On roads where deicer salt is sprayed, chloride is supplied only in winter and not in other seasons. The behavior of chloride penetration into concrete in such an unsteady environment has not been cleared, and the method of predicting future based on the measured data of the chloride ion distribution has not been standardized. Based on the above background, after actual states of spraying of the deicer salt and investigating of chloride penetration were organized, this study clarified the influences of type of salt used as deicer salt and seasonal behavior on chloride penetration in concrete. As a result, 2 types of NaCl and CaCl2 were sprayed as deicer salt at expressway in Hokuriku area, these salt types did not influence the chloride absorption on the mortar surface. In addition, the surface chloride ion concentration was high in spring and decreased from summer to autumn, and the chloride ion concentration distribution fluctuated depending on the season. Therefore, when the chloride profile after 100 years was predicted based on the data measured at summer and autumn, the corrosion occurrence time was estimated to be longer than the actual time. When water cement ratio was high, these phenomena were appeared conspicuously. Also it was verified that this tendency of seasonal fluctuation was similar in the actual data measured on one existing bridge, too.
Development of admixtures with wet curing effects has desired from the improvement of productivity and the labor saving of construction perspective. This study focused on latex used for the polymer cement concrete, and evaluated the influence of the amount of latex on the initial wet curing effect, the durability and the steel bar corrosion when using a small amount of latex. The main findings are: The concrete with latex whose an initial wet curing period was 3 days improved the surface unti-permeability and the mass transfer resistance, and was equal to or better than that of the normal concrete with the initial wet curing period of 7 days. Also the concrete with latex has preventing the macrocell corrosion of the steel bars.
The coefficient of linear thermal expansion of concrete is affected by the constituent materials. Coarse aggregate, which occupies about 40% of the concrete volume, is said to have a large effect on the coefficient of linear thermal expansion of concrete. The coefficient of linear thermal expansion of coarse aggregate is often measured using rock cores. However, it may be difficult to collect the rough aggregate core. Therefore, we examined a method for measuring the linear thermal expansion coefficient of coarse aggregate particles using a strain gauge. As a result, we clarified the influence of the measurement method on the measurement results and the coefficient of linear thermal expansion of the coarse aggregate particles. Specifically, the presence or absence of surface treatment on the coarse aggregate particles and the difference in the rate of temperature change have almost no effect on the measurement result of the coefficient of thermal expansion. In addition, the length of the strain gauge used has a slight effect on the measurement result of the coefficient of thermal expansion. Although the coefficient of thermal expansion of coarse aggregate particles of the same lot is different, the range is about 3 x10-6/°C. For chert and sandstone, it was revealed that the difference between the minimum and maximum principal strains is within about 25%. It was revealed that the coefficient of thermal expansion of limestone tends to be small on average of multiple particles, but there may be particles that shrink individually. The variation in measurement results differs depending on the type of coarse aggregate, and it is necessary to increase the number of measurements of coarse aggregate with large variation.
Pollen that invades through the opening by ventilation is a serious problem for hay fever patients. In this study, it was confirmed that pollen adsorption performance can be imparted to aluminum plates, galvalume steel plates, and vinyl chloride resin plates, which are building materials used around the openings, by applying a voltage and electrified them. Within the measurement range of this study, the surface potentials of the aluminum plate and the galvalume steel plate were almost uniform, but the surface potentials of the vinyl chloride resin plate were not uniform. In addition, the number of adsorptions increased as the absolute value of the output voltage increased for aluminum plate, galvalume steel plate, and vinyl chloride resin plate at all output voltages. The number of adsorptions of the aluminum plate was the largest at all output voltages and the number of adsorptions of the vinyl chloride resin plate was the smallest at all output voltages. The equation proposed in this study shows the relationship between the adsorption range and the adsorption amount by the aluminum plate at output voltages of 6 to 12 kV and -3 to -12 kV.
At Construction sites, curing sheets for temporary scaffolding is used to prevent the building materials from falling and dust from scattering. In this study, it was confirmed that by using the curing sheet whose inside is black with good transparency and whose outside is white that can keep the internal temperature low, it is possible to realize an environment with good transparency from the internal space and a low temperature in the internal space. Within the measurement range of this study, the white-and-black curing sheet has a lower internal temperature than the black and gray curing sheets, but the internal temperature is higher than that of the white curing sheet. Further, the white-and-black curing sheet has good transparency like the black curing sheet, and has better transparency than the white and gray curing sheets. The white-and-black curing sheet has a small change in the feeling of the internal space before and after the curing sheet is installed.
We investigated the occurrence of solvent cracking in unplasticized poly vinyl chloride pipes by preparing test materials based on the conventional method. As a results, it was confirmed that voids were occured on the inner surface of the pipe at holding time of 2 weeks under the conditions of room temperature (298 K), adhesive application amount 1.0 g and, U-band tightening torque 4 N/m. These voids were occurred linearly in the circumferential direction at the part in contact with the U-band and linearly in the axial direction at the part not in contact with the support materials. Tetrahidrofuran (THF) and 2-butane, and cyclohexanone were detected as a result of analysis of the void generation part on the inner surface of the pipe and the residual gas in the pipe. At these results, it is considered that the stress generated by the tightening of the U-band and the environmental agents THF, 2-butane, and cyclohexanone affected the void generation. Furthermore, the results of the stress analysis simulation of the U-band fixed portion showed that the tensile stress was in the part on contact with U-band and compressive stress was in the part not on contact with the support material. It was considered that the difference in these stresses and the regularity of the molecular arrangement during pipes manufacturing influence the direction of void generation. Such voids were considered to progress into cracks.
In recent years fatigue cracks have been detected in weld bead between deck and closed-section through-ribs in the orthotropic steel deck. Fatigue cracks are initiated from weld root toward bead surface. The authors have developed a new NDT technique termed “temperature-gap method” measuring a temperature drop due to thermal insulation by the crack using infrared thermography. In this study the applicability of the developed technique is investigated for shape evaluation of non-penetrating part of the weld bead penetrating fatigue cracks in the actual orthotropic steel deck. As a result, a high temperature gradient was observed at the non-penetrating part of the crack. The temperature gradient distribution tended to match the shape of the internal crack. The practicability of the temperature gap method to the shape evaluation of the non-penetrating part of weld-bead propagating fatigue crack was confirmed.
Modified 9Cr-1Mo steel is used for high temperature components such as steam turbine rotors because of its superior high-temperature property. Creep-fatigue damage progresses preferentially at stress concentration portions in the steam turbine rotors during cyclic start up- shut down operation. Therefore development of an accurate creep-fatigue failure life assessment method under multiaxial stress states at the stress concentration portions is necessary to maintain reliable operation. In this study, creep-fatigue tests using three kinds of round notch bar specimen on a modified 9Cr-1Mo steel and finite element(FE) creep analyses of the specimens have been conducted to clarify effect of multiaxial stress conditions on failure life. Larger life reduction of all kinds of notch specimen under the creep-fatigue tests than the fatigue lives was observed at lower strain range. Observation of notch root of the creep-fatigue damage specimens by a scanning electron microscope suggested that most of the creep-fatigue life was occupied by crack propagation up to 1mm from the notch root surface. Appropriate life prediction results were not obtained in the case of using the FE analysis results at the notch root surface. On the other hand, creep-fatigue lives of notch specimens were accurately predicted by applying the damage area rate concept, in which average creep-fatigue damage value was calculated within 1mm from the notch root surface, with both nonlinear damage accumulation model and ductility exhaustion theory.
Stress corrosion cracking is known to be affected by surface characteristics such as surface roughness, surface hardness and residual stress from past studies. As a processing for controlling such surface characteristics, shot peening capable of improving fatigue resistance and stress corrosion cracking resistance by imparting compressive residual stress are mentioned. In this study, we considered shot peening condition focusing on improvement of stress corrosion cracking resistance which is the purpose by shot peening. By using the response surface model of shot peened surface characteristics and robust optimization program created by MATLAB, optimal condition and robust optimal condition that can obtain effective surface characteristics to stress corrosion cracking are derived and compared. The conclusions were as follows: (1)Two kinds of robust optimization methodology can be used different depending on purpose and application. (2)The robust optimal condition in Ra and Rz from robust optimal program is selected larger coverage compared to optimal condition. (3)In RSm and Hv, optimal condition and robust optimal condition are almost the same.
Single-phase equiatomic high-entropy alloy (HEA); CrMnFeCoNi, exhibits high strength and ductility at room temperature and low temperature due to the effect of twinning. In this study, a concept of a bimodal microstructure design for HEA using powder metallurgy was proposed. Microstructures of the sintered compact fabricated from HEA powder mechanically-milled using SUJ2 balls were analyzed by EBSD. A network structure of fine grains (Shell), which surrounded the coarse-grained structure (Core), was formed in the HEA compact. The hardness of the HEA with bimodal microstructure were higher than the compact fabricated from as-received HEA powder, and the network structure showed high hardness than Core phase. Furthermore, W-rich surface layer was formed on the HEA powder mechanically-milled using WC-Co balls owing to the transfer of WC-Co balls to the surface of HEA powder during mechanical milling. A network structure of the W-rich phase, which surrounded the HEA phase, was formed in the compact fabricated from the mechanically-milled HEA powder. In particular, the hardness of compact fabricated from HEA powder mechanically-milled using WC-Co balls was high due to the high concentration of tungsten and formation of Shell phase. These results indicate that developed method can control the microstructure of HEA; grain size and elementary diffusion distributions.