• Explosives and Blasting
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• v.38 no.1
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• pp.30-37
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• 2020

In this study the split ring (SR) test was investigated for its applicability to the measurement of the tensile strength of rock specimen of NX size. The concept of the SR test is the same as the half ring (HR) test (Choi et al., 2019) except that the expected fracture plane is perpendicular to the loading direction. Because of this perpendicularity, however, it was believed that the SR test could be more accurate than the HR test. Like the HR specimen, the SR specimen is a curved prismatic bar with a uniform section. Appealing to a basic bending theory in strength of materials, the tensile strength for the special bar can be calculated analytically. Numerical simulations using LS-DYNA revealed, as expected, that the strength errors were 1% and 5% for the tensional and compressional SR tests, respectively, which were much lower than that (12%) of the HR test. To identify the performance of the two SR tests, laboratory experiments were conducted. The HR and Brazilian tests were also performed for comparison. The experiments showed that the ratios of the tensional and compressional SR to Brazilian strengths were 1.2~1.4 and 1.1~1.2, respectively, which are too small compared to empirical values in ordinary bend tests. Consequently, it is concluded that the SR test is not appropriate for use in tensile strength test of rock specimen of NX size. But the ratio of the HR to Brazilian strengths was within 1.7~2.0 for both the previous and present studies, showing a good consistency in their test results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.199-209
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• 2009

This paper deals with the three-dimensional finite element analysis of failure behavior of UHPFRC I-beam under monotonic load. Different from the constitutive law of normal and high strength concrete, an elastic-plastic fracture model that considers the tensile strain hardening is proposed to describe the material properties of UHPFRC. A multi-directional fixed crack criterion with tensile strain hardening is defined in the tensile region, and Drucker-Prager criterion with an associated flow rule is adopted in the compressive region. The influence of span, prestressing force and section on the behavior of UHPFRC I-beam are investigated. The comparison of the numerical results with the test results indicates a good agreement.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.105-113
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• 2016

Most studies on mechanical properties of concrete with recycled aggregate was focused on the concrete with compressive strength of less than 40 MPa. Therefore, this paper concerns the compressive strength and mechanical properties of concrete with compressive strength of greater than 40 MPa containing recycled coarse aggregate (RCA). The experimental parameters were compressive strength level and replacement ratio of RCA. Compressive strength level was 45 and 60 MPa, and replacement ratio of RCA was 30, 50, 70 and 100%. The results of the test were discussed: compressive strength, elastic modulus, split tensile strength and modulus of rupture. Test results of elastic modulus were compared to the design code predictions. The design code predictions for elastic modulus overestimated the experimental results. However, the design code predictions for modulus of rupture were generally in agreement with the measured values.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.45-52
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• 2002

It has been known that tensile residual stresses occurring by the thermal expansion coefficient mismatch between fiber and matrix is a cause of the weak strength of metal matrix composites(MMCs). In order to solve this problem, TiNi alloy fiber was used as a reinforced material in TiNi/A16001 shape memory alloy composite in this study. TiNi alloy fiber improves the tensile strength of the composite by causing compressive residual stress in matrix on the basis of its shape memory effect. Pre-strain was imposed to generate the compressive residual stresses inside the TiNi/A16001 shape memory alloy composites. AE technique was used to quantify the microscopic damage behavior of the composite at high temperature. The effect of applied pre-strains on the AE behavior was also evaluated.

• Journal of the Korea Institute of Building Construction
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• v.13 no.5
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• pp.449-456
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• 2013

This study was carried out to assess the suitability in terms of the standards of material quality of basalt aggregates from JEJU Island as a source for concrete aggregate. Quality assessments on the basalt aggregates were performed to assess the soundness of coarse aggregates using sodium sulfate solution, aggregate crushing test, and Los Angeles abrasion test. In addition, XRD, XRF, porosity, and compressive and tensile strength tests were performed to analyze the chemical components and the mechanical properties. In general, the mechanical properties of basalt aggregates from some areas did not meet the Korea Standards (KS), but the levels of compressive and tensile strength were higher than those of granite, andesite, and sandstone of other regions.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.243-251
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• 2022

The purpose of this study is to investigate experimentally the effect of polyethylene fibers with different tensile strength and aspect ratio on the properties of cementless composite. Three types of mixtures according to the types of polyethylene fibers and water-to-binder ratio were prepared and density, compressive strength and tension tests were performed. Test results showed that the mixture reinforced by polyethylene fiber with a low tensile strength by 10 % and a high aspect ratio by 8.3 % had a high tensile strain capacity by 11.7 %, a high toughness by 12.4 %, and a low crack width by 9.1 %. It was also observed that high tensile strain capacity and better cracking pattern could be achieved by increasing the water-to-binder ratio of composite although its strength is low.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.608-614
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• 2002

The effects of slag content and polymer-binder ratio on the strength properties of autoclaved SBR-modified concretes using ground granulated blast-furnace slag(slag) and a styrene-butadiene rubber (SBR) latex are examined. As a result, the compressive and tensile strengths of the autoclaved SBR-modified concretes using slag increase with increasing slag content, and reach a maximum at a slag content 40％, and increase with increasing polymer-binder ratio. In particular, the autoclaved SBR-modified concretes with a slag content of 40％ provide about three times higher tensile strength than unmodified concretes. Such high strength development is attributed to the high tensile strength of SBR polymer and the improved bond between cement hydrates and aggregates because of the addition of SBR latex.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.575-583
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• 2001

The purpose of this study is to present the method of utilizing the recycled aggregate that are obtained from waste concrete as the concrete aggregate. We manufactured the recycled aggregate concrete with compressive strength of over 300kgf/㎠ to increase its weaker strength than the normal concrete, and compared the physical features of the recycled aggregate concrete with that of the normal concrete. As a result of the study, the mechanical performances such as compressive and tensile strength were generally reduced as the mixing rate of the recycled aggregate increased; however, it was possible to manufacture the concrete with the compressive strength of 300∼600kgf/㎠ using the adequate mixing material such as unit quantity of cement, compounding water and silicafume. However, a continuous study on long-term durability performance is required to manufacture and utilize the recycled aggregate concrete for the structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.817-820
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• 2008

이 논문은 초고강도 섬유보강 I형 보의 거동을 Diana를 사용하여 3차원 유한요소해석을 수행하였다. 보통 또는 고강도 콘크리트의 구성방정식과 달리 초고강도 섬유보강 콘크리트의 재료적 특성 즉, 인장 변형률 강화를 고려한 탄-소성 파괴 역학적 모델을 제안하여 해석에 반영하였다. 인장영역에서는 인장 변형률 강화를 고려한 다차원 고정 균열 규준을 사용하였고, 압축영역에서는 associated flow rule을 고려한 Drucker-Prager Criterion을 채택하였다. UHPFRC(Ultra-High Performance Fiber Reinforced Concrete) I형 보의 하중변형관계, 최초 균열, 최초 대각 균열, 극한상태 등의 결과를 실험결과와 비교하여 해석법의 유용성을 입증하였다.

• Korean Journal of Agricultural Science
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• v.6 no.2
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• pp.185-191
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• 1979

Compressive and tensile strengths of commonly being used mortar and mortar specially hardened by adding 1%, 2% and 3% of $CaCl_2$ were compared under the different mixing ratio of mortar and ages to investigate the effect of $CaCl_2$ which is being used as a promotor for coagulation and hardness, on the strength of mortar. The results obtained were as follows: 1. The compressive strength of mortar hardened by addition of $CaCl_2$ was higher than that of commonly being used mortar. The highest compressive strength of mortar was obtained when 2% of $CaCl_2$ were added. 2. The tensile strength of mortar, which was made by adding $CaCl_2$ and aged for seven days, was higher than that of commonly being used mortar. The highest tensile strength of mortar was obtained when 1% of $CaCl_2$ was added and aged for 28 days. And the tensile strength of mortar with 2% of $CaCl_2$ was lower than that of commonly being used mortar. 3. When the amount of $CaCl_2$ added was higher than 3%, the mortar was abruptly hardened and thereby occurred crack was considered lowering strength of mortar. 4. The rich mix was effective for the increasing the compressive and tensile strength before seven days of age and less effective after seven days of age. Therefore, the addition of one to two per cent of $CaCl_2$ would be effective for promoting initial strength of mortar during winter season.