• The Journal of Korean Academy of Prosthodontics
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• v.38 no.6
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• pp.765-781
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• 2000

The purpose of this study was to compare the screw loosening characteristics of three avail-able cementation type abutments: one-piece cementation type abutment; two-piece cementation type abutment using titanium abutment screw; two-piece cementation type abutment using gold abutment screw. Two implant supported three-unit superstructures were fabricated using a pair of 3 kinds of abutments for each experimental model. Cyclic loading was applied on the specimen, and made to stop when the superstructure showed movement over threshold range. The loaded cycle was counted until the machine stopped. Frequency analysis was done to measure the change of natural frequency before and after the application of cyclic load and to find the effect of screw loosening on the change of natural frequency. The specimen assembly was modeled to perform the finite element analysis to see the distribution of the stress induced by the application of preload over the screw joint and to compare the pattern of the distribution of stress induced by the external force with the change of the preload condition. The following results were obtained: 1. The failure loading cycle of two-piece cementation type abutment using gold screw was significantly greater than those of the other groups. 2. One-piece cementation type abutment applied to multi-unit restoration case did not show greater resistance to screw loosening compared to two-piece cementation type abutments. 3. Frequency analysis showed decrease in natural frequency when screw loosening occured.

• Journal of the Korean Geotechnical Society
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• v.25 no.2
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• pp.67-77
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• 2009

In this study, the relations of cone tip resistances (qc) and DMT indices of cemented sand are analyzed from a series of calibration chamber tests. The experimental results show that, with increasing the cementation level, three DMT indices also increase. The CPT and DMT do not appear to properly reflect the cementation effect of sand, since the penetration induces the damage of cementation. Nevertheless, the DMT is more sensitive to deformation characteristics of cemented sand than CPT. It is also observed that the $E_D/q_c$ ratio of cemented sand is larger than that of uncemented sand. However, the $K_D-q_c/{\sigma}_v'$ relation is independant of cementation, unlike the result of previous study. In addition, this study evaluates the constrained modulus and cohesion intercept of cemented sand using the relation between cone resistance and dilatometer constrained modulus ($M_D$).

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.484-491
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• 2008

The purpose of this study is to compare the cementation effect on cone resistance and DMT indices and to evaluate the deformation characteristic of cemented sand using cone resistance and dilatometer modulus. Specimens of various relative densities with three different cementation levels are prepared in a large calibration chamber under different vertical stress levels. Test result shows that the cone resistance and dilatometer modulus underestimate the deformation modulus of cemented sand, since in situ penetration tests such as CPT and DMT damage the cementation bonds during penetration. By regression analysis, the constrained modulus of cemented sand is related with the cone resistance and the dilatometer modulus.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1173-1180
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• 2006

In this study, aluminum electrodes were put in marine clay which was taken from the south coast in Korea to increase the undrained shear strength by inducing the densification and cementation between clay particles and precipitates which were developed by electric decomposition in an electrode. To raise the cementation rate and reduce treatment time, high electric current (2.5A) was applied in each electrode at a semi-pilot scale soil box with marine clay. After the tests, the undrained shear strength was measured at designated points using a static cone penetration test device and sampling was conducted simultaneously in order to measure water content, pH and electric conductivity which would be the key for configuring the cementation effects indirectly. In the results of electric decomposition in aluminum electrode, the measured shear strength was increased considerably compared to the initial shear strength because of the cementation effect between iron ions and soil particles.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.143-151
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• 2007

The factors affecting the geotechnical properties of cemented sands are known to be relative density, cementation level, stress level, and particle characteristics such as particle size, shape and surface conditions. It has been widely accepted that the friction angle of cemented sands is not affected by cementation while the cohesion of cemented sands was significantly influenced by cementation. The cementation that is a critical component of the strength of cemented sands will be broken with increasing confining pressure and great caution is required in evaluating the cohesion of cemented specimens due to their fragilities. In this study, a series of drained shear tests were performed with specimens at various cementation levels and confining stresses to evaluate the strength parameters of cemented sands. From the experiments, it was concluded that the cohesion intercept of cemented sand experiences three distinctive zone(cementation control zone, transition zone, and stress control zone), as the cementation level and the confining stress varies. In addition, for accurate evaluation of the strength parameters, the level of confining stress triggering the breakage of cementation bond should be determined. In this study, the relationship between the maximum confining stresses capable of maintaining the cementation bond intact and unconfined compression strength of the cemented sand was established.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.87-97
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• 2008

Behaviors of cemented engineered soils, composed of rigid sand particle and soft rubber particle, are investigated under $K_o$ condition. The uncemented and cemented specimens are prepared with various sand volume fractions to estimate the effect of the cementation in mixtures. The vertical deformation and elastic wave velocities with vertical stress are measured. The bender elements and PZT sensors are used to measure elastic wave velocities. After cementation, the slope of vertical strain shows bilinear and is similar to that of uncemented specimen after decementation. Normalized vertical strains can be divided into capillary force, cementation, and decementation region. The first deflection of the shear wave in near field matches the first arrival of the primary wave. The elastic wave velocities dramatically increase due to cementation hardening under the fixed vertical stress, and are almost identical with additional stress. After decementation, the elastic wave velocities increase with increase in the vertical stress. The effect of cementation hinders the typical rubber-like, sand-like, and transition behaviors observed in uncemented specimens. Different mechanism can be expected in decementation of the rigid-soft particle mixtures due to the sand fraction. a shape change of individual particles in low sand fraction specimens; a fabric change between particles in high sand fraction specimens. This study suggests that behaviors of cemented engineered soils, composed of rigid-soft particles, are distinguished due to the cementation and decementation from those of uncemented specimens.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1431-1437
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• 2008

The small-strain shear modulus ($G_{max}$) of uncemented sand is affected by the the mean principal stress and void ratio, and it has been known that the cementation and aging also affect to $G_{max}$ of sand. For extensive understanding about the effect of cementation on the $G_{max}$ of sand, a series of bender element tests was conducted on the cemented specimens prepared in a large calibration chamber by pluviation of the sand-gypsum mixture. It was observed from the experimental results that the $G_{max}$ of cemented sand is higher above 10 times than value of uncemented one, and it increases exponentially with the gypsum content increases. Whereas, the increase of the vertical stress from 50kPa to 200kPa and the relative density from 40% to 80% result in 20~30% and 2 times increase of $G_{max}$, respectively. It means that the gypsum content, that is cementation level, is the most influential factor on the $G_{max}$ of cemented sand. In addition, the effect of relative density on $G_{max}$ was more apparent on cemented sand than uncemented one.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2C
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• pp.89-98
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• 2006

In this study, the iron and aluminium electrode was put in marine clay which was taken from south coast in Korea to increase the undrained shear strength by inducing the densification and cementation between clay particles and precipitation which was developed by electrode decomposition. For raising the cementation rate and reducing treatment time, high electric current( 2.5A) was applied in each electrode at semi-pilot scale soil box with marine clay. After the tests, the undrained shear strength was measured at designated points using cone penetration test device and sampling was conducted simultaneously in order to measure water content, pH and electric conductivity which would be the key for configuring the cementation effects indirectly. The iron electrode decomposition test results show that the water content adjacent to anode section decreased in 35% and increased in 13% at cathode section. The measured shear strength however, was increased considerably comparing to initial shear strength because of cementation effect between iron ions and soil particles. In case of aluminium electrode decomposition test, the distribution of measured shear strength and degree of improvement were more homogeneous than iron electrode decomposition test.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.169-176
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• 2014

To evaluate bio-cementation of microbial on sands, laboratory test was conducted using acrylic cubic molding boxes ($5cm{\times}5cm{\times}5cm$). It was incubated the microbial, called Bacillus Pasteurii, according to Park et al (2011, 2012). and applied 50ml each specimen. Two type of sand samples used were Jumoonjin sand and common sand (well graded). These sands were molded in acrylic boxes with the relative density of 30 % and 60 % respectively. Microbial were poured onto the samples molded in acrylic boxes and cured at the room temperature and humidity. After 7, 14 and 21days, it was measured the compressive strength, pH, EC, and density and it were observed SEM and XRD to verify the effect of bio-cementation. It was found that bio-cementation was increased a strength of sands and it was appeared that strengths were related to the type of sand and relative density. Therefore it was confirmed the solidification of sands using the bio-cementation by microbial activation and the usefullness of acrylic molding boxes when tests were conducted on the soil of sands.

• Journal of the Korean Geotechnical Society
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• v.26 no.4
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• pp.37-45
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• 2010

Salt cementation, a typical naturally-cemented phenomenon, may occur due to water evaporation under the change of climate. Capillary force may influence the distribution of cement in granular soils. This study addresses the effect of capillary force on salt cementation using five different techniques: cone penetration test, electrical conductivity measurement, photographic imaging technique, nondestructive imaging technique, and process monitoring by elastic wave. Glass beads modeling a particulate media was mixed with salt water and then dried in an oven to create the cementation condition. Experimental results show that salt cementation highly concentrates at the top of the small particle size specimens and at the middle or the bottom of the large particle specimens. The predicted capillary heights are similar to the locations of high salt concentration in the cemented specimens. Five suggested methods show that the behavior of salt-cemented granular media heavily depends on the capillary force.