• 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 Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.570-576
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• 2018

In reinforced concrete structures, the joints of ordinary rebars are usually lap joints, which are bound by binding wires with rebars, and mechanical joints by couplers. In domestic design standards (concrete design code), welded lap joints are restricted for ordinary rebars, but overseas standards allow welded lap joints of ordinary rebars through pre-heating. This study investigated the domestic and international standards/criteria and evaluated the fracture strength by performing the tensile test on the lap welded joint of SD400 grade rebars, which is used the most in the construction sites. The weld length of the specimen for weld lap joints is based on the minimum weld length (8d) given in the KS standard (KS B ISO 17660-1). According to AWS D1.4, the preheating temperature was set to $150^{\circ}C$ for D19 and below, and $260^{\circ}C$ for D22 and above. In the test results, the tensile strength of rebars with welded lap joints exceeded the required strength (125% of the yield strength) according to the concrete design code. To analyze the effect of preheating, the tensile strength of the welded rebars after preheating was not significantly different from that of the welded rebars without preheating. The carbon equivalent content (Ceq) of the rebars used in the test was 0.45% or less. Under AWS D1.4, no preheating is required if the carbon equivalent is less than 0.45%. All specimens with a welded lap length of 8d failed by a bar fracture. The effect of preheating was confirmed to be insignificant due to the low carbon equivalent of the rebar.

• Computers and Concrete
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• v.20 no.3
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• pp.311-318
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• 2017

This paper investigates the utilization of waste tyre crumb rubber as the fine aggregate in precast concrete Paving block (PCPB). PCPB's are generally preferred for city roads, pedestrian crosswalk, parking lots and bus terminals. The main aim of this paper is to evaluate the mechanical properties of wet cast PCPB containing waste tyre crumb rubber. The mechanical properties were investigated using a density, compressive strength, split tensile strength and flexural strength tests at 7, 28 56 days according to the IS 15688:2006 and EN1338. The wet cast method was followed for producing PCPB samples. The fine aggregate (river sand) was replaced with waste tyre crumb in percentage of 5%, 10%, 15%, 20% and 25% by volume. All the test results were compared with the conventional PCPB (Without rubber). The test results indicate its feasibility for incorporating waste tyre crumb rubber in the production of PCPB by the wet cast method.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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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.

• Journal of Korean Society for Quality Management
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• v.44 no.3
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• pp.509-526
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• 2016

Purpose: We would like to find the alternative method for the weathering test on rubber coated fabrics and adhesive-coated fabrics for the military products, KS M 0706 (Sunshine carbon arc) to KS M ISO 4892-2 (Xenon arc). Methods: We measured the tensile strength of adhesive-coated fabrics and adhesive products treated with sunshine carbon arc and xenon arc during 100, 150 and 200 hours, respectively. All of the results were treated with statistical test, ANOVA method. We also validate the surface modifications caused by treatment method and time by using FT-IR ATR and, SEM. Results: In case of the thick adhesive-coated fabrics (app. 1 mm), there was no distinctive difference on tensile strength by treatment method and time. In case of the thin mask hood (app. 0.22 mm) and TENT (app. 0.5 mm), there was distinctive difference on tensile strength. Especially, carbon arc showed a huge lowering properties. We could validate the curing from light and moisture, and the functional group change from cross-linking and oxidation using FT-IR ATR. In case of IBS, there was a surface cracks on SEM images. In case of mask hood, there was no distinctive differences, except for a particle falling from decreased affinity between rubber and particles caused by carbon arc. Conclusion: We concluded that there was no problems for changing xenon arc weathering test with same treatment time on IBS, KM7, K21 and adhesive products. In case of TENT and mask hood, there was a difference in tensile strength in accordance with the change of the treated time and method.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.237-247
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• 2001

In this study, the fracture mechanics model as well as the elastic model was reviewed theoretically and four field case studies were conducted to investigate the feasibility of fracture mechanics model for hydraulic fracturing test. There was a difference between the result by fracture mechanics model and the one by elastic model. And the smaller initial crack length is, the larger the difference is. It is considered that the fracture mechanics model can be applied to the specific case of which the crack length is known. In this study, the rock tensile strength is measured using fracture mechanics model, brazilian test and elastic model. The measured tensile strength by the fracture mechanics model is the largest and the elastic model is the smallest. This result is due to the size effect of the each test. And the tensile strength from the elastic model for hydraulic fracturing test can be used to estimate the in-situ rock tensile strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.693-696
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• 2008

The biaxial tensile strength of concretes was measured by the Biaxial Flexure Test(BFT) which was recently developed to measure the biaxial tensile strength of concretes. From the test result, The circular specimen is generally fractured after 1${\sim}$3 of the initial crack were formed on the top of specimen. The direction and number of the initial crack was completely arbitrary. As the specimen was larger, the number of the crack increased. And, the strengths of the different radii and thickness of specimens were calculated by the commercial finite element program to study the size effect of the biaxial tensile strength like the uniaxial tensile strength. The parameters such as radii to the support and to the load point, were studied using the program. The results of the FE analysis were entirely consistent with the predictive solution, when b/a>0.4, and the thickness of the specimens were increased. On the other hands, those with lesser free length showed good results.

• Geomechanics and Engineering
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• v.10 no.6
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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.

• Applied Microscopy
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• v.38 no.4
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• pp.339-345
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• 2008

In this study, we compared the stress and tensile strength of the hair treated with oxidative permanent dye with those of virgin hair. We investigated the fine structure of the hair section after the tensile test using scanning electron microscopy. The tensile strength of the virgin hair was measured as $14.66\;g/cm^2$, tensile energy was $108\;erg/cm^2$, and the maximum stress was 146.64g. Those of the dyed hair were $13.69\;g/cm^2$, $89.62\;erg/cm^2$ and 136.90 g, respectively. The differences in the tensile strength, the tensile energy and the maximum stress were $-0.97\;g/cm^2$, $-18.38\;erg/cm^2$, -9.74 g, respectively, which showed that the dyed hair had less elasticity and strength than the virgin hair. In the scanning electron microscopy investigation of the damaged hair after the tensile test, lift-off of the cuticle outer layer were shown in both virgin hair and dyed hair, which was more severe in the dyed hair than the virgin hair. Adjacent cuticular cells of the cuticle layer were separated by the destruction of intercellular membrane complex. The macrofibrils were exposed and separated from the cortex torn by tensile strength.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.115-119
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• 2013

The resistance spot welding of high strength steel degrades the weldability because of its high strength with rich chemical composition and coating layer to protect from corrosion. And the weld Expulsion is prone to occur and severely affect the nugget guality when the initial gap between automatic borrowing galvanied steel sheets(SGARC35) and Zn-coateel trip steels(GA580TRIP and GA980 TRIP) exist in resistance spot welding(RSW). RSW is one of the most popular welding processes used to join sheet metals. but weld guality sometimes do creases due to welding condition. in this paper to verity tue weldability using spot welding with the hemispherically concaved electrode, tensile shear strength and cross-tensile strength were measured by a universal test machine. in addition, the nugget size on cross-sectional area of the weld was observed by optical and electron microscopy. As a result, the nugget size of this specimen is increased with increasing welding current and Max load of tensile-shear strength is increased with welding current is increasing.