• Journal of the Korean Ceramic Society
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• v.51 no.1
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• pp.19-24
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• 2014

Three-layer porous alumina-mullite composites with a symmetric gradient porosity are prepared using a controlled freeze/gel-casting method. In this work, tertiary-butyl alcohol (TBA) and coal fly ash with an appropriate addition of $Al_2O_3$ were used as the freezing vehicle and the starting material, respectively. When sintered at $1300-1500^{\circ}C$, unidirectional macro-pore channels aligned regularly along the growth direction of solid TBA were developed. Simultaneously, the pore channels were surrounded by less porous structured walls. A high degree of solid loading resulted in low porosity and a small pore size, leading to higher compressive strength. The sintered porous layered composite exhibited improved compressive strength with a slight decrease in its porosity. After sintering at $1500^{\circ}C$, the layered composite consisting of outer layers with a 50 wt% solid loading showed the highest compressive strength ($90.8{\pm}3.7MPa$) with porosity of approximately 26.4%.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.439-442
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• 2005

This study is to consider the influence strength of concrete according to the kinds of coarse aggregate. The experimental study conditions are varied with different maximum size of coarse aggregate(13mm, 19mm, 25mm) and the weight of water and S/a are constant. The compressive strength properties of the concrete at 7 days, 28 days are examined. According to the experimental results, the compressive strength increased and air content, slump decreased with maximum size of coarse aggregate increased.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.485-488
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• 2003

The results of an experiment on the sound absorption of the porous concrete using recycled aggregates and its influence on the compressive strength are reported in this paper. The content of recycled aggregate of 0, 10, 30, 50 and 70%, and the design void ratio of 30 percent for a given size of aggregate were used. In the compressive strength, an aggregate of the size of 5~13mm is much higher strength than that of the 13~20mm, In sound absorption experiment, the sound absorption ratio was is subjected to decreased as the content of recycled aggregates was increased. As a result, Porous concrete using recycled aggregates and by-products sufficiently have the performance of sound absorption.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.13-16
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• 2005

Nanoscale materials are of great interest due to their unique optical, electrical and magnetic properties. Due to the recent amazing achievements in nano technology, new materials were developed. But these nano technology is not apply to the construction part in spite of exellent properties of nano size material. The purpose of this study is to apply to nano technology into building materials. To develop the high performance concrete, nano cement particles is prepared by mechanical method. In the results of this study, the nano silica powder increase effect according to increase of the mixing amount, appeared that compressive strength increased but is limit in increment. For the production of high-strength concrete, nano silica powder was suitable the binder ratio from 20$\%$. And, the compressive strength of concrete are especially dependent on the curing temperature.

• Geomechanics and Engineering
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• v.8 no.1
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• pp.53-66
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• 2015

Plastic wastes, particularly polyethylene terephthalate (PET) generated from used bottled water constitute a worldwide environmental issue. Reusing the PET waste for geotechnical applications not only reduces environmental burdens of handling the waste, but also improves inherent engineering properties of soil. This paper investigated factors affecting shear strength improvement of PET-mixed residual soil. Four variables were considered: (i) plastic content; (ii) plastic slenderness ratio; (iii) plastic size; and (iv) soil particle size. A series of unconfined compression tests were performed to determine the optimum configurations for promoting the shear strength improvement. The results showed that the optimum slenderness ratio and PET content for shear strength improvement were 1:3 and 1.5%, respectively. Large PET pieces (i.e., $1.0cm^2$) were favorable for fine-grained residual soil, while small PET pieces (i.e., $0.5cm^2$) were favorable for coarse-grained residual soil. Higher shear strength improvement was obtained for PET-mixed coarse-grained residual soil (148%) than fine-grained residual soils (117%). The orientation of plastic pieces in soil and frictional resistance developed between soil particles and PET surface are two important factors affecting the shear strength performance of PET-mixed soil.

• Journal of Industrial Technology
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• v.17
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• pp.137-143
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• 1997

The objective of this study is to find the strength properties of concrete using blast furnace slag. Its mechanical strength properties investigated include compressive strength, flexural strength, and tensile strength. The main expeirmental variables were cement type, coarse aggregate size(19, 25mm), and water/cement ratio(28, 32, 36%). The principal results obtained from this study are as follows ; it was possible to obtain the compressive strength of $500{\sim}700kg/cm^2$ concrete by using the blast furnace slag. Therefore, blast furnace slag was proved to be superior to ordinary portland cement in manufacturing the high strength concrete with the same mix conditions. In the near furture, concrete using blast furnace slag is expected to be practically used in the field.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1201-1216
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• 2015

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-${\delta}$ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

• Geomechanics and Engineering
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• v.33 no.2
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• pp.211-219
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• 2023

This study analyzes the changes in the physical properties of grout by irradiating it with ultrasonic energy and assesses the injectability of the grout into deep rock fractures. The materials used in the research are OPC (Ordinary Portland Cement) and MC (Micro Cement), and are irradiated depending on the water/cement ratio. After irradiating the grout with ultrasonic energy, viscosity, compressive strength, and particle size are analyzed, and the results of the particle size analysis were applied to Nick Barton's theory to evaluate the injectability of the grout into deep rock fractures under those conditions. It was found that the viscosity of the grout decreased after ultrasonic wave irradiation, and the rate of viscosity reduction tended to decrease as the water/cement ratio increased. Additionally, an increase in compressive strength and a decrease in particle size were observed, indicating that the grout irradiated with ultrasonic energy was more effective for injection into rock fractures.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.934-941
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• 2002

It is important to consider the effect of member size when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of a reinforced concrete (RC) beam was experimentally investigated. For this purpose, a series of beam specimens subjected to four-point loading were tested. More specifically, three different effective depth (d$\approx$15, 30, and 60 cm) reinforced concrete beams were tested to investigate the size effect. The shear-span to depth ratio (a/d=3) and thickness (20 cm) of the specimens were kept constant where the size effect in out-of-plane direction is not considered. The test results are curve fitted using least square method (LSM) to obtain parameters for the modified size effect law (MSEL). The analysis results show that the flexural compressive strength and the ultimate strain decrease as the specimen size increases. In the future study, since $\beta_1$ value suggested by design code and ultimate strain change with specimen size variation, a more detailed analysis should be performed. Finally, parameters for MSEL are also suggested.

• Advances in concrete construction
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• v.14 no.2
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• pp.93-102
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• 2022

In this study, limestone powder (LS) and fly ash (FA) were used as powder materials in self-compacting concrete (SCC) in increasing quantities in addition to cement, so that the two powders commonly used in the production of SCC could be compared in the same study. Considering the reduction of the maximum aggregate size in SCC, 10 mm or 16 mm was selected as the coarse aggregate size. The properties of fresh concrete were determined by slump flow (including T₅₀₀ time), V-funnel and J-ring experiments. The experimental results showed that as the amount of both LS and FA increased, the slump flow also increased. The increase in powder material had a negative effect on V-funnel flow times, causing it to increase; however, the increase in FA concretes was smaller compared to LS ones. The increase in the powder content reduced the amount of blockage in the J-ring test for both aggregate sizes. As the hardened concrete properties, the compressive and splitting strengths as well as the modulus of elasticity were determined. Longitudinal and transverse deformations were measured by attaching a special frame to the cylindrical specimens and the values of Poisson's ratio, initiation and critical stresses were obtained. Despite having a similar W/C ratio, all SCC exhibited higher compressive strength than NVC. Compressive strength increased with increasing powder content for both LS and FA; however, the increase of the FA was higher than the LS due to the pozzolanic effect. SCC with a coarse aggregate size of 16 mm showed higher strength than 10 mm for both powders. Similarly, the modulus of elasticity increased with the amount of powder material. Inelastic properties, which are rarely found in the literature for SCC, were determined by measuring the initial and critical stresses. Crack formation in SCC begins under lower stresses (corresponding to lower initial stresses) than in normal concretes, while critical stresses indicate a more brittle behavior by taking higher values.