Xonotlite, with a chemical formula of Ca₆(Si₆O₁₇)(OH)₂, has been widely used as a thermal insulation material due to its high porosity and chemical/physical stabilities. As a potential recycle use of Xonotlite, CO₂ fixation is promising when considering its high alkali content and macroporous structure. In this study, Xonotlite was chemically activated to form nanocomposites of silica and calcium salt by optimizing an acid treatment. It was found that Xonotlite treated with acetic acid at 1.0 mol/L keeps the original macroporous structure of Xonotlite, and simultaneously segregates calcium salt on the surface of the residual silica. The nanocomposite of silica and calcium salt exhibits the capability of CO₂ fixation and high cycle stability thanks to the unique structural feature of the composite.

In order to prevent water pollution in closed waters such as inner bays and lakes, it is essential to establish a method to remove phosphorus and organic substances which cause water pollution. We have tried to give organic substances removal ability to a crystallization type phosphorus remover composed of gypsum and CaCO₃ by supporting useful microorganisms on the surface of the remover. In this study, the effects of loading micro-organisms derived from activated sludge on the water purification ability of the phosphorus remover were investigated. In addition, the effects of adding bamboo charcoal as a carbon source to the phosphorus remover on the adherence of microorganisms and the organic matter removal capacity were examined. The phosphorus removal material was obtained by mixing gypsum, CaCO₃ and bamboo charcoal in specified volume proportions. Microorganisms were loaded on the specimens by immersing them in activated sludge for 5 days. The microorganisms supported samples by immersing in activated sludge showed higher organic matter removal capacity than the non-microbial-supported sample. Furthermore, the bamboo charcoal-added samples were able to remove organic matter in a short time than the samples without bamboo charcoal. The phosphorus removal ratio of the sample after immersing in activated sludge was almost the same as that before immersion, but when the amount of bamboo charcoal added was excessive, the phosphorus removal ratio decreased drastically. This decrease in phosphorus removal ratio would be attributed to a decrease in the content of CaCO₃, which acts as a crystallization site for calcium phosphate, and to the coating of CaCO₃ exposed on the surface of the phosphorus remover by the adherence of a large amount of microorganisms due to the excessive addition of bamboo charcoal.

Rice husk is a byproduct of rice production. Appropriate burning the husk produces the rice husk ash containing amorphous silica as a main component. Currently, the ash is expected as a biomass resource. In the present study, the rice husk ash was used to prepare potassium silicate solution. Geopolymer materials were synthesized by a reaction between the potassium silicate solution and metakaolin. In addition, Si powder and a dispersing agent were added to the geopolymer precursor paste to prepare a porous material, and its applicability as a heat insulating material was investigated. Assuming application to heat insulating materials, the effects of alkali concentration in the potassium silicate solution on the curing rate and density were investigated, and the thermal conductivity properties were evaluated. As a result, the curing rate of the geopolymer precursor increased with increasing alkali concentration of the potassium silicate solution. As the concentration increased, in addition, the bulk density and the thermal conductivity decreased. It was found that the heat insulation performance of the porous geopolymer is controlled by adjusting the alkali concentration in the potassium silicate solution.

Fabrication of high Curie point (Tc) PTCR materials using BaTiO₃ (BT)-(Bi_1/2K_1/2)TiO₃ (BKT) ceramics was investigated. Fine powders of BT, which was synthesized by hydrothermal process, were used as starting materials. BT powders, Bi₂O₃, KHCO₃, TiO₂ and Gd(NO₃)₃ (water solution) were mixed with (C₂H₅O)₄Si by wet milling for 24 h. After drying, the powders were pressed into disks, which were diameter of 20 mm and thickness of 2 mm. These disks were sintered at 1130 – 1280 °C for 2 h in air. The samples containing 5 – 7 mol% BKT have the room temperature resistivity lower than 600 Ωcm, PTCR jump higher than 2.4 order of magnitude, and Tc higher than 175 °C. Especially, the sample containing 6 mol% BKT has the room temperature resistivity of 270 Ωcm, PTCR jump of 2.4 order of magnitude, and Tc of 185 °C and it was the excellent high Tc lead-free PTCR materials which was fabricated by firing in air.

Alumina-magnesium castable refractories are used for the inner walls of molten steel ladles. The main cause of damage to these refractories is thermal shock caused by rapid temperature changes during the loading and unloading of molten steel. Therefore, the thermal shock damage resistance coefficient R'''' is a parameter that expresses the resistance of refractories to thermal shock, and the evaluation of effective fracture energy is important for improving R''''. In this refractory, CaO·6Al₂O₃ (CA6) is formed from the raw materials alumina and alumina cement; CA6 has the advantage of inhibiting crack propagation and improving mechanical properties. On the other hand, CA6 has the disadvantage of volumetric expansion during formation. Therefore, microstructural changes caused by the formation of CA6 significantly affect the mechanical properties of refractories. In this study, CA6 was used as raw material and replaced with CA6 generated in-situ. The amount of coarse-grained alumina added was adjusted to control the microstructure. The effect of the microstructure change on the effective fracture energy was then evaluated. As a result, the effective fracture energy was improved in the sample with more coarse-grained alumina added, due to the replacement of CA6 aggregate.

Numerical simulation is one of the effective tools for the long-term stability assessment of underground structures. The reliability improvement of the numerical simulation requires precise constitutive equations to reproduce time-dependent behavior of rock such as loading-rate dependence, creep, and relaxation. These time-dependent behaviors of rock have nonlinearity between stress and strain rate and are influenced by surrounding environment. A number of constitutive equations have been proposed in previous studies; however, the equations based on the theory of linear viscoelasticity have difficulty reproducing accurately the time-dependent behavior of rock, and most of the equations based on the theory of viscoplasticity have been applied to the limited loading condition such as creep. In this article, nonlinear viscoelastic constitutive equations for rock proposed by the authors were introduced, and their exact solutions and application to experimental results were summarized. These equations can reproduce nonlinear time-dependent behavior and not only brittle but also ductile failures of rock and can be applied to the behavior under various loading conditions and experiment environment. In the equations, compliance or inelastic strain is assumed to be increased with time, but the functions and their combinations are of great variety. Hence, the differences of the solutions and applicability of the equations were detailed, and in addition future subjects were presented.

Synergistic effect of hydrogen and sulfur on intergranular (IG) fracture and resultant ductility loss in pure nickel was quantitatively evaluated by means of Auger electron spectroscopy, thermal desorption analysis and slow strain rate tensile test. Both hydrogen and sulfur enhanced IG fracture, leading to the degradation of ductility. Increased sulfur concentration at grain boundaries (GBs) resulted in an appearance of second peak around 400°C in TDA profiles, indicating that the segregated GB sulfur trapped hydrogen. However, its trapped hydrogen hardly enhanced the hydrogen-induced ductility loss. Instead, hydrogen directly trapped at GBs was responsible for IG fracture and degradation of ductility. These results indicate hydrogen and sulfur independently induced the IG fracture and resultant ductility loss and therefore, the synergistic effect is negligible.

For Japan, one of the world's leading “disaster-prone countries,” measures are required to reduce or prevent damage caused by disasters as much as possible to ensure the people's safe and secure lives. As a measure of that, developing a solid transportation infrastructure and a lifeline is indispensable. Against this background, this paper considers road-slanting surface countermeasures that assess the soundness of lifelines often constructed along roads, using the mountainous areas of Kochi Prefecture as a model. On that basis, we proposed a new "rock-fall countermeasure construction method" (from now on referred to as "ORN method") that is effective and highly versatile in preventing road slope collapse and rock-fall events. Specifically, we planned to increase the space between props so that it could be applied to valley-shaped slopes and to strengthen the potential absorbed energy by adding reinforcing ropes. In addition, the outline and design calculation results of this ORN construction method were presented, structural rationality was explained through the consequences of full-scale model experiments, and the effect of improving regional disaster prevention resilience by adopting the construction method was also mentioned

Sustainability is the keyword of the times. Resilience and CO₂ reduction are being focused in the construction sector. In general, the current structural design system does not include environmental impacts and cost. The purpose of this study is to investigate a feasibility of sustainability design, in which social, economic, and environmental aspects are taken into account, through case studies. Sustainability evaluation for the selection of bank materials in a flood control embankment construction project was conducted. From the study, it was found that stabilization and crushed soil made of cementitious materials is less expensive than mechanical stabilization, has higher utilization of excavated soil and uses fewer natural resources, but generates more CO₂ emissions. In a comparison between cement-based stabilizer and blast furnace slag cements, the stabilizing material is superior in terms of cost, CO₂ emissions, and natural resource consumption. It can be concluded that sustainability assessment is beneficial as the material selection is easy and a direction of technology development is clarified.