• Elastomers and Composites
• /
• v.32 no.1
• /
• pp.20-28
• /
• 1997

This study have Investigated the effect of various factors related to the physical properties of vulcanizated rubber compounds. rubber type, carbon black type and carbon black loading were selected as main factors and evaluation were tested by tables of orthogonal arrays with 3 factors and 3 levels. rubber types have affected cure time, tensile strength, and $T_g$ as main factor and carbon black loading have affected viscosity, scorch time, maximum torque, hardness, 300% modulus, rebound, heat build-up, $0\;&\;60^{\circ}C$ tangent delta, PICO and CUT/CHIP loss as main factor but the effects of carbon black type have affected only bound rubber content.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.2 no.2
• /
• pp.115-127
• /
• 2014

Addition of fibers in cement or cement concrete may be of current interest, but this is not a new idea or concept. Fibers of any material and shape play an important role in improving the strength and deformation characteristics of the cement matrix in which they are incorporated. The new concept and technology reveal that the engineering advantages of adding fibers in concrete may improve the fracture toughness, fatigue resistance, impact resistance, flexural strength, compressive strength, thermal crack resistance, rebound loss, and so on. The magnitude of the improvement depends upon both the amount and the type of fibers used. In this paper, locally available waste fibers such as coir fibers, sisal fibers and polypropylene fibers have incorporated in concrete with varying percentages and l/d ratio and their effect on compressive, split, flexural, bond and impact resistance have been reported.

• Journal of Welding and Joining
• /
• v.11 no.1
• /
• pp.42-51
• /
• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• Advances in concrete construction
• /
• v.8 no.4
• /
• pp.321-333
• /
• 2019

The present study targets to access the consequence of utilization of coarse aggregates retrieved from waste concrete as a substitution of coarse fraction of natural aggregates and silica nano-particles as partial substitution of cement using principles of factorial design. Furthermore, procedures of design of experiments are employed to examine the effect of use of recycled aggregates and nano-silica. In this investigation, compressive strength found after at 7, 28, 90 and 365 days, split and flexural tensile strength, ultrasonic pulse velocity and rebound number and are chosen as responses, whereas the percentages of recycled coarse aggregates (RCA%) and nano-silica (NS(%)) are selected as factors. Analysis of Variance has been conducted on the experimental results for the selected responses with consideration the both factors, which indicates that RCA (%) and NS (%) have substantial impact on the various responses. However, the present analysis depicts that interaction between factors has considerable effect on the chosen parameters of concrete. Furthermore, validation experiments are carried to validate these models for compressive and tensile strength for 100% RCA and 1% NS. The results of comparative study indicates that that the error of the estimation determined using the relevant models are found to be small (±5%) in comparison with the analogous experimental results, which authenticates the calculated models.

• Proceedings of the KSR Conference
• /
• 2008.11b
• /
• pp.928-934
• /
• 2008

Resently, Fiber Reinforced Concrete is used for not only preventing crack of concrete but also reinforcing general methods. Steel Fiber and PP(poly-propylene) Fiber are usually used as fiber reinforced materials. However, using these materials for shotcrete on Railway tunnel can cause some problems such as damage of pressure hose and shotcrete rebound. In addition, Steel fiber is an expensive material and it can cause safety problems during applying to shotcrete. PP Fiber can cause a problem in fiber balling during applying to shotcrete railway tunnel construction. A purpose of the research is applying a development of PET(Poly Etylene Terephtalate) fiber by recycling pet bottles to the shotcrete tunnel exposed to explosion spalling. To investigate the reinforcement effect of the PET fiber, some basic tests are accomplished to physical properties and explosion spalling by fire. As a result of the tests, a concrete mixing the PET fiber has stronger resistance effect in the explosion spalling by high temperature than another strong fiber concrete does, and that the former concrete is also equal or more effective on the result of the above tests to physical properties like compression and strain than the latter one is demonstrated.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.33-40
• /
• 2021

Measuring the compressive strength of concrete is a very important factor in the safety review of concrete structures. Concrete compressive strength measurement methods include destructive and non-destructive methods. The destructive method includes the uniaxial compression failure method, and the non-destructive method includes the rebound hardness method and the elastic wave measurement method. In this study, the type of measurement method and the effect of reinforcing bars inside the concrete were tested to examine the relationship between them. Regardless of the type of specimen, the average compressive strength by the elastic wave measurement method among the three experimental methods was greater than the average compressive strength by the other methods. When the specimen type is the same, the standard deviation of the measured values of the elastic wave measurement method is smaller than that of the other measurement methods, so it can be seen that the elastic wave measurement method does not show large variance in the measured values compared to the other two measurement methods. When the average compressive strength according to the test method for each specimen was compared with the average compressive strength of the compressive failure test method, the average compressive strength was measured to be high in the order of the elastic wave measurement method, the compression failure test, and the rebound hardness method. Since the measured values of the compressive strength of concrete are different depending on the method of measuring the compressive strength of concrete and the presence or absence of reinforcing bars inside the concrete, further research is required considering the effect of various concrete covers.

• Tunnel and Underground Space
• /
• v.10 no.4
• /
• pp.526-532
• /
• 2000

The uniaxial compressive strength of rock mass is known as the major factor in the assessment of drillability and the optimum excavation design in full-face tunnel excavation by TBM. Referring to worldwide cases, TBM has been applied mostly to the rock mass within the strength range of 80~250 MPa. Recently, a water way tunnel has been constructed as a part of Milyang dam project by TBM within the rock masses where the rock type is mainly granite with some granophyre, hornfels and andesite. Their uniaxial compressive strengths in extended area are estimated higher than 260 MPa. In this paper, the relation between the penetration rate and the rock mass properties is analyzed and TBM application to the very hard rocks is discussed. As a result that three suggestions to predict the TBM net penetration rate are analyzed, NTH method seems a better approach than other methods in the extremely hard rocks. NTH prediction matches with the results of actual values with the variations of 2~20%. Hardness measurement by Schmidt hammer and RMR estimation are carried out along the L = 5.3 km entire TBM tunnel alignment. The net penetration rate measured monthly is shown to be reciprocally proportional to Schmidt rebound hardness and RMR where coefficients of correlation, $R^2$are 0.705 and 0.777 respectively. As a result, they are good quantitative indices for the prediction of TBM net penetration rate in the extremely hard rocks. Magnitude of in-situ stress has a certain effect on TBM performance, and it is required to measure the in-situ stresses in TBM excavation design.

• Journal of Ginseng Research
• /
• v.31 no.4
• /
• pp.175-180
• /
• 2007

To evaluate whether there is a relation between Korean red ginseng (KRG)-intake and the suppression of immune hyperactivation in HIV-1-infected patients, we measured serum soluble CD8 (sCD8) over 31-48 months in 168 patients. They were divided into four groups; HIV-1-infected control (n = 49), zidovudine (ZDV) group (n = 22), KRG group (n = 48), and combination of KRG and ZDV group (n = 49). In control, sCD8 and the ratio of sCD8/CD8+ T cells significantly increased by 33% (paired t-test, P < 0.05) and 54% over $21\;{\pm}\;13$ months (P < 0.001), respectively. In ZDV group, sCD8 decreased within first 6 months and then showed steady increase and the ratio also increased over $19\;{\pm}\;10$ months. In KRG group, sCD8 and the ratio of sCD/CD8+ T cells continuously decreased by 45% (P < 0.01) and 19% over $19\;{\pm}\;11$ months (P < 0.05), respectively. In combination group, sCD8 gradually decreased by 29% (P < 0.01). There was a clear difference in the changes in serum sCD8 over time among 4 groups. There was no rebound phenomenon in KRG group as shown in ZDV group. These results suggest that KRG-intake suppresses immune hyperactivation state by HIV antigen itself in the HIV-infected patients.

• Journal of Distribution Science
• /
• v.13 no.9
• /
• pp.13-18
• /
• 2015

Purpose - This study investigates the effects of thought suppression on depression and uneasiness among college students likely to be influenced by smart phone addiction. Research design, data, and methodology - A total of 151 valid questionnaires were collected. The following analyses were conducted using SPSS 19.0 and AMOS 19.0: frequency, descriptive statistics, correlation, simple regression, and multiple regression. Results - Smart phone addiction increased uneasiness, depression, impulsiveness, and aggression. Moreover, uneasiness, depression, impulsiveness and aggression from smart phone addiction, had a negative influence on psychological wellbeing resulting in potential delinquent behavior. In addition, the addiction treatment relied heavily on drugs; therefore, such psychological treatment should be strengthened to control intermittent addiction. Conclusions - The results indicate that various kinds of research are needed to investigate personality and environmental factors that influence smart phone addiction. Additionally, studies on lessening smart phone addiction and living healthy lifestyles are needed. Moreover, psychological rehabilitation and treatment should be developed to lessen the rebound effect after thought suppression, to verify the effects of clinical application, and to prevent intermittent addiction.

• Explosives and Blasting
• /
• v.28 no.2
• /
• pp.59-68
• /
• 2010

Building demolition and blasting work in urban areas has a possibility which has an effect on the structural stability of nearby structures. In this study, the compressive strength and chemical composition of decrepit concrete materials were estimated by Schmidt rebound test and XRD phase analysis. The damage index of the concrete materials was calculated by measured P-wave velocities. It was revealed that the constituents of the concrete materials affect on the compressive strength. The damage index decreases with increasing compressive strength and decreasing impact energy.