• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.425-428
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• 2008

Concrete bridge decks, as well as asphalt pavement, are directly exposed to traffic loads and environmental conditions like rain water and deiceing chemicals. In this reason, there are often observed the deteriorations of asphalt overlay and of concrete deck under pavement. In this reason, it is important to identify the clear cause of concrete quality from a practical point of view. Therefore, in this paper it was initiated to ultimately suggest a protocol offering guidance as to assurance the quality control of concrete bridge deck on the part of void characteristics of concrete. Examinations such as visual inspection, deteriorated depth, and various void characteristic performed from cored specimens of 19 concrete bridge decks of various local conditions on the expressway. This paper discuss that the bridge deck condition analyses from the testing results were compared to a foreign guide line.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.961-966
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• 2000

It is difficult to change or remedy concrete structure after hardened. It is usual to evaluate the quality of hardened concrete using several test method. This study was performed to make fundamental data that could be used to evaluate the quality of hardened concrete. This study is to estimate mix proportion of hardened concrete. Each elements of concrete needed different estimation methods. First, the cement that handled by the most important compounds measured by XRF(X-ray fluorecence) machine with scanning Ca-K${\alpha}$. Second, the coarse aggregate that divided by maximum size measured by the area comparison method that starts from the assumption of uniform distribution. Third, the fine aggregate measured by the weight comparison method that needs several prerequsite constants which concerned cement hydration reaction. Fourth, the water content would be estimated by expert system that has data base of design data, the contents of above estimation results, the characteristics of concrete strength. As the result of the above research, some conclusions are as follows. The cement estimation method resulted by reliability of mean 96.7%, standard deviation 3.92. The area comparison method resulted by reliability of mean 95.3%, standard deviation 2.08. The weight comparison method resulted by reliability of mean 93.3%, standard deviation 3.35.

• 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.

• Advances in concrete construction
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• v.1 no.1
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• pp.103-119
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• 2013

The applicability of limit analysis methods in design and assessment of concrete structures generally requires a certain plastic deformation capacity. The latter is primarily provided by the ductility of the reinforcement, being additionally affected by the bond properties between reinforcing steel and concrete since they provoke strain localization in the reinforcement at cracks. The bond strength of reinforcing bars is not only governed by concrete quality, but also by construction details such as bar ribbing, bar spacing or concrete cover thickness. For new concrete structures, a potentially unfavorable impact on bond strength can easily be anticipated through appropriate code rules on construction details. In existing structures, these requirements may not be necessarily satisfied, consequently requiring additional considerations. This two-part paper investigates in a theoretical study the impacts of the most frequently encountered construction details which may not satisfy design code requirements on bond strength, steel strain localization and plastic deformation capacity of cracked structural concrete. The first part introduces basic considerations on bond, strain localization and plastic deformation capacity as well as the fundamentals of the Tension Chord Model underlying the further investigations. It also analyzes the impacts of the hardening behavior of reinforcing steel and concrete quality. The second part discusses the impacts of construction details (bar ribbing, bar spacing, and concrete cover thickness) and of additional structure-specific features such as bar diameter and crack spacing.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.151-156
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• 1994

This study is to investigate the quality of superplasticizers in domestic market. Therefore, the physico-chemical characteristics, the fluidity characteristics of fresh cement paste and mortar were tested. Also fresh and hardened properties of mortars and concretes using these superplasticizers were tested. From these results, differences of quality among superplasticizers are checked clearly in low water/cement ratio. And it is concluded that several superplasticizers have better dispersion ability than others in every tests. It has known that all samples are naphtalene sulfornate formaldehede types by the UV(ultra-violet) test.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.497-500
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• 2006

Masonry buildings constructed using concrete brick and cement mortar after normal Poteulranteu cement appearance, but problem of colloquial Chinese and individual crack etc. happened. Also, domestic standard abroad standard being applied mostly just as it is various kinds problem have. Therefore, purpose of this research is that wish to analyze physical special quality for Masonry individual and mortar and present pabulum that can evaluate deviation structural special quality.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.389-392
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• 2008

Ultra-high strength concrete becomes one of the main research areas because recently concrete structure is larger. The quality of aggregate (ultra-high strength and uniformity) as well as chemical admixture and mineral additives is a key factor for ultra-high strength concrete development. However, natural aggregate including crushed aggregate is inappropriate for ultra-high strength concrete because ultra-high strength quality cannot be maintained uniformly over whole natural aggregate lot. In this study ceramic aggregate was applied for ultra-high strength concrete in order to assure uniform quality of ultra-high strength aggregate. Ultra-high strength concrete was achieved by applying coated ultra-high strength ceramic aggregate to enhance the bonding strength between aggregate and cement paste. Also for actual application light weight ceramic aggregate(density 2.2 $g/cm^3$) with zero water absorption was tested.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.577-583
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• 2022

On large-scale sites, concrete is often delivered from a number of ready-mixed concrete companies, but even if the same concrete mixture table is used, it is thought that there will be a difference in quality due to differences in materials and manufacturing equipment. Due to a lack of previous research in this area, this study measured the properties of fresh concrete, compressive strength, and chlorine ion diffusion coefficient using the concrete supplied by 12 ready-mixed companies in Busan. The fresh concrete properties met the criteria. The compressive strength increased by 137% for 30MPa, 131% for 45MPa, and 117% for 80MPa by specified compressive strength. For the chlorine ion diffusion coefficient, the average value for each specified compressive strength could be derived without significant variation. The higher the compressive strength, the greater the deviation , and the lower the compressive strength, the greater the deviation in the chlorine ion diffusion coefficient.

• Journal of the Korea Institute of Building Construction
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• v.7 no.2 s.24
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• pp.99-106
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• 2007

The purpose of this study presents in Relations between cracks in self-leveling material and quality of floor groundwork surface are experimentally examined. As the first stage, the experiment to observe cracks in self-leveling material constructed on floor groundwork made from various kinds of concrete was carried. As a result, following basic findings were obtained. First, observation of cracks should be continued until an increase in width of cracks stop, without constructing any finishing material. Second, degree of cracks may be indicated quantitatively by the product of length and width. Finally, Cracks and separation is not be influenced by specimen size. Based on these findings, the method of predicting cracks by evaluating surface layer quality of floor groundwork will be established.