• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.22-29
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• 2015

In this study, we tested to develop and apply structural insulation performance improvement concrete to field, which had compressive strength in 24 MPa and thermal conductivity twice as much as normal concrete. After experiment about slump and air contents, combination product of Plain and calcined diatomite powder showed reduction of slump and air contents and combination product with micro foam cell admixture, we cannot find result of slump and air contents reduction. Unit weight of combination product with insulation performance improvement materials decreased more than that of Plain. In the test of compressive strength, compressive strength of insulation performance improvement concrete decreased more than that of Plain but was content with 24 MPa. thermal conductivity of insulation performance improvement concrete tended to decrease. Freezing and thawing resistance of insulation performance improvement concrete was similar to that of Plain. In carbonation resistance test, combination product with calcined diatomite powder showed the result which was similar to that of Plain. In carbonation resistance test, combination product with micro foam cell admixture showed a increase compared to that of Plain and length variation of combination product generally increased.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.120-127
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• 2011

Recently, there are problems due to the exhaustion of natural aggregate resources, and strict restrictions. In this study, the possibility of using Water Granulated Ferro-Nickel slag as a substitutive material of fine aggregate is determined from the properties of mechanical and durability for the concrete that is made with Water Granulated Ferro-Nickel slag. According to the test results, when the mixing rate of Water Granulated Ferro-Nickel Slag aggregates concrete is adjusted, up to 50% of its aggregates by mixing rate can be mixed with general aggregates. The optimum mix ratio is considered to be 40%. The freezing and thawing resistance of Water Granulated Ferro-Nickel Slag aggregates concrete is identical to that of general aggregates concrete, while the carbonation resistance is found to be same as or lower than that of general aggregates concretes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.75-83
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• 2019

In order to fulfill the obligation to voluntarily reduce greenhouse gas emissions under the Paris Climate Agreement, the proportion of coal and nuclear power generation is reduced worldwide and national efforts are being made to spread renewable energy including solar power generation. Korea also intends to increase the proportion of renewable energy generation to 30~35% by 2040 by introducing laws and regulations. In addition, while the country is trying to apply solar power generation to sidewalks and roads, there is no research related to it in Korea. Therefore, as a precedent study to develop solar power generation roads, solar power generation concrete blocks applicable to sidewalks and plazas were developed and the applicability was evaluated by constructing them on the site. As a result of indoor experiment, compressive strength was measured by 25.5~35.7MPa and flexural strength was measured by 5.1~10.5MPa, which showed that all domestic standards were satisfied. However, the higher the unit cement amount, the lower the strength was measured according to the mixing of the broken fine aggregate. The absorption rate was 5.7%, which satisfied the domestic standard of 7% or less. As a result of the freeze-thawing test, the reduction rate of the compressive strength after 100 cycles was up to 6.3%. As a result of measuring the settlement amount after construction, the maximum of 2.498mm was measured and irregular settlement occurred in the overall area, which is because the resolution of the sand layer was poor during construction. Maintenance techniques of sidewalk concrete block and solar panel need to be established more efficiently through long-term operation in the further.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.47-56
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• 2007

Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcrete is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcrete practice. The purpose of the study is, therefore, to explore the trobles in the current shotcreting practice, and to develop high-quality silica fume shotcrete. For the purpose of security a long-term durability of shotcrete, this study conducted combined deterioration tests. In this study, a combined deterioration test in consideration of a variety of deterioration factors were proceeded. Especially, micro-silica fume that was used frequently in overseas because of a outstanding strength-promotion effect was applied to combined deterioration test, and a long-term durability of shotcrete was investigated according to additions mixing. As a result of test, the shotcrete mixed Micro-silica fume showed a good deterioration quality compared with the other mixes. And is shows that the Micro-silica fume has an outstanding strength-promotion effect and is effective to secure a long-term durability of shotcrete by means of decreasing a deterioration caused by steel fiber mixed.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.265-271
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• 2015

This study is intended to produce a PC (Precast Concrete) member without a steam curing process in developing the high early strength concrete satisfying the condition of 10MPa in compressive strength at the age of 6 hours, and is intended to ensure economic feasibility by increasing the turnover rate of concrete form. Hence, high early strength cement with high $C_3S$ content and the hardening accelerator of powder type accelerating the hydration of $C_3S$ was used. And the properties of concrete were evaluated according to the hardening accelerator mixing ratio (0, 1.2, 1.6, 2.0). No big difference was found from the tests of both slump and air content. When 1.6 % or higher amounts of the hardening accelerator were mixed, the compressive strength of 10MPa was achieved at the age of 6 hours. From the test results of autogenous (drying) shrinkage and plastic shrinkage, it can be seen that there was a difference according to hydration reaction rate due to the addition of the hardening accelerator. However, it was shown that no problem arose with crack and durability. And it was shown that resistance to freezing-thawing, carbonation, and penetration were excellent.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• Elastomers and Composites
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• v.46 no.3
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• pp.218-222
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• 2011

The effect of cycled temperature change on the mechanical properties of wood flour(50 wt.% and 70 wt.%) polypropylene WPC(Wood Plastic Composites) was investigated in this study. Flexural modulus and flexural strength of the WPC showed a decrease due to the degradation of interfacial adhesion between polymer matrix and wood flour by the freeze-thaw test regardless of the cycled number. At the higher loading level of wood flour, the reduction of the flexural modulus was remarkable. After the cycled heat-freeze test, it was found that the flexural modulus and flexural strength of the WPC were lower at the high temperature ($60^{\circ}C$) and higher at the low temperature ($-20^{\circ}C$). At the low temperature ($-20^{\circ}C$) which is below glass transition temperature of polypropylene ($-10^{\circ}C$), WPC is in a glassy state which brings about the high stiffness and strength. At the high temperature ($60^{\circ}C$), the flexural modulus and flexural strength of the WPC with 50 wt.% wood flour were lower because of the increase of polymer ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.29-36
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• 2015

In this study, to examine the use of sulfur polymer as a coating agent for concrete, durability and hazard evaluations were performed. The result of the evaluation indicated that the chemical resistance of the coating agent for concrete was outstanding against acidic, base, and alkaline solutions. The evaluation of the bond strength after an accelerated weathering test depending on the mixing condition indicated that the most outstanding strength characteristic was obtained when silica powder and fly ash were mixed at the same time. The bond strength exceeded 1 MPa in every mixing condition even after the repeated hot and cold treatment of the coating agent specimen for concrete, and the SFS mix proportion showed the highest bond strength. The examination of the accelerated carbonation and chloride ion penetration resistance of the concrete coated with the coating agent indicated that the specimen coated with the coating agent using silica powder as a filler showed the most outstanding durability. When a fish toxicity test was performed to examine the hazard of the use of the functional polymer as a coating agent for concrete, the functional polymer was found to have no effect on the organisms. When the chemical resistance, freezing and thawing resistance, carbonation, and chloride ion penetration resistance of the coating agent were considered, substituting silica powder and fly ash as the fillers of the functional polymer by 20%, respectively, was the optimal level in the range of this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.611-619
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• 2021

Porous asphalt pavement (PAP) has many functions, such as reducing accidents and decreasing noise. On the other hand, vulnerability is inevitable because PAP contains approximately 20% porosity. This study evaluated the effects of the maximum aggregate size (MAS), temperature, and porosity on the PAP durability. The indirect tensile strength measures durability. This study tested the samples that stayed dry and were moisturized by freezing and thawing for mixtures having the same porosity of 20% and MAS of 13mm, 10mm, and 8mm. The same test was performed on a mixture of 20% and 22% voids made of the same material with a MAS of 10mm. As a result, for 20% porosity, significant differences in the changes in MAS and temperature were found. A clear difference was observed between 8mm and 13mm under dry conditions, but there were no other significant differences in the MAS change. Furthermore, there was a clear difference in temperature for the change in porosity and temperature, but the gap in 2% porosity at 20% did not show a clear difference. Therefore, it is necessary to develop a more durable PAP through quantitative evaluations of the factors affecting the PAP durability.

• Tunnel and Underground Space
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• v.17 no.4
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• pp.266-284
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• 2007

Recently, many efforts have been made to construct the first unlined tunnel, without in-situ concrete lining, in Korea. However, the lack of reliability in the performance of shotcrete as permanent tunnel support prevented from its realization. Shotcrete has been regarded to have significant problems in field application and long term performance because of unsatisfactory strength level and durability compared to those of European countries. In this study, the high strength shotcrete satisfying compressive strength over 40 MPa and flexural strength over 4.5 MPa was developed from optimized mix design. The type of accelerators and the amount of silica fume were selected as the main factors in mixing process and the analyses were carried out up to the elapsed time of 2 years. In order to evaluate the short term durability of shotcrete, an array of laboratory test consisting of freeze-thaw, carbonation chloride penetration and permeability test was performed. For long-term durability tests, specimens have been put in an operated highway tunnel to expose them to the similar environment when they are actually used as an unlined tunnel support. From the strength and durability tests, it was found that only alkali-free based accelerator satisfied the target strength of this study and also, the developed shotcrete showed very high performance in its durability.