• Journal of the Korea Institute of Building Construction
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• v.14 no.5
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• pp.389-396
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• 2014

The set accelerator used for shotcrete at high pH environment often causes the dusting problem in practice. In this research, a slurry-type set accelerator was developed to avoid this problem and its effectiveness was investigated by applying it to shotcrete mortars. Set time, stiffening, compressive strength, and chloride ion penetration resistance were examined with different amounts of slag, used as partial replacement of cement. According to the experimental results, it was found that the earlier responses such as set time, stiffening, and 1-day compressive strength were probably affected by the amount of ettringite, formulated by the hydration between C12A7 and calcium sulfate polymorphs present in blast furnace slag. Whereas, it is believed that the result of compressive strength after 3 days was attributed to the hydration of tricalcium silicates. As for the results of a chloride ion penetration test, the partial replacement of cement with slag significantly reduced the total charge passed through the shotcrete mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.127-134
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• 2022

In this study, RCPTs (Rapid Chloride Penetration Test) were performed for fly ash concrete with curing age of 4 ~ 6 years. The concrete mixtures were prepared with 3 levels of water to binder ratio (0.37, 0.42, and 0.47) and 2 levels of substitution ratio of fly ash (0 and 30%), and the improved passed charges of chloride ion behavior were quantitatively analyzed. Additionally, the results were trained through the univariate time series models consisted of GRU (Gated Recurrent Unit) algorithm and those from the models were evaluated. As the result of the RCPT, fly ash concrete showed the reduced passed charges with period and an more improved resistance to chloride penetration than OPC concrete. At the final evaluation period (6 years), fly ash concrete showed 'Very low' grade in all W/B (water to binder) ratio, however OPC concrete showed 'Moderate' grade in the condition with the highest W/B ratio (0.47). The adopted algorithm of GRU for this study can analyze time series data and has the advantage like operation efficiency. The deep learning model with 4 hidden layers was designed, and it provided a reasonable prediction results of passed charge. The deep learning model from this study has a limitation of single consideration of a univariate time series characteristic, but it is in the developing process of providing various characteristics of concrete like strength and diffusion coefficient through additional studies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.27-33
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• 2016

Military textiles with breathable waterproof materials are expanding as form of winter clothes. Waterproof moisture-permeable clothes are very important for soldiers to survive in cold weather operations because they prevent loss of body heat from the penetration of water into the human body. Korea military uses the water resistance and moisture permeability to test the performance of waterproof moisture-permeable materials. Moisture permeability is measured according to the amount of evaporated water vapor passing through a fabric under specified temperature and humidity by using acetic acid potassium presented in KS K 0594. However, the test procedure for measuring the moisture permeability in the standard is presented only briefly and the preparation procedures for the test in accredited testing institutions are applied differently, leading to significant deviation of the results. This paper compares the procedures of testing institutions and examines the factors that affect moisture permeability. Finally, we propose a procedure to reduce the deviation of results and apply the proposed procedure in testing institutions. Our analysis results with one-way ANOVA under significant level (0.05) confirm that the deviation of results is reduced.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.161-168
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• 2008

The freeze-thaw deterioration and chloride attack, which are the typical degradation factors for durability of marine concrete, are significantly affected by pore structures in terms of penetration and diffusion. These pore structures of concrete are closely related to the types and amount of AE agent, used to guarantee the resistance of freeze-thaw deterioration, and the elapsed time before concrete pouring. This paper evaluates the durability of concrete based on the results of tests on cylinder specimens and core specimens from mock-up members with different air content of 4~6% and 8~10%, respectively. According to the test results, the air content of hardened concrete is 2.5~5.2% at 7 days and 2.4~5.1% at 28 days. These air contents are about half of the initial values just after the concrete mixing. Judging from the amount of scale after the freeze-thaw test completed, air content of 8~10% is slightly more beneficial against the deterioration of concrete than air content of 4~6%. Meanwhile, the core specimens from mock-up members exhibit somewhat unfavorable freeze-thaw deterioration and chloride migration characteristic compared with the cylinder specimens tested in the laboratory under the same mixing condition, as to show 106% in freeze-thaw test and 160% in chloride diffusion coefficient test, respectively.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.5-12
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• 2014

In this study, we developed the electric heating equipment and applied for soft ground improvement. The developed heat pipe is 4 m-length and consumes 1 kW/m, which is consisted of Ni-Cr wire. It was installed in 3.5~4.5 m below ground surface and heated for 96 hours (48 hours, 2 times). The temperature variation and vapor pressure caused by electric heating was measured by the thermometer and pressure gauge which were installed in the ground (5.0 m), and the tip resistances were measured by static electronic piezo-cone penetration test (CPT). As the results of experiments, 2-order polynomial curve was shown to adjust the variation of tip resistance and the temperature distribution with the horizontal distance from electric heater, whose R2 value is close to 1. In addition, in-situ pore-water pressure and water content was decreased.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1466-1483
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• 2008

This paper discusses the development of an up-to-date computerized CPT (Cone Penetration Test) based soil engineering classification system to provide geotechnical engineers with a handy tool for their daily design activities. Five CPT soil engineering classification systems are incorporated in this effort. They include the probabilistic region estimation and fuzzy classification methods, both developed by Zhang and Tumay, the Schmertmann, the Douglas and Olsen, and the Robertson et al. methods. In the probabilistic region estimation method, a conformal transformation is used to determine the soil classification index, U, from CPT cone tip resistance and friction ratio. A statistical correlation is established between U and the compositional soil type given by the Unified Soil Classification System (USCS). The soil classification index, U, provides a soil profile over depth with the probability of belonging to different soil types, which more realistically and continuously reflects the in-situ soil characterization, which includes the spatial variation of soil types. The CPT fuzzy classification on the other hand emphasizes the certainty of soil behavior. The advantage of combining these two classification methods is realized through implementing them into visual basic software with three other CPT soil classification methods for friendly use by geotechnical engineers. Three sites in Louisiana were selected for this study. For each site, CPT tests and the corresponding soil boring results were correlated. The soil classification results obtained using the probabilistic region estimation and fuzzy classification methods are cross-correlated with conventional soil classification from borings logs and three other established CPT soil classification methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.209-222
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• 1993

This article is a case study of the ground improvement project which was carried out for manmade landfill. The project area is located near to Kapchun, Teajon and composed of the municipal wastes dumped, demolished building debris, coal ash and industrial waste made between 1983 and 1989. The DDC(dynamic deep compaction) based on the results of the test compaction at two representative locations was carried out from March 16, 1992 to Oct. 25, 1992. Field measurements and laboratory tests were carried out for ground improvement assessment and quality control for the DDC(dynamic deep compaction) work. From the results of field measurements and laboratory tests, it was found that the DDC work was successful: waste landfill was compressed considerably (${\fallingdotseq}$ 15% of full depth); and the strength was increased satisfactorily (${\fallingdotseq}$ 100% of original penetration resistance), Also, it is expected that the results of this work could be a guide to the future DDC work with the similar ground conditions, i.e. man-made landfills.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.74-82
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• 2017

In this study, we prepared a core material based on the inorganic materials in liquid form for applying an inorganic-based core material to a core material for the self-healing capsules as a part of the basic study to manufacture of self-healing capsule that can heal cracks of cementitious composite. Manufactured core material based on the inorganic materials were applied directly to the cement composite before its encapsulation, were evaluated the effect on performance of cementitious composite as wall as repair performance of the cracks in the cracks. The test results showed that core material based on the inorganic materials was effective to improve the compressive and adhesion strength, had an absorption, permeation water, penetration of chloride iones and freeze-thaw resistance performance. Through the results of this paper, we want to utilize the results as a basis data of the performance of the cement composite that can be obtained when applied to inorganic core materials based on self-healing capsules and future advances localized self-healing capsule technology.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.13-26
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• 2005

It was known that the aging effect of sands is insignificant in comparison with clays, and hence the study on this effect had seldom been performed prior to the early 1980s. However, field tests for this effect have been actively carried out since it was investigated that penetration resistance of reformed sands increased with the lapse of time. Recently, the aging effect of sands has also been examined in laboratory testings. In this study, undrained static triaxial tests were performed to evaluate the effect on the Nak-dong River sands, with different .elative densities $(D_r)$, consolidation stress ratios $(K_c)$, and consolidation times. As a result of the tests, it was proved that the undrained cyclic shear strength $(R_f)$ increased with the aged time on the sands. The in situ range of Rf on the sands, which is applicable to the magnitude of earthquake in the Nak-dong River area, was proposed by using the test results.

• Geotechnical Engineering
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• v.2 no.3
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• pp.37-50
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• 1986

The uncertainties encountered in the stability analysis for the foundation of offshore structures on clay are formulated in probabilistic terms and used to evaluate the reliability of the foundation design. The major sources of uncertainty are: soil properties, f.ave loads, and methods of analysis. The major part of the uncertainty in safety factor is contributed by the uncertainty in the undrained shear strength. All sources of uncertainties that affect the shear strength of clay are modeled and systematically analyzed. The in situ undrained shear strengths are evaluated by laboratory tests and cone penetration tests. The undrained shear strengths from the laboratory test and CPT, respectively at Statfjord B site in the North Sea, are used as an example in risk analysis. Using the CPT alone, the failure probability on sliding of gravity platform at Statfjord B is much larger than the failure probability using the laboratory undrained shear strengths. The major uncertainty of using the CPT as the estimate of th2 undrained shear strength of clay results from the correlation between the cone resistance and the undrained shear strength.