• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.66-73
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• 2022

The purpose of this study was to develop self-heating concrete by utilizing the conduction resistance of concrete in order to reduce the risk of occurrence of black ice in the concrete pavement in winter and to prevent damage caused by freez-thawing effect. For this purpose, it was attempted to evaluate the strength and temperature exothermic characteristics using powder and liquid waste CNTs and a waste cathode agent as a conduction promotion. It was analyzed that liquid waste CNT had an effective dispersion degree in the mortar and a small decrease in strength occurred. In addition, DC 24 V was supplied by applying steel mesh, copper foil and copper wire to the mortar as electrodes, and the temperature change characteristics according to the mixing ratio of spent CNTs, anodes and carbon fibers were evaluated. In addition, by evaluating the temperature characteristics according to the electrode spacing from the selected optimal mixture, it was confirmed that it had sufficient heating characteristics up to an electrode spacing of 100 mm up to AC 50 V.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.623-630
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• 2007

Grouting materials are used for the unification of superstructural and substructural body like bridge seat (shoe) or machinery pedestal and e.t.c by filling their intercalary voids. Accordingly, grouting materials have been developed and used mainly with products of high strength because those materials are constructed specially in a part receiving large or impact load. In this situation, the structural body constructed by grouting materials with high stiffness-centered (caused by high strength) products is apt to cause brittle failure when receiving over a limit stress and to cause cracks according to cumulative fatigue by continuous and cyclic load. In addition, grouting materials are apt to cause cracks by using too much rapid hardening agents that give rise to high heat of hydration to maintain high strength at early age. In this study, to overcome these problems, cement type grouting materials including powder of waste tire and resin as elastic materials which aim to be more stable construction and to be improvement of mother-body's unification are developed and endowed with properties of high toughness and high durability add to existing properties of high flowability, non-shrinkage and high strength. Besides, this study contribute to of for green construction materials for being possible recycling industrial waste like waste tire and flyash. On the whole, seven type mixing conditions are tested and investigated to choose the best mixing condition.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.605-612
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• 2004

This study investigated the fundamental properties and shrinkage properties of high performance concrete with water/binder ratio of 0, 30 and with combination of expansive additive and shrinkage reducing agent. According to the results, the fluidity of high performance concrete showed lower the using method in combination with expansive additive and shrinkage reducing agent than the separately using method of that, so the amount of superplasticizer increased when the adding ratio of expansive additive and shrinkage reducing agent increased. However the air content of concrete increased when used in combination with expansive additive and shrinkage reducing agent, so the amount of AR agent decreased. The compressive strength showed the highest at $5\%$ of expansive additive, and decreased with an increase of the amount of shrinkage reducing agent. Furthermore, in order to reduce the shrinkage of high performance concrete, it was found that the using method in combination with expansive additive and shrinkage reducing agent was more effective than separately using method of that. Therefore, it analyzed that the combination of expansive additive of $5\%$ and shrinkage reduction agent of $1\%$ was the most suitable mixture, considering to the fluidity, strength and shrinkage under the condition of this experiment.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.141-148
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• 2017

This study is experimentally investigated the effects of various steam curing parameters on the early-age compressive strength development of high strength concrete (over 40 MPa) in the precast plant production. High strength concrete are used only ordinary portland cement (type I) and water-cement ratio selected 3cases (25%, 35% and 45%). Also, steam curing parameters are as followings ; (1) Preset period 2cases (3 hours and 6 hours) (2) Maximum curing temperature 3cases ($45^{\circ}C$, $55^{\circ}C$ and $65^{\circ}C$) (3) Maintenance time of curing temperature 3cases (4 hours, 6 hours and 8 hours) (4) Maximum rate of heating and cooling $15^{\circ}C$/hr. Initial setting time and adiabatic temperature rising ratio of these concrete according to water-cement ratio are tested before main tests and examined the compressive strength development for the steam curing parameters. Also compressive strength are compared with optimum steam curing condition and standard curing at test ages. As test results, the optimum steam curing conditions for high strength concrete(over 40 MPa) are as followings. (1) Preset period ; over initial setting time of concrete (2) Maximum curing temperature ; bellow $55^{\circ}C$ (3) Maintenance time of curing temperature ; bellow 6hours. Also strength development of steam curing concrete show in the reversed strength at 28 days. It is to propose an efficient steam curing condition for high strength concrete in the precast method.

• Resources Recycling
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• v.25 no.2
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• pp.60-68
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• 2016

In this study, earlier analyzed tetrapod, one of an original group of offshore constructions studied for manufacturability of the concrete using the properties of steel making slag aggregate. steel making slag aggregate assessment, RCS and Blast Furnace Slag : the 20 mm air-cooled slag and combinations by 50 %, aggregate properties on the most appropriate for the properties of recycled aggregate concrete optimal mix, and assessing it. Properties of concrete used to be derived are judged as to bury the studies show that the hollowing-out of the RCS, plastic sole use is in the workability of the aggregate, plastic in the 20 mm slag also assessed to be a slight disadvantage, but RCS by mixing air-cooled coarse and 50 percent to 20 percent 50 mm. Thus, steel making slag marine structures using recycled aggregate, in rapid chilled slag or air-cooled slag. The sole use of the aggregate them than to combine the aggregate of concrete. After they satisfy the quality standard quality shall be used will aggregate steel making slag who meet the criteria concrete manufacturing in general or par with the aggregate of concrete. Performance was assessed as to develop a more than that.

• Explosives and Blasting
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• v.22 no.1
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• pp.33-43
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• 2004

In this study, a comparison was made between the resulting behaviors of scaled model test and particle flow analysis for blasting demolition of a reinforced concrete structure. For the test and analysis, a progressive failure of a five-story structure was considered. The dimension analysis was carried out to properly scale down the real structure into the laboratory size. The test model was made of the mixture of gypsum, sand and water along with soldering lead to analogy reinforcing steel bars. The ratio of mixing components was chosen to best represent the scaled down strength and deformation modulus. The columns and girders of the structure were precasted in the laboratory and assembled right before the blasting test. The numerical analysis of the blasting demolition was carried out using PFC2D (Particle Flow Analysis 2-Dimension by Itasca). The results of the blasting of concrete lahmen structure showed roughly identical demolition behavior between scaled model test and numerical test. For the blasting of the reinforced concrete structure, the results were more identical and closer to the real demolition behavior, since the demolition behavior was better represented in this case due to the increased tensile strength of the component.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.221-228
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• 2004

Basic properties of artificial lightweight aggregate by using waste dusts and strength properties of LWA concrete were studied. Bulk specific gravity and water absorption of artificial lightweight aggregates varied from 1.4 to 1.7 and 13 to 16%, respectively. Crushing ratio of artificial lightweight aggregate was above 10% higher than that of crushed stone or gravel. As a result of TCLP leaching test, the leaching amount of tested heavy metal element was below the leaching standard of hazardous material. Slump, compressive strength and stress-strain properties of LWA concrete made of artificial lightweight aggregate were tested. Concrete samples derived from LWA substitution ratio of 30 vol% and W/C ratio of 45 wt% showed the best properties overall. Thermal insulation and sound insulation characteristics of light weight concrete panel with the optimum concrete proportion were tested. Average overall heat transmission of 3.293W/㎡$^{\circ}C$ was observed. It was higher by about 15% than those of normal concrete made by crushed stone. Sound transmission loss of 50.9 ㏈ in frequency of 500 ㎐ was observed. It was higher by about 13% than standard transmission loss.

• International Journal of Highway Engineering
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• v.18 no.6
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• pp.105-113
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• 2016

OBJECTIVES : This study is to develop the optimum mixing proportions for cement concrete pavement with using recycled aggregates. METHODS : The mixture varied recycled coarse aggregates content from 50 % to 100 % to replace the natural coarse aggregates by weight. Tests for fundamental properties as a cement concrete pavement were conducted before and after hardening of the concrete. RESULTS : It was found that the variation in the amount of the recycled aggregate affected the compressive and flexural strength development, as well as the chloride ion penetration resistance. As the amount of the recycled aggregate content increased the compressive and flexural strength and the resistance to chloride ion penetration decreased. However, the resistance to freeze-thaw reaction was affected significantly. In addition, the gradation of the aggregate became worse and hence so did the coarseness factor as the recycled aggregate amount increased. CONCLUSIONS : The fundamental properties of the concrete with recycled aggregate does not seem to be appropriate when the recycled aggregate quality is not guaranteed up to a some level and its replacement ratio is over 50%. The optimized gradation of the aggregates should also be sought when the recycled aggregate is used for the cement concrete pavement materials.

• Journal of the Korean Society of Safety
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• v.34 no.5
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• pp.111-118
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• 2019

Recently, a variety of special concrete structures have been designed in domestic and overseas construction markets and more advanced construction technology is required. Therefore, it is necessary to secure quantitative construction technology. For this purpose, it is essential to develop a standard reference material having a constant flow performance and quality to evaluate quantitative performance. On the other hand, the flowability of the concrete is greatly influenced by the flowability of the cement paste. Also, in consideration of design strength and workability, mix design is carried out at various mixing ratios according to the purpose of the site. Therefore, in this study, based on the derived components of standard reference materials for cement paste, we suggested mixing ratio of standard reference materials that can uniformly simulate the flow characteristics of cement paste according to W/C. As a result, it was found that the yield stress was determined by the ratio of water and glycerol but plastic viscosity was controled by limestone content. Finally, the ratio of standard reference materials to simulate the rheological range of cement paste by W/C was suggested.

• Journal of the Korea Institute of Building Construction
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• v.23 no.2
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• pp.133-142
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• 2023

In this study, the fire resistance capabilities of polypropylene fiber-reinforced polymer-modified cement mortar were assessed to guarantee the fire resistance fo this materials, commonly employed in the repair of concrete structures. Experimental outcomes revealed that an increased water and polymer content heightened the likelihood of spalling, while longer polypropylene fibers and elevated polymer concentrations proved more effective in mitigating spalling.