• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6D
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• pp.803-810
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• 2011

The public interest of global warming and energy shortage is gradually increased, and the related industries also have become interested in developing eco-friendly material and technology. Warm-mix asphalt (WMA) is a result of the developments to alleviate global warming and energy problems. This WMA is produced at lower temperatures than the temperature at which hot mix asphalt (HMA) is produced. Because most tests in Superpave are developed only for the performance and maintenance of HMA produced by hot temperatures, it is difficult for the tests to identify properly the material properties and then evaluate the performances between HMA and WMA. This study deals with the development of a new protocol to differentiate HMA and WMA performance, and especially the interfacial properties between asphalt and aggregate are targeted as the performance indicator; thus, an evaluation method and guideline are suggested. The concept and idea of the test method applied in this study were modified from the DSR moisture damage test protocol. In addition, TSR test was performed to affirm the relation between the asphalt-aggregate interface and the asphalt-aggregate mixture performances. The followings are the results of this study. Shear stress at 85% linear visco-elastic complex modulus (LVE $G^*$) can be a better parameter than LVE $G^*$, which can assess the interfacial or bonding performance between asphalt and aggregate. Moreover, measuring the bonding performance in thinner film thicknesses will be a better way to evaluate the real and field situation between asphalt and aggregate. The interfacial properties' criteria to apply the newly developed test and parameter should be developed, after the asphalt mixture criteria relating to the interfacial properties are completed.

• Tunnel and Underground Space
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• v.17 no.3 s.68
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• pp.203-215
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• 2007

Stability and mechanical deformation behavior of rock masses are highly dependent on the mechanical characteristics of contained discontinuities. Therefore, mechanical characteristics of the discontinuities should be considered in the design of tunnel and underground structures. In this study, direct shear tests for rough granite joints were carried out under constant normal stiffness conditions. Effects of initial normal stress, shear velocity, and surface roughness on the characteristics of shear strength and deformation behaviors were examined. Results of shear testing under constant normal stiffness conditions reveal that shear behaviors could be classified into two categories, based on the amount of decrease in shear stress at the Int peak shear stress. With initial normal stiffness increasing, it turned out that shear displacement at peak stress and the first peak shear stress increased, however friction angle and friction coefficient showed decrease. In case of shear stiffness and average friction coefficient, it turned out that they are not dependent on the initial normal stress. Minor effects of shear velocity on rough joints were observed in several shear quantities. However, the effects of shear velocity were insignificant regardless of the normal stress increase. Change of shear strength and deformation characteristics on joint roughness were examined, however, it turned out that the variations were attributed to deviation of shear test specimens.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.215-224
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• 2019

According to the recent civil engineering construction work site which is a complex process, development of multi-functional geotextiles is required. In this study, the characteristics of five different modified cross-section fiber yarns for the selection of wicking yarns were analyzed and yarns that can achieve target properties were selected. Experimental prototype geotextiles suitable for horizontal wicking drain property and reinforcement was developed and its tensile strength, 2% secant modulus, vertical water permeability, AOS, friction characteristics by the direct shear method, and vertical/horizontal wicking test were analyzed. These tests are conducted to verify the performance of the geotextiles with horizontal wick drain property, separation and reinforcement developed in this study. As a results of the indoor soil box test, it was confirmed that the geotextiles using the wicking yarn sufficiently exhibited the function of discharging excess pore water in the horizontal direction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.279-286
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• 2011

FRP (Fiber Reinforced Polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Material properties of FRP tendons-bond strength, transfer length, development length-must be determined in order to apply to concrete structures. First of all, in case of application for pretension concrete members with CFRP tendons, transfer length is an important characteristic. The bond of the material characteristics should be demanded clearly to apply to PSC structures prestressed with FRP tendons. This paper investigated on the bond characteristics of FRP reinforcements with various surface-type. To determine the bond characteristics of FRP materials used in place of steel reinforcement or prestressing tendon in concrete, pull-out testing suggested by CAN/CSA S806-02 was performed. A total of 40 specimens were made of concrete cube with steel strands, deformed steel bar and 6 different surface shape FRP materials like carbon or E-glass. Results of the bonding tests presented that each specimen showed various behaviors as the bond stress-slip curve and compared with the bond characteristic of CFRP tendon developed in Korea.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.237-244
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• 2016

This paper presents a nonlinear Moving Least Squares(MLS) difference method for material nonlinearity problem. The MLS difference method, which employs strong formulation involving the fast derivative approximation, discretizes governing partial differential equation based on a node model. However, the conventional MLS difference method cannot explicitly handle constitutive equation since it solves solid mechanics problems by using the Navier's equation that unifies unknowns into one variable, displacement. In this study, a double derivative approximation is devised to treat the constitutive equation of inelastic material in the framework of strong formulation; in fact, it manipulates the first order derivative approximation two times. The equilibrium equation described by the divergence of stress tensor is directly discretized and is linearized by the Newton method; as a result, an iterative procedure is developed to find convergent solution. Stresses and internal variables are calculated and updated by the return mapping algorithm. Effectiveness and stability of the iterative procedure is improved by using algorithmic tangent modulus. The consistency of the double derivative approximation was shown by the reproducing property test. Also, accuracy and stability of the procedure were verified by analyzing inelastic beam under incremental tensile loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1243-1248
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• 2011

Internal defects are a major concern in the casting process because they have a significant influence on the strength and fatigue life of casting products. In general, they cause stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of internal defects on mechanical properties such as fatigue life. In this study, fatigue experiments on tensile specimens with internal defects were performed. The internal defects in the casting product were scanned by an industrial CT scanner, and its shape was simplified by ellipsoidal primitives for the structural and fatigue analysis. The analysis results were compared with experimental results for casting products with internal defects. It was demonstrated that it is possible to consider internal defects of casting products in stress and fatigue analysis. The proposed method provides a tool for the prediction of the fatigue life of casting products and the investigation of the effects of internal defects on mechanical performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.37-45
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• 2021

This paper is a basic study to evaluate the possibility of earthquake-resistant reinforcement by reinforcing engineered cementitious composite in masonry members. In order to examine the performance according to the fiber mixing rate of the engineered cementitious composite, a test specimen was prepared according to the formulation design, and flow ability, compressive strength, flexural strength, length change rate, and direct tensile strain were measured. In addition, non-reinforced masonry members, masonry members reinforced with engineered cementitious composite, and masonry members in which glass fibers and wire mesh were separately reinforced with engineered cementitious composites were manufactured, and flexural strength and maximum displacement were measured. All specimens reinforced with engineered cementitious composite showed more than 16 times the effect of maximal strength compared to that of no reinforcement, and as a result of examining the crack shape, the energy dissipation ability was excellent, confirming the possibility of seismic reinforcement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.529-536
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• 2008

The failure behavior of structures is changed under different loading rates, which might arise from the rate dependency of materials. This phenomenon has been focused in the engineering fields. However, the failure mechanism is not fully understood yet, so that it is hard to be implemented in numerical simulations. In this study, the numerical experiments to a brittle material are simulated by the Molecular Dynamics (MD) for understanding the rate dependent failure behavior. The material specimen with a notch is modeled for the compact tension test simulation. Lennard-Jones potential is used to describe the properties of a brittle material. Several dynamic failure features under 6 different loading rates are achieved from the numerical experiments, where remarkable characteristics such as crack roughness, crack recession/arrest, and crack branching are observed during the crack propagation. These observations are interpreted by the energy inflow-consumption rates. This study will provides insight about the dynamic failure mechanism under different loading rates. In addition, the applicability of the MD to the macroscopic mechanics is estimated by simulating the previous experimental research.

• Geotechnical Engineering
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• v.14 no.4
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• pp.61-76
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• 1998

Various kinds of reinforced soil methods have been developed by many researchers or companies for their economic merits mainly. These methods have generally used sandy soils which have high permeability as embanking or backfill material. That is because, if poor embanking materials, especially like a clayey soil which has very low permeability, are used in a reinforced soil embanking, and if excessive pore water pressure is produced by external factors, the friction resistance between reinforcing members and Boils decrease, as a result possible damage or collapse of the body of a reinforced embankment. In fact, clayey Boils can also be used as a embanking materials with reinforcement which has high permeable capacity, and are expected to be able to dissipate the excess pore water pressure effectively. In this study reinforcing effects have been examined through a serries of direct shear tests in which clayey soils are reinforced with nonwoven geotextiles of which permeability is very high and tensile strength is relatively weaker than geogrids which are usually used in reinforced soil wall. Even though such nonwoven geotextile are used as reinforcement of high saturated clayey soils. the test results show the possibility that nonwoven geoteztiles could be used as a reinforcement for reinforced soil walls effectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.429-435
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• 2016

Cold stretching(CS) pressure vessels from ASS304 (austenitic stainless steel 304) are used for the transportation and storage of liquefied natural gas(LNG). CS pressure vessels are manufactured by pressurizing the finished vessels to a specific pressure to produce the required stress ${\sigma}_k$. After CS, there is some degree of plastic deformation. Therefore, CS vessels have a higher strength and lighter weight compared to conventional vessels. In this study, we investigate the tensile and fatigue behavior of ASS304 sampled by CS pressure vessels in accordance with the ASME code at cryogenic temperature. From the fatigue test results, we show S-N curves using a statistical method recommended by JSEM-S002. We carried out the fractography of fractured specimens using scanning electron microscopy (SEM).