• Journal of the Korean Society of Safety
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• v.20 no.3 s.71
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• pp.126-133
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• 2005

Behavior of saw-dust concrete has not studied because many people have thought that saw-dust concrete cannot be applicable for structural member, up to now. This study is to findout how much the concrete can be structurally applicated. 5mm grid sieve was used to select satisfactory sawdust for better concrete quality. Test molds size of ${\phi}10{\times}20cm$ long were made of normal without sawdust, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8% 2.0%, for making concrete strengh of 180kg, 210kg, 240kg, 270kg which they are normally used in practice presently. A various strengths tests such as compressive splitting tensile, flexible strength behavior of structural member named beam using size of $20{\times}30{\times}120cm$ have been done for the structural aspects. Tensile strength shows that it can be more affected than higher strength of it.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.253-263
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• 2015

Ultra-high strength concrete which have 100 MPa compressive strength or higher can be developed applying RPC(Reactive Powder Concrete). Preventing brittle failure under compression and tension, ultra-high strength concrete usually use the steel fibers as reinforcements. For the effective use of steel fiber reinforced ultra-high strength concrete, estimation of tensile strength is very important. However, there are insufficient research results are available with no relation between them. Therefore, in this study, correlation between compressive strength and tensile strength of ultra-high strength concrete was investigated by test and statistical analysis. According to test results, increasing tendency of tensile strength was also shown in the range of ultra-high strength. Evaluation of test results of this study and collected test results were carried out. Using 284 splitting test specimens and 265 flexural test specimens, equations suggested by previous researchers cannot be applied to ultra-high strength concrete. Therefore, using database and test results, regression analysis was carried out and we suggested new equation for splitting and flexural tensile strength of steel fiber reinforced ultra-high strength concrete.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.603-610
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• 2003

The influence of Poisson's ratio on the tensile strength of brittle materials is neglected in many studies. When brittle materials are loaded in compression or impact, substantial tensile stresses are induced within the materials. These tensile stresses are responsible for splitting failure of the materials. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the state of stress at the center of the particle is obtained. An analysis of the distribution of stresses along the z-axis due to distributed pressures and concentrated forces, and on diametrically horizontal plane due to concentrated forces, shows that it is reasonable to propose the tensile stress at the center of the particle at the point of failure as a tensile strength of the particle. Moreover, the tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well. Therefore, it can be proposed as the tensile strength for brittle materials generally. The effect of Poisson's ratio on the tensile strength is discussed.

• Journal of the Korea Institute of Building Construction
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• v.5 no.2 s.16
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• pp.89-95
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• 2005

Various tests are performed with the recycled concrete including compressive strength, flexural strength, splitting tensile strength, bonding strength and chloride ion penetration test. The basic data obtained from the presented test could be accumulated for the purpose of utilization in concrete structure. Most of the strength tests show that strength decrease a little extent with increasing substitution ratio of recycled coarse aggregate except splitting tensile test for the concrete with $100\%$ recycled fine aggregate. But in case of the $50\%$ substitution of recycled coarse aggregate, compressive strength, flexural strength and bonding strength are almost equal to the normal concrete. Chloride ion penetration test shows that the penetration amounts of chloride ion becomes more in proportion to the substitution ratio of recycled aggregate. But most of the results show that the permeability of recycled concrete is proper to use. The results of present study nay imply that the use of recycled aggregate for steam curing concrete is possible but the substitution ratio of recycled aggregate should be determined through further studies.

• Computers and Concrete
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• v.19 no.6
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• pp.667-675
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• 2017

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

• Computers and Concrete
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• v.18 no.1
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• pp.113-137
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• 2016

Extensive experimental studies on remarkable mechanical properties Polypropylene Fibre Reinforced Self-compacting Concrete (PFRSCC) have been executed, including different fibre volume fractions of Polypropylene fibers (0.25%, 0.5%, 0.75%, and 1%) and different water to cement ratios (0.21, 0.34, 0.38, and 0.41). The experimental program was carried out by using two hundred and sixteen specimens to obtain the impact resistance and mechanical properties of PFRSCC materials, considering compressive strength, splitting tensile strength, and flexural strength. Statistical and analytical studies have been mainly focused on experimental data to correlate of mechanical properties of PFRSCC materials. Statistical results revealed that compressive, splitting tensile, and flexural strengths as well as impact resistance follow the normal distribution. Moreover, to correlate mechanical properties based on acquired test results, linear and nonlinear equations were developed among mechanical properties and impact resistance of PFRSCC materials.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.5
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• pp.25-33
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• 2011

In this paper, the effects of aggregate and curing temperature on strength development characteristics of UP (Unsaturated Polyester)-MMA (Methyl Methacrylate) based polymer mortar under sub-zero temperature are experimentally investigated to provide a criterion for repair and production of precast products. The result showed that the setting time of the binder was 4 minutes at $20^{\circ}C$ whereas 35 minutes at $-20^{\circ}C$. The result also revealed that the compressive, flexural, and splitting tensile strengths of UP-MMA based polymer mortar significantly decreased as the aggregate and curing temperatures decreased. However, sufficient strengths which can be implemented in actual practices -36.6 MPa of compressive strength, 6.11 MPa of flexural strength, and 5.81 MPa of splitting tensile strength - were obtained even though both aggregate and curing temperatures were $-20^{\circ}C$. Strength development of polymer mortar is largely affected by curing temperature rather than aggregate temperature. It was found that the effects of aggregate temperature on strength development become smaller as the curing temperature becomes lower. Also, toughness, a ratio of compressive strength to flexural strength, increased from 3.5 to 5.9 as both aggregate and curing temperatures decreased from $20^{\circ}C$ to $-20^{\circ}C$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.52-59
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• 2014

This study examines the compressive strength, elastic modulus and splitting tensile strength of geopolymer concrete in order to evaluate its mechanical characteristics according to the admixing of fly ash and blast furnace slag. Moreover, identical tests are also conducted considering the amount of powder, the mixing ratio of alkali activator and the mixing ratio of silica fume for further comparative analysis considering various variables. The comparison with the formulae specified in Korean and overseas codes reveal that a mixing ratio of 18% is adequate for the alkali activator and that a replacement ratio of 5% by silica fume is recommended for silica fume. The elastic modulus of the geopolymer concrete appears to increase slightly with the increase of the compressive strength per variable and age and to be smaller than the values predicted by the formulae specified in Korean and overseas codes. In addition, the examination of the stress-strain curves shows that the geopolymer concrete exhibits ductile behavior compared to the conventional OPC. In view of the splitting tensile strength, high strength is observed for a powder content of $400kg/m^3$ and a replacement ratio of 18% by silica fume. The resulting ratio of the compressive strength to the splitting tensile strength is seen to range between 8.7 and 10.2%.

• Composites Research
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• v.36 no.4
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• Advances in concrete construction
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• v.13 no.2
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• pp.123-132
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• 2022

This paper aims to adapt Multilinear regression (MLR) to predict the strength and toughness of SIFCON containing various pozzolanic materials. Slurry Infiltrated Fibrous Concrete (SIFCON) is one of the most common terms used in concrete manufacturing, known for its benefits such as high ductility, toughness and high ultimate strength. Assessment of compressive strength (CS.), flexural strength (F.S.), splitting tensile strength (STS), dynamic elasticity modulus (DME) and impact energy (I.E.) using the experimental approach is too costly. It is time-consuming, and a slight error can lead to a repeat of the test and, to solve this, alternative methods are used to predict the strength and toughness properties of SIFCON. In the present study, the experimentally investigated SIFCON data about various mix proportions are used to predict the strength and toughness properties using regression analysis-multilinear regression (MLR) models. The input parameters used in regression models are cement, fibre, fly ash, Metakaolin, fine aggregate, blast furnace slag, bottom ash, water-cement ratio, and the strength and toughness properties of SIFCON at 28 days is the output parameter. The models are developed and validated using data obtained from the experimental investigation. The investigations were done on 36 SIFCON mixes, and specimens were cast and tested after 28 days of curing. The MLR model yields correlation between predicted and actual values of the compressive strength (C.S.), flexural strength, splitting tensile strength, dynamic modulus of elasticity and impact energy. R-squared values for the relationship between observed and predicted compressive strength are 0.9548, flexural strength 0.9058, split tensile strength 0.9047, dynamic modulus of elasticity 0.8611 for impact energy 0.8366. This examination shows that the MLR model can predict the strength and toughness properties of SIFCON.