Authors have been studying for eight years as for the effective utilization of sludge water produced in ready mixed concrete plants due to washing of a mixer, agitating truck dram etc. Nowadays, JIS A 5308 permits the usage under 3 percent as solids of sludge for the unit content of cement of new concrete. Recently, it is strongly requested to re-use a further large quantity of sludge water, in order to achieve the zero-emission. Sludge water consists of cement, fine particles of aggregate and water. All materials are one of the constituents of concrete. This study, in order to utilize the larger quantity of sludge water than that now allowed, is to verify the mix design of concretes containing sludge which has identical slump and compressive strength to comparative concrete. From the results of this study, it became clear that as for the lean mixture concrete containing stabilized sludge within the range of 3-15%, there was no problem about slump and compressive strength. It was possible to design the concrete of identical slump and compressive strength to comparative concrete. It was also confirmed that the bulk volume of coarse aggregate was available for the design method of concrete mixture.
The purpose of present paper is to study the influence of the properties, such as thickness or Cl− diffusivity, of Interfacial Transition Zone (ITZ) between aggregate (fine and coarse aggregate) and cement paste. To accomplish this propose, the evaluation methods for determining the thickness and the Cl− diffusion coefficient of ITZ were developed. Subsequently, these methods were used in the investigation to assess the influence of aggregate size on the thickness and the Cl− diffusivity of ITZ formed. Moreover, the influence of ITZ formed around fine and coarse aggregate on the Cl− diffusivity in concrete was clarified using the data obtained by above methods.
In recycling the sand originally produced from glass waste as a fine aggregate for concrete mixture, their alkali-silica reactivity and alkali-leaching ability are very important from the view-points of the long-term stability of the recycled glass sand in concrete. In this study, the alkali-silica reactivity of four types of glass sands was comparatively investigated according to the chemical method, JIS A1145, and three types of mortar bar methods, JIS A1146, ASTM C1260 and Danish method. Also, the amounts of the alkali ions, Na+ and K+, released from the sand itself in the saturated calcium hydroxide solution at 38°C was periodically measured. From the results of experiment, it was found out that the alkali-silica reactivity of recycled glass sands could not be properly determined by the chemical method because of relatively large amounts of alkali ions released from the sand itself during the test, and that the expansion behavior of mortar bars in accelerated curing conditions significantly changed depending on both the chemical compositions and the internal texture of glass sands used. Finally, the mitigation method of alkali-silica reaction by using fly ash or glass powder was discussed.
It is important to establish the verification method of load carrying capacity of RC flexural member deteriorated by the corrosion of reinforcing steel. Most of studies on the influence of reinforcement corrosion on load carrying capacity have focused on the corrosion of longitudinal tensile reinforcement in RC flexural member. However, not only the corrosion of longitudinal tensile reinforcement, but also that of longitudinal compressive reinforcement and/or lateral confinement will affect the load-carrying behavior of RC flexural member. In this paper, influences of the corrosion of longitudinal compressive reinforcement and lateral confinement on uniaxial compression behavior of confined concrete, that is the component of RC flexural compression zone, are investigated. As a result, it becomes clear that the corrosion of longitudinal compression reinforcement decreased the elastic modulus and compressive strength of confined concrete, and the corrosion of lateral confinement decreased the elastic modulus. On the other hand, the corrosion of confinement did not decrease the compressive strength, because of horizontally oriented crack due to corrosion of confinement. Furthermore, the corrosion of confinement reduced ultimate strain of confined concrete due to its rupture because the elongation of confinement was decreased by corrosion. Additionally, the calculating method of the ultimate strain of confined concrete based on strain energy balance concept was shown, where the reduction of elongation owing to the corrosion of confinement was taken into consideration.
It was obtained that compressive strength of concrete with low-quality recycled aggregate could be improved by oscillation of mixture inserting vibrators. Therefore, to evaluate properties of cracking in recycled aggregate concrete with the oscillation, compression test in concrete of recycled aggregate is conducted, applying AE measurement. As the results, compressive strength of recycled aggregate concrete with the oscillation is increased more than 10% with comparing to the concrete mixed by non-oscillation of mixture. From relationship between ratio of cumulative AE hits and load level, it is clarified that increasing of micro-cracking in recycled aggregate concrete is observed at lower stress level than normal concrete, but cracking of recycled aggregate concrete with the oscillation is similar as normal concrete. By applying the b value and Ib-value, it is recognized that scale of macro-cracking and failure in recycled aggregate concrete is larger than normal concrete, and recycled aggregate concrete is recovered by the oscillation.
This paper describes relationships between physical properties, mechanical properties and performance of NOx remediation of mortar incorporating titanium dioxide powder, and incorporating ratio of the powder. Physical properties such as a mortar flow and an air content were investigated by controlling dosage of a high-range water-reducing and air-entraining agent and of an air-entraining agent. Compressive strength, tensile strength, flexural strength and modulus of elasticity of the mortar decreased slightly with increase of the incorporating ratio of the powder. However, ratios of tensile and flexural strength to compressive strength, and Poisson’s ratios of the mortars were almost constant if the incorporating ratio changed. The mortar with the incorporating ratio of 15% showed about 30% of NOx remediation ratio. Performance of the NOx remediation had an effect of the incorporation of the powder. The mortar investigated in this study can be expected to apply to concrete structures such as a handrail, large scale pavement and a box culvert because of a high strength and a performance of NOx remediation.
The strain-induced self-assembly of islands in heteroepitaxial systems is a promising approach to the fabrication of quantum nanostructures for optoelectronic devices. In this study, a phase-field model which can simulate the growth process of self-assembled SiGe/Si quantum dots during deposition is developed. The novel feature of this model is that it can simulate the morphological changes of islands, i.e., from single-faceted pyramid to multifaceted dome, by taking a high anisotropy and a sixteen-fold anisotropy of surface energy into account. By using the developed model, two-dimensional simulations are performed on a large computational model. As a result, island nucleation on the surface of a wetting layer, island morphological change and Ostwald ripening due to an interaction between two neighbor islands were well reproduced. The bimodal distribution of island size, which is a very important phenomenon in self-assembled quantum dots, could also be generated. Furthermore, it is clarified that the bimodal distributions are largely affected by island morphological change from pyramid to dome. The variations of island size and energy variations are estimated for single island in detail. As a result, it is concluded that the island morphology transitions occur so as to reduce the elastic strain energy.
Both the electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) methods were used to investigate the active slip systems and crack initiation behavior in an austenitic stainless steel, SUS316NG, fatigued to one-fourth of the fatigue life under cyclic torsional loading. Most of the active slip systems under torsional loading took place on the primary planes with the largest Schmid factor. Fatigue cracks observed on the surface were classified into four types : GB (grain boundary), TB (twin boundary), SB (slip band) and TC (transcrystalline) cracks. The density distribution of TC cracks was maximum, followed by those of GB, SB, and TB cracks. The development of the surface topography due to fatigue was studied by AFM examination of replicated surfaces of the specimen. On the basis of EBSD and AFM observations, the following four parameters were measured : h, the depth of intrusion vertical to the surface ; S, the slip displacement ; SA, the component of slip displacement parallel to the surface ; SB, the component of the slip displacement perpendicular to the surface trace. Both h and SB values showed a sharp increase at the onset of crack initiation. The critical values of h and SB at crack initiation were 160nm and 170nm, respectively.
High power spallation targets for neutron sources are being developed in the world. Mercury target will be installed at the material and life facility in J-PARC, which will promote innovative science. Pressure waves will be generated in mercury by thermally shocked heat deposition when the high intense proton beams bombard the mercury target. Cavitation will be induced through the pressure wave propagation in the mercury and eroded the vessel inner surface contacting with the mercury. The eroded vessel wall is damaged by cyclic fatigue because pulsed proton beams strike the target repeatedly. It is, therefore, important to investigate the fatigue strength of the eroded vessel wall. Actually, the erosion and fatigue damages will be imposed on the vessel wall at the same time. In order to precisely investigate the effects of damages, at the first, the pitting damage by erosion was evaluated against the number of pulses, and then the fatigue test was carried out using the specimen with a certain pitting damage.
Round bar specimens of short glass fiber reinforced polybuthyleneterephthalate (PBT) were fatigued under axial-load controlled conditions with six different stress ratios including negative ratio. The tensile mean stress decreased the fatigue strength at a constant fatigue life and the modified Goodman relation gave a dangerous estimate for stress ratios larger than 0.7. The relation between the fatigue strength and the mean stress was expressed by Gerber parabolic relation except that the strength at zero mean stress was equal to the creep strength, but not to the tensile strength. A new method for predicting the mean-stress effect on the fatigue strength was proposed by using creep data and the fatigue strength at one stress ratio. Under cyclic loading with high mean stresses, the creep phenomenon became predominant and the ratcheting deformation increased with the number of cycles. The ratcheting deformation became larger for larger mean stresses at the same stress amplitude and for larger stress amplitudes at the same mean stress. The compliance of the specimen increased with the number of cycles. Fatigue cracks started from the center of the specimen and propagated outward. Fractographic observation revealed the feature of fatigue fracture surfaces made under high stress ratios resembled those of creep fracture surfaces, showing ductile extension of plastic matrix. On the other hand, fatigue fracture surfaces under low stress ratios were rather flat accompanied by pull-out of fibers.
This paper presents the effect of post-cure time on mechanical properties of plain woven glass/vinylester composites. The post-cure of composites was carried out by means of the post-cure duration at the constant temperature 80°C for 4, 8, 16, 24h. The mechanical properties such as Vickers hardness of resin, storage modulus, loss modulus, glass transition temperature, flexural strength and modulus were measured for plain woven GFRP laminates after 80°C post-cure treatment at times ranging from 4h to 24h. It was found that the post-cure treatment improved the dynamic viscoelastic properties and the mechanical properties of plain woven GFRP laminates except for the type of the prolonged post-cure time such as 24h. The shrinkage of the laminates appeared in only the transverse direction after post-cure. Then, the microscopic observation was carried out in order to estimate the degree of internal damage in plain woven GFRP. Delamination occured in the laminates of the type of the low post-cure time as 0h, 4h and the prolonged post-cure time as 24h. Matrix cracking occured in the laminates cured at 80°C from 8h to 16h. It was suggested that the post-cure accelerated the cross-linking reaction in plain woven GFRP laminates. In addition, it was shown that the adhesive strength of the fiber-matrix interface increased by means of post-cure. It was also found that the prolonged post-cure time has weakened the adhesive strength of the fiber-matrix interface.
In this study, a mechanically polished Ni-Ti alloy was subjected to isothermal oxidation (TO) in N2-20vol.%O2 at temperatures ranging from 300 to 800°C. TO-treated surfaces were then characterized by field emission type scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDX), X-ray electron spectroscopy (XPS) and X-ray diffraction (XRD). Electrochemical corrosion tests were also carried out using a three electrochemical cell connected to a computer driven potentiostat. Results showed that Ni-Ti alloy exhibited different oxidation behavior depending on the treatment temperatures. A Ni free layer was observed in the oxide layer for the specimens TO-treated at temperatures 500°C and above. Specimens TO-treated at temperatures ranging from 300 to 500°C showed higher corrosion resistance compared to that of the surface finished by polishing. This was because the TO-treatment created a thick oxide layer with an amorphous structure. Specimens TO-treated at above 600°C showed very low passive current densities, but lower pitting potential. This was because these samples were covered with crystalline oxide. Consequently, the TO-treatment at 500°C produced a smooth protective nickel free oxide layer, which contributes to good biocompatibility of Ni-Ti implants.