• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.235-242
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• 2016

As for a possibility of using high volume of recycled aggregate in concrete mixture, recycled fine one which is known to be worse in quality and hard to control was selected and investigated in terms of performance of mortar as the replacement ratio to natural fine aggregate was changed. As a result of test, it is found that grade of recycled fine aggregate was beyond standard one and fineness modulus of that itself was increased in compare to natural one. In case of making mortar with recycled fine aggregate, disadvantageous results such as less fluidity and air content including the increase of dry shrinkage were shown but strengths of mortar were comparable to the one making with natural aggregate, which means that planned strength of common concrete structure can be achieved by controlling W/C and the amount of chemical admixture, and also that large amount of recycled fine aggregate is applicable to the precast concrete products generally free to the amount of water.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.198-203
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• 2020

Cracking due to material behavior like drying shrinkage easily occurs since tensile strength in concrete is very low at initial curing stage. In this paper, workability such as air content and slump was evaluated on CFC(Cellulose Fiber Concrete) with 0.0 ~ 2.0% of fiber addition, and the tests for tensile/compressive strength were performed. With increasing addition ratio of fiber, air content and slump kept similar level to 1.0kg/㎥ of addition ratio, and this trend was effective to 2 hours after mixing. Strength was enhanced with increasing addition ratio, which showed 7.0 ~ 9.0% for compressive strength and 7.0 ~ 22.0% for tensile strength, respectively. The tensile strength increased relatively more, which show the addition of cellulose fiber was very effective to crack resistance. The workability in CFC can be guaranteed for 2 hours in the following conditions like 2 minutes of mixing period and 1.0kg/㎥ of addition ratio of fiber.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.123-130
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• 2019

The purpose of this study is to confirm the strength characteristics of concrete according to the mixing ratio of recycled fine aggregates and to use it as basic data for the use of recycled fine aggregates in concrete. For this purpose, the target design compression strength was set at 27MPa. Considering practical use of recycled aggregate, the mixing ratio of recycled fine aggregate was set at 0, 30, 60, and 100%, and the unconfined concrete and hardened concrete were tested. The LCA method was used to evaluate the environmental impact of recycled fine aggregate concrete, and the effectiveness of recycled fine aggregate in the production of concrete was verified.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.244-251
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• 2015

The paper evaluates the effect of the physical property, fineness modulus (FM) and replacement ratio of crushed sand on the characteristics of concrete. This is intended to use crushed sand from Daegu-Kyungbuk region as the fine aggregate of concrete. The experimental result indicates that the replacement ratio of crushed sand needs to be less than 50% to satisfy the mixed gradation of both natural and crushed sand when their FMs are 2.0 and 3.2, respectively. The slump of concrete with crushed sand increased as the replacement ratio of crushed sand increased, while the workability of concrete with the replacement ratio of more than 75% was significantly reduced. The air content and bleeding rate of concrete was reduced as the replacement ratio increased. Furthermore, due to the enhancement of the concrete adhesive regardless of the FM of crushed sand, compressive strength of concrete tended to improve as the replacement ratio increased.

• Journal of the Society of Disaster Information
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• v.9 no.4
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• pp.469-475
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• 2013

The purpose of this experimental research is to estimate compressive strength and resistance to freezing and thawing of recycled aggregate concrete containing ground granulated blast furnace slag. For this purpose, concrete specimens according to substitution ratio of recycled aggregate were made for different replacement ratio of ground granulated blast furnace slag(GGBFS), and then compressive strength and resistance to freezing and thawing were evaluated for those. It was observed from the test results that compressive strength at 28 days of recycled aggregate concrete containing GGBFS of 20% was much more excellent than plain concrete and when air content of concrete was maintained 4 to 6%, influence of substitution ratio of recycled aggregate and replacement ratio of GGBFS on resistance to freezing and thawing was little up to 300 cycles of freezing and thawing.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.2
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• pp.133-142
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• 2022

The purpose of this study is to develop an impact crusher with a radial rotating plate installed at the bottom, which is a shock absorber that can produce high-quality recycled coarse aggregate for concrete and to verify the effect of improving the quality performance of recycled coarse aggregate and its applicability through concrete tests. As a result, it showed improved quality in all items such as absolute dry density, absorption rate, abrasion resistance, Particle shape judgment rate, amount lost in the 0.08 mm sieve passing test, alkali aggregate reaction, clay mass, stability, and impurity content, and it was found to meet the criteria of recycled aggregate quality standards. In addition, the air volume and slump of concrete to which recycled coarse aggregate is applied meet all domestic standards. According to the test results of the compressive strength characteristics by age of concrete according to the mixing ratio of the recycled coarse aggregate, it was confirmed that the mixing ratio of the recycled coarse aggregate was applicable up to 60 %.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.549-551
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• 2016

In this paper, With the development of modern science and technology are Sheds to stay indoors rather than outdoors space it increased significantly compared to the past. And a wide variety of research about outdoor air quality until recently, efforts are underway but the issue of air quality in the room is the fact that all considered relatively lightly. As the contamination of the room air is polluted, unlike the natural environment, a large outdoor air dilution rate, the dilution rate is very low, once the contaminated air continuously circulating exerts a very bad influence on the health of people staying in the room. In this study, movement characteristics of the person living in a room, the air measuring device for the study of the active indoor environmental control system reflects the life form to measure the quality of the measured air in real time for transmitting the information to the user of the smart devices, alarm bot It was implemented and operational applications.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.568-575
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• 2023

This paper aims to evaluate the quality characteristics and healing performance of precast concrete incorporating self-healing technology as a key technique for the construction of smart cities. The study found that precast concrete mixed with hybrid capsules exhibited a tendency of reduced slump and air content, impacting the quality characteristics. Specifically, the slump decreased by up to 14 %, and the air content by up to 9 %. Moreover, the inclusion of hybrid capsules in the concrete resulted in a maximum decrease of 16 % in compressive strength and 18 % in flexural strength. However, the introduction of hybrid capsules significantly enhanced the crack healing performance. The assessment through water permeability tests showed that the healing rate of 0.3 mm crack width after a 28-day healing period improved as the mixing ratio increased, with the healing rates at 1 %, 3 %, and 5 % hybrid capsule mixtures observed to increase by approximately 16 %, 25 %, and 32 %, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.1
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• pp.1-8
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• 2009

The simulation of a heat pump dryer has been carried out to figure out the effect of air flow rate on the drying performance represented by MER, SMER, and so on. The simulation includes the analyses of one-stage heat pump cycle and simple drying process using the drying efficiency. The heat pump cycle with Refrigerant 134a has been considered. In the dryer, some of drying air from the drying chamber flows through the heat pump system, the rest of air bypasses the heat pump system. The two air flows joins before the drying chamber inlet. The performance parameters considered in the present study are MER, SMER, the temperature and humidity of drying air. Those parameters are compared for different total air flow rate or bypass air flow rate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.168-176
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• 2017

This study, as a research for using crushed sand as a fine aggregate of concrete for nuclear structures, we improved the performance of impact crusher in the existing crushed sand production process and adjusted grain size to conform to ASTM C 33 The shape and grain size characteristics of a crushed sand were examined and concrete was prepared according to the substitution ratio of the sand to investigate the properties of fresh concrete and hardened concrete. The experimental results show that most of the concrete characteristics are equivalent to those of concrete using only heavy sand. However, when the substitution rate of steel sand exceeds 50%, the amount of air, compressive strength and tensile strength are somewhat reduced.