• Journal of the Korea Institute of Building Construction
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• v.9 no.2
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• pp.85-91
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• 2009

W/C and unit volume, which significantly affect quality of concrete related to strength and durability, are regulated at below $185kg/m^3$ for regular concrete generally used in standard specification for constructions. The aim of this research is to develop chemical admixture and find out its potential use by identifying characteristics of admixtures added to soft concrete and hardening concrete, of which content ratio of component for each type of admixtures is subject to change in accordance with unit volume within KS' allowable range. Sodium gluconate, polyoxyethylene nonylphenyl ether, poly carboxylic copolymer in slump, which is characteristic of soft concrete, are deemed highly sensitive while there is no air entrainment except for $10\sim70%$ in WE, WR component content ratio and NP. In hardening concrete, strength in general showed higher action in compressive strength and tensile strength than in plain strength. Use of proper AE agent and AE water reducing agent at the same time is deemed to be used as chemical admixtures capable of manufacturing high-quality, high-quantity concrete.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.35-42
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• 2008

In this study, a sample was fabricated according to the recycled aggregate replacement level(0%, 30%, 60%), and the steel fiber mixing status in order to use recycled aggregate as a concrete alternative coarse aggregate, and then the materials and structural characteristics of recycled aggregate and steel fiber which impacted the reinforced concrete were analyzed. A conclusion was derived as follows. After considering the results of various material experiments and mock-up test, when a flexural strength and a ductility factor is increased and the replacement level is increased through mixing the steel fiber with the recycled aggregate concrete, the ductility and flexural strength reduction seems to be inhibited by adding the steel fiber. Also, it is indicated that the recycled aggregate has almost-similar compressive strength, tensile strength flexural strength and ductility capacity to the concrete which using the general gone even though the steel fiber is used and the replacement level is increased to 30%. Accordingly, the reinforced concrete frame using the steel fiber mixture and recycled aggregate seems to apply to the actual structure.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.27-38
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• 2003

The characteristics and prediction model of the shear strength of unsaturated residual granite soils were studied in this paper. In order to investigate the influence of the net normal stress on the shear strength, unsaturated triaxial tests and SWCC tests were carried out by varying the net normal stress. Experimental data for unsaturated shear strength tests were compared with predicted shear strength envelopes obtained from existing prediction models. It was shown that the soil-water characteristic curve and the shear strength of the unsaturated soil varied with the change of the net normal stress. Therefore, to achieve a truly descriptive shear strength envelope for unsaturated soils, the effect of the normal stress on the contribution of matric suction to the shear strength has to be taken into consideration. In this paper, a modified prediction model f3r the unsaturated shear strength was proposed.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.2
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• pp.34-41
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• 1999

Adsorption of cationic polyacrylamide dry strength resins onto the surface of papermaking fibers and fines is critical for their effective utilization. Since dry strength resins are frequently employed when recycled fibers containing a great deal of fines are used as a raw material, their adsorption characteristic onto the recycled fiber fines is of great importance. In this study, effects of recycling on adsorption characteristics of cationic polyacrylamide onto primary and secondary fines were examined. Never dried bleached hardwood kraft pulp was beaten and dried for recycling. In each recycling step the adsorption characteristic of a cationic PAM onto primary and secondary fines was evaluated by kjeldahl nitrogen analysis method. The influence of recycling on water retention value and carboxyl content along with the sheet density and tensile strength was examined. Secondary fines of never dried pulp adsorbed twice as much of C-PAM as the primary fines, however, the adsorption capacity of the secondary fines decreased rapidly during the course of recycling and showed lower adsorption capacily than primary fines.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.53-58
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• 2003

Concrete structures move wholly with concrete and rebar, so they endure external force, but recently the embedded rebar in concrete has been corroded by environmental, physical and chemical factors, the embedded rebar corrosion influences concrete structure to deteriorate structure capacity. To revaluate effect to deterioration of concrete structure according to corrosion of rebar, the researcher mostly examined into corrosion rebar and complex relation of concrete. In that there are flexural strength deterioration of corrosion concrete structure and the bond strength of concrete. But It has not sufficiently studied about physical characteristic of corrosion rebar itself. In this study I will compare specification of rebar through corrosion experiment with corrosion ratio of rebar according to diameter and revaluate. And will investigate the effect to strength characteristic of rebar according to corrosion ratio.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.53-58
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• 2003

Concrete structures move wholly with concrete and rebar, so they endure external force, but recently the embedded rebar in concrete has been corroded by environmental, physical and chemical factors. the embedded rebar corrosion influences concrete structure to deteriorate structure capacity. To revaluate effect to deterioration of concrete structure according to corrosion of rebar, the researcher mostly examined into corrosion rebar and complex relation of concrete. In that there are flexural strength deterioration of corrosion concrete structure and the bond strength of concrete. But It has not sufficiently studied about physical characteristic of corrosion rebar itself. In this study I will compare specification of rebar through corrosion experiment with corrosion ratio of rebar according to diameter and revaluate. And I will investigate the effect to strength characteristic of rebar according to corrosion ratio.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1478-1480
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• 1997

We investigated the breakdown characteristic of mineral oil according to applied voltage and tip radius. In this experiment, electrode system was point-plane geometry. The tip radius of needle was 5, 10, 20 and $25{\mu}m$, respectively. Applied voltage was AC and DC. We measured breakdown voltage for each tip radius with increasing electrode gap, 2mm to 10mm. Under nonuniform electric field, breakdown strength was higher when needle was negative than when needle was positive. Because it is polarity effects due to space charge. And the more sharp tip radius, whether we applied AC or DC, the higher breakdown strength. As tip radius increase, breakdown strength decreases exponentially.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.457-460
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• 2003

This paper discusses laboratory evaluations to assess the physical properties of antiwashout underwater concrete (AWC) containing pozzolanic materials such as fly ash (FA), blast furnace slag (SG) and metakaolin(MK). For the experiments, pH value, suspended solids, slump flow, efflux time and compressive strength were tested. According to the results from compressive strength test, MK10 showed the very high compressive strength characteristic during the entire curing days, but the rate of strength development was decreased as time goes by.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.250-255
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• 1993

This research is aimed at the experimental investigation of the characteristic contribution of the structural parameters, such as concrete over, concrete strength and reinforcing bar size on the dowel strength of the reinforced concrete stuctures. A total of twenty four specimens were tested for eight experimental conditions. The test results showed relatively close agreements with the values calculated by Vintzeleou-tassios equation. From the observations of the test results, it was found that the concrete cover affected almost linearly on the dowel strength , while the var size and the concrete strength showed coupled effects.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.989-999
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• 2016

Moist curing of concrete is a time consuming procedure. It takes minimum 28 days of curing to obtain the characteristic strength of concrete. However, under certain situations such as shortage of time, weather conditions, on the spot changes in project and speedy construction, waiting for entire curing period becomes unaffordable. This situation demands early strength of concrete which can be met using accelerated curing methods. It becomes necessary to obtain early strength of concrete rather than waiting for entire period of curing which proves to be uneconomical. In India, accelerated curing methods are used to arrive upon the actual strength by resorting to the equations suggested by Bureau of Indian Standards' (BIS). However, it has been observed that the results obtained using above equations are exaggerated. In the present experimental investigations, the results of the accelerated compressive strength of the concrete are used to develop the regression models for predicting the short term and long term compressive strength of concrete. The proposed regression models show better agreement with the actual compressive strength than the existing model suggested by BIS specification.