• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.44-49
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• 2016

Among the deteriorating agents, chloride ion is reported to be one of the most harmful ions due to its rapid diffusion and direct effect on steel corrosion. Cold joint which occurs in mass concrete placing is vulnerable to shear resistance and more severe deterioration. The paper presents an quantitative evaluation of chloride diffusion coefficient in OPC(Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag) concrete containing cold joint. GGBFS concrete shows $6.6{\times}10^{-12}m^2/sec$ which is almost 30% level of OPC concrete results and the trend is repeated in the case of cold joint concrete. Compared with OPC concrete, GGBFS concrete is evaluated to have better resistance to chloride penetration, showing 0.30 times of chloride diffusion coefficient in concrete without cold joint 0.39 times with cold joint, respectively.

• Journal of Energy Engineering
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• v.28 no.1
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• pp.17-21
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• 2019

Calcium sulfaluminate (CSA) was synthesized to improve the shrinkage of OPC. In this study, the setting time, the compressive strength and the length change ratio were confirmed by replacing the synthesized CSA with OPC by 10% and 13% by 16%. In the case of shrinkage-reducing type cement, formation of Ca-Al-$H_2$-based hydrate was activated. Therefore, the setting time was shortened. The compressive strength of the shrinkage - reducing type cement is comparable to that of OPC after 7 days' strength. However, shrinkage reducing type cement showed improved initial strength compared to OPC. The length change ratio was found to be improved by drying shrinkage from -0.075% to -0.047% on the 28th day.

• The Journal of the Convergence on Culture Technology
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• v.9 no.3
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• pp.803-809
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• 2023

This paper analyzes and evaluates to optimally build a data collection system essential for factory energy management systems on an edge-based lightweight platform. A "Sensor/OPC-UA simulator" was developed based on sensors in an actual food factory and used to evaluate the storage engine of edge devices. The performance of storage engines in edge devices was evaluated to suggest the optimal storage engine. The experimental results show that when using the RocksDB storage engine, it has less than half the memory and database size compared to using InnoDB, and has a 3.01 times faster processing time. This study enables the selection of advantageous storage engines for managing time-series data on devices with limited resources and contributes to further research in this field through the sensor/OPC simulator.

• Cement Symposium
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• no.28
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• pp.88-96
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• 2001

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.113-119
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• 2019

Concrete structures built on reclaimed land are combined with chemical erosion such as chlorine and sulfate ions from seawater. Chloride attack deteriorates the performance of the structure by corroding reinforcing bars. In addition, the waste water treatment structure has a problem that the concrete is deteriorated by the sulfate generated inside. Therefore, in this study, the characteristics and chemical resistance of low heat cement concrete used in wastewater treatment structures constructed on reclaimed land were evaluated. As a result of the experiment, the target slump and air content were satisfied under all the mixing conditions. The slump of low heat cement (LHC) concrete was higher than that of ordinary portland cement (OPC) concrete, while the air content of LHC concrete was smaller than that of OPC concrete with the same mix proportion. As a result of compressive strength test, OPC concrete showed higher strength at younger age compared to 28 days. In contrast, LHC concrete exhibited higher strength than OPC concrete at the age of 56 days. As a result of chlorine ion penetration tests, LHC-B concrete showed chlorine ion penetration resistance performance of the "very low" level at the age of 56 days. As a result of chemical resistance evaluation, when the LHC concrete is applied without epoxy treatment, chemical resistance is improved by about 18% compared to OPC concrete. In testing chemical resistance, the epoxy coated concrete exhibited less than 5% strength reduction when compared to sound concrete.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.19-26
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• 2012

In this study, geotechnical tests including unconfined compression test were carried out to evaluate the ground improvement effect of the hardening agent, which has been developed by using inter-chemical reactions between slag, fly ash, phosphogypsum and bypass dust on the weathered granite soil and dredged marine clay. Test results show that the strength of weathered granite soil mixed with hardening agent B-2, which uses phosphogypsum as an activator, is higher than that of B-1, which uses bypass dust as an activator. Strengths of B-1 & B-2 hardening agent mixed soil show only 44%~60% of strength of OPC(Ordinary Portland Cement, OPC) mixed soil. However, since B-1 and B-2 agents are made of industrial by-products, they seem economically more effective than ordinary portland cement as well as other present hardening agents. Test results on dredged marine clay show that unconfined compression strength increases with amount of agent and curing days. Unconfined compression strength of 14% B-1 agent mixed soil increases linearly with curing days and reaches only 40% of OPC mixed soil. While unconfined compression strength of 14% B-2 agent mixed soil increases exponentially and reaches 133% of OPC mixed soil. Relationship between deformation modulus and unconfined compression strength of B-1 and B-2 mixed soil can be expressed as $E_{50}=(20{\sim}47)_{qu,28}$, which is similar with lower limit of OPC mixed dredged marine clay.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.8-15
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• 2019

When RC(Reinforced Concrete) structures are exposed to harsh environment, deterioration phenomenon occurs, and the corrosion in rebar due to chloride intrusion is known as representative deterioration, so called chloride attack. In this paper, chloride resistance performance of 2 years aged concrete is evaluated considering 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%). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests referred to KS F 2405 are performed. With adaptation of the previous test results and the results from this study, time-dependent chloride diffusion characteristics are analyzed for each concrete. The FA(Fly Ash) concrete has higher chloride resistance performance than OPC(Ordinary Portland Cement) concrete. According to the evaluation standard of ASTM C 1202, the FA concrete has "Moderate" grade after 49 days while OPC concrete does "Moderate" grade after 365 days. As the results of time-parameter for chloride diffusion, OPC concrete and FA concrete show the decreasing behavior of time-parameters with increasing water to binder ratio. Also, FA concrete has 1.57~2.74 times of time-parameter than OPC concrete. That's cause is thought that the time-parameter indicates the gradient of decreasing of diffusion coefficient. FA concrete has higher time-parameters than OPC concrete by pozzolanic reaction of FA.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.417-424
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• 2004

Polycarboxylate type superplasticizers (PCA) with different graft chain (Polyethylene oxide) length were synthesized by Methoxypoly (ethyleneglycol)monomethacrylate (MPEGMAA) and methacrylic acid (MAA). The effects of PCA on the hydration of Ordinary Portland Cement (OPC) were investigated by Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) techniques. The effect of graft chain length of PCA on the hydration of OPC was different at early age, but, at long age, was similar. The ratio of relative peak intensity, (I［001］/I［101］), of Ca(OH)$_2$ compared with OPC also was reduced by PCA addition.

• Geomechanics and Engineering
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• v.3 no.3
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• pp.207-218
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• 2011

This article describes laboratory research done on strength evaluations for stabilized samples made of tropical fibrous peat. The stabilizing agents used were ordinary Portland cement (OPC) as binding agent and blast furnace slag (BFS) as additive. Stabilized samples were tested for their strength through unconfined compressive strength (UCS) and California bearing ratio (CBR). Different dosage rates of OPC and BFS were used in trial and error experiments for the most effective combination for stabilized peat samples that were at their natural moisture content. Stabilized trial samples were air cured for 90 days. After detecting the most effective dosage rate in the trial samples, their values were used to prepare CBR samples at their optimum moisture content (OMC). CBR samples were then air cured from 1 to 90 days and tested under un-soaked and soaked conditions. The most effective dosage rate for the stabilized peat samples was found to be close to when 75% for OPC and 25% of BFS per total weight of OPC, and BFS. As an example, if 11.25% OPC, and 3.75% BFS are mixed with peat and compacted at their OMC and air cured for 90 days, stabilized peat will have an increase in CBR of 0.8% to 45 % for un-soaked and 20% for soaked conditions.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.723-725
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• 2013

The compensation characteristics are investigated as a function of the position an optical phase conjugation (OPC) in the optical transmission links with a randomly distributed residual dispersion per span (RDPS). The simulation results show that the optimal net residual dispersion (NRD) is decided to be 10 ps/nm and -10 ps/nm by precompensation and postcompensation, respectively, which are independence of the OPC positions.