• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.505-508
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• 2006

This experimental study is to evaluate the effects of recycled coarse aggregate replacement level on the mechanical properties of concrete produced at Batcher plant. The main test parameter was replacement level of recycled coarse aggregate with the ratio of 0, 30, 60 and 100% to the natural coarse aggregate. From the test results, it was found that compressive strength, elastic modulus and splitting strength are decreased with the increased proportion of replacement level. Therefore, some design coefficients or recommendations for elastic modulus and splitting strength of concrete need to be reconsidered with minor reduction factor of '0.85'.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.525-528
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• 2006

Recently, Korea government prepared Act on facilitation of construction waste recycling in December 2003 for effective recycling of rapidly increasing construction wastes, and has enforced the Act on Jan. 2005. This Act limits the definition of recycled aggregates to the aggregates which obtained quality certificate and for this purpose, government has operated quality standard and certificate system of recycling aggregate. The objective of this experimental study is to evaluate the mechanical properties of recycled coarse aggregate concrete according to curing method by ready-mixed concrete. Compressive strength ratio of recycled aggregate concrete under air-dry curing/wet curing was $74{\sim}91%$. KCI code for conventional concrete overestimated elastic modulus for recycled coarse aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.245-248
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• 2006

The objective of this study is to take the first step in creating a user-friendly health monitoring system for recycled aggregate concrete structure using acoustic emission(AE). Each specimen was a cube, the edge of which was 150mm. For pull-out tests, a steel rebar, 13mm in diameter, was embedded in the center of each specimen and casting directions(i.e., vertical and horizontal) were considered in this paper. The AE parameters were analyzed for damage levels(i.e. internal cracking stage, pull-out stage) of all specimens. Results from this study show that event, duration versus amplitude of a signal, showed a clear difference for different loading stages depending upon the concrete casting directions.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.249-252
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• 2006

When concrete is subjected to uniaxial compression, the failure process is normally initialed from a localized zone. The localization of failure governs structural behaviors of concrete. In this paper, the compressive strength and failure behavior of recycled coarse aggregate concrete with different replacement level of recycled coarse aggregates are investigated using acoustic emission(AE). AE characteristics of concrete were investigated during the entire loading period. For these purpose, four recycled coarse aggregate replacement level (i.e 0%, 30%, 60% and 100%) were considered in this paper. Result from this study show AE signal, AE method can apply to investigate a compressive failure mode according to recycled coarse replacement level.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.101-111
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• 2016

It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like cement. This is necessary to evaluate mineral composition, particle shape, surface, size distribution, density and absorption ratio for fine aggregates due to few detailed research to examine influence of fine aggregates properties on unhardened geopolymer concrete. In this research, used two different fine aggregates, Jumunjin sand(having quartz, mica, feldspar, pyroxene in mineral composition, more than 96% of total size between -0.60 and +0.30mm, angular shape and rough surface) and ISO sand(having almost all quartz in mineral composition, more than 51% size between -1.40 and +0.60mm, simultaneously varied size distribution, spherical shape and smooth surface). After an experimental result of the varied ratio of Si/Al=1.0-4.1 geopolymer paste, mix proportion respectively applied Si/Al=1.5 having the highest compressive strength to mortar and Si/Al=3.5 having the highest consistency to concrete. Geopolymer mortar by mixing with Jumunjin and ISO sand in varied range of 20-50wt.% showed flow size increase between 69.5 and 112.0mm, between 70.5 and 126.0mm respectively. Geopolymer concrete at an addition of 77wt.% of total aggregates ratio showed that average compressive strength was 32MPa and the consistency was favorable to molding. Since ISO sand observing varied size distribution, spherical shape, smooth surface, low absorption ratio resulted in advantageous properties on consistency of geopolymer, geopolymer concrete can be suitable for using the fine aggregates similar to ISO sand.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.4
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• pp.21-28
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• 2014

In this study, evaluated ware the strength and durability of the vegetated water purification channel concrete to which recycled aggregates, hawang-toh and jute were applied. Box-Behnken method of response surface analysis in statistics was applied to the experimental design. Experimental variables are as follows, recycled coarse aggregates, hawang-toh, blast-furnace slag and jute fiber. In the experiment, conducted were the tests of compressive strength, chloride ion penetration, abrasion resistance and impact resistance the replacement rate effects of the recycled aggregates, blast-furnace slag and hwang-toh on the performance of vegetated water purification channel concrete were analyzed by using the response surface analysis method on the basis of the experimental results. In addition, an optimum mixing ratio of vegetated water purification channel concrete was determined by using the experimental results. The optimum mixing ratio was determined to be in 10.0% recycled coarse aggregates, 60.0% blast-furnace slag, 10.1% hwang-toh and 0.16% jute fiber. The compressive strength, chloride ion penetration, abrasion rate, and impact number of fracture test results of the optimum mixing ratio were 24.1 MPa, 999 coulombs, 10.30 g/mm3, and 20 number, respectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.31-32
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• 2013

ThThe purpose of this study is to investigate the compressive strength properties of fly ash using water eluted from recycled coarse aggregate. When fly ash come into contact with water, they have not a autonomously chemical reaction. But fly ash is a pozzolan reaction when fly ash come into contact with water and calcium hydroxide(Ca(OH)2) in alkaline environment. For that reason, if water eluted from recycled coarse aggregate use mixture water, fly ash is expected to reaction of pozzolan reaction property in early stage. According to the experimentation result, ICP-MS analysis showed water eluted from recycled coarse aggregate has a high alkali-ash value of pH of 12 and over. And mixing ratio 30% fly ash mortar using water eluted from recycled coarse aggregate showed a similar strength of plain mortar due to the pozzolan reaction. Also, poor strength in initial age, disadvantage of mortar using fly ash, can be improved as hydration in early age is expedited due to calcium hydroxide(Ca(OH)₂) and unhydrated cement component eluted from recycled aggregate mortar.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.367-374
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• 2019

Drying shrinkage in the hardened cement is known to change in volume by decreasing the moisture content in the hardened body, and it is known that the higher the W / C and the higher the content of the paste, the larger the drying shrinkage. In the case of ECC, more drying shrinkage occurs compared to concrete, since it does not contain coarse aggregate. Since ECC is an important material for tensile performance, the effect of restrained tensile stress on mechanical tensile behavior should be considered. The purpose of this study is to analyze the effect of stress caused by restraint on the tensile behavior of ECC. The mechanical properties of the specimens were tested by uniaxial tension tests with different restraints. As a result, the difference of tensile behavior according to restraint stress was observed and the cause was analyzed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.72-78
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• 2020

The present study developed shotcrete for fiber-net integrated tunnel support system, which consists of fiber-net support materials including netlike fiber and shotcrete and integration technology between support materials. In addition, in order to evaluate the field applicability of the developed tunnel support system and compare with the performance of steel fiber reinforced shotcrete, mock -up test was conducted on the mock -up structure. The test results show that in the case of shotcrete containing coarse aggregate(S20A5RP10-C), the excessive rebound rate occurred as the secondary shotcrete was dropped during construction due to the degradation in bond performance with fiber-net. Also, in the case of steel fiber reinforced shotcrete, the amount of cast shotcrete fell short of target value due to the fiber ball and the degradation of pumpability. On the other hand, the amount of cast mortar shotcrete(S20A5RP10-M) and the installation position of fiber-net were almost close to the target values, and the lower rebound rate occurred compared to the steel fiber reinforced shotcrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.3
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• pp.290-297
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• 2024

In this study, the gas permeability characteristics according to the construction joint were evaluated under pressure conditions ranging from 0 to 300 psi. The pore distribution and pore ratio were analyzed using X-ray CT. The average porosity of the OPC specimen was 0.74 %, while the FA specimen showed a relatively low pore ratio of 0.51 to 0.65 % regardless of the presence of the construction joint. For the OPC and FA plain specimens with a thickness of 50 mm without construction joints, no gas permeation occurred below 300 psi. At 300 psi, the gas permeation rates of the specimens with rough and smooth construction joint surfaces were 0.28 L/min and 0.31 L/min, respectively, which were 1.7 times higher than those of the specimens without construction joints. This is because the construction joints affected the distribution of the pores and coarse aggregates and the penetration path within the concrete. The porosity in the construction joint was the highest at about 2 %, and it was confirmed that the pore ratio gradually increased as it approached the joint.