• Title/Summary/Keyword: Compressive test

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Performance Evaluation for Dry Shrinkage of Dry Mortar Using Artificial Aggregate Made from Circulating Fludized Bed Combution Ash and Modified CaO Type Expansive Admixture (개질 CaO 팽창재 활용 CFBC 인공잔골재 건조 모르타르의 건조수축 성능평가에 관한 연구)

  • Park, Ji-Sun;Song, Tae-Hyeob
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.4
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    • pp.331-335
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    • 2018
  • The purpose of this study is to investigate the feasibility of CFBC artificial fine aggregate as a substitute for natural aggregate used in dry mortar. The basic performance of the flow, compressive strength and dry shrinkage of the dry mortar was evaluated. Four types of test dry mortar specimens using natural aggregate without expansion admixture, a specimen with modified CaO expansion admixture and natural aggregate, a specimen with modified CaO expansion admixture and CFBC artificial fine aggregate, and a specimen using CFBC artificial fine aggregate without modified CaO expansion admixture were evaluated respectively. As a result of evaluation of drying shrinkage performance at 20th day of age, the dry shrinkage performance of the specimen using modified CaO expansion admixture was found to be the highest at $250{\times}10^{-6}$. On the other hand, the specimen containing the modified CaO expansion admixture with CFBC artificial aggregate exhibited a shrinkage of $410{\times}10^{-6}$, and the drying shrinkage of specimen using natural fine aggregate without expansion admixture was $450{\times}10^{-6}$. When the modified CaO expansion material was used, and exhibited performance equal to or higher than that of the shrinkage-drying property.

Simulation study on effects of loading rate on uniaxial compression failure of composite rock-coal layer

  • Chen, Shao J.;Yin, Da W.;Jiang, N.;Wang, F.;Guo, Wei J.
    • Geomechanics and Engineering
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    • v.17 no.4
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    • pp.333-342
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    • 2019
  • Geological dynamic hazards during coal mining can be caused by the failure of a composite system consisting of roof rock and coal layers, subject to different loading rates due to different advancing velocities in the working face. In this paper, the uniaxial compression test simulations on the composite rock-coal layers were performed using $PFC^{2D}$ software and especially the effects of loading rate on the stress-strain behavior, strength characteristics and crack nucleation, propagation and coalescence in a composite layer were analyzed. In addition, considering the composite layer, the mechanisms for the advanced bore decompression in coal to prevent the geological dynamic hazards at a rapid advancing velocity of working face were explored. The uniaxial compressive strength and peak strain are found to increase with the increase of loading rate. After post-peak point, the stress-strain curve shows a steep stepped drop at a low loading rate, while the stress-strain curve exhibits a slowly progressive decrease at a high loading rate. The cracking mainly occurs within coal, and no apparent cracking is observed for rock. While at a high loading rate, the rock near the bedding plane is damaged by rapid crack propagation in coal. The cracking pattern is not a single shear zone, but exhibits as two simultaneously propagating shear zones in a "X" shape. Following this, the coal breaks into many pieces and the fragment size and number increase with loading rate. Whereas a low loading rate promotes the development of tensile crack, the failure pattern shows a V-shaped hybrid shear and tensile failure. The shear failure becomes dominant with an increasing loading rate. Meanwhile, with the increase of loading rate, the width of the main shear failure zone increases. Moreover, the advanced bore decompression changes the physical property and energy accumulation conditions of the composite layer, which increases the strain energy dissipation, and the occurrence possibility of geological dynamic hazards is reduced at a rapid advancing velocity of working face.

Durability Performance Evaluations on Resistance to Chloride Attack for Concrete Using LCD Waste Glass Powder (LCD 폐유리 미분말을 사용한 콘크리트의 염해내구성 평가)

  • Kim, Seong-Kyum;Lee, Kwang-Woon;Song, Jae-Ho;Jang, Il-Young
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.4
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    • pp.289-296
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    • 2018
  • In this study, we evaluated the feasibility and performance of LCD waste glass as a replacement for cement by using LCD waste glass powder which is generated from manufacturing process due to development of LCD industry. Experiments were carried out by replacing 10% and 20% cement of LCD waste glass with particle size of $12{\mu}m$ of LCD waste glass with OPC and particle size of $5{\mu}m$, respectively. Through experiments, basic properties, mechanical properties and durability of concrete were evaluated. Experimental results show that the compressive strength is high at 10% replacement ratio compared to 20%. The lower the particle size, the higher the strength. The durability test evaluated the chloride penetration performance through the chloride ion diffusion coefficient. The higher the substitution rate and the smaller the particle size, the lower the chloride ion diffusion coefficient and the better the OPC than the all substitution rate. As a result, LCD waste glass concrete with low granularity and proper replacement ratio is considered to be advantageous for durability under salt environment.

Non-contact Stress Measurement in Steel Member using Piezospectroscopy (압분광법을 이용한 강재의 비접촉식 응력측정)

  • Kim, Jongwoo;Kim, Namgyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.3
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    • pp.92-95
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    • 2019
  • In this paper, a novel laser-based non-contact and non-destructive stress measurement technique is newly proposed for measuring stress in steel structural members. As the demand of stress monitoring in structural members is increased, various non-destructive techniques are being applied to the field of structural health monitoring. Spectroscopic techniques are non-contact technique and widely used for chemical identification of target materials. Especially, piezospectroscopic technique is a residual stress measurement technique in thermal barrier coatings. Although the piezospectroscopic technique has high possibility of measuring structural stress in steel members, the technique has been rarely applied to this field. In this paper, piezospectroscopy-based stress measurement technique is, therefore, proposed for measuring stress in steel structural member. To do that, alumina particles have been coated onto a specimen of a structural steel rod using a thermal spray coating technique. And then, an uniaxial compression test has been conducted to the specimen to collect each fluorescence spectrum under different loading conditions. Finally, the linear relation of spectral shift and applied compressive stress of the specimen has been experimentally established.

The Strength Characteristics of Deep Mixing Ground According to Increasing Water Contents (함수비 증가에 따른 심층혼합지반의 강도특성)

  • Park, Choon-Sik;Choi, Jun-Sam
    • Journal of the Korean Geotechnical Society
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    • v.35 no.3
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    • pp.25-35
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    • 2019
  • A laboratory test on uniaxial compressive strength was carried out by making 640 specimens in total, which were divided into two groups by their curing time of 7 and 28 days for 3 water content conditions of a water content at 100% saturation level and 10% and 20% increased water content from the state with clay, sand and gravel mixed grounds of 20 ground conditions of 4 types of stabilizer mixing conditions which were 8%, 10%, 12%, 14%, to understand laboratory strength characteristics for strength design of deep mixing ground. In case of clayey grounds, although the strength increased depending on the increase of stabilizer content, it showed to be analogous regardless of the curing time. And the impact on the strength development of deep mixing specimen according to water content was considered to be comparatively little compared to other grounds. For sandy grounds, the strength increment amount clearly showed to increase as stabilizer content increased, and also the increase of water content was determined to be decreasing the strength increment effect. For gravel mixed grounds, at 14% or over of stabilizer content, the effect on strength development was big making a large increase in strength, but compared to sandy grounds, the strength ratio depending on the curing time showed to be small.

Evaluation of Chloride Diffusion Characteristics in Concrete with Fly Ash Cured for 2 Years (2년 양생된 Fly Ash 콘크리트의 염화물 확산 특성 평가)

  • Yoon, Yong-Sik;Hwang, Sang-Hyeon;Kwon, Seung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.7 no.1
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    • pp.8-15
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    • 2019
  • When RC(Reinforced Concrete) structures are exposed to harsh environment, deterioration phenomenon occurs, and the corrosion in rebar due to chloride intrusion is known as representative deterioration, so called chloride attack. In this paper, chloride resistance performance of 2 years aged concrete is evaluated considering 3 levels of water to binder ratio(0.37, 0.42, and 0.47) and 2 levels of substitution ratio of fly ash(0% and 30%). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests referred to KS F 2405 are performed. With adaptation of the previous test results and the results from this study, time-dependent chloride diffusion characteristics are analyzed for each concrete. The FA(Fly Ash) concrete has higher chloride resistance performance than OPC(Ordinary Portland Cement) concrete. According to the evaluation standard of ASTM C 1202, the FA concrete has "Moderate" grade after 49 days while OPC concrete does "Moderate" grade after 365 days. As the results of time-parameter for chloride diffusion, OPC concrete and FA concrete show the decreasing behavior of time-parameters with increasing water to binder ratio. Also, FA concrete has 1.57~2.74 times of time-parameter than OPC concrete. That's cause is thought that the time-parameter indicates the gradient of decreasing of diffusion coefficient. FA concrete has higher time-parameters than OPC concrete by pozzolanic reaction of FA.

Development of Filler Type Mechanical Splice for High Strength Re-bar (고강도 철근용 충전형 기계적 이음장치 개발 연구)

  • Lee, Seongsoo;Chun, Homin
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.12
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    • pp.686-693
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    • 2018
  • Various types of re-bar splicing methods have been developed and applied to reinforced concrete (RC) structures in the field. According to previous studies, the coupler splice is relatively superior to the lap splice in terms of cost efficiency when the diameter or strength of the re-bar is larger or higher. This study was performed to develop a filler type mechanical splice for a high-strength re-bar (SD600) in reinforced concrete structures. The deformed re-bars were inserted into a circular steel tube coupler and high-strength epoxy filler was then injected into the coupler. The splice system was completed by hardened filler in a coupler. The epoxy filler was used as the manufactured production epoxy to conduct experiments of filler type mechanical splice specimens, and to observe the failure loads and failure aspects of the specimens. For this goal, the experiment of one-way tensile test was conducted for the epoxy filler type mechanical splices specimens according to the compressive strength of epoxy, length of coupler, and diameter of re-bar. The shape of failure of the re-bar coupler splice showed that the re-bars were pulled between the lugs of the re-bars as a result of the shear fracture of the hardened epoxy. The actual failure load of the experiment specimen was approximately 2 times higher than the expected failure load of the epoxy filler, which greatly improves the failure load of the hardening epoxy filler due to the restraint of the steel coupler.

A Study on the Atmospheric Pressure Control of the VARTM Process for Increasing the Fiber Volume Fraction and Reducing Void (섬유부피분율 증가와 공극 감소를 위한 VARTM 공정의 대기압 제어에 관한 연구)

  • Kwak, Seong-Hun;Kim, Tae-Jun;Tak, Yun-Hak;Kwon, Sung-Il;Lee, Jea-Hyun;Kim, Sang-Yong;Lee, Jong-Cheon
    • Composites Research
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    • v.34 no.2
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    • pp.88-95
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    • 2021
  • VARTM (Vacuum-assisted resin transfer molding) process is a low-cost process technology and affiliated with OoA (Out of Autoclave). Besides, it has been widely used in various fields. However, because of its lower quality than the autoclave process, it isn't easy to apply the VARTM process to the aerospace industry, which requires high reliability. The main problem of the VARTM process is the loss of mechanical properties due to the low fiber volume fraction and high void content in comparison to the autoclave. Therefore, many researchers have studied to reduce void and increase fiber volume fraction. This study examines whether the method of controlling atmospheric pressure could increase the fiber volume fraction and reduce void during the resin impregnation process. Reliability evaluation was confirmed by compressive strength test, fiber volume fraction analysis, and optical microscopy. As a result, it was confirmed that increasing the atmospheric pressure step by step in the VARTM process of impregnating the preform with resin effectively increases the fiber volume fraction and reduces void.

Inspection Method Validation of Grouting Effect on an Agricultural Reservoir Dam (농업용 저수지 제체에서의 그라우팅 주입효과 확인방법의 검증)

  • Kim, Hyeong-Sin;Moon, Seong-Woo;Leem, Kookmook;Seo, Yong-Seok
    • The Journal of Engineering Geology
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    • v.31 no.3
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    • pp.381-393
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    • 2021
  • Physical, mechanical, hydraulic, and geophysical tests were applied to validate methods of inspecting the effectiveness of grouting on an agricultural reservoir dam. Data obtained from series of in situ and laboratory tests considered four stages: before grouting; during grouting; immediately after grouting; and after aging the grouting for 28 days. The results of SPT and triaxial tests, including the unit weight, compressive strength, friction angle, cohesion, and N-value, indicated the extent of ground improvement with respect to grout injection. However, they sometimes contained errors caused by ground heterogeneity. Hydraulic conductivity obtained from in situ variable head permeability testing is most suitable for identifying the effectiveness of grouting because the impermeability of the ground increased immediately after grouting. Electric resistivity surveying is useful for finding a saturated zone and a seepage pathway, and multichannel analysis of surface waves (MASW) is suitable for analyzing the effectiveness of grouting, as elastic velocity increases distinctly after grouting injection. MASW also allows calculation from the P- and S- wave velocities of dynamic properties (e.g., dynamic elastic modulus and dynamic Poisson's ratio), which can be used in the seismic design of dam structures.

A Characteristic Study on Shear Strength of Reinforced Concrete Beams according to Shear Reinforcement Ratio and Beam Section Size (전단철근비와 보의 단면크기에 따른 철근콘크리트 보의 전단강도 특성 연구)

  • Noh, Hyung-Jin;Yu, In-Geun;Lee, Ho-Kyung;Baek, Seung-Min;Kim, Woo-Suk;Kwak, Yoon-Keun
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.35 no.6
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    • pp.111-119
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    • 2019
  • The purpose of this study is to investigate the shear strength of reinforced concrete beam according to beam section size and shear reinforcement ratio. A total of nine specimens were tested and designed concrete compressive strength is 24 MPa. The main variables are shear reinforcement ratio and beam section size fixed with shear span to depth ratio (a/d = 2.5), the tensile reinforcement ratio (${\rho}=0.013$) and width to depth ratio (h/b = 1.5). The test specimens were divided into three series of S1 ($225{\times}338mm$), S2 ($270{\times}405mm$) and S3 ($315{\times}473mm$), respectively. The experimental results show that all specimens represent diagonal tensile failure. For $S^*-1$ specimens (d/s=0), the shear strength decreased by 33% and 46% with increasing the beam effective depth, 26% and 33% for $S^*-2$ specimens (d/s=1.5) and 16% and 20% for $S^*-3$ specimens (d/s=2.0) respectively. As the shear reinforcement ratio increases, the decrease range in shear strength decreases. In other words, this means that as the shear reinforcement ratio increases, the size effect of concrete decreases. In the S1 series, the shear strength increased by 39% and 41% as the shear reinforcement ratio increased, 54% and 76% in the S2 series and 66% and 100% in the S3 series, respectively. As the effective depth of beam increases, the increase range of shear strength increases. This means that the effect of shear reinforcement increases as the beam effective depth increases. As a result of comparing experimental values with theoretical values by standard equation and proposed equation, the ratio by Zsutty and Bazant's equation is 1.30 ~ 1.36 and the ratio by KBC1 and KBC2 is 1.55~.163, respectively. Therefore, Zsutty and Bazant's proposed equation is more likely to reflect the experimental data. The current standard for shear reinforcement ratio (i.e., $S_{max}=d/2$) is expected to be somewhat relaxed because the ratio of experimental values to theoretical values was found to be 1.01 ~ 1.44 for most specimens.