• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.1
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• pp.129-136
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• 1999

In this paper, the new non-destructive equation will be proposed and evaluated in comparison to the other foreign's non-destructive equation. Through the comparisons cores strength of mock structure with compressive strength obtained from new non-destructive equation ; rebound hammer, ultra-sonic pulse velocity and combined method, it will be analyzed about application of non-destructive equation. The results are following. The new non-destructive equations follow ; (1) $F_c=9.5R{\cdot}N+62.5$ (2) $F_c=243Vp-739$ (3) $F_c=8.1R_o+205.3V_p-802$ where, $F_c$ : Compressive Strength, $R_o$ : Rebound Number. $V_p$ : Ultra-Sonic Pulse Velocity Trough the result of mock structure test, the combined method is superior to rebound method and ultra-sonic pulse velocity method in the estimation of concrete strength. In order to apply the non-destructive equation of concrete strength to the structures, it is necessary that we should be made process study on the non-destructive equation for estimation of concrete strength in the range, time and strength of application under long-term.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.211-212
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• 2011

It was very important to evaluate concrete experimentally at elevated temperature because concrete was filled with aggregate of concrete volume about 70 percent. Concrete exposure to high temperatures produces changes in its internal structure, for instance loss of its strength and deformation capacity, in extreme cases risking the service life of the structure. The work of this paper is performed to evaluate the thermal behavior of ultra-high strength concrete having different water to cement ratio (strength), fine aggregate to aggregate ratio and maximum size of coarse aggregate. For exposure to 500℃ during 1 hour, residual mechanical properties of the ultra-high strength concrete decreased as the s/a ratio decreases and the maximum size of coarse aggregate increases.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.69-72
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• 2009

This research is focused on the applying of the foaming agent which can make the independent pore in the concrete structure in order to make a lightweight concrete structure. This lightweight foamed concrete can satisfy both the required strength and the mechanical properties as structural members. In addition, anti freezing-thawing properties also required. As a result of the unit volume-weight measurement, when the foaming agent mixed at 0.5% to 1%, the lightweight foamed concrete can be applied for the structural member. Also the density and compressive strength measurement results reveals that it will be suitable as structural member with 21MPa strength, when the density is betweenity8 to 1.9 and foaming agent quantities are 0.5% to 1%. Finally the result of freezing-thawing experiment, the effect freezing-thawing damage reduced according to adding foaming agent because those foaming agent make micro-pores in the structure which are not seen in the ordinary concrete structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.221-224
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• 2005

In order to traffic safety during winter season, snowfall and cold area has been spread the deicing chemicals, and the spraying amount is increasing every year. Use of deicing chemicals has been and will continue to be a major part of highway snow and ice control methods. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. Extensive use of chloride deicers is, however, the source of substantial cost penalties due to their corrosive action and acceleration to deterioration concrete structures. Deterioration due to de-icer salt occurs in practice in concrete pavement, dike, barrier and similar structure. This paper reports the results of effect of de-icer salt on durability of concrete structure in winter. To protect concrete structure from damage by de-icer salt in winter, the exposure test was performed using three methods such as increase in design strength upto 35MPa application of granulated blast furnace slag powder, and concrete sealer. Of these, the method of increase in design strength upto 35MPa showed better durability for deterioration by de-icer salt.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.523-526
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• 2005

In order to traffic safety during winter season, snowfall and cold area has been spread the deicing chemicals, and the spraying amount is increasing every year. Use of deicing chemicals has been and will continue to be a major part of highway snow and ice control methods. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. Extensive use of chloride deicers is, however, the source of substantial cost penalties due to their corrosive action and acceleration to deterioration concrete structures. Deterioration due to de-icer salt occurs in practice in concrete pavement, dike, barrier and similar structure. This paper reports the results of effect of de-icer salt on durability of concrete structure in winter. To protect concrete structure from damage by de-icer salt in winter, the exposure test was performed using three methods such as increase in design strength upto 32MPa application of granulated blast furnace slag powder, and concrete sealer. Of these, the method of increase in design strength upto 32MPa showed better durability for deterioration by de-icer salt.

• Journal of the Korean Society of Safety
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• v.28 no.6
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• pp.29-35
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• 2013

The purpose of this study is to investigate the steel bar corrosion and degree of reinforced concrete bridge, and analyze the cause of corrosion occurrence. Therefore they could ensure the durability and stability as to suggest the corrosion prevention of reinforced concrete structure. To study the corrosion state reinforced concrete structure, We investigate the cover of concrete, the compressive strength by schmidt hammer, the neutralization test of site, the compressive strength of core and the measurement of neutralized depth. As the results of test, the corrosion-grade of reinforced concrete structure which the degree of corrosion is 3, 4 degree get to 18% in the used time of 40 years and the time elapsed of 25 years. Therefore the corrosion of steel bar give rise to public discussion. The degree of corrosion is serious, and the neutralization come to the cover of concrete.

• Structural Engineering and Mechanics
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• v.64 no.6
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• pp.793-802
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• 2017

The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2001.11a
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• pp.40-45
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• 2001

The purposes of this study were mix design and quality control of high strength concrete for the construction of high rise complex structure. Desired performances of this high strength concrete were slump flow 50$\pm$10cm, air content 4.5$\pm$1.5% and design strength 400kgf/$cm^2$. Experimental flow was that optimal mix design was selected in the indoor experiment and after that, producing test was done in the batcher plant. Excel lent results of experiment was obtained from binder content 475kg/$m^2$ with replacement ratio 10% of fly ash. The results of field application of high strength concrete was sufficiently satisfied both flowability and compressive strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.147-148
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• 2023

Recently, as blast furnace slag concrete has become widely used, managing the strength of concrete has become important. mSn is a method of correcting the difference in strength between standard cured specimens and concrete exposed to changes in temperature. In this study, the predicted strength based on the maturity of the central and outer parts of the blast furnace slag concrete structure is compared with the actual strength measured through coring. As a result, the actual strength difference between the center and the outer part of the concrete mixed with blast furnace slag was larger than the predicted strength difference.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.145-148
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• 2004

The purpose is to prove the newly established 'UNBONDED CAPPING' method for Concrete Strength Tests. Day by day, concrete buildings and structure became high-rising and magnificently vast scheduled, as contributed from the development of improved equipments that suitable to specific construction works and high qualitied Admixture, the qualities of the concrete was highly improved. It is very important that the concrete strength tests and evaluation should be carried out in the manner that as soon as the concrete is placed so that dismantling form works can be done in time and that may enabling reducing construction period directly related with the costs of the project. However, the conventional capping method of concrete specimen requires more manpower and consuming times, As for the Sulfur capping, there may be incurred accidential fire and generation of Gas, what is more there stands limitation in precise evaluation of strength test results because of variation in capping method results may vary in concrete strength test results. Not necessarily emphasize, the compression strength of the concrete is the most valuable basic data essential to control the qualities of the concrete and that should be carried out accurately. in this study evaluation of the compressive strength test results comparing stabilized concrete capping method for Cement Paste capping, Sulfur-paste capping ,High Gypsum capping and recently flowing the Grinding with the UNBONDED CAPPING' method to provide reliable and economical concrete strength testing.