• Structural Engineering and Mechanics
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• v.41 no.4
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• pp.495-508
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• 2012

The strength theory of concrete is significant to structure design and nonlinear finite element analysis of concrete structures because concrete utilized in engineering is usually subject to the action of multi-axial stress. Experimental results have revealed that lightweight aggregate (LWA) concrete exhibits plastic flow plateau under high compressive stress and most of the lightweight aggregates are crushed at this stage. For the purpose of safety, therefore, in the practical application the strength of LWA concrete at the plastic flow plateau stage should be regarded as the ultimate strength under multi-axial compressive stress state. With consideration of the strength criterion, the ultimate strength surface of LWA concrete under multi-axial stress intersects with the hydrostatic stress axis at two different points, which is completely different from that of the normal weight concrete as that the ultimate strength surface is open-ended. As a result, the strength criteria aimed at normal weight concrete do not fit LWA concrete. In the present paper, a multi-axial strength criterion for LWA concrete is proposed based on the Unified Twin-Shear Strength (UTSS) theory developed by Prof Yu (Yu et al. 1992), which takes into account the above strength characteristics of LWA under high compressive stress level. In this strength criterion model, the tensile and compressive meridians as well as the ultimate strength envelopes in deviatoric plane under different hydrostatic stress are established just in terms of a few characteristic stress states, i.e., the uniaxial tensile strength $f_t$, the uniaxial compressive strength $f_c$, and the equibiaxial compressive $f_{bc}$. The developed model was confirmed to agree well with experimental data under different stress ratios of LWA concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.58-63
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• 1999

Almost all concrete structures have many inevitable cracks for various reasons such as drying shrinkage, heat liberation of cement, fatigues or repeating loads and movements. Conventionally, they are repaired with epoxy materials. The Epoxy resins used by repair materials are different from properties of the base concrete materials such as thermal and mechanical properties - thermal expansion coefficients, bending strength. And the epoxy resin cannot release the water inside the concrete structure and cause corrosion of the steel bars. In this study, before the experiment got launched, we had analyzed cement and slag. Then We blended the two grades of ultra fine cement using high blaine cement and slag. And the cement slurry was produced by water and suprplasticizer to each blended ultra fine cement in various conditions. The slurry produced by each conditions was evaluated with flow properties such as viscosity, dropping time, segregation and observation of dry surface after injection.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.365-368
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• 2008

This research is related to 240MPa ultra-high strength concrete(UHSC) with extremely loss W/B ratio. For this development, High flow cement is mainly used which has a short reaction rate due to the high blaine and high early strength, which can make greater fluidity in case of very low W/C ratio. It made the best mixture using the mineral admixtures silica fume, slag powder and special admixture. For dispersibility and homogeneity of cement binder, cement of premix type is produced using omni-mixer. Moreover, it ensures the fluidity of ultra-high strength concrete(UHSC). For having a good fire performance, we made an experiment special coarse aggregate. As a result, we got 180MPa in case of water curing, 200MPa in case of steam curing and uniform UHSC of 240MPa in case of a special curing method.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.7
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• pp.55-67
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• 2004

In this paper, the flowability, strengths, impact resistance and sulfuric acid resistance of steel fiber reinforced high performance concrete (SFHPC) for the steel fiber content and fly ash and blast furnace slag as admixtures were presented. For evaluating flowability particularly, tests of slump flow, box-type passing ability and L-type filling ability were performed. The slump flow of SFHPC was some decreased with increase of the steel fiber content. At the box-type passing ability, the difference of box height of SFHPC is greatly increased with increasing the fiber content. The L-type filling ability of SFHPC was not excellent above $0.75\% of the steel fiber content. Also, the compressive strength of SFHPC was decreased with increase of the steel fiber content, but the flexural strength of SFHPC was much higher than that of the concrete without the steel fiber. At the impact resistance, drop number of SFHPC for reaching final fracture was increased with increase of the fiber content. Also, the drop number for reaching initial fracture of lmm was increased with increase of the fiber content. At the sulfuric acid resistance, 4-week weight change of SFHPC with the steel fiber was almost similarity that of HPC without the steel fiber and was in the range of 73.6 to 81.5.

• Advances in concrete construction
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• v.11 no.1
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• pp.19-32
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• 2021

In the present experimental study, the high performance hybrid fiber reinforced concrete (HPHFRC) is prepared using the Modified Andreasen and Andersen (A&A) particle packing model. Total of 16 trial mixes of HPHFRC with Indian standard sand (SS) and natural river sand (NS) are prepared to achieve the selection criteria (flow percent>150 and compressive strength>80 MPa). Based on the flow percent and compressive strength criteria, the selected mixes evaluated to study the effect of usage of natural river sand (NS) and the expensive Indian standard sand (SS) on the mechanical, durability, and microstructure property of designed HPHFRC. It has been found that the Modified A&A model is reliable to design the mix for HPHFRC with excellent mechanical, durability, and microstructure properties. In addition to that, a moderate difference in the mechanical and durability properties of NS contained HPHFRC and SS contained HPHFRC is found. Based on the obtained results of NS contained HPHFRC, it can be concluded that the use of natural river sand (NS) can be successfully adopted for the production of HPHFRC, resulted in a reduction of the production cost without compromising the excellent performance of HPHFRC.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.473-480
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• 2005

In this study, a mix design for self compacting concrete was based on Okamura's method and concrete incorporated just a ground granulated blast furnace slag. Replacement ratio of slag is in the range of $20-80\%$ of cement matrix by volume. For the optimal self compactability in mixture incorporating ground granulated blast furnace slag, the paste and mortar tests were first completed. Then the slump flow, elapsed time of 500mm slump flow, V funnel time and filling height by U type box were conducted in concrete. The volume of coarse aggregate in self compacting concrete was in the range of $50-60\%$ to the solid volume percentage of coarse aggregate. Finally, the compressive and splitting tensile strengths were determined in the hardened self compacting concrete incorporating ground granulated blast furnace slag. From the test results, it is desirable for self compacting concrete that the replacement of ground granulated blast furnace slag is in the range of $40-60\%$ of cement matrix by volume and the volume of coarse aggregate to the solid volume percentage of coarse aggregate with a limit of $55\%$.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.318-321
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• 2000

Most compressive strengths commonly used in the construction field are in a range of 240 to 300 kgf/$\textrm{cm}^2$ at 28 days. To get this rage of strengths, however, high-flowing concrete requires cementitious binders more than 400 to 450 kg/$\textrm{cm}^2$ for preventing segregation and sedimentation of aggregates. This amount of cementitious binder generates a large emission of excessive hydration heat, which may consequently induce harmful cracks in concrete structure. In order to reduce excessive hydration heat, thus, this paper aims at fabricating a high-flowing concrete under the condition that cement content is kept as low as 350kg/$\textrm{cm}^3$ by using viscose agents. In a parametric study, effects of cement types such as a ternary blended cement and Type V on he physical characteristics of high-flowing concrete were evaluated. In addition, the influence of viscosity was also investigated by applying two different viscose agents, one in a range of 6,000 to 10,000 cps and the others of 10,000 to 14,000 cps. In terms of chemical admixtures used in concrete mixture, the superplasticizer was Sulfonated Melamine-Formaldehyde Condensate with about 30,000 of molecular weight, and main component of viscose agent was HPMC (Hydroxy Propyl Methyl Cellulose). Slump flow was fixed at 50cm with different dosages of superplasticizer in weight.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.235-240
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• 1995

A 36 stories high multi-use building was designed with the specified concrete strength range of 300~400kg/$\textrm{cm}^2$ On the ground of the concept of compressive strength, adequate mix designing for the concrete, which has the target strength range of 390-520kg/$\textrm{cm}^2$, was carried out to provide enough strength margin. And with due regard to the workability and transportation time, the slump and slump flow ranged 16~21cm and 30~45cm respectively, maintaining these properties up to 2-hours from the beginning of the mix. The high-range water reducer is incorporated into the mix as a admixture. The building construction is controlled satisfactorily, so far. The actual average 28-day compressive strength is 370kg/$\textrm{cm}^2$, the standard deviation is 28kg/$\textrm{cm}^2$ and the coefficient of variation is 7.6% for concrete of 300kg/$\textrm{cm}^2$ specified strength.

• Computers and Concrete
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• v.4 no.2
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• pp.101-117
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• 2007

A new model predicting the nonlinear basic creep behaviour of concrete structures subjected to high multi-axial stresses is proposed. It combines a model based on the thermodynamic framework of the elasto-plastic continuum damage theory for time-independent material behaviour and a rheological model describing phenomenologically the long-term delayed deformation. Strength increase due to ageing is regarded. The general 3D solution for the creep theory is derived from a rate-type form of the uniaxial formulation by the assumption of associated creep flow and a theorem of energy equivalence. The model is able to reproduce linear primary creep as well as secondary and tertiary creep stages under high compressive stresses. For concrete in tension a simple viscoelastic formulation is applied. The material law is then incorporated into a finite element solution procedure for analysis of reinforced concrete structures. Numerical examples of uniaxial creep tests and concrete members show excellent agreement with experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.707-714
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• 2001

This paper presents the fundamental study on rational manu(acture of Very High Strength(VHS) concrete using industrial by-products as like silica fume, slag and fly ash. In this study, we had tested various mixing cases to manufacture the VHS concrete(target compressive strength : over 1,000 kgf/$cm^{2}$) which is easily workable (target slump flow : 60$\pm$l0cm), The main variables studied are; 1) test variables to find the optimum replacement ratio of mineral admixture, 2) test variables to find a rational water-binder ratio, a proper binder content, 3) test variables to find the method for reduction of slump loss, 4) test variables to know the influence of air entrainment on frost resistance. From the test results, it is concluded that the rational mix design can be made by using 40% slag, 10% silica fume, and water reducing agent(slump loss reduction type). We found that it is unnecessary to entrain air for freeze-thawing resistance.