• Geomechanics and Engineering
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• 제17권3호
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• pp.261-270
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• 2019

Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the $45^{\circ}$ line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.29-37
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• 2016

The paper presents a research project on the tensile properties of RPC mixed with both steel and polypropylene fibers after exposure to $20-900^{\circ}C$. The direct and the indirect tensile strength (in bending) were measured through tensile experiment on dog-bone specimens and bending experiment on $40{\times}40{\times}160mm$ prisms. RPC microstructure was analyzed using scanning electron microscope. The results indicate that, steel fibers can significantly improve the tensile performance of hybrid fiber-reinforced RPC, whereas polypropylene fibers have no obvious effect on the tensile performance. With increasing temperature, the flexural and axial tensile strength of hybrid fiber-reinforced RPC substantially decrease linearly, which attributes to the deteriorating microstructure. Based on the experimental results, equations are established to express the decay of the flexural and tensile strength with increasing temperature.

• 대한토목학회논문집
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• 제9권4호
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• pp.83-92
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• 1989

강성포장(剛性鋪裝)에 대하여 더 좋은 공용성능(供用性能) 기대를 위한 개발과 파손발생에 대한 파손과정에 관하여 포장상태를 조사하게 된다. 본 논문(論文)은 공용중(供用中)인 시멘트콘크리트 포장(鋪裝)의 피로거동(疲勞擧動)과 탄성특성(彈性特性)에 대한 연구결과이다. 공용중(供用中)인 각(各) 포장(鋪裝)의 평균인장강도(平均引張強度)를 측정하기 위하여 Indirect tensile시험을 실시한 것이다. 변형측정(變形測定)은 이러한 특성의 변화 및 콘크리트의 탄성특성(彈性特性)을 구하기 위한 피로(疲勞)시험을 통하여 이루어진 것이다.

• 한국도로학회논문집
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• 제4권3호
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• pp.35-42
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• 2002

본 연구는 동절기에 많이 발생하는 포장의 저온균열에 대한 폴리머 개질 아스팔트 혼합물의 저항 특성을 알아보기 위하여 수행하였다. 저온에서의 간접인장강도를 측정 분석한 결과 혼합물들이 $-10^{\circ}C의 저온 대에서 최대 인장강도를 나타냈다. 최대 인장강도를 보이는 온도 이하에서는 시차열 응력이 인장강도 이상으로 발생하여 내부에 손상이 발생하기 때문에 나타나는 인장강도 저하현상을 ITS 시험으로 증명하여 보였다. 저온의 시험 결과는 폴리머 개질 아스팔트 혼합물이 일반 아스팔트 혼합물에 비하여 보다 낮은 온도에서까지도 강도가 높게 나타나 폴리머 개질에 따른 효과를 보였으며, 바인더가 저온균열에 대한 저항에 큰 영향을 미치는 것으로 나타났다. 따라서 추운 지역에서는 저온균열을 예방하기 위하여 폴리머 개질 아스팔트의 사용이 추천된다.

• Advances in concrete construction
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• 제4권3호
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• pp.207-220
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• 2016

The objective of this study was to evaluate the influence of recycled materials, namely, shredded scrap tire (SST), reclaimed asphalt pavement (RAP) and class C fly ash (CFA) on compressive and tensile strength of concrete. Either SST or RAP was used as an aggregate replacement and class C fly ash (CFA) as Portland cement replacement for making concrete. A total of two types of SST and RAP, namely, chips and screenings were used for replacing coarse and fine aggregates, respectively. A total of 26 concrete mixes containing different replacement level of SST or RAP and CFA were designed. Using the mix designs, cylindrical specimens of concrete were prepared, cured in water tank, and tested for unconfined compressive strength (UCS) and indirect tensile strength (IDT) after 28 days. Experimental results showed aggregate substitution with SST decreased both UCS and IDT of concrete. On the contrary, replacement of aggregate with RAP improved UCS values. Specimens containing RAP chips resulted in concrete with higher IDT values as compared to corresponding specimens containing RAP screenings. Addition of 40% CFA was found to improve UCS values and degrade IDT values of SST containing specimens. Statistical analysis showed that IDT of SST and RAP can be estimated as approximately 13% and 12% of UCS, respectively.

• Geomechanics and Engineering
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• 제23권2호
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• pp.165-178
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• 2020

This paper investigates the effect of the jaw's curvature, also known by contact angle and jaw arc central angle (2α), of the Brazilian test apparatus on indirect tensile strength of various rock types. That's why, ten rock samples including limestone, marble, skarn, granite, diorite, and granodiorite were collected from some quarries in different provinces of Iran. Petrographic, mineralogical and textural investigations were performed using thin section analyses. Physical properties of the selected rock samples namely dry and saturated unit weights, porosity, water absorption, and specific gravity were determined for the rock samples. In addition, Brazilian tensile strength at different 2α angles (i.e., 2α = 0°, 10°, 15°, 20°, 45°, and 60°) were determined for the rocks in the laboratory. Results show that the parameter for the rocks is between 3.81 MPa at 2α=0° and 54.76 MPa at 2α=60°. This means that Brazilian tensile strength increased with increasing 2α angle from 0° to 60°. Also, it was found that the highest change rate of the Brazilian tensile strength occurs in range of 2α=15°-30° for most studied rock samples. In some tested samples, the parameter is decreased only at 2α = 60°. The values of Brazilian tensile strength of the rocks tested by flat and standard jaws are near to each other.

• 대한토목학회논문집
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• 제34권3호
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• pp.947-954
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• 2014

일반적으로 Mohr-Coulomb 파괴 이론을 바탕으로 한 재료 파괴는 최대수직응력이나 최대전단응력 상태에서 파괴가 일어나는 것이 아니라 수직응력과 전단응력의 임계결합상태에서 파괴된다. 이에 본 연구에서는 배수성 아스팔트 혼합물 2종과 SMA 10mm혼합물 및 일반 밀입도 아스팔트 19mm를 이용한 $45^{\circ}C$와 $60^{\circ}C$에서 삼축압축시험을 실시하였다. Mohr-Coulomb의 파괴 이론을 바탕으로 삼축압축시험 결과를 정리한 결과 내부마찰각은 $38.9^{\circ}{\sim}46.9^{\circ}$로 다소 불규칙하게 측정되었으나 점착력의 경우 온도와 시편의 수침여부에 따라 다르게 나타났다. 또한, 아스팔트 혼합물의 간접인장강도시험과 삼축압축시험 상관관계를 알아보기 위해 삼축압축시험 결과로 평가된 점착력과 내부마찰각을 이용하여 계산된 이론적인 간접인장강도와 시험을 통해 직접 측정된 간접인장강도를 분석하였다. 두 간접인장강도 값은 비례하는 경향을 보였다.

• Geomechanics and Engineering
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• 제10권6호
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• pp.775-791
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• 2016

The indirect tensile strengths (ITSs) of different cemented paste backfill mixes with different curing times were determined by considering crack initiation and fracture toughness concepts under different loading conditions of steel loading arcs with various contact angles, flat platens and the standard Brazilian test jaw. Because contact area of the ITS test discs developes rapidly and varies in accordance with the deformability, ITSs of curing materials were not found convenient to determine under the loading apparatus with indefinite contact angle. ITS values increasing with an increase in contact angle can be measured to be excessively high because of the high contact angles resulted from the deformable characteristics of the soft paste backfill materials. As a result of the change of deformation characteristics with the change of curing time, discs have different contact conditions causing an important disadvantage to reflect the strength change due to the curing reactions. In addition to the experimental study, finite element analyses were performed on several types of disc models under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the cemented paste backfill materials. Both experimental and numerical analyses concluded that loading arcs with definite contact angles gives better results than those obtained with the other loading apparatus without a definite contact angle. Loading arcs with the contact angle of $15^{\circ}$ was found the most convenient loading apparatus for the typical cemented paste backfill materials, although it should be used carefully considering the failure cracks for a valid test.

• 한국도로학회논문집
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• 제17권1호
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• pp.77-82
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• 2015

PURPOSES : The purpose of this paper is to evaluate the moisture susceptibility of asphalt mixtures containing developed liquid anti-stripping agents using the boiling water test as a screening test. METHODS : The boiling water test was used to evaluate the moisture susceptibility of asphalt mixtures containing different anti-stripping agents. The tensile strength ratio was calculated to compare the moisture susceptibility of the asphalt mixtures after indirect strength tests were performed. Additionally, image analysis techniques were used to calculate and analyze the quantity of stripped area in the asphalt mixtures. RESULTS : In general, the asphalt mixtures containing anti-stripping agents showed a higher resistance of anti-stripping based on the boiling water test and tensile strength ratio. CONCLUSIONS : The boiling water test can be used to differentiate the resistance of moisture susceptibility of asphalt mixtures, except for asphalt mixtures containing hydrated lime. The boiling water test can be used as a screening test for asphalt mixtures before conducting time consuming and expensive indirect tensile strength tests.

• Geomechanics and Engineering
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• 제16권5호
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• pp.559-567
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• 2018

Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young's modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better 'soil-reinforcing material' interaction is achieved and desired properties of the soil are improved at nanolevel.