• 제목/요약/키워드: Engineering Properties of concrete

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A self-confined compression model of point load test and corresponding numerical and experimental validation

  • Qingwen Shi;Zhenhua Ouyang;Brijes Mishra;Yun Zhao
    • Computers and Concrete
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    • v.32 no.5
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    • pp.465-474
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    • 2023
  • The point load test (PLT) is a widely-used alternative method in the field to determine the uniaxial compressive strength due to its simple testing machine and procedure. The point load test index can estimate the uniaxial compressive strength through conversion factors based on the rock types. However, the mechanism correlating these two parameters and the influence of the mechanical properties on PLT results are still not well understood. This study proposed a theoretical model to understand the mechanism of PLT serving as an alternative to the UCS test based on laboratory observation and literature survey. This model found that the point load test is a self-confined compression test. There is a compressive ellipsoid near the loading axis, whose dilation forms a tensile ring that provides confinement on this ellipsoid. The peak load of a point load test is linearly positive correlated to the tensile strength and negatively correlated to the Poisson ratio. The model was then verified using numerical and experimental approaches. In numerical verification, the PLT discs were simulated using flat-joint BPM of PFC3D to model the force distribution, crack propagation and BPM properties' effect with calibrated micro-parameters from laboratory UCS test and point load test of Berea sandstones. It further verified the mechanism experimentally by conducting a uniaxial compressive test, Brazilian test, and point load test on four different rocks. The findings from this study can explain the mechanism and improve the understanding of point load in determining uniaxial compressive strength.

Bond, Flexural Properties and Control of Plastic Shrinkage Cracking of Crimped type Synthetic Fiber Reinforced Cement Based Composites (Crimped Type 합성섬유로 보강된 시멘트 복합재료의 부착, 휨 및 소성수축균열제어 특성)

  • Won, Jong Pil;Park, Chan Gi;Lim, Dong Hee;Back, Chul Woo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.6A
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    • pp.1033-1039
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    • 2006
  • The purpose of this study are to evaluated bond, flexural properties and control of plastic shrinkage cracking of crimped type synthetic fiber with amplitude 6 mm and height 1.8 mm reinforced cement based composites. Bond and flexural test were conducted in accordance with the JCI-SF 8 and JCI SF-4 standard, respectively. The plastic shrinkage cracking test was conducted for evaluating the effect of fiber in reducing shrinkage cracking in cement based composites. Test results indicated that the crimped typel synthetic fibers performed significantly better than the straight type fiber in terms of interface toughness and pullout load and the crimped type synthetic fibers improved the flexural toughness of concrete. Also, the increasing the crimped type synthetic fiber volume fraction from 0.00% to 1.00% improved the plastic shrinkage cracking resistance. Specially, the effect of control of plastic shrinkage cracking is excellent at the more than 0.5% fibre volume fraction.

Investigation of the Effects of CNT Dosages on the Hydration and Heating Properties of Cement Composites with Low Water-to-binder Ratio (낮은 물-바인더 비를 갖는 시멘트 복합체의 CNT 첨가량에 따른 수화특성 및 발열특성)

  • Oh, Sungwoo;Jung, Sang-hwa;Chung, Wonseok;Choi, Young Cheol
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.6
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    • pp.182-188
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    • 2018
  • Recently, various researches on the utilization of carbon nanotube(CNT) with superior electrical conductivity and large surface areas into concrete have been actively conducted. Thus, mechanical and thermal properties of cement-flyash composites were evaluated concerning the CNT replacements. Based on the low binder-to-water ratio, the cement composites were produced with 0.2 % and 0.5 % of CNT solids. The compressive strengths with various ages, isothermal calorimetry measurement, SEM analysis, thermal conductivity of cement composites and thermal gravimetry analysis were implemented. As the amount of CNT addition was increased, the thermal conductivity of cement composites were also increased. Also, there was no significant mechanical property differences between mixtures with and without CNTs.

Study on the Physical Properties of the Artificial Lightweight Aggregate Recycled from the Dyestuff Sludge Treated Chemically With Ti and Fe Salt (Ti염 및 Fe염으로 화학처리된 염색공단 슬러지를 재활용한 인공경량골재의 물리적 특성에 관한 연구)

  • Choi, Jong-Oh;Jung, Yong-Wook
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.3 no.1
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    • pp.34-42
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    • 2015
  • The paper investigates environmental hazards and characteristics of the artificial lightweight aggregate manufactured by using dyestuff sludge from dyeing industrial complex. The dyestuff sludge used in this study is chemically treated with Ti and Fe salt for the purpose of recycling. The artificial lightweight aggregate is manufactured through 3 step; 1) Selecting the optimum moisture content by evaluating plasticity from the mixing ratio of the clay and sludge, 2) shaping round type based on the optimum mixing ratio, 3) drying and Sintering process. Based on KS F 2534 "Lightweight Aggregate for Structural concrete", the particle size, fineness modulus, the density, absorption, unit volume weight, stability and environmental hazards of the manufactured lightweight aggregate are evaluated. Experimental results show that the particle size and fineness modulus is out of the range. However, it is observed that other physical properties are within criteria. In addition, it is confirmed that the problem of the particle size and fineness modulus could be solved in the manufacturing process.

Estimation of Allowable Drop Height for Oriental Pears by Impact Tests (충격시험에 따른 배의 허용낙하높이 추정)

  • Kim, M. S.;Jung, H. M.;Seo, R.;Park, I. K.;Hwang, Y. S.
    • Journal of Biosystems Engineering
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    • v.26 no.5
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    • pp.461-468
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    • 2001
  • Impact between fruits and other materials is a major cause of product damage in harvesting and handling systems. The oriental pears are more susceptible to bruising than other fruits such as European pears and apples, and are required more careful handling. The interest in the handling of the pears for the processing systems has raised the question of the allowable drop height to which pears can be dropped without causing objectionable damage. Drop tests on pears were conducted using an impact device developed by authors to estimate the allowable drop height without bruising. The impact device was constructed to hold in a selected orientation and to release a fruit by vacuum for dropping on to a force transducer. The drop height was adjustable for zero to 60 cm to achieve the desired distance between the bottom of the fruits and the top of the impact force transducer. The transducer was secured to 150 kg\subf/ concrete block. The transducer signal was sampled every 0.17 ms with a strain gage measurement board in the micro computer where it was digitaly stored for later analysis. The selected sample fruit was Niitaka cultivar of pears which is one of the most promising fruit for export in Korea. The pears were harvested during the 1998 harvest season from an orchard in Daejeon. The sample fruit was selected from two groups which were stored for 3 months and 5 months respectively by the method of current commercial practice. The pears were allowed to stabilize at environmental condition(18C, 65% rh) of the experimental room. One hundred fifty six pears were tested from the heights of 5, 7.5. 10 and 12.5 cm while measurement were made of impact peak force, contact time, time to peak force, dwell time, pear diameter and mass. The bioyield strength and modulus of elasticity were measured using UTM immediately after each drop test. The allowable drop height was estimated on the base of bioyield strength of the pears in two ways. One was assumed the peak force during impact test increasing linearly with time, and the other was based on the actual drop test results. The computer program was developed for measuring the impact characteristics of the pears and analyzing the data obtained in the study. The peak force increased while contact times decreased with increasing drop height and contact times of the sample from the hard tissue group. The allowable drop height increased with increasing bioyield strength and contact times, and also varied with Poisson\`s ratio, mass and equilibrium radius of the pears. The allowable drop height calculated by a theoretical method was in the range from 1 to 4 cm, meanwhile, the estimated drop height considering the result of the impact test was in the range from 1 to 6 cm. Since the physical properties of fruits affected significantly the allowable drop height, the physical properties of the fruits should be considered when estimating the allowable drop height.

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The Effect of Recycled Glass Sand Usage Conditions on the Mechanical Properties and Alkali-Silica Reaction of Mortar (순환유리 잔골재의 사용 조건이 모르타르의 역학적 특성 및 알칼리-실리카 반응에 미치는 영향)

  • Min-Jae Son;Gyu-Yong Kim;Hyun-Sang Choi;Gyeong-Cheol Choi;Tae-Hyeob Song
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.12 no.3
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    • pp.263-270
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    • 2024
  • In recent years, there has been an increasing amount of waste glass that cannot be recycled and is landfilled among construction and household waste. To address this issue, research has been conducted to recycle waste glass as sand, but conflicting results have emerged depending on the type of waste glass and the manufacturing method of recycled glass sand(RGS). To promote the use of RGS, it is necessary to review its performance under field conditions, such as mass production processes and real scale concrete applications. This study introduces examples of mass production system process for RGS and evaluates the effects of the usage conditions(color, content, particle size) of mass-produced RGS on the mechanical properties and alkali-silica reaction(ASR) of mortar. As a result, the mass production system process of RGS causes microcracks inside the particles, which are the cause of mortar strength reduction and ASR expansion. The number of microcracks is highest in clear RGS. Based on these results, it is proposed that RGS can be used as a replacement for natural sand with a content of less than 25 % or a particle size of less than 0.5 mm.

Physiochemical Characteristics and its Applicable Potential of Blast Furnace Slag Grout Mixtures of Sodium Silicate and Calcium Hydroxide (규산소다 및 수산화칼슘을 적용한 고로슬래그 그라우트의 적용성 및 물리화학적 특성)

  • Kim, Joung-Souk;Yoon, Nam-Sik;Xin, Zhen-Hua;Moon, Jun-Ho;Park, Young-Bok;Kim, Young-Uk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.1
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    • pp.200-207
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    • 2019
  • Cement is one of the most commonly used materials in the construction and civil engineering industry. However, emissions of carbon dioxide generated during the production of cement have been linked to climate change and environment pollutants. In order to replace cement, many studies have been actively performed research to utilizing Blast Furnace Slag(BFS), which is a byproduct of the steel industry. This study aims to investigate the physiochemical properties of the BFS powder based grout to determine whether it can be used as an environment-friendly grout material. As a fine powder, BSF can be used instead of cement grout due to its potential hydraulic property. BSF has also been known for its ability to strengthen materials long-term and to densify the internal structure of concrete. In order to investigate the physicochemical properties of the BFS powder based grout as a grout material, in this study assessment tests were performed through a gel-time measurement, uniaxial compressive strength, and chemical resistance tests, and heavy-metal leaching test. Characteristics and advantages of the slag were studied by comparing slag and cement in various methods.

Evaluation on Properties of Sea Water Cement Paste Made of Poly-Aluminum Chloride Solution (폴리 염화 알루미늄 수용액을 사용한 해수 배합 시멘트 페이스트의 특성 평가)

  • Kim, Ji-Hyun;Kim, Min-Jeong;Chung, Chul-Woo
    • Journal of the Korea Institute of Building Construction
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    • v.24 no.6
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    • pp.651-661
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    • 2024
  • The use of seawater concrete for the construction of infrastructure facilities in coastal and island areas can be a sustainable solution to address global environmental problems such as water shortage. However, the use of seawater has been limited for reinforced concrete due to the rebar corrosion and loss of long-term strength. In this study, poly-aluminum chloride(PAC) aqueous solution was used to overcome the reduction in strength since the amount of dissolved aluminum is higher and thus promotes the ettringite formation in early age to prevent loss of strength at 28 day. For this purpose, various concentrations of PAC solution were added to cement paste made of deionized and sea water, and the hydration and strength development were evaluated. According to the experimental results, seawater promoted the initial hydration of the cement paste and reduced 28 day compressive strength. The reduction in strength was greater when cement paste was cured in seawater. Regardless of whether deionized or sea water was used, the maximum compressive strength was shown at a PAC concentration of 0.8%. Above 0.8% concentration, the hydration was delayed and the compressive strength decreased as PAC concentration increased. However, it should be noted that a further research needs to be conducted to clarify whether 0.8% PAC concentration was the optimal concentration or not.

Setting and Micro-structures of the Cement Pastes Using Sugar-Based Super Retarding Agents (당류계 초지연성 혼화제를 사용한 시멘트 페이스트의 응결 및 미시구조 특성)

  • Jeong, Yeong-Jin;Hyun, Seung-Yong;Han, Jun-Hui;Kim, Jong;Han, Min-Cheol
    • Journal of the Korea Institute of Building Construction
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    • v.23 no.6
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    • pp.703-714
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    • 2023
  • This research conducts a series of tests to investigate the setting retarding properties and strength development in cement pastes incorporating various types and dosages of sugar-based super retarding agents. Six such agents, including Sucrose, Sugar powder, Saccharin, Aspartame, Stevioside, and Mogroside, commercially available, were selected for evaluation. The study also examines the micro-structural properties of these cement pastes. The test mixtures were prepared using a 27.5% water-to-cement ratio and ordinary Portland cement. Micro-structural analyses were conducted using Scanning Electron Microscopy(SEM), X-Ray Diffraction(XRD), and Energy Dispersive Spectroscopy(EDS). The findings reveal that the incorporation of sucrose, sugar powder, and stevioside significantly retards the setting time. Particularly, adding 0.1% sucrose extended the setting time by approximately two-fold compared to the control(Plain) mixture. Most mixtures, barring those with sugar powder and stevioside, exhibited compressive strength comparable to the Plain mixture. Notably, with 0.2% sucrose, strength measurements were not feasible at 1 day, but at 3 days, the strength gains aligned with the Plain mixture. XRD, SEM, and EDS analyses confirmed the hydration delay(set retarding) of C3S due to sucrose, with further quantitative corroboration provided by EDS. SEM was used to verify the presence or absence of hydration products. The study concludes that sucrose, as a sugar-based retarder, offers effective set retarding capabilities and compressive strength development in concrete.