• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.609-612
• /
• 1999

Recently, the antiwashout underwater concrete with an antiwashout admixtures has been increasingly used for underwater structures. However, the credibility of antiwashout underwater concrete was brought up as problems because it seldom was applied to fields. In this study, experiments were made on the basic properties of antiwashout underwater concrete replaced with fly ash up to 30% to improve its properties. Resultant to the test, we got the results as follow; funnel flow time was decreased, the slump flow was increased and the elevation of head was decreased rapidly whereas the amount of suspended solids became high, pH became low. In view of 70%, the standard ratio of compressive strengths between cast in water and in air, it was obtained the result that the ratio was over 90% at 28days.

• KCI Concrete Journal
• /
• v.11 no.3
• /
• pp.79-88
• /
• 1999

Most difficulties of inducing high fluidity on the concrete mixing design with a strength range of 210 to 240kg/$\textrm{cm}^2$ result from the segregation of aggregates due to the shortage of cementitious binders. To solve the problem, this study concentrated on finding the optimized amount of binder material which does not affect the concrete strength and is also economical. Also there were studies on the use of intermediate sized aggregates to avoid the gap-grading between coarse and fine aggregates so that the material segregation in high flowing concrete was and minimalized the fluidity and penetration capacity of the reinforcing bars was enhanced. Throughout the parametric study with respect to water/binder ratio. superplasticizer. replaceable mineral admixture, the size of coarse aggregate and mixing methods, the effect of each constituent on the characteristics of high flowing concrete could be observed. As a result or partially using stone powder or an intermediate class of aggregate (max. diameter 13mm) . it was fund that the fluidity of concrete significantly increased without material segregation and any change of compressive strengths. It was also proved in this study that proper mixing time and speed are significant factors influence the performence of high flowing concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.543-544
• /
• 2009

The fiber(NY, PP) known to the effective material on improvement of the fire-resistance of HSC(high strength concrete) has a difference for fluidity according to the variation of a length and contents of fiber. In this study, to analyze the effect of a length and contents of the fiber on the fluidity of HSC and fheological characteristics, we calculated a viscosity of mortar by mini slump-flow, simple V-lot and viscometer. With the test results, the fluidity characteristic showed a moderate difference by a length and contents of the fiber, but showed a significant difference by increase of the fiber contents. ${\ast}$ AFR Concrete (Advenced Fire Resistant Concrete)

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2020.06a
• /
• pp.197-198
• /
• 2020

A study was conducted on UHPC production using the silicone mold method. UHPC (Ultra-High-Performance Concrete) has the advantage of being able to shape the product in a free-form shape on concrete, but when mass-producing products in one design, such as electronic products, rather than one-time products such as buildings and decorations Demolition is difficult with wood and mold. This study uses silicone molds, UHPC mix to ensure fluidity, self-integrating performance and mechanical performance Prototyping was done proportionally.

• Magazine of the Korea Concrete Institute
• /
• v.7 no.3
• /
• pp.156-163
• /
• 1995

In the previous study, styrene mdleic dnhydride copolymer(SMA) as synthesized flom styrene and rnale~c dnhydr~de and further redcted with sulfuric acid to obtam water soluble SMA. In thls study, the flow dnd strcngth tests of cement mortar rmxed wth copolymers wele carried out to evaluate the capability of copolymers as high range water reducer for the con crete. It was found from flow exper~ment that the fluidity of cenient mortar rmxed wth sulfonated SMA(SSMAj was larger thdn that mxed ulth amnophenol substituted SSMA (SmSMAj. The decreasing rate of the flow of cement mortar rmxed ulth SSMA and SmSMA was significantly lower than that mixed ulth naphthalene condensate(NSC) The compressslve strength of the hardened cement mortars containing 0.5% copolymers after 28 dys curing was exarmned. 'The compressive strength of hdrdened cement mortar containing SSMA and SmSMA was mcreased up to 31% and 13%, respectively, when omp pared to the plain. As the results, the copolyniers(SSMA and SrnSMA) used in thls study are greatly expected as a good high range water reducers for the concrete.

• Journal of the Korea Institute of Building Construction
• /
• v.7 no.1 s.23
• /
• pp.57-62
• /
• 2007

Generally, the strength of concrete depends on factors of materials, mix proportions, compaction, manufacturing methods and curing and so on. And recently, it has increased the using of crushed sand for concrete due to the exhaustion of good natural aggregate. In case of Korea, in 2004, the using ratio of crushed sand occupies about 28% of whole fine aggregate. This is an experimental study to compare and analyze the influence of W/B ratio and replacement ratio of crushed sand on the fluidity and compressive strength of high strength concrete. For this purpose, the mix proportions of concrete according to the W/B (31.5, 27.5, 23.5%) and replacement ratio of crushed sand (0, 20, 40%) was selected. And then air content, slump-flow, a-lot, compressive strength test were performed.

• Journal of the Korea Concrete Institute
• /
• v.24 no.1
• /
• pp.37-44
• /
• 2012

Recently, due to developments in construction technology, the use of high-performance concrete became popular. High-performance concrete when compared to the ordinary concrete can better satisfy required performances by using mineral admixture and superplasticizer. Various studies on the effect of admixture materials on the quality of high-performance concrete have been reported. But there exist limited number of reported results on the effect of cement qualities, which is the most important constituent material in concrete. Therefore, in this study, the relationship between the quality of cement and the flowability of high flowing concrete is investigated. Qualities of domestically produced cement were identified, and then the influence of the qualities of cement on the flowability of high flowing concrete is evaluated. The result showed that the dosage of required superplasticizer was dependent on cement fineness, to brain, free-CaO, and interstitial phase, which all trigger initial hydration process of cement. Particularly, the results showed that fineness of cement has a high impact on the dosage of the superplasticizer. For strength property of concrete, the dosage of superplasticizer had a significant effect on the early age strength, but had negligible effect in the long term strength.

• Computers and Concrete
• /
• v.32 no.2
• /
• pp.185-206
• /
• 2023

This article aimed to explore the optimization of mineral admixtures and retarding admixture for high-performance concrete. In essence, fresh concrete can be regarded as a mixture in which both coarse and fine aggregates are suspended in a cement-based matrix paste. Based on this view, the test procedure was divided into three progressive stages of binder paste, mortar, and concrete to explore their rheological behavior and mechanical properties respectively. At each stage, there were four experimental control factors, and each factor had three levels. In order to reduce the workload of the experiment, the Taguchi method with an L9(3⁴) orthogonal array and four controllable three-level factors was adopted. The test results show that the use of the Taguchi method effectively optimized the composition of high-performance concrete. The slump of the prepared concrete was above 18 cm, and the slump flow was above 50 cm, indicating that it had good workability. On the other hand, the 28-day compressive strength of the hardened concretes was between 31.3-59.8 MPa. Furthermore, the analysis of variance (ANOVA) results showed that the most significant factor affecting the initial setting time of the fresh concretes was the retarder dosage, and its contribution percentage was 62.66%. On the other hand, the ANOVA results show that the most significant factor affecting the 28-day compressive strength of the hardened concretes was the water to binder ratio, and its contribution percentage was 79.05%.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.1029-1034
• /
• 2003

The basic Physical properties, Slump, Slump Flow, Air content, Bleeding, and Settlement of concrete was investigateed to test Characteristic of Setting and to evaluate the relation between Model Specimen and Heat of hydration for construction Over the High Temperature (CFT). The objective of this study is to take the partial core after the cementation of Model Specimen, test the compression intensity and analyze the relation to Test Piece.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2008.05a
• /
• pp.193-197
• /
• 2008

Recently, it increases in use of CFT(Concrete filled steel tube, below CFT) that is an excellent internal force and deformation capacity because material and method are required to be diversification and High-Performance according to increase the super-high structure. And it is proposed to use high-strength Concrete Filled steel Tube Column. But it is difficult quantitative evaluation about fire-resist performance of CFT because steel tube bind concrete. Also, the case of high strength CFT is feared that spalling occur inside. Therefore, this study made CFT specimen that determine the factor(which is strength of concrete) and then CFT column was exposed to heating controlled as closely as possible the ISO-834 standard fire curve. Also, it tried to analyze internal temperature through nonlinear transient heat flow analysis.