the ignition temperature, the ignition loss of cement on the cement content and the percentage of dissolution of cement were investigated to establish a test method. From the results of these tests, the fundamental test method for cement content of hardened concrete by sodium gluconate is proposed.

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The Experimental Study on the Development of Estimation Technique for the Mix Proportion of Hardened Concrete (경화 콘크리트의 배합비 추정기법 개발에 관한 실험적 연구)

  • 이준구;박광수;김석열;김명원;김관호;박미현
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.10b
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    • pp.961-966
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    • 2000
  • It is difficult to change or remedy concrete structure after hardened. It is usual to evaluate the quality of hardened concrete using several test method. This study was performed to make fundamental data that could be used to evaluate the quality of hardened concrete. This study is to estimate mix proportion of hardened concrete. Each elements of concrete needed different estimation methods. First, the cement that handled by the most important compounds measured by XRF(X-ray fluorecence) machine with scanning Ca-K${\alpha}$. Second, the coarse aggregate that divided by maximum size measured by the area comparison method that starts from the assumption of uniform distribution. Third, the fine aggregate measured by the weight comparison method that needs several prerequsite constants which concerned cement hydration reaction. Fourth, the water content would be estimated by expert system that has data base of design data, the contents of above estimation results, the characteristics of concrete strength. As the result of the above research, some conclusions are as follows. The cement estimation method resulted by reliability of mean 96.7%, standard deviation 3.92. The area comparison method resulted by reliability of mean 95.3%, standard deviation 2.08. The weight comparison method resulted by reliability of mean 93.3%, standard deviation 3.35.

Study for the Determination of chloride ion in hardened concrete using Potentiometic Methods (전위차법을 이용한 경화 콘크리트 및 콘크리트재료의 염화물 측정기술 개발)

  • Lee, Kyoung-Moon;Yoon, In-Jun;Seo, In-Ho
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05a
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    • pp.578-581
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    • 2006
  • This study was performed to develop acid-soluble extraction solution and water-soluble extraction solution for hardened concrete. By use of this potentiometric method one can determinate chloride ion concentration in hardened concrete without pre-treatment and it can be used on-site.

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Proposal of Matrix Spacing Factor for Analyzing Air Void System in Hardened Concrete (콘크리트 내부공극 분석을 위한 행렬간격계수 모델식의 제안)

  • Jeong Won-Kyong;Jun In-Koo;Kim Yong-Kon;Lee Bong-Hak
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.11a
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    • pp.679-682
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    • 2004
  • Air void systems in hardened concrete has an important influence on concrete durability such as freeze-thaw resistance, water permeability, surface scaling resistance. Linear traverse method and point count method described at ASTM is the routine analysis of the air void system that have been widely used to estimate the spacing factor in hardened concrete. Recently, many concretes often have a spacing factor higher than the generally accepted $200-250{\mu}m$ limit for the usual range of air contents. This study is proposed to estimate the matrix spacing factor by calculation of simplicity. The matrix spacing factor needs two parameters that are air content and numbers of air voids in the hardened concrete. Those are obtained from the standard air-void system analysis of the ASTM C 457. The equation is valid for all values of paste-to-air ratio because the estimation of paste content is unnecessary at the using ASTM C 457. The matrix spacing factor yields a similar estimate of the standard spacing factor.

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