• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.56-64
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• 2021

Leakage due to deterioration and damage is one of the major causes of volume change by freezing and thawing, and it leads micro-cracking and surface scaling in concrete structures. The deterioration of damaged concrete accelerates with the chloride attack. Thus, in the detailed guidelines for facility performance evaluation (2020), the quality of cover concrete and the freeze-thaw (FT) repetition cycle were newly suggested for concrete durability assessment. The quality of cover concrete should be evaluated by the rebound hammer test and the FT repetition cycle should be also considered in the deterioration environmental assessment. This study suggested the application of fast dynamic based nonlinear ultrasound method to monitor initial micro-scale damage under freezing and thawing environment. Concrete specimens were fabricated with different water-cement ratios (40%, 60%) and air contents (1.5% and 3.0%). The compressive strength, rebound number, relative dynamic modulus, and nonlinear ultrasound were measured with different FT cycles. The scanning electron microscopy was also performed to investigate the micro-scale FT damage. As a result, both the rebound number and the relative dynamic modulus had difficulty to detect early damage but the proposed method showed a potential to detect initial micro-scale damage and predict the FT resistance performance of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.355-365
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• 2015

This study examined the fluidity and strength properties, water resistance, durability, and freeze-thaw of cementless loess mortar using an eco-friendly hardening agent. The experimental result indicates that 28 days compressive and flexural strength of the loess mortar was increased regardless of the weathered granite soil and loess mixture ratio as the replacement ratio of the hardening agent increases. The strengths were significantly increased until 14 days regardless of the hardening agent, while the effect on the strengths increasement was relatively low after 14 days. Thus, the strength development of loess mortar concrete was found to be faster than that of the normal concrete. In addition, when the hardening agent of 10% was used, the average flexural strength was 1.7MPa which is insufficient compared to the 28-day flexural strength of 4.5MPa for the paving concrete. However, the flexural strengths of the loess mortar concrete using the hardening agents of 20% and 30% were 4.0MPa and 5.3MPa, respectively. Thus, the hardening agent need to be at least 20% so that the loess mortar can be used for paving concrete. The experiment for water resistance shows that the repeated absorption and dry reduced mass regardless of the mixing ratio of the loess. The maximum length change also decreased with increasing the substitution rate loess mixture ratio and the hardening agent. The result of the freeze-thaw resistance test indicates that the relative dynamic modulus of elasticity at 300 cycle freeze-thaw with the hardening agents of 20% and 30% were 75% and 79%, relatively. Thus, the hardening agent of at least 20% is required to obtain the relative dynamic modulus of elasticity of 60% for the loess mortar.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.2
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• pp.159-167
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• 2022

The present study assessed the micro structure and durability characteristics of ternary blended cement with different types of alkali activators. Ground granulated blast furnace slag(GGBS) and ferronickel slag(FNS) was replaced until 50 % of the weight of cement. In addition, potassuim hydroxide and sodium hydroxide were used for comparing the properties of different type of alkali activator. Ternary blended cement with alkali activators showed higher peak portlandite peak than that of OPC(Ordinary Portlande Cement) and non activated ternary blended cement. Also, there was no new hydration products in ternary blended cement or/and alkali activators. Based on the mercury intrustion porosimetry(MIP) test result, ternary blended cement increased macro pore while alkali activated ternary blended cement modified pore structure and increased microp pore as compared to OPC as control. Combination with alkali activators is desirable to enhance the compressive strength and freeze thaw resistance.

• International Journal of Highway Engineering
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• v.4 no.2 s.12
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• pp.1-8
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• 2002

Latex modified concrete(LMC) became to be applied as a new material for newly constructed bridge deck overlays in Korea due to its excellent bond strength, flexural strength and impermeability against water and chloride. However, it could not be adopted at repair job site because of its long curing time required. Thus, a research on latex modified concrete with rapid-setting cement(RSLMC) is necessary if it could develope the sufficient strength for early opening to traffic. This study focused on the durability of latex modified concrete with rapid-setting cement mainly on water permeable resistance and freeze-thaw resistance. The main experimental variables were latex contents(0, 5, 10, 15 and 20%) and antifoamer contents (0, 1.6, 3.2, 4.8 and 6.4%). Test results show that the permeability of RSLMC is very low indicating below 100 coulombs at 15% of latex contents at all antifoamer contents. The freeze-thaw resistance of RSLMC maintains above 90% of relative dynamic modulus at 3.2% of antifoamer content until 300 freezing-thawing cycles.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.701-704
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• 2008

The case of failure of Alkali-silica reaction (ASR) on the cement concrete pavement was reported in Korea. In the United States America, the fly ash has less than 10 percent Cao reported that prevent expansion by ASR. Most of all fly ash in Korea have less than 10 percent CaO, therefore it is similar ASTM F fly ash in the USA. Crushed aggregates of the test section had expansion behavior by potential ASR that the ASTM C 1260 test method tested expansion 0.17 percent during 14 days. The test section of concrete pavement used crushed aggregate was constructed that fly ash have 20 percent weight of cementitious materials to prevent expansion by ASR. This study was performed flexural strength test for elapsed days and durability by freeze-thaw test. It was shown that flexural strength was increased elapsed days and good performed freeze-thaw test. This study shown that fly ash concrete pavement was good performance in the test section.

• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.3
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• pp.68-80
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• 1984

This study was attempted in order to investigate the effects of superplasticizers on fresh and hardened concrete. The experimental program included tests on the slump and slump loss, bleeding, time of set, air content, the compacting, factor Vee Dee, compressive strength, tensile and flexural strength, permeability, shrinkage and freege-thaw durability. The major conclusions that can be drawn on the study are as follows. 1. Superplasticizers were observed to have an appreciable fluidifying action in fresh concrete so that tinder appropriate conditions, they either considerably improved its workability or permitted a water reduction of at least 8-12% to be made while maintaining normal workability. 2. The bleeding ratios of base and S,P. Concrete were much lower than those of the conventional concrete. Differences between the base and S.P. Concrete were insignifician. 3. The setting time was the longest for conventionla concrete, followed by S.P. concrete and base concrete in thatorder. And AE water reduction admixtures showed an appreciable influence on the setting and hardening characteristics of concrete and prolonged the stiffening times. 4. The high initial slump values of S.P. concrete generally decreased rapidly with increased standing time. CF values showed increasing tendencies with the increase of S.P. content, and excessive addition of S.P. caused the segregation of fresh concrete, resulting in its rejection. 5. Though there was a slight increase in strength, no significant differences are observed between base and S.P. concrete in terms of the compressive, tensile and flexural strength. 6. The permeability of S.P. concrete was significantly less than that of the conventional concrete, and the shrinkage of S.P. concrete was considerably smaller than that of the conventional concrete, but there were no significant differences between base and S.P. concrete. 7. Compared to base concrete, S.P. concrete without entrained air tended to slightly increase freeze-thaw durability, and S.P. concrete with an appropriate entrained air gave satisfactory resistance to freezing and thawing.

• Nuclear Engineering and Technology
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• v.45 no.3
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• pp.393-400
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• 2013

Concrete undergoing early frost damage in cold weather will experience significant loss of not only strength, but also of permeability and durability. Accordingly, concrete codes like ACI-306R prescribe a minimum compressive strength and duration of curing to prevent frost damage at an early age and secure the quality of concrete. Such minimum compressive strength and duration of curing are mostly defined based on the strength development of concrete. However, concrete subjected to frost damage at early age may not show a consistent relationship between its strength and durability. Especially, since durability of concrete is of utmost importance in nuclear power plant structures, this relationship should be imperatively clarified. Therefore, this study verifies the feasibility of the minimum compressive strength specified in the codes like ACI-306R by evaluating the strength development and the durability preventing the frost damage of early age concrete for nuclear power plant. The results indicate that the value of 5 MPa specified by the concrete standards like ACI-306R as the minimum compressive strength to prevent the early frost damage is reasonable in terms of the strength development, but seems to be inappropriate in the viewpoint of the resistance to chloride ion penetration and freeze-thaw. Consequently, it is recommended to propose a minimum compressive strength preventing early frost damage in terms of not only the strength development, but also in terms of the durability to secure the quality of concrete for nuclear power plants in cold climates.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.137-145
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• 1999

The use of steel fiber reinforced to improve the strength and flexural toughness of concrete is well known, but reinforcement of polymer concrete with steel fibers has been hardly reported till now. Polymer concrete has high strength, durability and freeze-thaw resistance than that of cement concrete, but it has disadvantage such as low flexural toughness. In this paper, the strength characteristics and flexural toughness of steel fiber reinforced polymer concrete are investigated experimentally with various steel fiber aspect ratios($\ell$/d), and contents(vol.%). As the result, the flexural and splitting tensile strengths and flexural toughness were increased aspect ratio, and reach the maximums at a aspect ratio of 50. The relationship between the compressive, flexural and splitting tensile strength were high. And the relationship between flexural strength and strain energy was approximately linear.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.810-813
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• 2004

Air void systems in hardened concrete has an important influence on concrete durability such as freeze-thaw resistance, water permeability, surface scaling resistance, and etc. Linear traverse method and point count method described at ASTM have been widely used to estimate the air void system in hardened concrete. These methods, however, are rarely used at present, because they require many efforts, are time consuming works, depend on each person's decision, and are not repeatable. Thus, new image analysis method using microscope and computer processes has been approached for analyzing air void system in hardened concrete. However, it is just in initial step. The purposes of this study were to develope an effective and reliable image analysis technique for estimating air void system in hardened concrete. The developed technique was proved to be accurate, reasonable and repeatable.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.50-56
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• 2005

The mechanical properties of glass fiber reinforced polymer reinforcing bars(rebar) in various environment conditions such as moisture, chloride, alkali and freeze-thaw actions at temperature ranging from room temperature($25^{\circ}C$) to high temperature of up to $80^{\circ}C$ have been studied. The test results indicated that tensile strength and interfacial shear strength of GFRP bar were decreased with the increasing of temperature and holding time of each environment condition. The degradation in alkali environment. was more serious than those in the other environments.