• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.563-564
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• 2009

Ultra-High Performance Concrete (UHPC) compared to normal concrete is exhibiting extremely high strength characteristics with compressive strength and tensile strength reaching 200MPa and 15MPa, respectively. The mechanical characteristics of UHPC can be thus exploited advantageously in the construction of structure through the reduction of the cross-sectional area and fabrication of slim and light-weight of the structural members. In the case where the structural member is made of UHPC, the occurrence of crack can be prevented by releasing the restraint provided by the form in due time. This research performs parametric study of the failure characteristics of concrete such as failure energy and softening curve suggested by the viscous crack model approximating the failure of concrete. The scope of this research contains the results of tests performed to investigate the strength of UHPC during early elapsed time.

• Nuclear Engineering and Technology
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• v.42 no.2
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• pp.175-182
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• 2010

As part of a fundamental study on the volume reduction of contaminated concrete wastes, the separation characteristics of the aggregates and the distribution of the radioactivity in the aggregates were investigated. Radioisotope $^{60}Co$ was artificially used as a model contaminant for non-radioactive crushed concrete waste. Volume reduction for radioactively contaminated dismantled concrete wastes was carried out using activated heavy weight concrete taken from the Korea Research Reactor 2 (KRR-2) and light weight concrete from the Uranium Conversion Plant (UCP). The results showed that most of the $^{60}Co$ nuclide was easily separated from the contaminated dismantled concrete waste and was concentrated mainly in the porous fine cement paste. The heating temperature was found to be one of the effective parameters in the removal of the radionuclide from concrete waste. The volume reduction rate achieved was above 80% for the KRR-2 concrete wastes and above 75% for the UCP concrete wastes by thermal and mechanical treatment.

• Magazine of the Korea Concrete Institute
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• v.22 no.1
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• pp.21-24
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• 2010

• KEPCO Journal on Electric Power and Energy
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• v.7 no.2
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• pp.295-299
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• 2021

Recently, interest in maintenance has been increasing due to the enlargement and aging of infra structures. Therefore, a new paradigm is required to secure and improve the durability of structures differentiated from the past. Accordingly, research on smart concrete incorporating the concept of self-healing into concrete is being actively conducted. In this study, the crack healing performance and durability performance of self-healing concrete applied with a hydrogel containing biomineral-forming microorganisms were evaluated. As a result of evaluating the dispersion of the hydrogel in concrete, it was confirmed that the hydrogel was well distributed in concrete matrix with a dispersion coefficient of 0.35 to 0.46. The crack healing performance evaluation was verified by a water permeability test, and showed a recovery rate of 95% or more at the age of 28 days, confirming the applicability of self-healing concrete. The durability performance of self-healing concrete was evaluated in terms of resistance to penetration of chloride ion and freezing and thawing. Regardless of the mixing of the hydrogel, the same level of durability performance was shown for various compressive strength level. Therefore, it was confirmed that the microbial admixture did not affect concrete durability. In the future, long-term crack healing performance and durability verification studies should be supplemented.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.237-240
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• 1999

This study was performed to analyze strength characteristics of concrete using FWS(foundry waste sand), as a way of study for reusing the FWS disused in the foundry as the fine aggregate for concrete. As the experimental results, the slump of concrete showed a decline with the increase of replacement ratio of FWS. The compressive strength of concrete made with FWS 25% replacement river sand showed higher value than that of concrete not containing FWS, but the flexural strength of concrete containing FWS was decreased 21% compared with that of concrete not containing FWS at age of 28days.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.355-362
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• 2001

This study deals with cracking control of concrete deck in steel-concrete composite bridges according to the concrete slab casting sequences. In correlation studies between casting sequences, time dependent effects of concrete creep and shrinkage are implemented in the analytical model. Finally, the methods of cracking control in terms of concrete slump and relative humidity are suggested to prevent early transverse cracking of concrete slab.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.241-246
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• 2000

In the strut-tie model design of structural concrete, the importance of the effective strength of concrete strut has been overlooked by many practitioners. The authors believe that the effective strength of concrete strut is an important factor not only in determining steel tie forces but also in verifying the nodal zone strength and geometric compatibility condition of a selected strut-tie model. This study evaluate the effect of the effective strength of concrete strut on structural concrete design by applying the different effective strut strengths to the strut-tie model design of a post-tensioned anchorage zone and a continuous concrete deep beam.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.232-236
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• 1993

The Tunnel Form(T/F) system instead of traditional euro form has been tried to reduce construction duration and to improve concrete quality in reinforced concrete wall type apartment construction. To find the relationship for concrete compressive strength between cylinder mold and slab, the different curing locations of concrete cylinder mold in the room have been investigated. The test results showed that the compressive strength of the cylinder concrete with middle-upper location in the room was most near concrete compression strength with respect to slab concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.649-656
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• 1997

The properties of super-flowing concrete with low heat cement were experimentally investigated and compared with ordinary 25-240-15 concrete with type Vcement. The cement content of super-flowing concrete with the low heat cement was 400 kg/$\textrm{m}^3$. However the hydration heat of super-flowing concrete is relatively lower than that ordinary concrete with type V cement. Also the ability to resist chloride ion penetration of super-flowing concrete with low heat cement is 5 times better than that of the ordinary concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.81-84
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• 2005

We investigated the effect of inorganic impurities such as clay bricks and asphalt concrete in recycled aggregate on the properties of lean concrete. The optimized moisture content of lean concrete with clay bricks increased, because the absorption ratio of clay bricks is high. On the other hand, lean concrete with asphalt concrete produced an opposite result owing to low absorption ratio. The results showed that inorganic impurities did not have a significant effect on compressive .strength of lean concrete containing below 30$\%$ clay bricks and below 10$\%$ asphalt concrete.