• Magazine of the Korean Society of Agricultural Engineers
• /
• v.13 no.4
• /
• pp.2419-2425
• /
• 1971

In many cold weather concrete constructison jobs calcium chloride $CaCl_2$ can be used safely as an accelerating admixture. For producing satisfactory concrete during cold weather calcium chloride is used to develop the level of strength required in a shorter period by obtaining higher early strength, the resulting in crease in heat of hydration. In this paper, to get adequated data and information of the effect on strength of concrete in using calcium chloride as an accelerating admixture, Portland cement (Type I), High-early-strength cement(Type II) and Pozzolans cement with certain 1.5 percentage of calcium chloride by weight of the cement were tested. As the result of this experiment, followings were founded: 1. At the 1.5 percent of calcium chloride cement ratio, the early strength was accelerated to the highest level, and some 1.5 percent of calcium chloride cement ratio was suitable for the stabilization of the concrete structures. 2. For Some 50 percent of Water Cement ratio was suitable, making good Concrete in the Cold weather by admixture of Calicum Chloide. 3. The concrete of Pozzorans cement in early strength was weak but that in later rised by degree. 4. As abtaining higher early strength the curing period can be reduced, but the finishing work should be done as early as possible.

• Journal of the Korean GEO-environmental Society
• /
• v.22 no.12
• /
• pp.15-24
• /
• 2021

In Korea, which is mostly mountainous, the proportion of tunnel and underground space development are increasing. Although the ground is reinforced by applying the ground improvement method during underground space development, accidents still occur frequently in Korea. In the grouting method, a representative ground reinforcement method, the effect was judged by comparing the total amount of injection material with the amount of injection material used during the actual grouting construction. However, it is difficult to determine whether the ground reinforcement is properly performed during construction or within the target ground. In order to solve this problem, it is necessary to study a new method for quality control during or after construction by measuring electrical resistivity after performing grouting by mixing carbon fiber, which is a conductive material, and microcement, which is a grout material. In this study, as a basic study, a cement specimen mix ed with 0%, 3%, 5%, 7% of carbon fiber was prepared to evaluate the performance of the grout material mixed with carbon fiber, which is a conductive material. The prepared specimens were wet curing for 3 days, 7 days, and 28 days under 99% humidity, and then compression wave velocity and shear wave velocity were measured. As a result of the compression wave velocity and shear wave velocity measurement, it showed a tendency to increase with the increase in the compounding ratio of carbon fibers and the number of days of age, and it was confirmed that the elastic modulus and shear modulus, which are the stiffness of the material, also increased.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.15 no.2
• /
• pp.3018-3030
• /
• 1973

This study was carried out to investigate the effects of various mix designs of concrete on the compressive strengths and corrosive rates when the concretes were immersed in sea water of the West Sea, as the part of study related to durated to durability of concrete by action of the sea water. Concrete mix designs used in this study were ordinary Concrete mix, Concrete mixes with different admixtures such as fly ash, pozzolith and vinsol resin, and pozzolan concrete mix. The concrete specimens were made and cured for 7 days and 28 days in the fresh water in accordance with the Korean Standard specification for concrete. Compressive strengths of the specimens were measured after immersing the specimens for one year in fresh water and sea water which were placed indoors. The sea water used in this test was taken from the Bay of Ahsan. Corrosive rate was also tested after immersing the specimens in the same sea water and placed indoors for one year. The results obtained from the tests are summarized as follows; 1. Compressive strength of an ordinary concrete was the lowest of the various mix desings of concrete immersed both in the fresh water and the sea water. Therefore, the uses of pozzolan cement, fly ash, pozoolith and vinsol resin in mix design of concrete had and effect on increasing compressive strength. 2. Pozzolan concrete was the most effective on compressive strength in the fresh water, but it had less effect than concrete with fly ash admixture immersed in the sea water. 3. The use of fly ash admixture in mix design of concrete showed higher strength as the immersing age is longer both in fresh water and sea water than the other concretes besides pozzolan concrete, but the concretewith fly ash admixture had lower strength than pozzolan concrete in the sea water. Therefore, concrete with fly ash admixture might be better than the pozzolan concrete as far as durability of concrete to sea water was concerned. 4. The use of pozzolith admixture in mix design of concrete had less compressive strength than the use of pozzolan cement for fly ash admixture both in fresh water and sea water. However, the concrete with pozzolith admixture was much stronger than one with vinsol resin admixture in fresh water, but somewhat stronger in the sea water. 5. Though the use of vinsol resin admixture was more effective than ordinary concrete on compressive strength both in fresh water and sea water, it was the least compressive strength among the other concretes. 6. Relation between compressive strengths and absorption rates of every kind of concrete besides concrete with fly ash admixture showed a linear regression line and the compressive strength is highee as the absorption rate is lower. Concrete with fly ash admixture had extremely high strength in comparison with corresponding adsorption rates of the other concretes. 7. Corrosive appearance on the surface of concretes was not occured significantly when exposed to the sea water for one year, However, the specimens of concretes besides ordinary concrete were a little heavier than those cured in fresh water for 28 days.

• Journal of the Korean Geotechnical Society
• /
• v.36 no.7
• /
• pp.15-28
• /
• 2020

As the skin friction of an embedded pile is produced by the cement paste injected into the borehole, the skin friction cannot be evaluated by the end of initial driving test, which is conducted before the cement paste is cured. In addition, the total resistance of an embedded pile may not be properly evaluated during the restrike test if the base resistance is not fully mobilized because of the insufficient driven energy. The objective of this study is to suggest a new load-settlement curve of embedded piles by combining the results of the end of initial driving and restrike tests. Test piles are installed at fields by using the embedded pile method, and the results of the dynamic pile tests are analyzed using CAse Pile Wave Analysis Program (CAPWAP) after the end of initial driving and restrike tests are conducted. A new load transfer curve, which combines the behaviors of the pile base at the end of initial driving and of the pile shaft at the restrike, is suggested, and a new load-settlement curve is obtained. Subsequently, the resistances of the test piles are evaluated using the combined load-settlement curve, and compared with the results from the end of initial driving and restrike tests. The results showed that the resistances, which are evaluated using the combined load-settlement curve, may overcome the underestimation of the resistance because of the insufficient driven energy. In addition, the resistance resulted from the combined load-settlement curve may be more similar to that from the static load test because the suggested load transfer curve is closer to the behavior of the embedded pile compared to the results of end of initial driving and restrike tests. Therefore, this study demonstrates that the combined load-settlement curve may be effectively used for the evaluation of the bearing capacity of embedded piles.

• Tuberculosis and Respiratory Diseases
• /
• v.45 no.5
• /
• pp.1058-1066
• /
• 1998

Background: Actinomycotic infection is uncommon and primary actinomycosis of the lung and chest wall has been less frequently reported. This disease may present as chronic debilitating illness with radiologic manifestation simulating lung tumor, pulmonary infiltrating lesion, or chronic suppuration. Diagnosis of choice was not definded yet and role of bronchoscopy on diagnosis was not described yet. Methods: From 1989 to 1998, we experienced 17 cases of thoracic actinomycosis. We have reviewed the case notes of 17 patients with thoracic actinomycosis. The mean age at presentation was $53{\pm}13$ years, 11 were male. Results: Cough, hemoptysis, sputum production, chest pain and weight loss were the commonest symptoms. The mean delay between presentation and diagnosis was $6.6{\pm}7.8$ months. There were six patients who presented with a clinical picture of a suppurative lesion and eleven patients were suspected of having primary lung tumor initially. In no cases was made an accurate diagnosis at the time of hospital admission. Associated diseases were emphysema (1 case), bronchiectasis (2 cases) and tuberculosis (2 cases). Bronchoscopic findings were mucosal swelling and stenosis(n=4), mucosal swelling, stenosis and necrotic covering (n=2), mass (n=3), mass and necrotic covering (n=1) and normal(n=6). Radiologic findings were mass lesion(n=8), pneumonitis(n=3), atelectasis(n=3), pleural effusion(n=2), and normal(n=3). Final diagnosis was based on percutaneous needle aspiration and biopsy (n=3), bronchoscopic biopsy specimens (n=9), mediastinoscopic biopsy (n=1) and histologic examination of resected tissue in the remaining patients(n=4) who received surgical excision. Among 17 patients, 13 were treated medically and the other 4 received surgical intervention followed by antibiotic treatment. Regarding the surgically treated patients, suspected malignancy is the most common indication for operation. However. both medically and surgically treated patients achieved good clinical results. Conclusion: Thoracic actinomycosis is rare. but should still be considered in the differential diagnosis of a chrinic, localized pulmonary lesion. Thoracic actinomycosis may co-exist with pulmonary tuberculosis or lung cancer. If the lesion is located in the central of the lung. the bronchoscopy is recommanded for the diagnosis.