Tae-Ho Bong

Analysis of Strength Characteristic for Bottom Ash Mixtures as Mixing Ratio and Curing Methods

Bottom Ash is industrial by-product from a thermoelectric power plant. An immense quantities of bottom ash have increased each year, but most of them is reclaimed in ash landfill. In this study, in order to raise recycling rate of Bottom Ash, it is suggested to cure Bottom Ash (BA) mixtures mixed with cement, lime, Fly Ash (FA), and oyster shell (OS). Mixtures of 5~20 % mixing ratio had been cured for 1, 3, 7, 14, and 28 days using sealed curing and air-dry curing method. Unconfined compressive strength test was conducted to determine strength and deformation modulus () change for mixtures as mixing ratio and curing day, water contents of mixtures were measured after test. As a result, strength and were increased as mixing ratio and curing days, but values and tendencies of them appeared in different as kind of mixture, mixing ratio, curing method, and curing days. The results showed the addition of cement, lime, Fly Ash, and oyster soil in Bottom Ash could improved strength and and enlarge its field of being used.

Characterization of CO2 emissions during construction of reservoir embankment elevation in South Korea

PurposeThe environmentally friendly construction of agricultural infrastructure is much needed for sustainable development because construction is recognized as a cause of environmental degradation. The objective of this study was to estimate and characterize carbon dioxide (CO2) emissions during construction of agricultural reservoir embankments for the quantitative environmental assessment and management of CO2 emissions using life cycle assessment method.MethodsTwo reservoirs with different foundation treatment and construction components were selected in this study and their characteristics in CO2 emissions were compared. And CO2 emissions were calculated separately for each of the following major components: construction materials, equipment, and transport. The basic unit of CO2 emissions for construction materials was calculated using the 2009 input–output tables in Korea and the basic unit of CO2 emissions for equipment of transport and construction was also calculated based on the amount of fuel used in a unit time.Results and discussionAccording to the study results, the construction of a water supply process appeared to generate the most emissions among all processes for the two sites. Emissions due to equipment were the highest in site A, while materials generated the most emissions in site B. Differences in emissions are due to differences in the construction process. While the operation time of the equipment in site A increased due to the cofferdam process and a large amount of cement was used in the foundation process in site B.ConclusionsCharacteristic of CO2 emissions differs with different construction processes and thus construction processes need to be optimized for environmental friendly development of agricultural infrastructure through estimation and characterization of CO2 emissions.

The Electrical Properties and Unconfined Compression Strength of Bottom Ash

The objective of this study is to find the electrical properties of Bottom ash from thermoelectric power plants in Korea. By using Parallel Plate Method, the electrical resistivity and dielectric constant were measured at the frequency from 20 Hz to 10 MHz. Also, unconfined strength test, XRF and sieve analysis were performed for finding the relationship between strength, physiochemical properties and electrical properties. In the result, the change of electrical resistivity and dielectric constant of bottom ash against frequency was similar to that of general soil. The proportion of fine grain in bottom ash had the positive correlation with dielectric constant and negative correlation with electrical resistivity. Chloride and sulfur trioxide were proportional to dielectric constant and the more bottom ash had chloride content, the lower electrical resistivity appeared in bottom ash. Unconfined strength of bottom ashes had a range from 200 kPa to 780 kPa and strength was inverse proportional to electrical resistivity.

Creep Characteristics of Weathered Soils and Application of Singh-Mitchell's Creep Formula

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In Korea, weathered soil is abundant and occupies around one-third of the country. Weathered soil is visually described as a sandy or gravelley soil, but the behavior is quite different from the behavior of usual sand and gravel. In particular, the permeability of weathered soil is similar to sand, but the durability of settlement is similar to clay. Therefore analysis of time-dependent behavior of weathered soil is very important. In this study, Creep tests with weathered soils were carried out under constant principal stress differences of various stress levels which were experimentally obtained by triaxial compression test. The results of these tests showed the creep behavior for which the deformation increased with time, and the results are consistent with phenomenological model by creep equation of Singh-Mitchell.

The Time-Dependent Behavior Characteristic of Bottom Ash by Maximum Particle Size and Application of Creep Models

This study finds the characteristics of long-term settlement of Bottom Ash and to review the application of Singh-Mitchell creep equation and Burgers Model to the creep behavior of Bottom Ash. In the undrained state, it was confirmed that creep behavior appeared in the range to 30-80 % of the maximum deviator stress by applying condition in other three stresses through triaxial compression test after isotropically consolidation. By using sieve analysis, it was compared to each sample that was passed through 9.5 mm, 2 mm, 0.25 mm sieves. Also, using Singh-Mitchell creep equation and Burgers Model, it was compared between the theoretical behavior and the observed behavior for each sample. In the result, it is found that creep behavior of Bottom Ash is similar to the theoretical behavior of Singh-Mitchell creep equation and Burgers Model in early stage and it is possible to predict creep behavior of Bottom Ash by these models.

Undrained Creep Characteristics of Silty Sands and Comparative Study of Creep model

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In this study, A series of triaxial tests were performed under constant principal stress in order to interpret the undrained creep characteristics of silty sands. Although samples are non-plastic silty sands, the results of tests show that the creep deformation increasing over time. Based on the results of test, Singh-Mitchell model parameters and Generalized model coefficients were calculated. Generalized model showed slightly larger deformation in the primary creep range but secondary creep deformation was almost identical. Although Singh-Mitchell model showed relatively large errors compared to Generalized model because it uses the average of test results, but Singh-Mitchell model can be easily represented by three creep parameters.

The Coefficients of Variation Characteristic of Stress Distribution in Silty Sand by Probabilistic Load

Recently, Load and Resistance Factor Design (LRFD) based on reliability analysis has become a global trend for economical and rational design. In order to implement the LRFD, quantification of uncertainty for load and resistance should be done. The reliability of result relies on input variable, and therefore, it is important to obtain exact uncertainty properties of load and resistance. Since soil stress is the main reason causing the settlement or deformation of ground and load on the underground structure, it is essential to clarify the uncertainty of soil stress distribution for accurately predict the uncertainty of load in LRFD. In this study, laboratory model test on silty sand bed under probabilistic load is performed to observe propagation of upper load uncertainty. The results show that the coefficient of variation (COV) of soil stress are varied depending on location due to non-linear relationship between upper load increment and soil pressure increment. In addition, when the load uncertainty is transmitted through ground, COV is decreased by damping effect.

An Experimental Study for Soil Pressure Increment Ratios according to Strip Load in Sandy Soil

Soil stress distribution under loading is one of the important problems in civil engineering. Many models have been proposed to interpret the stress distribution in soil and most models assume that the soil is homogeneous and isotropic. Therefore, the actual stress distribution may be different. In addition, With the increase of the top load, soil stress does not increase linearly. In this study, vertical stress changes in sandy soil according to top load increase were measured through experiments. Experimental results, vertical soil stress due to top load increase showed an initial nonlinear behavior and when the load increases to some extent, vertical soil stress showed a linear behavior. value obtained by existing theories always 1.00. But, value by experiment was observed from 0.91 to 1.22 and value was increased with increasing distance from the loading plate.

Electrical Characteristics against Frequency and Concentration of Contaminated Soils by Mercury and Arsenic

In general, ground pollution can be classified with soil pollution and underground water pollution. And ground pollution contaminates the land with garbage dumps and other harmful waste products as heavy metals that can also eventually enter our water supply. This study was conducted to define a characteristics of the electrical resistivity and the permittivity of weathered soil that was contaminated with heavy metals as Mercury and Arsenic. It is not easy whether contamination of soil as subsurface contamination is decided or not and at an early stage especially do that. Therefore the electrical resistivity and the permittivity were used to make up for this defects. These methods are more economical and more effective than the existing methods. And variation of the electrical resistivity and the permittivity values were found against the change of concentration of Mercury and Arsenic aqueous solutions and measuring frequency. These analyzed results indicate that the electrical resistivity and the permittivity tend to decrease against increasing measuring frequency. The electrical resistivity and the permittivity are also found to show the function of frequency.

Model of resalinization by capillary rise in reclaimed land

Large areas of reclaimed land have recently been required to be developed as environmentally friendly centers of vegetation, such as dryland fields for cultivation of high-income crops and green fields. However, reclaimed lands in coastal areas such as reclaimed tidal flats have a setback in this regard: The capillary rise of groundwater from deeper levels causes resalinization, resulting in concentration of salt at the surface. The existing studies conducted on resalinization of soils in reclaimed lands are either insufficient or employ complex experimental and analytical methods. In this study, resalinization testing equipment was developed, and a laboratory model test on reclaimed-land soil was carried out. We identified the relationship between the capillary rise rate and initial volumetric water content and proposed a simple experimental model. The proposed model was verified by a comparison with experiment results and measured data of the field and could more accurately predict the resalinization according to the volumetric water content. In addition, proposed model can be applied in the field as the predicted results showed a similar trend to that of the measurements of the field.