• Computers and Concrete
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• v.17 no.3
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• pp.323-336
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• 2016

Although the self-compacting concrete (SCC) offers several practical and economic benefits and quality improvement in concrete constructions, in comparison with conventionally vibrated concretes confronts with autogenously chemical and drying shrinkage which causes the formation of different cracks and creates different problems in concrete structures. Using different fibers in the mix design and implementation of fibrous concrete, the problem can be solved by connecting cracks and micro cracks together and postponing the propagation of them. In this study an experimental investigation using response surface methodology (RSM) based on full factorial design has been undertaken in order to model and evaluate the polypropylene fiber effect on the fibrous self-compacting concrete and curing time, fiber percentage and fiber amount have been considered as input variables. Compressive strength has been measured and calculated as the output response to achieve a mathematical relationship between input variables. To evaluate the proposed model analysis of variance at a confidence level of 95% has been applied and finally optimum compressive strength predicted. After analyzing the data, it was found that the presented mathematical model is in very good agreement with experimental results. The overall results of the experiments confirm the validity of the proposed model and this model can be used to predict the compressive strength of fibrous self-compacting concrete.

• Advances in concrete construction
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• v.9 no.3
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• pp.249-256
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• 2020

This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.202-208
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• 2014

For evaluating basic structural behavior of HVFA (High Volume Fly Ash) concrete, several tests are performed considering different ratios of fly ash replacement and structural evaluation regarding compressive strength, elasticity modulus, stress-strain relationship, and bond strength is also performed. Test results show that elasticity modulus of HVFA concrete has close relationships with compressive strength and fly ash replacement ratio. The ultimate strain shows slight difference from domestic design code. On the other hand, there are no differences between general concrete and HVFA concrete for elasticity modulus and bond strength.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1630-1635
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• 2005

The microstructure of the parts made by the microcellular injection molding process influence properties, including impact strength, tensile strength and density of material. Microstructure of microcellular plastics is divided into core foaming region and solid skin region. Core foaming region is influenced by pressure drop rate, viscosity and cell coalescence. However, actual mechanism of the skin layers is not known despite its importance. The study on the skin layer is getting important because foaming rate of the plastics is determined by the thickness ratio of the skin layer. Especially in case of large molded part, control of the skin layer is needed because skin layer thickness is changed largely. Therefore it is necessary to study variation in skin layer thickness with processing parameters. In this paper, the influence of temperatures in the mold cavity on the skin layer s thickness was also addressed. In addition, the relationship between the temperature distributions across cavity of the mold with impact strength on parts made with the microcellular injection molding process was addressed. In addition, the method to predict the variation in skin layer thickness with mold temperature is discussed.

• Journal of Haehwa Medicine
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• v.18 no.2
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• pp.13-20
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• 2009

Objectives : In order to investigate change of isokinetic trunk muscle strength according to decrease of body composition analysis parameter after obesity treatment. Methods : 2 obese patients have been treated with oriental medical obese treatment for 1 month. One patient got the exercise treatment, another didn't. Before and after treatment, the segmental bioelectrical impedance analysis, isokinetic trunk muscle strength test were performed. Then we analyzed the relationship of data. Results : After obesity treatment, BMI(Body Mass Index), PBF(Percentage of Body Fat), WHR(Waist Hip Ratio) were decreased in all patient and LBM(Lean Body Mass) was increased. In non-exercise patient, Ext.PT(extension Peak Torque) was decreased and Flex.PT(flexion Peak Torque) was increased. In exercise patient showed the opposite results. E/F ratio became more imbalance. Conclusions: Ext.PT was decreased in non-exercise patient but increased in exercise patient. And the trunk muscle strength became imbalance in both patients, right after the treatment. So trunk muscle exercise should be carried out and it is necessary to do long term study.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.136-141
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• 1995

The early evaluation on strength of concrete is useful to achieve on quality control and improvement of properties of concrete. Especially, we could say that the confidence of construction is increased by the increase durability and safety building, due to early evaluation. In this study, was proposed to ultra-sonic pulse method as a early evaluation method for strength of concrete with main parameter, sush as W/C ratio and S/A ratio. The experiment results are summarized to follow as : $\circled1$ The ultra-sonic pulse was decreased as the increase of W/C ratio. $\circled2$ The maximum value for the ultra-sonic pulse velocity and compressive strength was presented in the case of 40% S/A ratio and these value was decreased as the change of S/A ratio over 40% $\circled1$ The relationship of the ultra-sonic pulse velocity and compressive strength on 28days according to the change of W/C and S/A ratio is to be: $F_{28} = -209193R^2 + 384417R - 1763441$(W/C Ratio) $F_{28} = 1726R^2 - 774R - 502 (S/A Ratio)

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.233-240
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• 1998

A rational expression, developed to predict the shear strength of reinforced concrete beams, is derived from the relationship between shear and the rate of change of bending moment along a beam coupled with experimental findings for the arch action. The proposed ultimate shear strength equation, arising from analytical premises and then calibrated with experimental data, is a similar form to the ACI 318 equation derived mainly from empirical approach. The proposed equation depends on the concrete compressive strength, amount of longitudinal steel content, and the shear span-to-depth ratio, and rationally reflects the shear resistance mechanism of combined beam action and arch action in reinforced concrete beams. The proposed equation applied to existing test data and the results were compared with those predicted by the ACI 318 equation and the Zsutty's equation.

• Advances in concrete construction
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• v.6 no.3
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• pp.297-309
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• 2018

The objective of this study was to evaluate the influence of silica fume (SF) on the hydration heat and compressive strength of concrete. Portland cement with w/(c+sf) ratios varying between 0.25 to 0.45 was substituted by 10%, 20% and 30% of SF by mass. A superplasticizer was used to maintain a fluid consistency of the concrete. The heat of hydration was monitored continuously by a semi-adiabatic calorimetric method for 10 days at $20^{\circ}C$. Compressive strengths are tested for each mixture until age of 180 days. The results show that silica fume considerably influences the evolution and the ultimate values of the compressive strengths as well as the hydration heat especially for 10% rate. The w/b ratio has a considerable effect where its decrease modifies compressive strength and hydration heat more than silica fume. The correlation of the obtained results allows deducing of ultimate properties as well as the ages to reach half of their values. The correlation coefficients are close to unity and reflect the judicious choice of these relationships to be used to predict compressive strength and hydration heat.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.1
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• pp.21-30
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• 2014

The objective of this study is to find the electrical properties of Bottom ash from thermoelectric power plants in Korea. By using Parallel Plate Method, the electrical resistivity and dielectric constant were measured at the frequency from 20 Hz to 10 MHz. Also, unconfined strength test, XRF and sieve analysis were performed for finding the relationship between strength, physiochemical properties and electrical properties. In the result, the change of electrical resistivity and dielectric constant of bottom ash against frequency was similar to that of general soil. The proportion of fine grain in bottom ash had the positive correlation with dielectric constant and negative correlation with electrical resistivity. Chloride and sulfur trioxide were proportional to dielectric constant and the more bottom ash had chloride content, the lower electrical resistivity appeared in bottom ash. Unconfined strength of bottom ashes had a range from 200 kPa to 780 kPa and strength was inverse proportional to electrical resistivity.

• The Journal of Korean Society for School & Community Health Education
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• v.1 no.1
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• pp.107-118
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• 2000

This study was designed to contribute to the right development of children's physical strength and growth by making a comparative analysis of 6 graders' physical strength with the help of the 6 events of physical strength tests according to sex and trying to work out some relationship between obese children and normal ones. With this in mind, the subjects were 400 elementary students, obese and normal, who reside in Seoul. The results were made by means of the average records and standard deviation test of 6-event physical strength tests per sex and group. The conclusions were as follows; 1. The normal children's average score was better than those of their counterparts, showing a significant difference in the 6-event of physical strength tests. 2. There was a little difference per sex. And there was a significant static interrelations in 4 events except a 100 m race and a standing broad jump when the subjects do well in the two afore-mentioned events. All the other groups minus female normal one show a low interrelations in such events as a 100 m race, a chin-up, and hanging down from the horizontal bar. 3. The obese group was inferior to the normal one regardless of sex. In terms of the physical interrelations, there was no difference among the three groups minus the female normal one.