• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.39-49
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• 2018

In this study, aimed at determining the elastic modulus of deep mixed samples, 320 test specimens were developed by mixing 8%, 10%, 12%, and 14% of stabilizer mixture in the granular conditions of clay, sand and gravel. Uniaxial compression tests were carried out using these specimens, and the uniaxial compression strength and strain were analyzed to determine the secant elastic modulus and tangent elastic modulus. Laboratory test results showed that the uniaxial compression strength of all deep mixed samples increased with increasing curing time and stabilizer mixing ratio, and that the secant elastic modulus and the tangen elastic modulus also increased. The increase of the elastic modulus according to the curing period turned out greater in the tangent elastic modulus than in the secant elastic modulus. In order to measure elastic modulus with changes in stabilizer mixing ratio, the correlation coefficient between the elastic modulus for stabilizer mixing ratio of 8% and that of 10%, 12% and 14% was calculated respectively by the specimen condition. The elastic modulus tended to increase as the grain size in a deep mixed specimen increased. The distribution of grain size that had the greatest effect appeared when the composition ratio of sand was high. On the other hand, the increase in the elastic modulus was larger in the sand specimens than in the clay and gravel specimens. Based on these results, it is suggested that a pertinent soil parameter of the deep mixed ground in the field may be obtained by the particle size distribution and the mixing ratio of stabilizer of the deep mixed soil.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.30-31
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• 2019

Carbonation of the root concrete reduces the durability of the reinforced concrete, and it is important to check the carbonation resistance of the concrete to ensure the durability of the reinforced concrete structure. In this study, a basic study on the prediction of carbonation progress was conducted by considering the mixing conditions of concrete using deep learning algorithm during the theory of artificial neural network theory. The data used in the experiment used values that converted the carbonation velocity coefficient obtained from the mixing conditions of concrete and the accelerated carbonation experiment into the actual environment. The analysis shows that the error rate of the deep learning model according to the Hidden Layer is the best for the model using five layers, and based on the five Hidden layers, we want to verify the predicted performance of the carbonation speed coefficient of the carbonation test specimen in which the exposure experiment took place in the real environment.

• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.27-36
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• 2014

In this study, laboratory test was carried out on uniaxial compressive strength by making 320 specimens in total, which were divided into two groups considering the curing time of 7 and 28 days for 80 cases mixed with stabilizers of 8%, 10%, 12%, 14% of 20 cases of clayey, sandy, and gravel mixed ground conditions to understand laboratory strength characteristics of deep mixing specimen for field application in various ground conditions. As a laboratory result, all specimen showed a clear tendency to have uniaxial compressive strength increase as the curing time and the stabilizer mixing ratio increased, and the strength increments depending on the age by ground types were, around 40.0% for clayey and gravel mixed grounds, 48.4% for sandy grounds which was the highest, and for the increment of stabilizers, around 37.0% for grounds with mixing ratio less then 14%, and 49.6% when the ratio was 14% which was the highest. Also, with sandy grounds, it showed a tendency to have a constant amount of strength increment as the stabilizer mixing ratio increased, for clayey mixed grounds, the strength increment tendency seemed to be similar to gravel mixed grounds. Due to these tendencies, it is concluded that we are able to propose a stabilizer mixing ratio for various ground conditions.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.71-79
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• 2012

Sand compaction pile and stone column replacement methods have been commonly used for improving soft ground in the nearshore. Recently, DCM (Deep cement mixing) method, which can harden soft clays by mixing with cement, is more popularly used in such soft ground improvement. Sandy soils also exist in the seashore. Therefore, in this study, the effect of salinity in sea water and curing methods on the strength of cemented sand was evaluated in terms of unconfined compressive strength (UCS). The sand was mixed with five different cement ratios and distilled water or sea water, and then compacted into a cylindrical specimen. They were cured for 3 days under sea water for DCM construction condition and air cured for onshore curing condition. When a specimen was cured under sea water without confinement, it was easily collapsed due to initiation of cracks. When the cement ratio and curing method were the same, the UCS of the specimen without sea water was at maximum 3.5 times higher than those with sea water. The sea water used for mixing sand had more influence on strength reduction than the sea water used for curing. When the cement ratio was the same, the UCS of air-cured specimen was at average 2 times higher than those of water-cured specimen, regardless of water used.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.99-103
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• 2009

This research is the result of investigating engineering characteristics of slime generated during construction of deep mixing method. Mechanical characteristics of slime have been studied through literature review and laboratory tests of unconfined compression test, permeability test and settling tests were performed. As result of field observation of slime being generated, slime started to be produced right after flight auger was penetrated into a ground and its amount was increased in progress. Unconfined compressive strength of specimen with slime obtained from in field was measured in the range of $929.7{\sim}3,509.8kN/m^2$ and the value of unconfined compressive strength was found to be changed significantly with mixing ratio of soil, cement and binder. Permeability of them was measured in the range of $4.53{\times}10^{-7}{\sim}6.62{\times}10^{-6}cm/sec$ so that the mixture was appropriate as a impervious barrier. It was also know that the value of permeability was changed with the mixing ratio of binder. As test results of solidifying slime specimen prepared in the laboratory, good quality of cement mixture with coarse soil of sand were produced, compared with fine soils of silt and clay.

• Journal of the Korean Geotechnical Society
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• v.35 no.3
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• pp.25-35
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• 2019

A laboratory test on uniaxial compressive strength was carried out by making 640 specimens in total, which were divided into two groups by their curing time of 7 and 28 days for 3 water content conditions of a water content at 100% saturation level and 10% and 20% increased water content from the state with clay, sand and gravel mixed grounds of 20 ground conditions of 4 types of stabilizer mixing conditions which were 8%, 10%, 12%, 14%, to understand laboratory strength characteristics for strength design of deep mixing ground. In case of clayey grounds, although the strength increased depending on the increase of stabilizer content, it showed to be analogous regardless of the curing time. And the impact on the strength development of deep mixing specimen according to water content was considered to be comparatively little compared to other grounds. For sandy grounds, the strength increment amount clearly showed to increase as stabilizer content increased, and also the increase of water content was determined to be decreasing the strength increment effect. For gravel mixed grounds, at 14% or over of stabilizer content, the effect on strength development was big making a large increase in strength, but compared to sandy grounds, the strength ratio depending on the curing time showed to be small.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.2
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• pp.187-195
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• 2022

This study investigated the effect of artesian pressure on mechanical properties of deep cement mixing (DCM)-improved specimens. Various laboratory tests such as unconfined compression test and scanning electron microscope (SEM) were conducted on DCM specimens which curied in a water tank with different artesian pressures. The artesian pressure was determined in consideration of the laboratory scale and the hydraulic gradient in field conditions. Results of experimental tests indicated that unconfined compressive strength, secant modulus, and unit weight of specimen decreased and water content tended to increase as an artesian pressure increased. The stress-strain behavior changed brittle to ductile behaviors as an artesian pressure increased. The outflow water from the water tank reacted with the phenolphthalein solution due to the leaching phenomenon of the improved specimen. SEM analysis also confirmed that a small amount of ettringite was formed between soil particles in the specimens with artesian pressure.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.1
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• pp.52-60
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• 2005

Purpose. The intent of this study was to evaluate the effects of curing conditions on self-curing denture base resins to find out proper condition in self-curing resin polymerization. Materials and methods, In this study, 3 commercial self-curing denture base resins are used Vertex SC, Tokuso Rebase and Jet Denture Repair Acrylic. After mixing the self curing resin, it was placed in a stainless steel mold(3$\times$6$\times$60mm). The mold containing the resin was placed under the following conditions: in air at 23$^{\circ}C$; or in water at 23$^{\circ}C$; or in water at 23$^{\circ}C$ under pressure(20psi); or in water at 37$^{\circ}C$ under pressure(20psi) or in water at 50$^{\circ}C$ under pressure(20psi) , or in water at 65$^{\circ}C$ under pressure(20psi), respectively. Also heat-curing denture base resin is polymerized according to manufactures' instructions as control. Fracture toughness was measured by a single edge notched beam(SENB) method. Notch about 3mm deep was carved at the center of the long axis of the specimen using a dental diamond disk driven by a dental micro engine. The flexural test was carried out at a crosshead speed 0.5mm/min and fracture surface were observed under measuring microscope. Results and conclusion . The results obtained were summarized as follows : 1. The fracture toughness value of self-curing denture base resins were relatively lower than that of heat-curing denture base resin. 2. In Vertex SC and Jet Denture Repair Acrylic, higher fracture toughness value was observed in the curing environment with pressure but in Tokuso Rebase, low fracture toughness value was observed but there was no statistical difference. 3. Higher fracture toughness value was observed in the curing environment with water than air but there was no statistical difference. 4. Raising the temperature in water showed the increase of fracture toughness.