• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.1-7
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• 2018

As part of a research dedicated to the field evaluation of the durability of concrete subjected to freezing-thawing, this study analyzes the relationship between the surface roughness and the relative dynamic elastic modulus through image analysis. Four mix compositions with water-to-binder ratios (W/B) of 40%, 50%, 60% and 70% and without AE agent were considered to provoke early freezing. The basic physical properties of the mixes including the relative dynamic elastic modulus and the compressive strength were first evaluated experimentally according to W/B. Then, tests were performed to measure the surface roughness followed by photographs and SEM image analysis. The measured surface roughness tended to increase with larger number of freezing-thawing cycles regardless of W/B. The relative dynamic elastic modulus appeared to increase gradually with the number of cycles for the relatively denser mixes with W/B of 40% and 50%. Besides, the surface roughness increased only at rupture for the mixes with W/B of 60% and 70%. Moreover, the analysis of the photographs of the surface of the mixes with W/B of 40% and 50% revealed that the degradation progressed gradually from the surface with the freezing-thawing cycles. However, for the mixes with W/B of 60% and 70%, apparent change of the surface remained very insignificant until rupture at which damage like cracking could be observed. Consequently, the analysis of surface photograph or the measurement of the surface roughness presented some limitation in assessing the degree of freezing-thawing-induced degradation in case of relatively porous specimens. On the other hand, the photograph and surface roughness appeared to be sufficient for assessing such degradation for the mixes with W/B of 40% and 50%. Accordingly, the image of the surface and the surface roughness are potentially applicable on site for the assessment of freezing-thawing damages in relatively dense mixes.

• Korean Journal of Weed Science
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• v.32 no.1
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• pp.25-34
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• 2012

Characteristics related to grain quality and physiochemical components such as mineral, total amino acid, free amino acid, and free sugar composition were investigated in Protox inhibitor resistanttransgenic rice (MX, PX, and AP37) and its nontransgenic counterpart (WT). Head rice, palatability, protein, and whiteness (except for MX and AP37) of milled transgenic rice were high or similar to those of the non-transgenic counterpart. Immature rice, unfilled grain, and cracked kernels (PX and AP37) of milled transgenic rice were lower than those of its non-transgenic counterpart. However, there were no significant differences in damaged grain between the transgenic rice lines and its counterpart. Potassium content in PX and copper contents in PX and AP37 were only low compared with their non-transgenic counterparts, but other mineral contents in transgenic rice lines were high or showed no significant differences compared with non-transgenic counterparts. Contents of most total amino acid composition in transgenic rice lines were high or similar to those in non-transgenic counterparts, but the content of isoleucine in AP37 was only low compared with its non-transgenic counterpart. On the other hand, free amino acid, leucine and tyrosine in PX and AP37, and total free amino acid in PX were low compared with their non-transgenic counterparts. However, the content of free amino acid in other kinds in transgenic rice lines were similar to those in their non-transgenic counterparts. Contents of sucrose in MX and PX were low compared with non-transgenic counterpars, but contents of fructose, glucose, and maltose in transgenic rice lines were high or similar compared with their non-transgenic counterparts. This results indicated that Protox genes had no negative affect on the nutritional composition of rice.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.201-209
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• 2010

Generally, PSC girder bridge uses total gross cross section to resist applied loads unlike reinforced concrete member. Also, it is used as short and middle span (less than 30 m) bridges due to advantages such as ease of design and construction, reduction of cost, and convenience of maintenance. But, due to recent increased public interests for environmental friendly and appearance appealing bridges all over the world, the demands for longer span bridges have been continuously increasing. This trend is shown not only in ordinary long span bridge types such as cable supported bridges but also in PSC girder bridges. In order to meet the increasing demands for new type of long span bridges, PSC hollow box girder with H-type steel as compression reinforcements is developed for bridge with a single span of more than 50 m. The developed PSC girder applies compressive prestressing at H-type compression reinforcements using unbonded PS tendon. The purpose of compressive prestressing is to recover plastic displacement of PSC girder after long term service by releasing the prestressing. The static test composed of 4 different stages in 3-point bending test is performed to verify safety of the bridge. First stage loading is applied until tensile cracks form. Then in second stage, the load is removed and the girder is unloaded. In third stage, after removal of loading, recovery of remaining plastic deformation is verified as the compressive prestressing is removed at H-type reinforcements. Then, in fourth stage, loading is continued until the girder fails. The experimental results showed that the first crack occurs at 1,615 kN with a corresponding displacement of 187.0 mm. The introduction of the additional compressive stress in the lower part of the girder from the removal of unbonded compressive prestressing of the H-type steel showed a capacity improvement of about 60% (7.7 mm) recovery of the residual deformation (18.7 mm) that occurred from load increase. By using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and rehabilitation of PSC girders are relatively easy, and the cost of maintenance is expected to decrease.

• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.144-161
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• 2007

The studied Nangsan area is widely covered by the Jurassic biotite granodiorite, which is mainly light grey in color and medium-grained in texture. Results of the regional fracture pattern analysis for the granodiorite body are as follows. Strike directions of fractures show three dominant sets in terms of frequency order. The sets are in an order of a (1) $N80^{\circ}{\sim}90^{\circ}E$ (1st-order)>(2) $N70^{\circ}{\sim}80^{\circ}E$ (2nd-order)>(3) $NS{\sim}N10^{\circ}E$ (3rd-order). Spacings of the fractures are mostly predominant in less than 200 cm. Therefore, the granodiorite of the area has more potential for non-dimensional stones than dimension ones. And orientations of vertical quarrying planes can be also divided into two groups in terms of frequency $N14^{\circ}W{\sim}N16^{\circ}E$ (1st-order) and (2) $N78^{\circ}E{\sim}N88^{\circ}E$ (2nd-order). The orientations of the two groups are more or less different from those of the regional fracture patterns. These can be mainly attributed to the preferred orientations of microcrack developed in the quarries. Of physical properties, specific gravity, absorption ratio, porosity, compressive strength, tensile strength and abrasive hardness are 2.65, 0.28%, 0.73%, $1,628kg/cm^2,\;100kg/cm^2$ and 31, respectively. Contrary to the porosity, both granites of the Nangsan and Sogrisan areas show almost similar values of the abrasive hardness. These can be explained by the differences of Qz+Af modes, which can be regarded as an index for abrasive resistance. Meanwhile, it is anticipated that comprehensive understanding of the orientations of vertical quarrying planes and characteristics of various physical properties will be utilized as an important information for stone resources.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4602-4609
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• 2013

In summer and winter, the difference between the temperature during the day and that during the night is high, which leads to various problems during concrete placement, such as cracks and defects in the concrete as well as low durability and strength. Although nuclear power plant concrete is widely used for placement in all seasons, particular attention must be paid to its quality during the summer. Therefore, we evaluated the effects of a cooling method for mixing water, which is a commonly used hot weather precooling method, and the use of a retarder, on the characteristics of Nuclear Power Plant concrete. In the cooling method for mixing water, cold water at 5 was used, with 50% of the water content consisting of ice flakes. The effects of using a retarder were evaluated by reviewing the characteristics of the cement at the unset stage and after hardening. To evaluate the characteristics of the unset cement, we measured the slump, air volumes, setting times, and pressure strengths after hardening. Furthermore, we measured the heat of hydration at different temperatures; the loss of heat was minimized using insulation. Both the slump time and the complete ageing time of the air volume were found to be 120 min at $20^{\circ}C$ and 40 min at $40^{\circ}C$. In the case when the cooling method for mixing water was used and in the case when a retarder was used, the initial and final sets by penetration resistance were delayed, and the delay decreased with increasing air temperature. For the heat of hydration, the cooling method for mixing water not only lowered the maximum temperature but also delayed its attainment. However, the use of a retarder had no effect on the maximum temperature. Moreover, in the early ages (e.g., 3 and 7 days), the pressure strength of the concrete was lower than that of plain cement. However, the strength of 28-day concrete met the standard construction specifications.