• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.511-520
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• 2011

Recent studies to improve reinforcement of structures have developed stiff type Polyurea by using highly polymized compound Polyurea, but the reinforcing effect of it appears to be merely good. To find the proper usage of Polyurea as structural reinforcement, stiff type Polyurea has developed by manipulating the ratio of the components that consist flexural type Polyurea and the developed stiff type Polyurea shows higher hardness and tensile capacity. The reinforcement effect evaluation of has been performed by the polyurea applied RC slab specimens, and the reinforcement effect of the combination of fiber sheet and polyurea has been tested. The results shows that the Polyurea applied specimens have significant improvement on hardness and ductility compare to those of unreinforced. Also, the specimens that stiff type Polyurea is sprayed on fiber sheet reinforcement has higher reinforcing effect than only sheet reinforced specimens. However, the specimens that and fiber sheet attached after polyurea applied on showed that the high toughness of fiber sheet restrains the ductile behavior of Polyurea due to the high ductility, thereby the specimen suffers the concentration of load, which leads the brittle fracture behavior.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.145-152
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• 1999

In the applying of the reinforced soil method, it would be possible to obtain reinforcement effect more than before in terms of economic if high water content clayey soils could be used as embanking material. Futhermore it would be possible to expect the expansion of the applying field of reinforced soil method too. In this study, the authors describe the analysis results on the behavior of 5 meter high walls reinforced with nonwoven geotextile having the permeability and woven geotextile or geogrid having large tensile strength on the soil ground. The behavior of the walls were investigated for about 100 days after construction and the deformations of reinforcements, lateral soil pressures, vertical and horizontal displacements of the walls were examined by automatical measuring system. It was found that this kinds of reinforcing system might effectively improve the performance of the steep walls by virtue of the reciprocal action between soil and reinforcements, and it might be concluded that construction of the clayey reinforced soil walls with three kinds of geotextiles could be done successfully even on the comparative weak ground.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.513-518
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• 1998

In general, flexural strength and ductility of reinforced concrete beam with stirrup depend on the compressive strength of concrete and longitudinal steel ratio. In this study, nine reinforced high strength lightweight concrete beams and three reinforced normalweight concrete beams with stirrup were tested to investigate their behavior and to determine their ultimate moment capacity. The variable were strength of concrete (400, 500kg/$\textrm{cm}^2$) and the ratio of tensile steel content to the ratio of the balanced steel content(0.22<$\rho$/$$\rho$_b$<0.56). Test results are presented in terms of load-deflection behavior, ductility index, and cracking patterns.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.401-404
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• 2006

Much of requirements to the civil and building structures have been changed in accordance with the social and economic progress. Ductility of high performance fiber reinforced cementitious composites(HPFRCCs), which exhibit strain hardening and multiple crackling characteristics under the uniaxial tensile stress is drastically improved. In HPFRCC application, PVA fiber has been dominantly used as a reinforcement because of its excellent alkali resistant nature as well as high strength. But the inherent strong hydrophilicity of PVA fiber promotes the moisture absorption in cement matrix and thus it may cause the corrosion of steel structure. Therefore, it is necessary to control the interfacial adhesion of cement composites. In present study, to control the interfacial adhesion of the cementitious composites reinforced by PVA fiber, UV irradiation of the PVA fiber were performed and their effects on the adhesion property and general characteristics were investigated extensively.

• Carbon letters
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• v.6 no.1
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• pp.6-14
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• 2005

The study of mechanical properties and fracture behaviour of carbon/carbon composites is significant to its application and development. These are dependent on microstructure and properties of reinforcing fibers and matrix, fiber/matrix interface and porosity/cracks present in the composites. In the present studies high-density carbon/carbon composites have been prepared using PAN and various pitch based carbon fibers as reinforcements and pitch as matrix with repeated densification cycles using high-pressure impregnation and carbonization technique. Scanning electron microscopy has been used to study the fracture behaviour of the highly dense composites and correlated with structure of the composites. The geometry of reinforcement and presence of unfilled voids/cracks was found to influence the path of crack propagation and thereby the strength of composites. The type of stresses (tensile or compressive) accumulated also plays an important role in fracture of composites.

• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.453-459
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• 2004

TiNi/ Al6061 shape memory alloy (SMA) composite was fabricated by hot press method to investigate the microstructure and mechanical properties. Interface bonding between TiNi reinforcement and A1 matrix was observed by using SEM and EDS. Pre-strain was imposed to generate compressive residual stress inside composite. A tensile test for specimen, which under-went pre-strain, was performed at high temperature to evaluate the variation of strength and the effect of pre-strain. It was shown that interfacial reactions occurred at the bonding between matrix and fiber, creating two inter-metallic layers. And yield stress increased with the amount of pre-strain. Acoustic Emission technique was also used to nondestructively clarify the microscopic damage behavior at high temperature and the effect of pre-strain of TiNi/ Al6061 SMA composite.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.1
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• pp.63-72
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• 1988

The primary objective of the study was to find the deformation characteristics of reinforced polymer concrete beams. A test program was carried out to compare the behavior in deformation of polyester and MMA concrete beams with cement concrete beams but with varying ratios of tensile reinforcement. From the results the following conclusions can be made. 1.The various strengths of polymer concrete ware very high compared to the strengths for cement concrete. Also, compared to conventional concrete beams, flexural strength of reinforced polymer concrete beams was distinctly higher for the same section and steel ratios. 2.The polymer concrete beams exhibit large deflections accompanied by relatively high strengths as compared to cement concrete beams. 3.The average ultimate strain at the extreme compression fiber of polymer concrete beams was 0.01 1 cm / cm, and this value was about three to four times as large as that of cement concrete beams, 4.The polymer concrete beams developed more cracks which were more wide crack distribution spacing than the cement concrete beams, and the beams failed in a more ductile manner. 5.The reinforcing steel ratio has a significant effect on the beam strength, load-deflection response, stress-strain curve, and crack pattern of polymer concrete beams.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.107-112
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• 1991

The object of this study is to investigate material characteristics and flexural behavior of high strength concrete. Principal causes of variations of high compressive strength include the strength-producing capabilities of cement and silica hume. Compressive strength of 1200 kgf/$\textrm{cm}^2$ is introduced for identifying the effect of the variation of the size of porocity and alternative method of measurement, Acoustic Emition method, is applied to examine the phenominon of concrete failure. The main test variables in the beam element are tensile steel ratios, presence of shear reinforcement, and change of steel shape. The estimation of stress block in the flexural test of this element tends to support the present theory and may suggest a desirable shape of the stress block.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.107-114
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• 2013

In this study we experimentally evaluated an impact resistant performance of fiber reinforced concrete in the moment of explosion by high-velocity projectile with emulsion explosive. To assess the impact resistance, we conducted the impact test of high-velocity projectile which reaches an impact speed of 350 m/s and the experiment of contact exploding emulsion explosive. As a result, bending and tensile performance depending on type of PVA, PE fiber (polyvinyl alcohol fiber, polyethylene fiber) and steel fiber affects destruction of rear side in the form of spalling. Destroying the backside of the concrete compressive strength compared to suppress the bending and tensile performance is affected. In addition, the experiment shows that the destruction patterns of concrete specimen producted by high velocity impact and contact explosion are significantly similar. Therefore, it is possible to predict the destruction patterns of specimens in the situation of contact explosion by high-velocity projectile.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.29-34
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• 2006

Elastic modulus, tensile and bond capacities are important factors for developing an effective reinforcing action of a flexural member as a reinforcing material for concrete structures. Reinforcement must have enough bond capacity to prevent the relative slip between concrete and reinforcement. This paper presents an experimental study to clarify the bond capacity of prestressed carbon fiber reinforced polymer(CFRP) rod manufactured by an automatic assembly robot. The bond characteristics of CFRP rods with different pitch of helical wrapping were analyzed experimentally. As the result, all types of CFRP rods show a high initial stiffness and good ductility. The mechanical properties of helical wrapping of the CFRP rods have an important effect on the bond of these rods to concrete after the bond stress reached the yield point. The stress-slip relationship analyzed from the pull-out test of embedded cables within concrete was linear up to maximum bond capacity. The deformation within the range of maximum force seems very low and was reached after approximately 1 mm. The average bond capacity of CF20, CF30 and CF40 was about 12.06 MPa, 12.68 MPa and 12.30 MPa, respectively. It was found that helical wrapping was sufficient to yield bond strengths comparable to that of steel bars.