• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.415-423
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• 2006

As the shortage of natural & good quality aggregate for concrete, it is needed development of alternative aggregate. At the present time, the crushed sand is widely used among the alternation aggregate, and the usage of crushed sand will be increased more and more. Generally, crushed sud is produced with wet process in domestic, but some manufacturing companies which are handicapped with local restrict are produced by dry process. In this study, analyzing the facilities of dry crushed sand, the quality properties of dry crushed sand was done by Korean Industrial Standards. Based on the quality results of dry crushed sand, the experiment of concrete with the dry crushed sand which is substitute for sea sand was done. As the results of basic qualities, the amount of 0.08 mm sieve passing ratio was over KS criteria, and the fineness modulus was higher than sea sand, and the other physical properties of dry crushed sand was similar to sea sand. The results of concrete experiment, according to the substitutive ratio of dry crushed sand is increased, the slump and air content of concrete was decreased by increase of fine particles of dry crushed sand, and the unit weight content, compressive & tensile strength of concrete were increased on the contrary. The physical properties of concrete used dry crushed sand were showed same tendency without relation to W/B. Consequently, if the fine particle contents of dry crushed sand was lower, it is judged that dry crushed sand is no problem to use for concrete aggregate and the amount of usage will be increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.83-90
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• 2008

The purpose of this study is to attempt to use broken red brick, which is categorized as impurities of circular aggregate to thick aggregate, as a replacement for concrete. Through the material test and performance test for each mixing rate of the broken red brick (0%, 30%, 60%), the following conclusion was reached by studying the material and structural characteristics of circular aggregate to the concrete. Even though broken red brick, which is categorized as impurities of circular aggregate, is mixed 30% with normal rubble, the compression strength, intensity strength, and curving strength was similar to that of concrete that uses normal rubble. Therefore, concrete beam made with broken red brick can be applied to the real construction field. Also, the study regarding the cutting test of the concrete that uses broken red brick and regarding applying and mixing admixture that can increase the ductility factor will be required in the future.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.116-122
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• 2016

This study was intended to evaluate the properties of concrete incorporating stone powders which are created during crushing natural stones to produce crushed aggregates. For concretes with 0~30 wt.% partial replacement fine aggregates with stone powders, experiments of slump, air content, strength and drying shrinkage were carried out. The experiments found that the increase of the amount of stone powders sharply decreased slump and air content. Partially using stone powders instead of fine aggregates was found to increase both compressive and tensile strength slightly. Substituting higher amount of stone powders presented higher drying shrinkage. When HRWRA was added into the concrete with stone powders in order to obtain workability similar to that of plain concrete without stone powders for the same water-cement ratio and unit weight of cement, air content increased with the amount of HRWRA but strength and drying shrinkage were hardly affected by adding HRWRA.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.219-231
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• 2024

A survey of concrete plants in Incheon Metropolitan City and Gyeonggi Province was used to conduct an analysis of aggregate transport distance and production forms, as well as to evaluate the features and current status of aggregates distribution. As a result, areas such as Incheon, Siheung, Bucheon, Gimpo, and Siheung, where the distance to the demand points is less than 20 km, exhibited bidirectional distribution whereas Paju, Yongin, Yangju, and Pocheon, with distances ranging from 20 to 50 km is showed a unidirectional distribution pattern supplying aggregates exclusively to Incheon. Survey on manufacturing forms, more than 85% of the gravel dispersed in the Incheon area is made up of crushed aggregates derived from rocks discharged at construction sites indicating a considerable skew in supply chain. These findings are predicted to have a detrimental influence on aggregate supply in the long run, necessitating policy changes targeted at building an optimal aggregate distribution market.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.113-119
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• 2006

It is now established that more than two types of blended aggregate have beneficial effects on quality and supply of concrete in the long run. However, studies on blended aggregate have not widely been progressive and the evaluation method of its most favorable mixture proportion is still needed. Therefore this study investigated the most favorable mixture proportion through the physical experiment of fresh and hardened state's cement mortar, in response to three types of composite ratio, natural fine aggregate(Ns), crushed fine aggregate(Cs) and recycled fine aggregate(Rs). Test showed that increase of blending ratio of Ns and Cs improved fluidity of mot1ar. For the properties of compressive and flexural strength, mortar blending Ns and Cs properly, exhibited similar value to one using only Cs, while mortar mixing Rs showed lower strength value as less as 6% of control one. Mortar using only Rs exhibited the largest drying shrinkage value. In addition, even thought it is not a clear quantitative analysis, technical-imaging-skill presenting the most favorable mixture proportion 3-dimensionally is proposed in this research, in order to notify the proportion easily.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.785-792
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• 2017

In recent times, the lack of good quality natural aggregate has led to the alternative use of recycled aggregate. However, the adhered mortars in recycled aggregate lower the performance of the concrete, such as by reducing its strength and causing deterioration and cracking. In this study, the effects of nylon fiber (NF) on the mechanical and durable performance of recycled coarse aggregate concrete (RAC) were experimentally examined. Concrete specimens with natural coarse aggregate (NA) or RA were produced by adding 0, 0.6 and $1.2kg/m^3$ of NF. Various mechanical properties and the durability of the RAC were measured and compared with those of the NAC. In addition, in order to observe the hydrates and ITZ, SEM observations were made of the 28-day concrete samples. From the test results, as expected, it was found that the RAC exhibited lower performance than the NAC. However, the addition of NF to the concrete was effective in significantly enhancing the performance of the RAC due to the bridge effect of the NF.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.459-467
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• 2006

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river as to grow construction demand and the low grade of nature sand like sea sand. Following, need is to diversify the supply sources of fine aggregates which are excessively relying on sea sand and urgency is to find as soon as possible aggregate resources that can substitute sea sand. On the other hand, various fine aggregates are utilized to produce concrete in the domestic construction fields. However, few studies have been systematically investigated on the effects of such fine aggregates on concrete properties. Therefore, this study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the quality of concrete through the analysis of the effects of such fine aggregates on the physical properties of fresh concrete and strength of hardened concrete. Results revealed that crushed sand degraded the fluidity and air entraining of concrete compared to natural aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting bad grain shape and grade was larger adverse effect on the physical properties of concrete. The type of fine aggregates appeared to have negligible influence on the strength for W/C of 55%, 45% while crushed sand decreased the strength for W/C of 35% compared to natural aggregates. It analyzed that the combination of crushed sand exhibiting bad grain shape and grade with natural aggregates improved the characteristics of fresh concrete and had negligible influence on the strength.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• 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 Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.15-21
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• 2015

Recently, attempts of replacing some of natural aggregate with mix of low quality aggregate are carried out for stable supply of aggregate. However, low quality aggregate such as recycled aggregate produced during the disposal process of construction wastes and by-product aggregate produced by industrial activities has problem of failing to comply to KS Standards. Therefore, we have compared fundamental properties of concrete by using granite crushed aggregate, recycled aggregate, blast furnace and electric arc furnace slag aggregate for effective utilization of lacking aggregate resources. As the result, slump in case of mixed use of aggregate was increased 0~10% compared to single use. Therefore, it is judged to be economically advantageous as it can expect effects in unit quantity or reduction of SP agent. Compressive strength in case of mixed use of aggregate was increased 0~10% compared to single use as it filled internal crevice of concrete with continuous particle size distribution. Accordingly, if we utilize by satisfying standard particle scope through mix of aggregate with different cause of formation in proper ratio, it was possible to confirm utility of mixed aggregate with demonstration of effects of increases of fluidity and compressive strength of concrete.