• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.70-77
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• 2010

This study is to investigate experimentally the influence of mixing factors, such as a mortar mix proportion of non-cement mortar, flow, and W/B, on quality characteristics of blast furnace slag powder mortar incorporating dry type recycled fine aggregates. In the characteristics of fresh mortar, the W/B increased according to the increase in the flow due to the increase in water contents, but air contents decreased due to loss of air contrary to the increase in the W/B. In the case of hardened mortar, the compressive strength showed a decrease due to the highly determined W/B inversely according to the increase in the flow through the entire age in which the compressive strength increased proportionally according to the increase in the B/W. Also, the increasing rate of such compressive strength increased more largely due to the latent hydraulic property of the BS according to the passage of the age. The flexural strength at the age of 28 days according to the increase in the B/W represented a similar level in strength values without any increases. The flexural strength for the compressive strength was distributed as a range of 1/2 ~ 1/3 and that showed a higher range than that of conventional concretes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.163-170
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• 2012

With the advantage of a rapid exothermic reaction property, jet set concrete may be used as a cold weather concrete because it can reach the required strength before being damaged by cold weathers. And it can be hardened more quickly if the field temperature is properly compensated by heating. Because ordinary concrete cannot be hardened well under sub-zero temperatures, anti-freeze agents are typically added to prevent the frost damage and to ensure the proper hardening of concrete. While the addition of a large amount of anti-freeze agent is effective to prevent concrete from freezing and accelerates cement hydration resulting in shortening the setting time and enhancing the initial strength, it induces problems in long-term strength growth. Also, it is not economically feasible because most anti-freeze agents are mainly composed of chlorides. Recent studies reported that magnesia-phosphate composites can be hardened very quickly and hydrated even in low temperatures, which can be used as an alternative of cold weather concrete for cold weathers and very cold places. As a preliminary study, to obtain the material properties, mortar specimens with different mixture proportions of magnesia-phosphate composites were manufactured and series of experiments were conducted varying the curing temperature. From the experimental results, an appropriate mixture design for cold weathers and very cold places is suggested.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.441-448
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• 2011

In this study, experimental tests of chemical and autogenous shrinkage were performed to evaluate the early age shrinkage behaviors of ultra high performance cementitious composites (UHPCC) with various replacement ratios of silica fume (SF), shrinkage reducing agent (SRA), expansive admixture (EA), and superplasticizer (SP). Starting time of self-desiccation, was analyzed by comparing the setting times and the deviated point of chemical and autogenous shrinkage strains. The test results indicated that both SF and SRA augment the early age chemical shrinkage, whereas SP delays the hydration reaction between cement particles and water, and reduces chemical shrinkage. About 49% of autogenous shrinkage was depleted by synergetic effect of SRA and EA. The hardening of UHPCC was catalyzed by containing EA. Self-desiccation of UHPCC occurred prior to the initial setting due to the high volume fraction of fibers and low water-binder ratio (W/B).

• Geomechanics and Engineering
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• v.12 no.4
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.177-183
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• 2011

VES-LMC(very-early strength latex modified concrete) has been widely used as repair material for bridge deck overlay or rehabilitation, because it could be opened to the traffic after 3 hours of curing. However, the bright color of VES-LMC disturb driver's sigh. A black VES-LMC, matching to asphalt concrete, was developed and applied at a filed for driver's comfort and safety. The black VES-LMC included 2% carbon black in cement weight ratio. A series of performance evaluation for black VES-LMC was done in terms of field applicability, pavement color and temperature change. The field applicability test result showed that there were no change of workability, slump and air void, and the compressive strengthen developed more than 20MPa after 4 hours of placement. The thermal stress of black VES-LMC was smaller than that of OPC and asphalt concrete, which means the stability of black VES-LMC. The performance evaluation result showed that the black VES-LMC could prevent road icing at below zero temperatures and promote thawing at melting temperature.

• Resources Recycling
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• v.27 no.3
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• pp.86-92
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• 2018

The amount of construction waste generated is steadily increasing every year, and the Law for Promotion of Recycling is enacted. However, it is difficult to use it as a recycled aggregate for concrete, which is presented in the quality standard of recycled aggregate with high water uptake and low density due to low separation of aggregate between concrete and cement paste. Therefore, in this study, a multi-stage impact crusher was used to remove mortar, which is essential for improving the quality of recycled aggregate. In analyzing the characteristics of the equipment, the spectrum of energy generated in each part between the particle and the equipment was calculated by using DEM. In order to generate an effective separation phenomenon, it was confirmed that the operation condition of 900 RPM was appropriate based on the ratio of the number of collisions (L/H) of the low energy group (L) to the number of collisions of the high energy group (H).

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.389-392
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• 2008

Ultra-high strength concrete becomes one of the main research areas because recently concrete structure is larger. The quality of aggregate (ultra-high strength and uniformity) as well as chemical admixture and mineral additives is a key factor for ultra-high strength concrete development. However, natural aggregate including crushed aggregate is inappropriate for ultra-high strength concrete because ultra-high strength quality cannot be maintained uniformly over whole natural aggregate lot. In this study ceramic aggregate was applied for ultra-high strength concrete in order to assure uniform quality of ultra-high strength aggregate. Ultra-high strength concrete was achieved by applying coated ultra-high strength ceramic aggregate to enhance the bonding strength between aggregate and cement paste. Also for actual application light weight ceramic aggregate(density 2.2 $g/cm^3$) with zero water absorption was tested.

• Journal of the Korean earth science society
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• v.43 no.1
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• pp.41-59
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• 2022

In accordance with the enactment of 'the Paris Agreement' in 2015 and 'the Framework Act on Carbon Neutrality and Green Growth for Response to the Climate Crisis' in 2021, each local government has set appropriate reduction target of greenhouse gas to achieve the nationally determined contribution (NDC, the reduction target of 40% compared to 2018) of greenhouse gas (GHG) emissions in 2030. In this study, the current distribution of GHG emissions was analyzed in a time series centered on the Chungbuk region for the period from 1990 to 2018, with the aim of reducing GHG emissions in Chungbuk by 2030 based on the 2030 NDC and scenario. In addition, the prospected reduction by 2030 was estimated considering the projected emissions according to Busines As Usual in order to achieve the target reduction of GHG emissions. Our results showed that GHG emissions in Chungbuk and Korea have been increasing since 1990 owing to population and economic growth. GHG emissions in 2018 in Chungbuk were very low (3.9 %) relative to the national value. Moreover, emissions from fuel combustion, such as cement and lime production, manufacturing and construction industries, and transportation industries, were the main sources. Furthermore, the 2030 target of GHG emission reduction in Chungbuk was set at 40.2% relative to the 2018 value, in accordance with the 2030 NDC and 2050 carbon-zero national scenario. Therefore, when projected emissions were considered, the prospected reduction to achieve the target reduction of GHG emissions was estimated to be 46.8% relative to 2018. The above results highlight the importance of meeting the prospected reduction of GHG emissions through reduction means in each sector to achieve the national and local GHG reduction target. In addition, to achieve the 2030 NDC and 2050 carbon zero, the country and each local government, including Chungbuk, need to estimate projected emissions by year, determine reduction targets and prospect reductions every year, and prepare specific means to reduce GHG emissions.

• Environmental and Resource Economics Review
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• v.18 no.2
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• pp.279-309
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• 2009

Greenhouse gas emissions should be precisely forecast to reduce the emissions from industrial production processes. This study calculated the direct and indirect $CO_2$ emission intensities of 401 industries using the Input-Output tables 2003 and statistical data on the amount of energy use. This study had some limitations in drawing study findings because overseas data were used given the lack of domestic data. Other limiting factors included the oil distribution problems in the oil refinery sector, re-review of carbon neutral, and insufficient consideration of waste treatment. Nonetheless, this study is very meaningful since the direct and indirect $CO_2$ emission intensities of 401 industries were calculated. Specifically, this study considered from the zero-waste perspective the effects of waste, which attract interest worldwide since coke gas and gas from the steel industry are obtained as byproducts for the first time in Korea. According to the results of the analysis of $CO_2$ emission intensity per industry, typical industries whose indirect $CO_2$ emission intensity is high include crude steel making, Remicon, steel wire rods & track rail, cast iron, and iron reinforcing rods & bar steel. These industries produce products using the raw materials produced in the industrial sector whose $CO_2$ emission intensity is high. The representative industries whose direct $CO_2$ emission intensity is high include cement, pig iron, lime & plaster products, andcoal-based compounds. These industries extract raw ore from nature and refine them into raw materials that are useful in other industries. The findings in this study can be effectively used for the following case: estimation of target $CO_2$ emission reduction level reflecting each industrial sector's characteristics, calculation of potential emission reduction of each policy to reduce $CO_2$ emissions, identification of a firm's $CO_2$ emission level, and setting of the target level of emission reduction. Moreover, the findings in this study can be utilized widely in fields such as System of integrated Environmental and Economic Accounting(SEEA) and Material Flow Analysis(MFA) as the current topic of research in Korea.