• Structural Engineering and Mechanics
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• v.90 no.5
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• pp.481-492
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• 2024

This research examined the mechanical behavior of fiber-reinforced concrete at unstable environmental conditions. Concrete composites with varying percentages of steel and glass fibers were analyzed. Compressive, indirect tensile, and fracture toughness properties were evaluated using the Edge Notched Disc Bend (ENDB) test under freezing-thawing and acidic environments and the results were compared with normal conditions. Steel fibers decreased the strength in the specified cycles, while glass fibers showed a normal strength trend. The compressive, tensile and fracture toughness of the samples containing 1.5 vol.% fibers showed a 1.28-, 2.13- and 4.5-fold enhancement compared to samples without fibers, after 300 freezing-thawing cycles, respectively.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1997.05a
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• pp.47-52
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• 1997

The experimental investigations considered in this paper are similar in many respects to those of Lee$^1$, with some key differences. First, there is no layering of the soils in a heterogeneous liner. The only soil investigated is the clay component of the cover liner. This ensures that the clay is exposed to freezing and that frost propagation in the clay can be investigated separate from other processes. Second, a closed system approach to the simulation was adopted. According to Jones$^2$, closed-system freezing occurs when there is no source of water available beyond that originally present in the soil voids. Freezing under such conditions results in very thin or non-existent ice lenses. One of tile objectives of the experiments described in this paper was the moisture migration and the changing of moisture contents of the compacted clay liner in landfill. The closed-system was used to limit tile variables in the experimental simulation to make these calculations more direct, although the final results could be applied to an open system also. As a result, the moisture content decreased about 45%-46% after two freeze/thaw cycles.

• Korean Journal of Remote Sensing
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• v.33 no.1
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• pp.47-60
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• 2017

The permafrost active layer plays an important role in permafrost dynamics. Ecological patterns, processes, and water and ice contents in the active layer are spatially and temporally complex depending on landscape heterogeneity and local-scale variations in hydrological processes. Although there has been emerging interest in the application of optical remote sensing techniques to permafrost environments, optical sensors are significantly limited in accessing information on near surface geo-cryological conditions. The primary objective of this study was to investigate capability of L-band SAR data for monitoring spatio-temporal variability of permafrost ecosystems and underlying soil conditions. This study exploits information from different polarimetric SAR observables in relation to permafrost environmental conditions. Experimental results show that each polarimetric radar observable conveys different information on permafrost environments. In the case of the dual-pol mode, the radar observables consist of two backscattering powers and one correlation coefficient between polarimetric channels. Among them, the dual-pol scattering powers are highly sensitive to freeze/thaw transition and can discriminate grasslands or ponds in thermokarst area from other permafrost ecosystems. However, it is difficult to identify the ground conditions with dual-pol observables. Additional backscattering powers and correlation coefficients obtained from quad-pol mode help understanding seasonal variations ofradar scattering and assessing geo-cryological information on soil layers. In particular, co-pol coherences atHV-basis and circular-basis were found to be very usefultools for mapping and monitoring near surface soil properties.

• International Journal of Highway Engineering
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• v.15 no.5
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• pp.75-79
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• 2013

PURPOSES : The objective of this study is to evaluate the environmental resistance of bio-polymer concrete for use of pavement materials developed for reducing the carbon-dioxide. METHODS : The compression, tension, and bending strength tests were conducted on the bio-polymer concrete specimens with and without environmental conditioning. The specimens were conditioned using the freezing-thaw and accelerated weathering process for long period of time. To assess the resistance against chloride, the chloride ion penetration resistance tests were carried out on the bio-polymer concrete specimens. RESULTS : Test results show that the maximum difference in strength between specimens with and without conditioning is about 2.6MPa indicating that the effect of environmental conditioning on specimen strength is negligible. Based on the chloride ion penetration resistance test, the penetration quantity of electric charge of the specimens is zero and there is no ion penetration within the bio-polymer concrete. CONCLUSIONS : It is found from this study that there is slight change in strength of bio-polymer concretes before and after environmental conditioning process and no chloride ion penetration observed in these specimens. Therefore, the developed bio-polymer concretes can be applied effectively as pavement materials due to the small change of physical properties with environment change.

• Advances in concrete construction
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• v.5 no.6
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• pp.671-683
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• 2017

Commonly used concrete in general, consists of cement, fine aggregate, coarse aggregate and water. Natural river sand is the most commonly used material as fine aggregate in concrete. One of the important requirements of concrete is that it should be durable under certain conditions of exposure. The durability of concrete is defined as its ability to resist weathering action, chemical attack or any other process of deterioration. Durable concrete will retain its original form, quality and serviceability when exposed to its environment. Deterioration can occur in various forms such as alkali aggregate expansion, freeze-thaw expansion, salt scaling by de-icing salts, shrinkage, attack on the reinforcement due to carbonation, sulphate attack on exposure to ground water, sea water attack and corrosion caused by salts. Addition of admixtures may control these effects. In this paper, an attempt has been made to replace part of fine aggregate by tailing material and part of cement by fly ash to improve the durability of concrete. The various durability tests performed were chemical attack tests such as sulphate attack, chloride attack and acid attack test and water absorption test. The concrete blend with 35% Tailing Material (TM) in place of river sand and 20% Fly Ash (FA) in place of OPC, has exhibited higher durability characteristics.

• Computers and Concrete
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• v.29 no.5
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• pp.335-346
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• 2022

Geopolymers are an important alternative material supporting recycling, sustainability, and waste management. Durability properties are among the most critical parameters to be investigated; in this study, the durability of manufactured geopolymer samples under the attack of 10% magnesium sulfate and 10% sodium sulfate solution was investigated. 180 cycles of freezing and thawing were also tested. The experimentally obtained results investigate the durability of geopolymer mortar prepared with fly ash (class F) and alkali activator. Three different quarry dust wastes replaced the river sand aggregate: limestone, marble, and basalt powder as fine filler aggregate in three different replacement ratios of 25%, 50%, and 75% to produce ten series of geopolymer composites. The geopolymer samples' visual appearance, weight changes, UPV, and strength properties were studied for up to 12 months at different time intervals of exposure to sulfate solutions to investigate sulfate resistance. In addition, Scanning Electron Microscopy (SEM), EDS, and XRD were used to study the microstructure of the samples. It was beneficial to include quarry waste as a filler aggregate in durability and mechanical properties. The compact matrix was demonstrated by microstructural analysis of the manufactured specimens. The geopolymer mortars immersed in sodium sulfate showed less strength reduction and deterioration than magnesium sulfate, indicating that magnesium sulfate is more aggressive than sodium sulfate. Therefore, it is concluded that using waste dust interrogation with partial replacement of river sand with fly ash-based geopolymers has satisfactory results in terms of durability properties of freeze-thaw and sulfate resistance.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.116-121
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• 2016

The amount of carbon dioxide ($CO_2$) released while producing building materials is substantial and has been targeted as a leading contributor to global climate change. One of the most typical methods of reducing $CO_2$ in building materials is the addition of slag and fly ash, like pozzolan material another method is to reduce $CO_2$ production by developing carbon negative cement. MgO-based cement from the low-temperature calcination of magnesite required less energy and emitted less $CO_2$ than the manufacturing of Portland cements. It is also believed that adding reactive MgO to Portland-pozzolan cements can improve their performance and also increase their capacity to absorb atmospheric $CO_2$. In this study, basic research on magnesia cement using $MgCO_3$ and magnesium silicate ore (serpentine) as the main starting materials, as well as blast furnace slag for the mineral admixture, was carried out for industrial waste material recycling. In order to increase the overall hydration activity, $MgCl_2$ was also added. In the case of the addition of $MgCl_2$as accelerating admixture, there was a promoting effect on the compressive strength. This was found to be due to the production of needle-like dense Mg-Cl hydrates. Mgnesia cement has a high viscosity due to its high specific surface area therefore, when the PC-based dispersing agent was added at a level of more than 1.0%, it had the effect of improving fluidity. In particular, the addition of $MgCl_2$ in magnesia cement using $MgCO_3$and magnesium silicate ore (serpentine) as main starting materials led to a lower expansion ratio and an increase in the freeze-thaw resistance finally, the addition of $MgCl_2$ as accelerating admixture led to good overall durability.

• Journal of the Korean Geographical Society
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• v.36 no.3
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• pp.217-232
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• 2001

One of the molt debatable Issues on geomorphological study in Korea should be the discussion over the formation process of gent1e slope surfaces on the piedmont area. In this study, the characteristics of spatial distribution and the formation process of geomorphic surfaces were investigated by classifying the alluvial fans as three geomorphic surfaces alluvial the Bulguksa fault-line The fan surfaces, distributed along the west slue of Bulguksa Mts, consists the confluent alluvial fans continuously along the N-S direction The surfaces of Sincheon-Hyomun district juxtaposed to the Ulsan Bay must be infulenced by sea-level chance during the Quaternary Taken together, these observation suggests that the major four factors contributed to the fan formation 1) rather longer freeze-and-thaw cycle during the Glacial period. 2) the steep mountain slope along the west side of Bulguksa Mts.. which had been resulted from the horizont stress of EAst Sea 3)the tectolinear fault system developed by structural movement along the Bulguksa Fault-line valley. and 4) the erosion-labile characteristics of bedrock In this urea which is consisted of the Bulguksa granite and the sedimentary rock formed in Cretaceous period.

• International Journal of Highway Engineering
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• v.15 no.4
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• pp.65-73
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• 2013

PURPOSES : As a research to develop a cement treated base course for an airport pavement which can enhance its drainage, this paper investigated the strength, infiltration performance and durability of the pervious concrete with respect to maximum coarse aggregate sizes and compaction methods. METHODS : This study measured compressive strength, infiltration rate, continuous porosity and freeze-thaw resistance of pervious concrete specimens, which were fabricated with five different compaction methods and different maximum aggregate sizes. In addition, in order to reduce the usage of Portland cement content and to enhance environment-friendliness, a portion of the cement was replaced with Ground Granulated Blast Furnace Slag (GGBS). RESULTS: Compressive strength requirement, 5 MPa at 7 days, was met for all applied compaction methods and aggregate sizes, except for the case of self-compaction. Infiltration rate became increased as the size of aggregate increased. The measured continuous porosities varied with the different compaction methods but the variation was not significant. When GGBS was incorporated, the strength requirement was successfully satisfied and the resistance to freezing-thawing was also superior to the required limit. CONCLUSIONS: The infiltration rate increased as the maximum size of aggregate increased but considering construct ability and supply of course aggregate, its size is recommended to be 25mm. With the suggested mix proportions, the developed pervious concrete is expected to successfully meet requirements for strength, drainage and durability for cement treated base or subbase course of an airport pavement.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.16-23
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• 2002

In construction field, million tons of demolished concrete are produced in korea. It is urgently needed that they are used as recycled materials in order to prevent environment pollution and gain economic profits. However, existing recycling methods of demolished concrete have their limits for wide application. They have been only focused on the burying and banking. Therefore, in this paper, physical and mechanical properties of planting concrete using construction wastes for aggregates are described in order to investigate the validities of demolished concrete as recycled aggregates. The Properties of strength and durability are tested. According to the experimental results, compressive strength and freeze-thaw resistance of planting concrete using recycled aggregates shows worse performance than those using crushed stone concrete. But, it shows positive performance on the absorption ratio and thermal conductivity. Especially, considering the side of recycling of concrete wastes, it is recommended that recycled aggregates made with construction wastes is applied to planting concrete.