• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.76-79
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• 1999

The purpose of this study is to investigate the spalling properties of high-performance concrete with the kinds of aggregates and polypropylene(below PP) fiber contents. According to the experimental results, concrete contained no PP fiber take place in the form of the surface spalling and the failure of specimens after fire test regardless of the kinds of aggregates. Concrete contained more than 0.05% of PP fiber with the kinds of aggregates does not take place the spalling. Concrete using basalt has better performance in spalling resistance that concrete using granite and limestone. It is found that residual compressive strength has 50~60% of their original strength. Although specimens after exposed at high temperature are cured at water for 28days, they do not recover their original strength.

• Journal of the Society of Disaster Information
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• v.15 no.2
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• pp.249-258
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• 2019

Purpose: The purpose of this study is to attain the correlation analysis and thereby to deduce the uniaxial compressive strength of rock specimens through the elastic wave velocity and the elastic modulus among the physical characteristics measured from the rock specimens collected during drilling investigations in Seoul and Gyeonggi region. Method: Experiments were conducted in the laboratory with 119 granite specimens in order to derive the correlation between the compressive strength of the rocks and elastic wave velocity and elastic modulus. Results: In the case of granite, the results of the analysis of the interaction between the compressive strength of a rock and the elastic wave velocity and elastic modulus were found to be less reliable in the relation equation as a whole. And it is believed that the estimation of the compressive strength by the elastic wave velocity and elastic modulus is less used because of the composition of non-homogeneous particles of granite. Conclusion: In this study, the analysis of correlation between the compressive strength of a rock and the elastic wave velocity and elastic modulus was performed with simple regression analysis and multiple regression analysis. The coefficient determination ($R^2$) of simple regression analysis was shown between 0.61 and 0.67. Multiple regression analysis was 0.71. Thus, using multiple regression analysis when estimating compressive strength can increase the reliability of the correlation. Also, in the future, a variety of statistical analysis techniques such as recovery analysis, and artificial neural network analysis, and big data analysis can lead to more reliable results when estimating the compressive sterength of a rock based on the elastic wave velocity and elastic modulus.

• Journal of Industrial Technology
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• v.31 no.A
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• pp.53-57
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• 2011

Recently due to dramatically increasing demand of liquid crystal display (LCD) panel in IT industry, the used LCD panel glass has been wasted from electronic items, and also panel glass of poor quality during manufacturing process. The wasted LCD panel glass was crushed in the range of 0.42 to 2mm and evaluated for its usefulness as a aggregate in production of cement concrete brick. Cement concrete specimens with various mixing ratios of weathered granite soil, LCD panel glass and cement were cured in wetness for 7 days at $40^{\circ}C$ and then tested for uniaxial comprehensive strength (UCS)(KS F 4004 method). Specimen with a mixing ratio, 1:6:3, of weathered granite, LCD panel glass and cement, respectively, showed the highest average in the UCS test($26.51N/mm^2$). It is much higher than that of commercial brick without glass($17.00N/mm^2$). Conclusively waste LCD panel glass can be reutilized economically as a raw building material of good quality.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.1
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• pp.75-85
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• 2021

Evaluating the quantitative damage to rocks through acoustic emission (AE) has become a research focus. Most studies mainly used one or two AE parameters to evaluate the degree of damage, but several AE parameters have been rarely used. In this study, several data-driven models were employed to reflect the combined features of AE parameters. Through uniaxial compression tests, we obtained mechanical and AE-signal data for five granite specimens. The maximum amplitude, hits, counts, rise time, absolute energy, and initiation frequency expressed as the cumulative value were selected as input parameters. The result showed that gradient boosting (GB) was the best model among the support vector regression methods. When GB was applied to the testing data, the root-mean-square error and R between the predicted and actual values were 0.96 and 0.077, respectively. A parameter analysis was performed to capture the parameter significance. The result showed that cumulative absolute energy was the main parameter for damage prediction. Thus, AE has practical applicability in predicting rock damage without conducting mechanical tests. Based on the results, this study will be useful for monitoring the near-field rock mass of nuclear waste repository.

• Geomechanics and Engineering
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• v.24 no.2
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• pp.157-166
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• 2021

This paper aims at the temperature and slenderness ratio effects on physical and mechanical properties of Beishan granite. A series of uniaxial compression tests with various slenderness ratios and temperatures were carried out, and the acoustic emission signal was also collected. As the temperature increases, the fracture aperture of intercrystalline cracks gradually increases, and obvious transcrystalline cracks occurs when T > 600℃. The failure patterns change from tensile failure mode to ductile failure mode with the increasing temperature. The elastic modulus decreases with the temperature and increases with slenderness ratio, then tends to be a constant value when T = 1000℃. However, the peak strain has the opposite evolution as the elastic modulus under the effects of temperature and slenderness ratio. The uniaxial compression strength (UCS) changes a little for the low-temperature specimens of T < 400℃, but a significant decrease happens when T = 400℃ and 800℃ due to phase transitions of mineral. The evolution denotes that the critical brittle-ductile transition temperature increases with slenderness ratio, and the critical slenderness ratio corresponding to the characteristic mechanical behavior tends to be smaller with the increasing temperature. Additionally, the AE quantity also increases with temperature in an exponential function.

• Journal of the Korean Geosynthetics Society
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• v.10 no.1
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• pp.19-28
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• 2011

This paper presents the results of an investigation into the effect of cyclic freezing-thawing on the compressive strength characteristics of decomposed granite soils. A plane strain compression (PSC) tests were performed on a series of test specimens with different freezing-thawing cycles and fine contents to investigate the change in compressive strength under the process of freezing-thawing cycles. Also performed were scanning electron microscope (SEM) tests to investigate the change in structural rearrangement from a micro-scale point of view. The test results showed that the soil particles tend to conglomerate when subject to cycles of freezing and thawing, and that the soil with less fines exhibited decreased shear strength due to the cyclic freezing-thawing while the soils with a larger fine content showed the opposite trend.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.6
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• pp.103-110
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• 2019

The purpose of this study is to investigate the reaction mechanism of soil and bacteria solution by various mixing ratios. For this purpose, in order to understand the reaction mechanisms of microorganisms and weathered granite soil, the tests were carried out under various mixing ratios additives such as soil, bacteria solution, $Ca(OH)_2$ and fixture. The test results from this study are summarized as follows. Firstly, the reaction between the bacteria solution and fixture produced a precipitate called vaterite, a type of silicate and calcium carbonate. Secondly, as a result of SEM analysis, the resulting precipitates generated from the test results using the specimens with various mixing ratios except SW condition and the irregular spherical microscopic shapes were formed in the size of $150{\mu}m$ to $20{\mu}m$. In addition, it can be seen that the bacteria solution and the fixture reacted between the granules to form an adsorbent material layer on the surface, and the microorganisms had a biological solidifying effect when the pores are combined into hard particles. Finally, The XRD analysis of the sediment resulting from the reaction between the microorganism and the deposit control agent confirmed the presence of a type of calcium carbonate ($CaCO_3$) vaterite, which affects soil strength formation, as well as silicate($SiO_2$).

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.25-35
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• 2014

The sedimentary rocks exposed around Mt. Palgong were subjected to metamorphism due to a granitic magma intrusion at late Cretaceous, and they eventually metamorphosed to hornfels by the action of both hydrothermal solution and high temperature supplied from the magma. The hornfels zone around the granite body ranges from 2.0 to 3.5 km in width but the boundary between hornfels and sedimentary rocks is not obviously defined because the metamorphic grade gradually decreases with distance from the granite boundary. A series of laboratory tests on 350 core specimens made by 35 fresh rock blocks obtained from 5 selected locations around Mt. Palgong are performed to verify the variation of physical and mechanical properties related to metamorphic grade of the rock. Water content and absorption ratio of the hornfels linearly increase with distance to the granite boundary whereas dry unit weight, p-wave velocity, point load strength, and slake durability index linearly decrease with the distance. These results imply that the metamorphic grade of the hornfels also linearly decrease with the distance to granite boundary. Empirical equations for the variation of properties with the distance to granite boundary and relationship between a property and another one are deduced by regression analyses. And a criteria for classification of hornfels exposed in the study area based on the P-wave velocity and point load strength is proposed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.419-434
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• 2020

In this study, the damage parameters of Mazars model for KURT (KAERI Underground Research Tunnel) granite are measured form uniaxial compressive and Brazilian tests under the simulated coupled condition of a deep geological disposal. The tests are conducted in three different temperatures (15℃, 45℃, and 75℃) and dry/saturated conditions. Major model parameters such as maximum effective tensile strain (𝜖_d0), A_t, B_t, A_c, and B_c differ from the typical reference values of concrete specimens. This is likely due to the difference in elastic modulus between rock and concrete. It is found that the saturation of specimens causes an increase in value of B_t and B_c while, the rise in temperature increases 𝜖_d0 and B_t and decreases B_c. The damage model obtained from this study will be used as the primary input parameters in the development of coupled Thermo-Hydro-Mechanical Damage numerical model in KAERI.

• The Journal of Engineering Geology
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• v.12 no.4
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• pp.405-419
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• 2002

Fracture roughness of rock specimens is observed by a new confocal laser scanning microscope (CLSM; Olympus OLS1100). The wave length of laser is 488 nm, and the laser scanning is managed by a light polarization method using two galvano-meter scanner mirrors. The function of laser reflection auto-focusing enables us to measure line data fast and precisely. The system improves resolution in the light axis (namely z) direction because of the confocal optics. Using the CLSM, it is Possible to measure a specimen of the size up to $10{\;}{\times}{\;}10{\;}cm$ which is fixed on a specially designed stage. A sampling is managed in a spacing $2.5{\;}\mu\textrm{m}$ along x and y directions. The highest measurement resolution of z direction is $10{\;}\mu\textrm{m}$, which is more accurate than other methods. Core specimens of coarse and fine grained granite are provided. Fractures are artificially maneuvered by a Brazilian test method. Measurements are performed along three scan lines on each fracture surface. The measured data are represented as 2-D and 3-D digital images showing detailed features of roughness. Line profiles of the coarse granites represent more frequent change of undulation than those of the fine granite. Spectral analyses by the fast Fourier transform (FFT) are performed to characterize the roughness data quantitatively and to identify influential frequency of roughness. The FFT results suggest that a specimen loaded by large and low frequency energy tends to have high values of undulation change and large wave length of fracture roughness.