This paper describes the applicability assessment of light-element measurable energy dispersive fluorescent X-ray analyzers to estimate the chloride content of recycled fine aggregate produced from waste marine concrete. In this study, various types of chloride-containing recycled fine aggregate were prepared. Then, the water soluble chloride content and the total chloride content of each type of aggregate and its fluorescent X-ray intensity were measured by using non-treated samples of each aggregate and samples crushed to a size of less than 0.15 mm. It was found that the relation between the fluorescent X-ray intensity and the chloride content could be represented by one equation not dependent on the type of aggregate, and that the X-ray intensity had a high correlation with the total chloride content. Furthermore, it was determined that samples crushed to a size of less than 0.15 mm should be used in order to improve the estimate accuracy. Lastly, a procedure for the estimation of the chloride content of fine aggregate produced from waste marine concrete using a light-element measurable energy dispersive fluorescent X-ray analyzer was proposed.
In this study, bond stress behavior of corroded reinforced concrete was investigated by carrying out pull-out tests for RC specimens with different corrosion crack widths. Moreover, restraint stress of concrete was evaluated by expansion simulation using non-explosive demolition agent, and a restraint stress model equation for reinforced concrete with corrosion cracking was proposed. Bond strength was observed to decrease linearly as the restraint stress in the concrete decreases, and the degree of decreases was found to be almost the same regardless of the longitudinal corrosion crack widths at the concrete surface, the cover thickness and the diameter of the reinforcement. Furthermore, using the relationship between the bond strength and restraint stress in concrete, a bond strength model equation and bond-slip relationship model equation were proposed. The predicted values showed generally good agreement with the experimental results of other researchers.
This study evaluated the radiation shielding performance of high density (4.57g/cm3) concrete containers against gamma rays radiated from soil volume source contaminated by radioactive cesium (134Cs and 137Cs), through experiments and analysis. From the results of the experiment, it was demonstrated that high density cylindrical concrete containers with thickness of 100mm can reduce radiation dose equivalents emitted from the soil volume source contaminated by radioactive cesium by up to 90%. Good agreement was observed between the experimental and analytical values of shielding performance if the shielding of radiation from the background by the concrete container is properly taken into account. From the analysis, it was demonstrated that the difference between the shielding performances against point and volume sources can reach several tens of percent, although shielding performance against point sources is often used in shielding design.
The mechanical performance of many RC road bridge slabs constructed over the past several decades is decreasing. The application of the depth thickening method to the lower part of slabs is promising in terms of enhancing the mechanical behavior of damaged slabs. This research examines the damaged RC beam strengthening effect obtained by attaching a lattice-form CFRP with a joint and shotcreting polymer cement mortar. To study the mechanical behavior of RC beams attached with these reinforcing materials, static loading tests were performed with a number of variables such as the type of mechanical fastener, the number of rivets used for the purpose of fixation of the CFRP, the lattice number and length of jointed CFRP, the mechanical shotcreting methods of jointed part, and the type of polymer mortar. It is clear from the experimental results that the use of lattice-form CFRP for strengthening RC road bridge slabs is highly effective, especially when using a sufficient number of rivets that are well distributed, jointed CFRP, and a professional system for applying good-quality polymer mortar.