• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.147-156
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• 2008

In an uniaxial compressive test of a concrete standard specimen (150$\times$300 mm) the crack initiation and extension with the stress increase are the major reason of the failure, which is similar to the breakage of the particle bonding in the simulation by using particle bonded model, especially particle flow code in 3 dimensions (PFC3D) developed by Itasca Consulting Group Inc. That is the main motive to study the possibility of an uniaxial compressive strength test simulation. It is important to investigate the relationship between the micro-parameters and the macro-properties because the 3-dimensional particle bonded model uses the spherical particles to analyze the physical phenomena. Contact bonded model used herein has eight micro-parameters and there are five macro-properties; Young's modulus, Poisson's ratio, uniaxial compressive strength and the crack initiation stress and the ratio concerning the crack propagation with the stress. To simulate the compressive test we made quantitative relationships between the micro-parameters and the macro-properties by using the fractional factorial design and various sensitivity analyses including regression analysis, which result in the good agreement with the previous studies. Also, the stress-stain curve and the crack distribution over the specimen given by PFC3D showed the mechanical behavior of the concrete standard specimen under the uniaxial compression. It is concluded that the particle bonded model can be a good tool for the analyzing the mechanical behavior of concrete under the uniaxial compressive load.

• Computers and Concrete
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• v.20 no.4
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

• International Journal of Aerospace System Engineering
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• v.7 no.1
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• pp.16-20
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• 2020

The recent trend is increasing towards the usage of polymer matrix composites since they have a wide variety of applications. They have applications in the field of aircraft and space industry, sporting goods, medical devices, marine and automotive applications and also in commercial usage. The most commonly used fibre-reinforced polymer matrix composite is Glass fibre reinforced epoxy (GFRE) composite which is used in aviation, sports and automotive industries. However, the strength of GFRE composites is not adequate for structural applications. Therefore, the current research focuses on increasing the strength of GFRE composites by reinforcing with micro Graphite (Gr) particulates. The Gr used is an ultra-fine powder with particle size 250 ㎛. Gr is known to have good wear resistance, thermal conductivity and can operate at high temperatures. Gr particulates are mixed with the epoxy matrix in various weight ratios. Hand-lay technique is used for fabricating the composites. Mechanical properties such as tensile strength, elongation, compressive strength and flexural strength are obtained experimentally to study the effect of change in Gr content (0-5 wt. %). The tests were done as per ASTM standards.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.113-114
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• 2015

This paper is to investigate the effect of poor quality aggregate source used in Korea on the mixture proportion and strength development of the high strength concrete fixed at 450 kg/m3 of cement contents. For aggregate kinds, good quality crushed stone from KS certified manufacturer and low quality crushed stone from non certified construction field are used. For fine aggregates, river sand, land sand, sea sand and mixed sand are also used. It is found that the use of low quality aggregates resulted in an increase of water demand considerably due to poor gradation of aggregate and excessive fine particles. Test results indicate that the use of low quality aggregate also decreases the compressive strength compared with that of good quality aggregate.

• Advances in materials Research
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• v.4 no.3
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• pp.179-192
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• 2015

The study presents a preliminary investigation on the applicability of Shirasu (a pyroclastic flow deposit characterized by high percentage of volcanic glass) in geopolymer. Comparative study on compressive strength and internal pore structure has been done between geopolymers with alkali activated Shirasu and fly ash as aluminosilicates. Mortar mix proportions are selected based on variations in ratio of alkaline activators to aluminosilicate and also on silica to alkali hydroxide ratio. From the experimental study, Shirasu geopolymer exhibited fairly good compressive strength. Mix proportion based on silica to alkali hydroxide ratio is observed to have profound effect on strength development.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.42-43
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• 2013

Nowadays, Precast Concrete is adopted on most of construction, because of shortening construction period and good quality. In precast concrete, steam curing is necessary for getting proper strength, but it causes much CO₂ and economc. Therefore, on this study, by using type III cement and hardening accelerator, early compressive strength was shown 13MPa for 6hr. From the result, removal form could be shorten. Furthermore, annual CO₂ was reduced as much as 24% and also annual cost was decreased as much as 12%.

• Computers and Concrete
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• v.32 no.4
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• pp.425-438
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• 2023

In this article, the performance of steel fiber-reinforced concrete (SFRC) flat slabs was investigated numerically. The influence of flexural steel reinforcement, steel fiber content, concrete compressive strength, and slab thickness were discussed. The numerical model was developed using ATENA-Gid, user-friendly software for non-linear structural analysis for the evaluation and design of reinforced concrete elements. The numerical model was calibrated based on eight experimental tests selected from the literature to validate the actual behavior of steel fiber in the numerical analysis. Then, a parametric study of 144 specimens was generated and discussed the impact of various parameters on the punching shear strength, and statistical analysis was carried out. The results showed that slab thickness, steel fiber content, and concrete compressive strength positively affect the punching shear capacity. The fib Model Code 2010 for specimens without steel fibers and the model of Muttoni and Ruiz for SFRC specimens presented a good agreement with the results of this study.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.263-266
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• 1999

This study aims to make high performance concrete for normal strength using crushed stone fines to control high strength of the high performance concrete. According to the experimental results, when crushed stone fines are increased every 10%, 15% of compressive strength is decreased, and 5% of drying shrinkage is increased, compared to normal high performance concrete. Also, high performance concrete has been evaluated to have good durability factor more than 100% in the 480cycle of freezing and thawing test, without regard to using AE and crushed stone fines.

• Journal of the Korea Institute of Building Construction
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• v.14 no.6
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• pp.523-529
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• 2014

Large amounts of waste shells have been produced each year from shellfish raising industries located in Korean costal areas. Due to the limited space for the waste shell disposal, the related environmental problem has been a serious issue. It is believed that using the waste shells as a source of aggregate for mortar, concrete or bricks can be a good solution. In this research, possibility of utilizing waste shells as an aggregate of mortar is investigated. Waste shells of manila clam, cockle, clam, sea mussel, and oyster were properly crushed, sieved, and sorted to meet the requirements of the grading of standard fine aggregate. After that, the waste shells were used as partial and total replacement of the fine aggregate, and their absorption and 28-day compressive strengths of mortar were measured. In general, replacement of waste shells increased the absorption and decreased the strength. However, one specimen with cockle increased compressive strength as replacement ratio increased. Mortar with cockle of 50% and 100% replacement showed higher compressive strength than that of control mortar. This increase of compressive strength was found to be affected by the strong interfacial bonding properties of the cockle and a cement matrix.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.566-571
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• 2003

Hydroxyapatite (HAp)/Polyacrylic Acid(PAA) homogeneous composites of four different composition ratio were preparation by co-precipitation process with synthetic HAp and PAA as a binder. HAP/PAA composites were molding by cold isostatic pressing and were sintering by various condition in air. Crystallinity and structure of sintered HAp/PAA composites were investigated by XRD and FT-IR. Also, the compressive strength and the fracture surface of sintered specimens were measured by UTM and SEM. HAp/PAA composites were showed phase transformation of partially ${\alpha}$, ${\beta}$-tricalcium phosphate at sintering condition of 1200$^{\circ}C$ and 3 h. The pore size and porosity of sintered body were showed the range of 0.2∼3.0 $\mu\textrm{m}$ and 0.49∼13.43%, respectively. The compressive strength of sintered specimens were appeared the range of 36.6∼58.2 MPa. From these results, the sintered HAp/PAA comosites can be accounted for the microporous HAp having a good compressive strength due to homogeneous pore morphology.