• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.237-243
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• 2015

In this research, isothermal conduction calorimetry analysis has been conducted to investigate the reactivity of alkali activated slag binders. In order to secure the reactivity and workability of alkali activated slag binders, experiences with various types and concentrations of alkali activators were performed. Isothermal conduction calorimetry were measured with different alkali activators and mass ratio of $SO_3$ to binders as variables, and sodium tripolyphosphate ($Na_2P_3O_{10}$) and hydrated sodium borate ($Na_2B_4O_710H_2O$) were used to control setting time. As a results, alkali activated slag binders required alkali activators with 4 to 5 percent of concentration to accelerate the formation of calcium silicate hydrate(C-S-H) by alkali-activation, and overall heat generation rate delayed as accumulated heat decreased due to the high $SO_3$ contents. Moreover, the use of hydrated sodium borate as setting retarder causes elongated setting time due to delaying heat generation, so it can be considered that setting retarder played an important role in delaying total heat generation rate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.181-188
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• 2013

This paper is to investigate experimentally an effect of carbon amino silica black-superplasticizer(CASB-SP)on the engineering properties and chromaticity of black color concrete with 0.45 of W/C(water to cement). CASB-SP and carbon black were applied for pigment of the concrete. To prevent efflorescence of concrete, four different water repellent agents were also applied. As results, it was found that use of CASB-SP increased the slump and air contents. Furthermore, the use of CASB-SP increased the compressive strength. As CASB-SP dosages increased, chromaticity was well developed. For the effect of water repellent agent, the use of epoxy type was effective for protection from efflorescence. Based on test results, it was evaluated that 0.5% of CASB-SP effectively improve the concrete quality as well as enhance the chromaticity with proper dosage.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.175-181
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• 2009

In this research, experiments were conducted to find out whether polycarboxylate could be used as a crude steel admixture for practical work, depending on the change in the replacement level of the compound mixed into polycarboxylate. Its fluidity was satisfactory, its airspace was a bit smaller than the KS standard, and its unit volume weight was proven to meet the standard. The amount of bleeding was smallest in B2, and in terms of the solidification time, the first and the last solidification was faster in A1, B1, and C1. With regard to the compressive strength in early days as acharacteristic of hardened concrete, all addition rates of 7-day C2 displayed the highest strength value, among which the addition rate of 1.3% had the biggest strength performance tendency. The seal strength also showed the strength performance rate which was about one tenth as big as that of the compressive strength. The length change rate resulting from dryness and contraction was proven to be good, and once the appropriate AE air entraining agent is used, it is evaluated to be a very useful and practical compound out in the field.

• Journal of the Korea Institute of Building Construction
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• v.21 no.1
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• pp.31-39
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• 2021

The aim of this paper is to improve durability of cement paste by imparting hydrophobicity to the surface and sphere of cement-based materials. A cement paste mixed with a silane/siloxane-based water repellent, and the initial hydration performance, flow performance, and age-specific compressive strength were measured. In addition, the water contact angle, SEM, and XRD before and after surface polishing were measured. When 0.5% of the silane/siloxane-based water repellent was mixed into the cement paste, the compressive strength increased, but the compressive strength decreased as the mixing amount increased by 1.5% and 3.0%. When a silane/siloxane water repellent was incorporated into the cement paste, the hydrophilicity was improved and the contact angle was increased due to hydrophobicity. In addition, the contact angle after surface polishing was found to be larger than the contact angle before surface polishing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.57-62
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• 2020

Among the sewage pipes installed in Korea, the length of concrete pipes exceeding 20 years is 66,334 km (42.5%). Deteriorated concrete sewer pipes need to be repaired due to the leakage of internal sewage, which causes problems such as sink holes by expanding the cavity around the pipeline. In this study, we tried to apply anti-washout underwater mortar with ultra rapid hardening cement and segregation reducing agent to sewage pipe repair. As a result of the setting time test, the final set time was delayed by up to 172% by incorporating segregation reducing agent. In the test for measuring the degree of mortar segregation in water, it was measured at pH 12 or less under all mixing conditions. In addition, the suspension amount was measured to be 50 mg / l or less to satisfy the KCI-AD102 standard by incorporating a segregation reducing agent. In terms of the average value of mortar compressive strength, by incorporating segregation reducing agent, the strength of the specimens produced in air was more than 80% of that of the specimens produced in water. Conversely, the bond strengths of the specimens produced in water were measured to be higher than those of the specimens produced in air. Water resistance was evaluated by measuring water absorption and water permeability. Water absorption and water permeability were reduced by 42.6% and 36.6%, respectively, by mixing segregation reducing agent.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.42-49
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• 2020

This paper is a basic study to improve durability by imparting hydrophobicity to the surface and sphere of cement-based materials. A cement mortar to which a silane/siloxane-based mixed water repellent was added was prepared, and its initial hydration performance, flow performance, and compressive strength were measured. In addition, after the surface was abraded, the water contact angle and water absorption were measured. The flow of cement mortar to which the water repellent was added was found to decrease up to 1.5% in the addition amount of the water repellent agent, and increased at 3.0% in the addition amount. It was found that the setting time of the cement paste was delayed in both the initial setting and the termination when the water repellent was added. It was found that the compressive strength decreased from 3.0% of the maximum added amount of the water repellent to a maximum of 30%. The contact angle was found to increase when the water repellent was added to the cement mortar, and the contact angle after surface polishing was found to be larger than before surface polishing. The addition of the water repellent showed hydrophobicity not only on the surface but also on the surface and cross section damaged by polishing. The water absorption rate was found to decrease when the water repellent was added to the cement mortar, and the water absorption rate after surface polishing was found to be greater than before surface polishing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4602-4609
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• 2013

In summer and winter, the difference between the temperature during the day and that during the night is high, which leads to various problems during concrete placement, such as cracks and defects in the concrete as well as low durability and strength. Although nuclear power plant concrete is widely used for placement in all seasons, particular attention must be paid to its quality during the summer. Therefore, we evaluated the effects of a cooling method for mixing water, which is a commonly used hot weather precooling method, and the use of a retarder, on the characteristics of Nuclear Power Plant concrete. In the cooling method for mixing water, cold water at 5 was used, with 50% of the water content consisting of ice flakes. The effects of using a retarder were evaluated by reviewing the characteristics of the cement at the unset stage and after hardening. To evaluate the characteristics of the unset cement, we measured the slump, air volumes, setting times, and pressure strengths after hardening. Furthermore, we measured the heat of hydration at different temperatures; the loss of heat was minimized using insulation. Both the slump time and the complete ageing time of the air volume were found to be 120 min at $20^{\circ}C$ and 40 min at $40^{\circ}C$. In the case when the cooling method for mixing water was used and in the case when a retarder was used, the initial and final sets by penetration resistance were delayed, and the delay decreased with increasing air temperature. For the heat of hydration, the cooling method for mixing water not only lowered the maximum temperature but also delayed its attainment. However, the use of a retarder had no effect on the maximum temperature. Moreover, in the early ages (e.g., 3 and 7 days), the pressure strength of the concrete was lower than that of plain cement. However, the strength of 28-day concrete met the standard construction specifications.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.4
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• pp.323-330
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• 2006

As the interest in environmental pollution resulting from recent industrial development is converging, wastewater treatment problem of dying processing is one of important pending issue. Usually, flow mediation earth and settling pond etc. of processing plant to handle water or wastewater. Mediation is the wastewater that flowed past settling pond than material of heavy particles, water weight colloid particles that big solids are removed but are suspensibility material settlement exclusion impossible. So, we need flocculation and coagulation action to remove materials from this colloid state. For flocculation and coagulation action chemical agents to add back, addition of chemical agents forms floc of could settle size. That is, shorten the sedimentation time and quality of processing water because promoting sedimentation doing to do fines or suspended solids and colloid can materials large size and also, flocculation to annex efficiency of filtration augment. Therefore, I executed this research to prove that improving organic matter and chromaticity of treated water of processing epochally using organic coagulant informed positive ion co-polymerization superior in color wastewater through this research.

• Journal of Life Science
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• v.14 no.2
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• pp.301-308
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• 2004

The morphology of the apical pore complex, the first apical plate and the posterior sulcal plates in a new isolate of Alexandrium tamarense (Lebour) Balech from the Bay of Chinhae was compared with other that of toxic strains of A. tamarense previously isolated from Korean waters. Although this isolate was morphologically identical to these toxic strains, high performance liquid chromatography and mouse bioassay showed no evidence of toxin production. The nontoxic A. tamarense strain showed a strong positive binding activity with PNA lectin, indicating a high density of lactose and galactose residues on the cell surface, and in SDS-PAGE and Western blot analysis a unique protein of about 21-kDa molecular sizes was observed. These findings demonstrate that the use of PNA and immunobioassay could be used to discriminate between toxic and nontoxic strains of A. tamarense.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.4
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• pp.35-41
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• 2019

Contrail is a kind of cloud that is formed during the flight by vapor condensation of engine exhaust in a cold atmospheric condition. Owing to the negative effects of contrails on the environment and in military applications, several studies for contrail mitigation had been performed in developed countries. The goal of this research is to design a lab-scale contrail generator, and to validate the contrail mitigation technology suggested by previous studies. The contrail generator was made using superheated vapor and a low temperature wind tunnel. Using this generator, the ineffectiveness of ethanol and surfactant suggested in the previous paper on contrail mitigation was found experimentally.