PURPOSES : The purpose of this study is to experimentally analyze the flexural strength characteristics of cement mortar mixtures simultaneously incorporated with graphene oxide (GO) and polyvinyl alcohol (PVA) fibers, and to understand the composite effect of those on enhancing resistance against the initiation and progression of micro-cracks, as well as the control of macro-cracks in flexural behavior. METHODS : Cement mortar(w/c=0.5) specimens for flexural strength test, mixing 6 mm and 12 mm PVA fibers at 1% and 2% volume ratios, were fabricated. Additionally, specimens incorporating GO at a cement weight ratio of 0.05% were prepared for each mixture to analyze the effect of GO. Therefore total eight types of mixture were prepared. The fabricated specimens were subjected to flexural strength tests after curing in waterbath for 7 and 28 days. Concurrently, digital images for analyzing deformation in accordance with loading history were obtained at a rate of 20 Hz using the DIC technique. Through displacement and strain calculation via DIC, the flexural behavior characteristics of the mixtures combined with GO and PVA fibers were precisely analyzed. Furthermore, the composite effect on flexural behavior characteristics when GO and PVA fibers are incorporated was discussed. RESULTS : For the PVA fiber-reinforced cement mortar mixture, the incorporation of 0.05% GO increased the crack initiation load by up to 23%, and the maximum resistive load after cracking by up to 24%. Moreover, introducing GO into the PVA fiber-reinforced mixture increased the flexural strain just before cracking by approximately 30 to 50%, while the maximum resistive load after cracking exhibited similar strain levels with or without GO incorporation. Therefore, under flexural behavior, the integration of GO might delay crack initiation by increasing the strain concurrent with the rise in flexural stress before crack occurrence. It also seems to contribute to reducing crack expansion by synergistically interacting with PVA fibers after crack occurrence. CONCLUSIONS : It was experimentally examined that the flexural strength of PVA fiber reinforced cement mortar is improved by incorporating GO. Moreover, GO enhances resistance of crack occurrance and reduces crack propagation in combination with PVA fibers. This study suggests that simultaneous incorporation of GO and PVA fibers can synergistically improve the performance of cement composites.

For transport containers for radioactive wastes, a drop test should be performed at a height of 0.3– 1.2 m on a rigid target depending on the weight as a normal condition in the regulation. In the drop test, a strain gauge is commonly used to measure the local strain, and the position of the strain gauges is determined by the experiences of the engineer in advance of the test. For this reason, the strains can be measured at only predetermined points. The DIC (Digital Image Correlation) method using highspeed cameras can be used to measure the change in strain over the region of interest. In addition, it is possible to measure effectively even in areas with high strain gradients that are difficult to measure with strain gauges. Therefore, the DIC method can measure the strain change according to time over the entire load path. When the drop test of the transport container is performed, the impact load is delivered through the lower corner fittings-corner posts-upper corner fittings-lids. In this study, white spray was sprayed on these main load path, and black speckles were created on the spayed surface to trace the rigid motion of speckles. The images taken during the drop test can be used to create a strain field over region of interest.

Climate change is a very vital issue that can be no longer avoided. Korea has been a top-level country Iin dealing with carbon dioxide emissions since 1960. Many studies have been conducted to suppress or eliminate carbon dioxide emissions, which account for a large portion of greenhouse gases. Carbon Capture and Storage (CCS), the most practical method of them, plays a significant role. However, these methods have the disadvantage of the limits of geographical distribution and high possibility of re-emission into the atmosphere. Recently, ocean storage has been studied using Accelerated Weathering of Limestone (AWL), a technique for storing carbon dioxide in the ocean as an alternative to CCS, an underground storage. AWL is a method of converting carbon dioxide into concentrated water in the form of bicarbonate ion and discharging it to the ocean to dilute and store it. It does not cause re-emission to the atmosphere, and the discharged concentrated water increases the alkalinity of the ocean to prevent marine acidification. The objective of this study was to understand the behavior of DIC (Dissolved Inorganic Carbon) including carbon dioxide during the ocean discharge of bicarbonate ion concentrated water in AWL method. This study area was set near Ulleung-do where sufficient water depth and operational efficiency were secured. CORMIX model was used to calculate the material diffusion by submerged discharge using ship.