• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.123-130
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• 2010

In this study, mixed recycled coarse aggregate (RCA) was produced by mixing RCA from waste concrete in order to evaluate a new method of RCA production. Bond strength between reinforcing bars and RCA concrete was qualitatively evaluated as a part of continuous studies to establish design code of reinforced concrete structural members using recycled aggregate. For practical application, specimens were manufactured with the ready mix RCA concrete. Parameters investigated include: concrete compressive strength (i.e 21, 27 and 40 MPa), replacement levels (i.e 0, 30, 60 and 100%), bar position (i.e vertical and horizontal) and bar location (75 and 225 mm). For the pull-out test, each specimen was in the form of a cube, with each side of 150 mm in length and a deformed bar, 16 mm in diameter, was embedded in the center of each specimen. From the test results, the most of HT type specimen with compressive strength of 21 and 27 MPa showed lower bond strength than the ones provided in CEB-FIP and considered in reinforcement location factor ($\alpha\;=\;1.3$). It was reasoned that bonded area of top bar specimen was reduced at the soffit of reinforcement because of bleed water of fresh concrete. Therefore the reinforcement location factor in current KCI design code should be reviewed and modified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.603-609
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• 2008

The recycled aggregates which were produced from the waste concretes have the disadvantages of inferior properties for natural aggregate. Therefore, in order to reuse the recycled aggregate it must be solved to improve the quality of recycled aggregate. In this study, the quality of recycled aggregate was improved by the surface treatment method using the colloidal silica solution. And, in order to examine the possibility of reusing the surface coated recycled aggregate in constructing concrete structures, we studied the mechanical properties and durability of the concrete using the surface coated recycled aggregates and the other concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.71-72
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• 2009

For practical application of recycled aggregate concrete, it is very important to study bond behavior of reinforcing bars in recycled aggregate concrete. Pull-out test was performed in order to investigate the bond behavior between recycled aggregate concrete and deformed bars.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.26-32
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• 2020

Concrete recycling is becoming mandatory rather selective due to depletion of constructional materials and increase of concrete waste. Studies on recycling concrete are conducted in various point of view for long time. However, standard or guideline of many countries for the application of recycled aggregate concrete(RAC) has restrictions such as low replacement rate of coarse aggregate and no fine aggregate allowed due to inferior material properties of recycled aggregate. This study intends to figure out the feasibility of casting natural aggregate concrete(NAC) and RAC separately in a structural member. In making RAC, replacement rate of coarse aggregate was 50, 100% in RAC and treatment of interface of two concretes is introduced. RAC treatment of recycled aggregate or inclusion of additives was not done as it can increase embodied energy of concrete work. Double-shear test with uniformly distributed loading was adopted to evaluate shear strength at the interface of two concretes. After curing it was hard to distinguish interface of two concretes. Experimental result revealed that specimen with higher replacement rate showed higher shear-to-compressive strength ratio, which is possibly attributed to coarse aggregate size and roughness of sheared section. Further study on the effect of various parameters is required and subsequent research activity is on-going.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.445-454
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• 2016

With the increase of decrepit facilities, construction waste increased to a certain level and now the increase is more or less stabilized. Yet construction waste still constitutes the largest portion of the overall wastes. Also, it is inevitable to spend a huge amount of the national budget due to the aggravating shortage of aggregate caused by prohibition on collection of natural aggregates as well as due to the damage to the land and environment caused by development of the sources of aggregates. As a countermeasure to the situation, the Ministry of Land, Infrastructure and Transport promulgated the quality standard for recycled aggregate to manage the usage of recycled aggregate according to its quality. But use of recycled aggregate for the purpose of high added value still remains nominal. Therefore, this research aims to study the applicability of recycled aggregate concrete as structural concrete by evaluating the quality improvement effects and the performance of the recycled aggregate concrete including recycled fine aggregate and recycled coarse aggregate that have undergone carbonation for 4 days and 14 days respectively in the condition of 60% RH, 20% $CO_2$ and $20^{\circ}C$ temperature, suggested for carbonation modifying from the advance research. The result shows carbonation modify contributed to quality improvement with 0.91% decrease in absorption rate for recycled fine aggregate and 0.7% decrease in absorption rate for recycled coarse aggregate. The physical properties and durability of the recycled aggregate made of aggregate modified by carbonation showed results similar to general concrete, which confirmed the possibility of applying the recycled aggregate made of recycled aggregate modified by carbonation to structural concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.63-69
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• 2020

The volume of construction waste material from the entire waste material volume in Korea is approximately 47.3% to take the biggest ratio, and from them, the waste concrete takes up approximately 62.8% that recycling is an urgent issue to address. Therefore, the government recommends more diverse and broader facilitation of the recycled aggregate in order to promote recycling the construction waste materials. In addition, when using concrete recycled aggregate in building, building standard such as floor area ratio and building height are being mitigation. The standard is a condition that mitigation the floor area ratio by up to 15% when using up to 25% of concrete recycled aggregate. Therefore, this study reviewed the relaxation of construction of construction standards when using concrete recycled aggregate in order to actively recommend the use of concrete recycled aggregate. And using the recycled coarse aggregate among the recycled aggregate, the appropriate mixing time in the batch plant according to the substitution rate was derived. In addition, using recycled aggregate admixture in order to improve the drying shrinkage, did comparative analysis about physical and mechanical property of concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.122-129
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• 2017

The aim of this study is a large amount use of recycled aggregates. The considering recycled aggregates replacement ratio is 50% that of natural aggregates. In order to increase the shear capacity of beams, that may be weaken by use of recycled aggregates, steel fibers are reinforced. The main variables are steel fiber volume fractions such as 0%, 0.5%, 0.75% and 1.0%. After the test, it could confirm that the strength and deformation capacity of beams with the steel fiber content values of 0.5% and 0.75% are comprehensively enhanced compared to non reinforcement. After evaluating the shear strength by using shear strength equations of previous researches, it concluded that the strength equation of Oh et al. (2008) is able to predict the shear strength of SFRC beams on the safety side.

• Magazine of RCR
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• v.4 no.2
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• pp.46-49
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• 2009

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.72-80
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• 2005

A recycled aggregate contains impurities that affect negative effects on physical properties of concrete. Therefore, a test method for examining impurities content in recycled aggregate is necessary before use of recycled aggregate. In this study, the test method by visual examination for separating impurities in recycled fine and coarse aggregates was developed. The results of the test are as follow: 1. The current KS F 2576 was necessary for comprehensive revision including types of tested recycled aggregate, definition of terminology, quantity of sample, and test method. 2. Visual examination is appropriate for larger than impurity panicle size of 1.2mm, and the larger panicle size the shorter time was required. 3. For the impurity content test by visual examination, the easiness and accuracy of the test can be obtained from the condition of sample weight of 30 grams with particle size of 2.5mm to 5mm for recycled fine aggregate and the condition of sample weight of 1 kilogram with panicle size of larger than 5mm for recycled coarse aggregate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.28-36
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• 2019

The adhered mortars in recycled aggregate may lower the performance of the concrete, such as by reducing in strength and durability, and cracking. In the present study, the effects of nylon fiber (NF) on the mechanical and durable properties of 100% ordinary portland cement (OPC) and 50% ground granulated blast furnace slag (GGBFS) concretes incorporating recycled coarse aggregate (RA) were experimentally investigated. Concrete was produced by adding 0 and $0.6kg/m^3$ of NF and then cured in water for the predetermined period. Measurements of compressive and split tensile strength, water permeable pore and total charge passed through concrete were carried out, and the corresponding test results were compared with those of concrete incorporating crushed coarse aggregate (CA). In addition, the microstructures of 28-day concretes were observed by using SEM technique. Test results revealed that the RA concrete showed lower performance than CA concrete because of the adhered mortars in RA. However, it was obvious that the addition of NF in RA concrete was much effective in enhancing the performance of the concretes due to the bridge effect from NF. In particular, the application of NF2 (19 mm) exhibited a somewhat beneficial effect compared with concrete incorporating NF1 with respect to mechanical properties, especially for RA concrete.