• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.416-424
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• 2019

In Korea, press concrete in basements is mainly applied using plain concrete. This system has undesirable defects such as cracks caused by plastic shrinkage and irregular temperature distribution. To solve this problem, metal lath and fibers have been used in the past. However, they have not been effective in controlling cracks. This study analyzed the reduction of plastic shrinkage cracking for press concrete using various admixtures in a basement has been. In the air contents test, the specimens with various admixtures showed air contents similar to plain concrete (4.5±1.5%). The specimens using silica fume, super plasticizer agent, and SBR showed higher compressive strength by about 10-15% than plain concrete. Cracking decreased when the MC, super plasticizer, and SBR were added. When MC was used in the concrete, the plastic shrinkage did not occur.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.177-183
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• 2011

VES-LMC(very-early strength latex modified concrete) has been widely used as repair material for bridge deck overlay or rehabilitation, because it could be opened to the traffic after 3 hours of curing. However, the bright color of VES-LMC disturb driver's sigh. A black VES-LMC, matching to asphalt concrete, was developed and applied at a filed for driver's comfort and safety. The black VES-LMC included 2% carbon black in cement weight ratio. A series of performance evaluation for black VES-LMC was done in terms of field applicability, pavement color and temperature change. The field applicability test result showed that there were no change of workability, slump and air void, and the compressive strengthen developed more than 20MPa after 4 hours of placement. The thermal stress of black VES-LMC was smaller than that of OPC and asphalt concrete, which means the stability of black VES-LMC. The performance evaluation result showed that the black VES-LMC could prevent road icing at below zero temperatures and promote thawing at melting temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.673-676
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• 2008

Color concrete utilizes peculiar texture and color sense in external appearance actively as a finish. But, this color concrete is essential use of pigment for required color revelation, and color cone cleat from mixing of this pigment are different existent achromatic color concrete and basic properties of matter. this study progressed slump test and setting time examination through mortar injection resistance examination of mortar that mix Pigment.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.249-256
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• 2002

High performance concrete is prone to large autogenous shrinkage due to its low water to binder ratio (W/B). The autogenous shrinkage of concrete is caused by self-desiccation as a result of water consumption by the hydration of cement. In this study, the autogenous shrinkage of high performance concrete with and without fly ash was Investigated. The properties of fresh concrete, slump loss, air content, and flowability as well as the mechanical properties, compressive strength and modulus of elasticity, were also measured. Test results was shown that the autogenous shrinkage of concrete increased as the W/B decreased. For the same W/B, the autogenous shrinkage of high strength concrete with fly ash was considerably reduced although the development of its compressive strength was delayed at early ages. Furthermore, the autogenous shrinkage and compressive strength of high strength concrete were more rapidly developed than those of normal strength concrete. It was concluded that fly ash could improve the quality of high strength concrete with respect to the workability and autogenous shrinkage.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.81-88
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• 1990

For the protectioon of radioactive leakage, the quality control of main concrete structure in nuclear power plants is very important. So, this studey is designed to analyze the influence of kind of cement and aggregate on the mechanical properties of high density concrete. Test results of this study are as follows; 1)The slump of magnetite aggregate concrete(MAC) is found half value of nat.ural aggregate concrete (NAC). 2)As the effect of cement, the compressive strength of concrete using moderate heat cement is found higher 5-19 % than that of ordinary portland cement. 3)As the effect of fine aggregate, t.he compressive strength of MAC is found higher than that. of NAC below 340kg/$cm^2$ and lower t.han NAC above 340kg/$cm^2$. 4)As the effect of coarse aggregate, the compressive strength of MAC is found higher 17-22% than that of NAC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.58-63
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• 2015

Several researches on cement zero concrete using alkali-activators have been conducted to investigate its fundamental material properties such as slump, strength and durability, however, research on the structural behavior of relevant members involving the elastic modulus, stress-strain relationship is essential for the application of this cement zero concrete to structural members. In this paper the shear behavior of reinforced concrete beams using 50 MPa-alkali activated slag concrete was experimentally evaluated. To achieve such a goal, six reinforced concrete beam specimens were fabricated and their shear behaviors were observed. The maximum difference between test results and analysis results in crack shear stress for beam specimens without stirrups is 31%, while that for beam specimens with stirrup is 15%. Furthermore, it is also found that the shear strength of alkali activated slag concrete is by 22~57% greater than the nominal shear strength calculated by design code, implying that shear design equations would provide conservative results on the safety side.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.43-49
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• 2015

The objective of this paper is to investigate experimentally the effect of the substitution of recycled aggregates under 13mm on the properties of the concrete using coarse aggregate with size of 13~25mm. Recycled aggregate under 13mm were substituted to the concrete ranged from 10% to 100%. To compare the properties with the case of recycled aggregate, crushed stone with smaller than 13mm was also substituted to the concrete by 20% and 40%. Test results showed that increase of recycled aggregate under 13mm resulted in the increase of slump and compressive strength compared with plain mixture, which was made with only aggregate with 13~25mm size. This is due to the dense gradation of aggregate in association with addition of relatively small particle. It is thought that the use of recycled aggregate under 13mm along with 30% contributes to the quality improvement of the concrete made with only 13~25mm aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.181-188
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• 2013

This paper is to investigate experimentally an effect of carbon amino silica black-superplasticizer(CASB-SP)on the engineering properties and chromaticity of black color concrete with 0.45 of W/C(water to cement). CASB-SP and carbon black were applied for pigment of the concrete. To prevent efflorescence of concrete, four different water repellent agents were also applied. As results, it was found that use of CASB-SP increased the slump and air contents. Furthermore, the use of CASB-SP increased the compressive strength. As CASB-SP dosages increased, chromaticity was well developed. For the effect of water repellent agent, the use of epoxy type was effective for protection from efflorescence. Based on test results, it was evaluated that 0.5% of CASB-SP effectively improve the concrete quality as well as enhance the chromaticity with proper dosage.

• International Journal of Highway Engineering
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• v.16 no.6
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• pp.79-86
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• 2014

PURPOSES : In this study, wasted vinyl aggregate, which possesses better thermal properties than natural aggregate, was used in cement concrete mixture to develop more economical concrete with thermal insulation and freeze prevention effects. METHODS : Slump and air content of the fresh concrete, which substituted its 0%, 5%, and 10% of coarse aggregate with wasted vinyl aggregate, were measured. Compressive strength, Poisson's ratio, elastic modulus, and splitting tensile strength of hardened concrete were measured by laboratory tests. Thermal properties of concrete such as coefficient of thermal expansion, thermal conductivity, and specific heat were also measured according to replacement ratio of wasted vinyl aggregate. Finally, the thermal insulation and freeze prevention effectiveness of the concrete mixed with wasted vinyl aggregate was confirmed through finite element analysis of road pavement crossing above concrete box culvert made from wasted vinyl aggregate. RESULTS : Even though the physical properties of wasted-vinyl-aggregate concrete such as compressive strength, Poisson°Øs ratio, elastic modulus, and splitting tensile strength were inferior to those of ordinary concrete, they met requirements for structural concrete. The thermal properties of concrete were improved by wasted vinyl aggregate because it decreased thermal conductivity and increased specific heat of the concrete. According to the result of finite element analysis, temperature variation in pavement subgrade was mitigated by box culvert made from wasted-vinyl-aggregate concrete. CONCLUSIONS : Through the laboratory test and finite element analysis of this study, it was concluded that the concrete structures made from wasted vinyl aggregate showed thermal insulation and freeze prevention effects.

• Computers and Concrete
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• v.21 no.4
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• pp.407-417
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• 2018

Concrete which is a composite material is one of the most important construction materials. Compressive strength is a commonly used parameter for the assessment of concrete quality. Accurate prediction of concrete compressive strength is an important issue. In this study, we utilized an experimental procedure for the assessment of concrete quality. Firstly, the concrete mix was prepared according to C 20 type concrete, and slump of fresh concrete was about 20 cm. After the placement of fresh concrete to formworks, compaction was achieved using a vibrating screed. After 28 day period, a total of 100 core samples having 75 mm diameter were extracted. On the core samples pulse velocity determination tests and compressive strength tests were performed. Besides, Windsor probe penetration tests and Schmidt hammer tests were also performed. After setting up the data set, twelve artificial intelligence (AI) models compared for predicting the concrete compressive strength. These models can be divided into three categories (i) Functions (i.e., Linear Regression, Simple Linear Regression, Multilayer Perceptron, Support Vector Regression), (ii) Lazy-Learning Algorithms (i.e., IBk Linear NN Search, KStar, Locally Weighted Learning) (iii) Tree-Based Learning Algorithms (i.e., Decision Stump, Model Trees Regression, Random Forest, Random Tree, Reduced Error Pruning Tree). Four evaluation processes, four validation implements (i.e., 10-fold cross validation, 5-fold cross validation, 10% split sample validation & 20% split sample validation) are used to examine the performance of predictive models. This study shows that machine learning regression techniques are promising tools for predicting compressive strength of concrete.