• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.2
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• pp.37-46
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• 2007

The service life of agricultural concrete structures is designed in about 30 to 100 years, but actual service lift is estimated in an average 18 years. Therefore, as the service life of the agricultural concrete structures increases, necessity of repair by aging from various environment condition exposure increases. This study was to determinate the optimum mix proportion of latex modified repair mortar and to improve the durability performance of agricultural concrete structures. The physical and mechanical tests of latex modified repair mortar were performed. Tests of flow, compressive strength, flexural strength and bond strength tests were conducted. Test results show that the optimum nex proportion of latex modified repair mortar, when used in 5% latex volume fraction (weight of cement), 1.5% antifoaming agent (weight of latex), 0.2% PVA fiber volume fraction, 1:2 (binder-sand ratio), 10% silica fume replacement ratio (weight of cement), could result in best performance for the repair of agricultural concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.57-60
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• 2004

Recently, Many researchers are interested in ultra-high performance cementitious compostie characterized by high strength and high durability and trying to apply for structural members. In this paper, twelves fiber-reinforced UHPCC with high compressive strength over 150MPa I shaped beam without stirrups were tested under various conditicns to investigate the mechanical behavior of UHPCC I shaped beam without stirrups. Variables considered in this study includes steel fiber volume fraction, reinforcememt steel ratio, and shear spar ratio.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.89-99
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• 1997

Although discontinuously reinforced metal matrix composite(MMC) is one of the most promising materials for applications of aerospace, automotive industries, the thermal residual stresses developed in the MMC due to the mismatch in coefficients of thermal expansion between the matrix and the fiber under a temperature change has been pointed out as one of the serious problem in practical applications. There are very limited nondestructive techniques to measure the residual stress of composite materials. However, many difficulties have been reported in their applications. Therefore it is important to establish analytical model to evaluate the thermal residual stress of MMC for practical engineering application. In this study, an elastic model is developed to predict the average thermal residual stresses in the matrix and fiber of a misoriented short fiber composite. The thermal residual stresses are induced by the mismatch in the coefficient of the thermal expansion of the matrix and fiber when the composite is subjected to a uniform temperature change. The model considers two-dimensional in-plane fiber misorientation. The analytical formulation of the model is based on Eshelby's equivalent inclusion method and is unique in that it is able to account for interactions among fibers. This model is more general than past models to investigate the effect of parameters which might influence thermal residual stress in composites. The present model is to investigate the effects of fiber volume fraction, distribution type, distribution cut-off angle, and aspect ratio on thermal residual stress for in-plane fiber misorientation. Fiber volume fraction, aspect ratio, and distribution cut-off angle are shown to have more significant effects on the magnitude of the thermal residual stresses than fiber distribution type for in-plane misorientation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1A
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• pp.55-64
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• 2012

Experimental investigation on the structural behavior of steel fiber-reinforced ultra high performance concrete (UHPC) beams subjected to shear are presented. Six tests carried out on simply supported I-beams under concentrated loads are presented. The parameters varied were the volume fraction of the fibers (1.0, 1.5 and 2.0%) and shear span-effective depth ratio (2.5, 3.4). The test results indicated that ultimate shear strength increased with increasing fiber volume, and that ultimate shear strength decreased with increasing shear span-effective depth ratio. In addition, applicability of predictive equations for evaluating the ultimate shear strength of steel fiber-reinforced UHPC beams are estimated based on the test results. The comparison between computed values and the experimentally observed values are shown to validate the proposed theoretical equations. It is found that predictions by using AFGC and JSCE recommendations provide the most accurate estimates of shear strength of steel fiber-reinforced UHPC beams.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.87-95
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• 2014

Experimental investigation on the structural behavior of steel fiber-reinforced ultra high performance concrete (UHPC) beams subjected to torsion are presented. Six tests carried out on square beams under torsional moment are presented. The experimental parameters were the volume fraction of the fibers and closed-stirrup ratio. The volume fraction of the fibers was 1.0% and 2.0%. The closed-stirrup ratio was 0, 0.35%, and 0.70%. The test results indicated that ultimate torsional strength increased with increasing fiber volume, and that ultimate torsional strength also increased with increasing the closed-stirrup ratio. In addition, predictive equations for evaluating the ultimate torsional strength of UHPC beams were proposed. The comparison between computed values and the experimentally observed values was shown to validate the proposed analytical equations. It was found that predictions by using proposed equation provides good agreement with test results of UHPC beams.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.703-708
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• 2006

The slurry infiltrated fiber concrete(SIFCON) is recognized as one of the most promising new construction materials. Compressive and direct tensile tests are performed to investigate the mechanical property of SIFCON. Hooked-end steel fibers are used in the mix with fiber volume fraction varied from 4% to 10%. The water/cement ratio is kept constant at 0.4. The amount of silica fume added is 10% by weight of cement and 0.5% of water reducing agent is added to improve the workability of the slurry. The test results in this study show that the compressive strength of SIFCON is about 1.59 to 2.68 times in comparison with the cement paste. Tensile strength is showed the enhancement of about 2.51 to 8.77 times. It is also observed that the toughness and ductility of SIFCON are increased significantly with the increasing in fiber volume fraction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.51-60
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• 2010

Recently, a new type of polyolefin fiber having a good mechanical properties is being developed, and it is necessary to examine a possibility for the new fiber together to be used as a reinforcing fiber with other types of fiber or by itself. The objective of this study is to find flexural toughness and tensile strength of concrete reinforced with steel and polyolefin fibers. Four point beam tests were performed with 324 specimens following two standard tests methods: KS F 2566 and ASTM C 1399-02. From the test results, the effects of volume fraction of fibers, and aspect ratio of steel fiber on the toughness and tensile strength were investigated, and the optimal ratio of steel fiber to polyolefin fiber was suggested.

• Composites Research
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• v.19 no.6
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• pp.16-22
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• 2006

The puncture properties under various conditions were investigated for the optimum conditions to yield the best properties. Fiber aspect ratio(AR: length of fiber/diameter of fiber), interphase condition and fiber content were considered as variables which impact the puncture force and friction force. The puncture force of short-fiber reinforced rubber increases up to 3.4 times compared to the virgin material. The better interphase condition shows the higher puncture force at given fiber AR and fiber content. The friction force of the matrix and reinforced rubber with a fiber AR below 155 does not exist. The friction force of the reinforced rubber with the good interphase condition and high fiber AR is higher than puncture force of matrix. Overall, it was found that the interphase condition, fiber AR and fiber content have an important effect on the puncture properties.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.48-56
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• 2013

In this paper, the equivalent elastic properties of fiber reinforced plastic laminar are investigated using various homogenization schemes. Although there are several methods for predicting the equivalent elastic properties such as analytical formula or semi-empirical formula, most of them have some limitations or are not much accurate when handling new composite material consisting of various fiber, matrix and fiber-volume fraction ratio. To resolve the issues, computational homogenization scheme is adopted with a representative volume element (RVE) comprised of a set of finite elements. Finally, the equivalent elastic properties are obtained by applying periodic boundary conditions. The obtained results are compared with those by the existing methods and test results. Also its effect on structural analysis results of the composite satellite panel is investigated.

• Computers and Concrete
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• v.29 no.6
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• pp.375-391
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• 2022

This paper examined the impact of the cross-sectional structure on the structural results under different loading conditions of reinforced concrete (RC) members' management limited in Carbon Fiber Reinforced Polymers (CFRP). The mechanical properties of CFRC was investigated, then, totally 32 samples were examined. Test parameters included the cross-sectional shape as square, rectangular and circular with two various aspect rates and loading statues. The loading involved concentrated loading, eccentric loading with a ratio of 0.46 to 0.6 and pure bending. The results of the test revealed that the CFRP increased ductility and load during concentrated processing. A cross sectional shape from 23 to 44 percent was increased in load capacity and from 250 to 350 percent increase in axial deformation in rectangular and circular sections respectively, affecting greatly the accomplishment of load capacity and ductility of the concentrated members. Two Artificial Intelligence Models as Extreme Learning Machine (ELM) and Particle Swarm Optimization (PSO) were used to estimating the tensile and flexural strength of specimen. On the basis of the performance from RMSE and RSQR, C-Shape CFRC was greater tensile and flexural strength than any other FRP composite design. Because of the mechanical anchorage into the matrix, C-shaped CFRCC was noted to have greater fiber-matrix interfacial adhesive strength. However, with the increase of the aspect ratio and fiber volume fraction, the compressive strength of CFRCC was reduced. This possibly was due to the fact that during the blending of each fiber, the volume of air input was increased. In addition, by adding silica fumed to composites, the tensile and flexural strength of CFRCC is greatly improved.