• 한국농공학회지
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• 제30권2호
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• pp.82-94
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• 1988

The purpose of this study is to introduce the Double Punch test method which is an indirect testing method of tensile strength of concrete, and to compare with the tensile strength of concrete as determined by the split-cylinder test, a practical method for performing the Double Punch test to obtain the tensile strength of concrete is proposed and recommended for general use. In this study, the dimensions of cylindrical specimens used in the Double-Punch test were 15X30cm, 15X15cm, 10${\times}$(20cm, and 5${\times}$l0cm, and in the split-cylinder test were 15${\times}$(30cm, 15${\times}$(15cm, and 10${\times}$(20cm. And the diameters of loading punches used in the Double-Punch test were 1.5cm, 2.5cm, and 3.5 cm. The results obtained from tests are summarized as follows ; 1. In the split-cylinder test, the tensile strength of concrete by the linear elasticity theory is similar to that of plasticity theory. 2. Both split-cylinder test and Double-Punch test, tensile strength of concrete is increased with decreasing specimen size. This tendency is identical when the ratio of specimen diameter to height is 1: 2, but that tendency is quite different when the ratio is 1: 3. In the Double-Punch test, if specimen size is constant, by increasing the punch size, tensile strength of concrete is increased, too. 4. Using a 15 ${\times}$( 15 cm cylinder specimen and 3.5 cm diameter punch in the Double Punch test would give the most uniform and consistent result in tensile strength, and the result showed a gQod correlation with splitting tensile strength from 15 x 30cm specimen. 5. In order to obtain satisfactory results and to nuninuze variability, it is proposed that specimens of 15 cm in diameter and 15 cm in height with two 3.5 cm diameter punches should be used. It seems, therefore, reasonable tt) take f't=0.0024 P(kg / cm$^2$) as a working formula for computing the tensile strength in the Double Punch test for concrete.

• Computers and Concrete
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• 제20권1호
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• pp.39-47
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• 2017

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.343-363
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• 2017

The objective of this work was finding out the most advisable testing conditions for an effective and robust characterization of the tensile strength (TS) of concrete disks. The independent variables were the loading geometry, the angle subtended by the contact area, disk diameter and thickness, maximum aggregate size, and the sample compression strength (CS). The effect of the independent variables was studied in a three groups of experiments using a factorial design with two levels and four factors. The likeliest location where failure beginning was calculated using the equations that account for the stress-strain field developed within the disk. The theoretical outcome shows that for failure beginning at the geometric center of the sample, it is necessary for the contact angle in the loading setup to be larger than or equal to a threshold value. Nevertheless, the measured indirect tensile strength must be adjusted to get a close estimate of the uniaxial TS of the material. The correction depends on the loading geometry, and we got their mathematical expression and cross-validated them with the reported in the literature. The experimental results show that a loading geometry with a curved contact area, uniform load distribution over the contact area, loads projected parallel to one another within the disk, and a contact angle bigger of $12^{\circ}$ is the most advisable and robust setup for implementation of BT on concrete disks. This work provides a description of the BT carries on concrete disks and put forward a characterization technique to study costly samples of cement based material that have been enabled to display new and improved properties with nanomaterials.

• 한국도로학회논문집
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• 제20권4호
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• pp.27-34
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• 2018

PURPOSES : The objective of this study is to evaluate the physical properties of recycled asphalt mixtures reinforced with glass fiber. METHODS : Firstly, mixing design was conducted on recycled asphalt mixture for use of 50% recycled aggregate. Various laboratory tests were performed on four types of recycled asphalt mixtures with different glass fiber content to evaluate the physical properties. The laboratory tests include indirect tensile strength test, dynamic modulus test, Hamburg wheel tracking test and tensile-strength ratio to evaluate cracks, rutting and moisture resistance of mixtures. RESULTS : The indirect tensile strength of fiber reinforced glass increased about 139.4%. As a result of comparing the master curves obtained by the dynamic modulus test, the elasticity was low in the low temperature region and high in the high temperature region when the glass fiber was reinforced. The glass fiber contents of PEGS 0.3%, Micro PPGF 0.1% and Macro PPGF 0.3% showed the highest moisture resistance and rutting resistance. CONCLUSIONS : The test results show that use of glass fiber reinforcement can increase the resistance to cracking, rutting, and moisture damage of asphalt mixtures. It is also necessary to validate the long-term performance of recycled asphalt mixtures with glass fiber using full scale pavement testing and field trial construction.

• 한국도로학회논문집
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• 제4권1호
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• pp.161-170
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• 2002

본 연구는 폐폴리에틸렌필름(폐비닐)을 아스팔트 혼합물에 첨가하여 아스팔트 포장재료의 품질특성을 향상시키고 환경적으로 문제가 되고 있는 폐비닐을 재활용하기 위한 연구의 일환으로 수행되었다. 폐비닐 사용시 나타날 수 있는 포장체의 특성을 파악하기 위하여 국내에서 가장 많이 수거되는 LDPE 폐비닐을 사용하여 현장에서의 실용성을 고려한 건식혼합법으로 아스팔트 혼합물을 제조하였다. 제조한 혼합물에 대하여 마샬안정도 시험, 간접인장강도 시험, 반복주행시험 및 피로시험을 수행한 결과 폐비닐을 혼합한 혼합물이 일반혼합물에 비하여 인장강도가 향상되고 윤하중에 의한 소성변형 저항성 및 피로균열 저항에 크게 효과적인 것으로 나타났다.

• Computers and Concrete
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• 제12권3호
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• pp.285-301
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• 2013

This paper concentrates on the results of experimental work on tensile strength of self-compacting concrete (SCC) caused by flexure, which is called rupture modulus. The work focused on concrete mixes having water/binder ratios of 0.35 and 0.45, which contained constant total binder contents of 500 $kg/m^3$ and 400 $kg/m^3$, respectively. The concrete mixes had four different dosages of a superplasticizer based on polycarboxylic with and without silica fume. The percentage of silica fume that replaced cement in this research was 10%. Based upon the experimental results, the existing equations for anticipating the rupture modulus of SCC according to its compressive strength were not exact enough. Therefore, it is decided to use artificial neural networks (ANN) for anticipating the rupture modulus of SCC from its compressive strength and workability. The conclusion was that the multi layer perceptron (MLP) networks could predict the tensile strength in all conditions, but radial basis (RB) networks were not exact enough in some circumstances. On the other hand, RB networks were more users friendly and they converged to the final networks quicker.

• 한국건설순환자원학회논문집
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• 제5권3호
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• pp.305-312
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• 2017

본 연구에서는 국내 화력발전소에서 발생되고 있는 산업부산물을 활용하여 아스팔트 콘크리트용 채움재를 개발 및 혼합물에 적용하여 함량에 따른 특성 및 소성변형 저항성에 미치는 영향을 관찰하였다. 실험결과 석탄회 기반 채움재를 사용할 경우 최적아스팔트함량(OAC)는 기존 채움재 대비 0.1% 낮은 값을 나타내었다. 도출된 최적아스팔트함량에서 채움재 함량에 따른 간접인장강도 및 인장강도비 측정 결과 함량 증가에 따라 높은 성능을 발현하였고, 2.0% 이상의 함량에서 국내 단체표준 품질관리 기준 각 0.8 이상과 0.75 이상을 만족하는 결과를 얻을 수 있었다. 동적안정도는 채움재 2.5%의 함량에서 가장 높은 저항성을 나타내었으며, 함량이 2.5%를 넘어설 때 오히려 성능발현이 저하되는 결과를 나타내었다. 과도한 채움재의 혼입은 상대적으로 아스팔트 함량이 감소되기 때문에 취성파괴를 유발할 수 있으므로 최적의 채움재/아스팔트 의 비율을 찾아 적용하는 방안이 필요할 것으로 판단된다.

• 터널과지하공간
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• 제26권4호
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• pp.316-326
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• 2016

본 연구는 화강암에 존재하는 결 이방성이 간접인장강도에 미치는 영향을 평가하였다. 표준 간접인장시험 및 3개의 서로다른 중공 크기에 대한 중공 간접인장시험을 수행하였다. 2차원 개별요소 수치해석을 통해 간접인장시험에서의 파괴 과정 및 메커니즘을 고찰하였다. 간접인장강도는 화강암의 결에 따라 하드웨이, 그레인, 리프트 면의 순으로 감소하였다. 중공 간접인장강도는 일반 간접인장강도에 비해 2.5~6.4배 정도 크게 나타났으며, 중공 크기가 클수록 크게 나타났다. 중공 시편에 대한 간접인장 파괴 유형은 중공 크기 및 결과 하중방향 각도에 영향을 받는 것으로 나타났다.

• 한국방재학회 논문집
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• 제3권2호
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• pp.89-97
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• 2003

폐타이어 재활용 아스팔트 콘크리트의 기술개발과 기초 자료의 확립을 위해서 건식공법 및 습식공법으로 생산되어진 폐타이어 재활용 아스팔트 콘크리트와 재래식 밀입도 아스팔트 콘크리트 공시체를 제작하여 아스팔트 혼합물의 내구성을 평가할 수 있는 간접인장강도시험과 회복 탄성계수시험을 수행하였다. 간접인장강도시험 결과 골재 입도의 영향으로 간접인장강도는 재래식 아스팔트 콘크리트가 폐타이어 재활용 아스팔트 콘크리트보다 우수하게 나타났지만, 인성과 최대수직변형률의 경우 골재 입도의 영향에도 불구하고 폐타이어 재활용 아스팔트 콘크리트가 우수하게 나타났다. 또한, 회복 탄성계수시험 결과에서도 폐타이어 재활용 아스팔트 콘크리트가 재래식 아스팔트 콘크리트보다 우수한 성능을 보여줌으로써 폐타이어 재활용 아스팔트 콘크리트의 공학적 특성이 우수하게 나타났다. 특히, 습식공법 활용 폐타이어 재활용 아스팔트 콘크리트의 모든 공용특성은 건식공법활용 혼합물보다 우수한 것으로 평가되었다.

• 한국도로학회논문집
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• 제20권1호
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• pp.47-58
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• 2018

PURPOSES : The purpose of this study is to evaluate the mechanical properties of a cold-recycling asphalt mixture used as a base layer and to determine the optimum emulsified-asphalt content for ensuring the mixture's performance. METHODS : The physical properties (storage stability, mixability, and workability) of three types of asphalt emulsion (CMS-1h, CSS-1h, and CSS-1hp) were evaluated using the rotational viscosity test. Asphalt emulsion residues, prepared according to the ASTM D 7497-09 standard, were evaluated for their rheological properties, including the $G*/sin{\delta}$and the dynamic shear modulus (${\mid}G*{\mid}$). In addition, the Marshall stability, indirect tensile strength, and tensile-strength ratio (TSR) were evaluated for the cold-recycling asphalt mixtures fabricated according to the type and contents of the emulsified asphalt. RESULTS : The CSS-1hp was found to be superior to the other two types in terms of storage stability, mixability, and workability, and its $G*/sin{\delta}$ value at high temperatures was higher than that of the other two types. From the dynamic shear modulus test, the CSS-1hp was also found to be superior to the other two types, with respect to low-temperature cracking and rutting resistance. The mixture test indicated that the indirect tensile strength and TSR increased with the increasing emulsified-asphalt content. However, the mixtures with one-percent emulsified-asphalt content did not meet the national specification in terms of the aggregate coverage (over 50%) and the indirect tensile strength (more than 0.4 MPa). CONCLUSIONS : The emulsified-asphalt performance varied greatly, depending on the type of base material and modifying additives; therefore, it is considered that this will have a great effect on the performance of the cold-recycling asphalt pavement. As the emulsified-asphalt content increased, the strength change was significant. Therefore, it is desirable to apply the strength properties as a factor for determining the optimum emulsified-asphalt content in the mix design. The 1% emulsified-asphalt content did not satisfy the strength and aggregate coverage criteria suggested by national standards. Therefore, the minimum emulsified-asphalt content should be specified to secure the performance.