• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.161-164
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• 2008

In recent years, carbon fiber-reinforced polymer (CFRP) has been widely used for repairing and/or strengthening structural elements in concrete. Not enough test data, however, are available to predict the long-term performance of the repaired and improved structures exposed to weathering. The objective of this research is to study the effect of freeze-thaw cycling on the behavior of reinforced concrete (RC) beams strengthened in shear with carbon fiber sheet. Six small-scale RC beams (100mm${\times]$100mm${\times]$400mm) were strengthened with CFRP in shear, subjected to up to 400 cycles freeze-thawing from -17${\sim}4^{\circ}C$, and tested to failure in four-point bending. Test result, there was no significant damage to carbon fiber sheet strengthened concrete beams had been suffered 30 cycles of freeze-thawing, and more over 60 cycles of freezing-thawing brought about a reduction in resistance of only 25% of the initial level.

• Journal of the Korean GEO-environmental Society
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• v.19 no.3
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• pp.5-13
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• 2018

Recently, construction disasters in thawing season are increasing due to the ground collapse and it is related to the improper compaction during winter season. Compaction at sub-zero temperature reduces the compaction effect and the research of mechanical properties of thawed soil after winter compaction can be used as useful data to understand the behavior of the ground in the thawing season. On the other hand, the research interest in the unsaturated soil mechanics has been increasing in the field of the geotechnical engineering. Therefore, it is expected that the research of unsaturated characteristics under the compaction of sub-zero temperature and freezing & thawing condition provides information to the researchers in the related fields. Therefore, in this research, unsaturated soil-water characteristics test and unsaturated uniaxial compression test were conducted on the specimens compacted at sub-zero temperature and continuous freezing & thawing condition to investigate change of unsaturated characteristics and matric suction. Based on the test results, the change of matric suction and the decrease of strength and stiffness were observed with the freezing & thawing conditions. Especially in case of the weathered soil, the strength and matric suction were significantly reduced with lower temperature and more repetition of freezing & thawing cycles. This result implies that compaction of sub-zero temperature and freezing & thawing cycles will have a considerable influence on the stability of the ground.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.319-323
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• 2018

Ferronickel slag is a by-product from the ferronickel smelting process and it is divided into air-cooled ferronickel slag and water granulated ferronickel slag according to cooling system. The purpose of this experimental resesrch is to investigate the mechanical properties and resistance to freezing and thawing of concrete using air-cooled ferronickel slag(ACFNS) fine aggregate. For this purpose, the concrete specimens with water-cement ratio of 50% were made with ACFNS's replacement ratios of 0%, 20%, 30%, 40%, 50%, 70%, and 100% by volume of fine aggregate. It was observed from the test results that the compressive strength and static modulus of elasticity of ACFNS fine aggregate concrete were increased with increasing replacement ratio of ACFNS and the resistance to freezing and thawing of this was similar to reference concrete which had the relative dynamic modulus of elasticity of more than 90% during the freezing and thawing of 300 cycles.

• Journal of Food Hygiene and Safety
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• v.31 no.1
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• pp.42-50
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• 2016

The effects of freezing and thawing conditions on microbiological quality and microstructure change of inoculated (Listeria monocytogenes and Campylobacter jejuni) and non-inoculated chicken breasts were investigated. Chicken breasts were frozen with air blast freezing (-20, -70, and $-150^{\circ}C$), ethanol ($-70^{\circ}C$) and liquid nitrogen ($-196^{\circ}C$) immersion freezing. There were no significant differences on the populations of L. monocytogenes inoculated with chicken breasts under different freezing conditions. However, air blast freezing ($-20^{\circ}C$) resulted in significant reductions for total aerobic bacteria and C. jejuni compared to the control and other freezing treatments. The frozen samples were thawed with (hot or cold) air blast, water immersion, and high pressure thawing at $4^{\circ}C$ and $25^{\circ}C$. the populations of total aerobic bacteria, and yeast and mold in the frozen chicken breast increased by 5.78 and 4.05 log CFU/g after water immersion thawing ($25^{\circ}C$) treatment. After five freeze-thaw cycles, the populations of total aerobic bacteria, yeast and mold, and C. jejuni were reduced by 0.29~1.40 log cycles, while there were no significant differences (P > 0.05) in the populations of L. monocytogenes depending on the freeze-thaw cycles. In addition, the histological examination of chicken breasts showed an increase in spacing between the muscle fiber and torn muscle fiber bundles as the number of freeze-thaw cycles increased. These results indicate that freezing and thawing processes could affect in the levels of microbial contamination and the histological change of chicken breasts.

• Clinical and Experimental Reproductive Medicine
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• v.28 no.4
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• pp.287-293
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• 2001

Objective : To investigate the efficacy of high infusion frequency of liquid nitrogen on pregnancy in human embryo after freezing and thawing. Materials and Methods: 150 infertile patients underwent 162 consecutive thawing-ET cycles. In the high infusion frequency group (Group A), 47 patients (50 cycles) underwent cryopreservation with high infusion frequency of liquid nitrogen. In the low infusion frequency group (Group B), 103 patients (112 cycles) underwent cryopreservation with low infusion frequency of liquid nitrogen. We analyzed the clinical characteristics, fertilization rates, development of embryo, good quality embryo ratio, implantation rates, and pregnancy rates between these two groups. Results: There was no difference between the groups with regard to clinical characteristics (mean age, infertility duration, infertility factors, hormone profile), mean number of oocyte retrieval, fertilization rates, and mean embryo number of transfers. The survival rates in group A was 64.9% (228 of 350 embryos), and among the 228 embryos 190 embryos (83.3%) which progressed to the two- to eight-cell stage. After thawing, the embryo numbers were 65 (34.2%), 29 (15.3%), 35 (18.4%), and 37 (19.5%) of grades 1, 2, 3, and above 4, respectively. The survival rates in group B was 63.8% (482 of 755 embryos), and among the 482 embryos 465 embryos (96.5%) which progressed to the two- to eight-cell stage. After thawing, the embryo numbers were 106 (22.8%), 94 (20.2%), 89 (19.1%), and 112 (24.1%) of grades 1, 2, 3, and above 4, respectively. There was no difference in embryo quality change after the freezing-thawing procedure between the groups. Implantation rates (31.1% vs. 34.3%) were not significant. However hCG positive rates in group A (40%) were higher than group B, but not statistically significant. Clinical pregnancy rate (26% vs. 25.9%), on going pregnancy rates (>20 weeks) were not significant (26% vs. 25%). Conclusion: We compared embryo quality change, survival rates, and pregnancy rates between high infusion frequency group and low infusion frequency group and the results were similar between the two groups. Therefore, high infusion frequency of liquid nitrogen for cryopreservation is a worthy method to preserve in human embryos.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.2
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• pp.230-238
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• 2016

This study examined the effects of freezing and thawing conditions on quality of Hanwoo bottom round. The beef samples were frozen by air blast freezing at $-20^{\circ}C$ or ethanol immersion freezing at $-70^{\circ}C$ and then stored at $-20^{\circ}C$ for 10 days. After 10 days of storage, the frozen samples were thawed with air blast thawing at $4^{\circ}C$ or water immersion thawing at $4^{\circ}C$ and subjected to subsequent analyses of drip loss, water holding capacity, thiobarbituric acid reactive substance (TBARS), volatile basic nitrogen (VBN), total aerobic bacteria, and microstructure. Drip loss significantly increased in samples treated with air blast freezing compared to ethanol immersion freezing, whereas freezing and thawing processes had no significant impact on water holding capacity of the samples. Thawing conditions had a much stronger influence on the TBARS and VBN of the samples than freezing conditions. There was no significant difference in the population of total aerobic bacteria among the four samples subjected to one freeze-thaw cycle. In addition, to analyze the effects of freeze-thaw cycle on the quality of beef, three freeze-thaw cycles were performed during storage. Multiple freeze-thaw cycles increased drip loss, TBARS, and VBN and decreased water holding capacity, accelerating microstructural damage. These data indicate that Hanwoo bottom round can be rapidly frozen and thawed by using ethanol immersion freezing and water immersion thawing methods with minimal impact on meat quality.

• Computers and Concrete
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• v.21 no.2
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• pp.209-217
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• 2018

The dynamic compressive behavior of concrete after freezing and thawing tests are investigated by using the split Hopkinson pressure bar (SHPB) technique. The stress-strain curves of concrete under dynamic loading are measured and analyzed. The setting numbers of freeze-thaw cycles are 0, 25, 50, and 75 cycles. Test results show that the dynamic strength decreases and peak strain increases with the increasing of freeze-thaw cycles. Based on the Weibull distribution model, statistical damage constitutive model for dynamic stress-strain response of concrete after freeze-thaw cycles was proposed. At last, the fragmentation test of concrete subjected to dynamic loading and freeze-thaw cycles is carried out using sieving statistics. The distributions of the fragment sizes are analyzed based on fractal theory. The fractal dimensions of concrete increase with the increasing of both freeze-thaw cycle and strain rate. The relations among the fractal dimension, strain rates and freeze-thawing cycles are developed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.275-284
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• 2012

The Antarctic continent exposed to strong wind, very low temperature, and extremely dry condition. The freezing-thawing cycles under this extreme environment change the mechanical characteristics of rocks near the ground surface. To investigate the effect of freezing-thawing cycles under the extreme environment understand on geotechnical properties of rocks, rocks from the Antarctica were collected from two places: (1) West Antarctic Cape Burks and (2) East Antarctic Terra Nova Bay areas. The rock characteristics of these two areas were described and compared. For Terra Nova Bay area, rock characteristics of rocks near the surface and depths exceeding 2.9 m were examined. The 'near-the-surface rocks' averages of absorption rate, P-wave velocity, and unconfined compressive strength were 0.56%, 3,717 m/s, and 109MPa, respectively; while, those values of 'deep-sited rocks' were 0.24%, 4,670 m/s, and 88MPa. From the measurements, it was found that the effects of weathering were not significant on mechanical characteristics (strength) but were pronounced on physical characteristics(absorption and P-wave velocity).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.227-233
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• 2008

Porous concrete has large continuous voids of 20-30 % by volume, and this concrete is attractive as environmental material in Japan i.e. permeable road pavement, river bank protection with vegetation and green roof system which influence thermal environment. It is necessary to confirm the frost resistance when constructing porous concrete structure in cold region. However applicable test method and evaluation criterion of porous concrete has not defined yet. Therefore, the object of this study is to investigate the frost resistance of porous concrete and this investigation attempts to address this concern by comparing 4 kinds of specified freezing and thawing tests methods (JIS A1148 procedure A/B and RILEM CIF/CDF test) in consideration of actual environment. RILEM freeze-thaw tests are different from JIS A1148 freeze-thaw tests, which are widely adopted for evaluating the frost resistance of conventional concrete in Japan, in water absorption, cooling rate, length of freezing and thawing period, and number of freezing and thawing cycles. RILEM CIF test measures internal damage and is primarily applicable for pure frost attack. CDF test is appropriate for freeze-thaw and de-icing salt attack. JIS A1148 procedure A/B showed extremely low frost resistance of porous concrete if the large continuous voids were filled with water and the ice expansion in the large continuous voids set in during cooling. Frost resistance of porous concrete was improved by mixing coarse aggregate (G7) which particle size is smaller and fine aggregate in JIS freezing and thawing tests. RILEM CIF/CDF test showed that freeze-thaw and de-icing resistance of porous concrete was seems to be superior in that of conventional concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1097-1100
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• 2008

The purpose of this study to investigate the bond strength of recycled coarse aggregate concrete deteriorated by freezing and thawing. Concrete specimens with recycled coarse aggregate representing lower limit of the quality standard (water absorption : 3.0%, specific gravity : $2.5g.cm^3$) were manufactured and tested. The replacement ratio (0, 30, 60 and 100%) of recycled coarse aggregate and freezing-thawing cycles were considered in this test. From the test results, it was found that the bond strength of normal strength concrete is not affected by the replacement ratio of recycled coarse aggregate under freezing and thawing conditions. Also, the bond strength of the natural and recycled coarse aggregate concrete using AE admixtures was not decreased by frost action.