• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.575-583
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• 2001

The purpose of this study is to present the method of utilizing the recycled aggregate that are obtained from waste concrete as the concrete aggregate. We manufactured the recycled aggregate concrete with compressive strength of over 300kgf/㎠ to increase its weaker strength than the normal concrete, and compared the physical features of the recycled aggregate concrete with that of the normal concrete. As a result of the study, the mechanical performances such as compressive and tensile strength were generally reduced as the mixing rate of the recycled aggregate increased; however, it was possible to manufacture the concrete with the compressive strength of 300∼600kgf/㎠ using the adequate mixing material such as unit quantity of cement, compounding water and silicafume. However, a continuous study on long-term durability performance is required to manufacture and utilize the recycled aggregate concrete for the structure.

• Computers and Concrete
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• v.23 no.3
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• pp.155-160
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• 2019

The use of recycled aggregate concrete for the purpose of environmental and resource conservation has gained increasing interest in construction engineering. Nevertheless, few studies have reported on the bonding performance of the bars in recycled aggregate concrete after exposed to high temperatures. In this paper, 72 pull-out specimens and 36 cubic specimens with different recycled coarse aggregate content (i.e., 0%, 50%,100%) were cast to evaluate the bond behavior between recycled aggregate concrete and steel bar after various temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$). The results show that the recycled aggregate concrete pull-out specimens exhibited similar bond stress-slip curves at both ambient and high temperature. The bond strength declined gradually with the increase of the temperature. On the basis of a regression analysis of the experimental data, a revised bond strength mode and peak slip ratios relationship model were proposed to predict the post-heating bond-slip behavior between recycled aggregate concrete and steel bar.

• Journal of the Korea Institute of Building Construction
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• v.7 no.1 s.23
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• pp.115-121
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• 2007

Ordinary concrete uses aggregate sufficiently soaked with water, and is weighed, mixed with other materials and placed in accord with performances required in the construction field. Recently special concrete with high fluidity and durability is required but it is difficult to use top-quality concrete due to lack of high-quality aggregate, delayed transportation because of traffic jam, etc. In addition, sometimes the use of a remicon is inevitable just for small-sized concrete constructions or it is difficult for a remicon to reach remote construction places such as mountainous areas. To solve these problems, this study attempted to pack concrete materials. In other words, it is to instantize concrete. This study dried aggregate, a material of concrete, and compared the change of absorption phase of the aggregate in water and in paste in order to examine the effect of the dryness of aggregate on its absorption rate and, based on the absorption rate, decided water addition ratio necessary for the reduction of unit quantity caused by the use of dry aggregate in designing concrete mixture, and analyzed the properties of unhardened concrete according to water addition ratio in manufacturing concrete using aggregate in the state of absolute dryness and in the state of surface dryness.

• International Journal of Highway Engineering
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• v.17 no.1
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• pp.7-16
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• 2015

PURPOSES : This study was performed to determine a systematic approach for measuring the coefficient of thermal expansion (COTE) of concrete specimens. This approach includes the initial calibration of measurement equipment. Test variables include coarse aggregate types such as natural aggregate, job-site produced recycled concrete aggregate, and recycled aggregate processed from an intermediate waste treatment company. METHODS : First, two cylindrical SUS-304 specimens with a known COTE value of $17.3{\times}10^{-6}m/m/^{\circ}C$. were used as reference specimens for the calibration of each measurement system. The well-known AASHTO TP-60 COTE apparatus for concrete measurement was utilized in this study. Four different measurement apparatuses were used with each LVDT installed and a calibration value was determined using each measurement apparatus. RESULTS : In the initial experimental stage, calibration values for each measurement apparatus were assumed to be almost identical. However, using the SUS-304 samples as a reference, the calibration values for the four different measurement apparatuses were found to range from 3.49 to $8.86{\times}10^{-6}m/m/^{\circ}C$. Using different adjusted values for each measurement apparatuses, COTE values for the three different concrete specimens were obtained. The COTE value of concrete made with natural coarse aggregate was $9.91{\times}10^{-6}m/m/^{\circ}C$, that of job-site produced recycled coarse aggregate was $10.45{\times}10^{-6}m/m/^{\circ}C$, and that of recycled aggregate processed from the intermediate waste treatment company was $10.82{\times}10^{-6}m/m/^{\circ}C$. CONCLUSIONS : We observed that the COTE value of concrete made from recycled concrete aggregates (RCA) was higher than that of concrete made from natural coarse aggregate. This difference is due to the fact that the total volumetric mortar proportion in the RCA mix is higher than that in the concrete mix made with natural coarse aggregate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.87-91
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• 2009

Recycling demolished concrete as an alternative source of coarse aggregates for the production of new concrete can help solve the growing waste disposal crisis and the problem of depleted natural aggregates. The purpose of this study is to investigate chloride migration of recycled aggregate concrete containing pozzolanic materials by chloride migration coefficient. The specimens were made with recycled coarse aggregate as various replacement ratio(10, 30, 50%) and metakaolin, blast furnace slag, fly ash is replaced for recycled concrete with mixing ratio 20%. The major results are as follows. 1) Compressive strength of recycled aggregate concrete containing pozzolanic materials increase as curing age and chloride migration decrease. 2) When the replacement ratio of recycled coarse aggregate is 30%, the chloride migration coefficient of recycled concrete containing blast furnace slag, metakaolin shows the similar or lower value than plain concrete at all ages.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.12-15
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• 1993

Critical shortage of natural aggregate for production of concrete is developing in many urban area. At the same time increasing quantities of demolished concrete form deteriorated and obsolete structures are generated as a waste material in the same areas. The reuse of a waste concrete may settle the problems of environmental pollution and shortage of adquate aggregate, Therefore, this study is to reuse a waste concrete as aggregate for concrete, It is the purpose of this present study to investigate and analyze how the addition rates of superplasticizer and curing condition affect the properties of fresh and hardened recycled aggregate concrete comparing with those of ordinary concrete and crushed stone concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.326-329
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• 2003

In practice, recycled aggregate is not used for a structural member due to its high absorbability and abrasion. It is, however, highly expected that the usage of recycled aggregate increases as the processing technique of the recycled aggregate progresses. In this study herein, the compressive strength of the recycled aggregate concrete was investigated. Coarse aggregate was replaced with 100% of the recycled aggregate, and cement and fine aggregate was replaced with various amount. The specimen was steam-cured at $80^{\circ}C$. It was shown that the concrete can obtain desirable strength when fine aggregate was replaced with up to 60% of recycled fine aggregate, and when cement was replaced with up to 15% of fly ash.

• Computers and Concrete
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• v.26 no.6
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• pp.505-513
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• 2020

Grading of aggregate influences significantly almost all of the concrete performances. The purpose of this paper is to propose practicable equations that express the optimized total aggregate gradation, by weight or by number of particles in a concrete mix. The principle is based on the fractal feature of the grading of combined aggregate in a solid skeleton of concrete. Therefore, equations are derived based on the so-called fractal dimension of the grain size distribution of aggregates. Obtained model was then applied in such a way a correlation between some properties of the dry concrete mix and the fractal dimension of the aggregate gradation has been built. This demonstrates that the parameter fractal dimension is an efficacious tool to establish a unified model to study the solid phase of concrete in order to design aggregate gradation to meet certain requirements or even to predict some characteristics of the dry concrete mixture.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.223-228
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• 2003

Recently, owing to the deterioration of reconstruction and the construction, much of the construction waste is discharged in our construction field, and the amount of construction waste is rapidly increased. These waste are raised to financial and environmental problems, so the method of reusing waste concretes has been studied and carried out many direction. Especially being want of resources, if waste concrete could be recycled as aggregates for concrete, it will contribute to solve the exhaustion of natural aggregate, in terms of saving resources and protecting environment. This study is that the mechanical properties of concrete with recycled coarse aggregate were investigated for types of mineral admixture and the substitution of recycled coarse aggregate. The result of this study, in case of using mineral admixture, the property of fresh concrete was rised. And the property of harden concrete for the substitution ratio of recycled coarse aggregate was decreased. But the property of concrete with mineral admixture was better than that of concrete used only cement.

• International Journal of Highway Engineering
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• v.6 no.1 s.19
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• pp.37-45
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• 2004

The characteristics of concrete strength and fracture parameters of recycled aggregate concrete were investigated to apply to the concrete pavements. As the results, the early strength of recycled aggregate concrete showed to be lower than that of natural coarse aggregate concrete, whereas strength at 28 days showed to be similar. Young's modulus of recycled aggregate concrete was lower than that of natural coarse aggregate concrete due to the difference of aggregate strength. And recycled aggregate concrete contained with ground granulated blast furnace slag seemed to have an effect of strength increasing. The critical stress intensity factor of recycled aggregate concrete at the early age was increased, and converged to be similar, compared to natural aggregate concrete at later age. The reliability of two-parameter fracture model was identified by the good correlation between the theoretical value computed by P-CMOD relationship and experimental results for Young's modulus and tensile strength.