Aiming at the structural application of ultra-high-strength synthetic fiber reinforced concrete (PVA-UFC), which can reduce the weight and extend the service life of structures, a trial design of a superstructure was conducted assuming the replacement of an actual bridge, and the performance was confirmed through loading tests on the test-designed girder. High-strength steel bars were used for the main bars, and the limit value was set higher than usual. However, the crack width remained within a range that poses no durability issues owing to the crack suppression effect of the fibers.

This paper investigates the capacity curves for the structural design of reinforced concrete (RC) columns with wing walls. This RC column with wing walls is characterized by joints without reinforcement between the column and wing walls, and horizontal slits at the bottom of the wing walls. In evaluating the initial stiffness, stiffness decreasing rate, and rigid zone, the influence of the horizontal slits can be disregarded due to their minimal impact on the results. The flexural ultimate strength is determined by summing the ultimate bending moments of both the column and the wing wall at their upper end, and the ultimate bending moment of the column at its base. The findings from this study enable the establishment of an appropriate capacity curve for structural design.

In this study, we investigated the influence of the type of post-added chemical admixture on the properties of plasticized concrete controlled by slump flow. The change in slump flow (SF) over time was smaller for chemical admixtures with a smaller SF increments per addition ratio, and setting time tended to be delayed as SF increments from the base concrete increased. In this experiment, the plastic viscosity of mortar taken from plasticized concrete was higher when using admixture including viscosity agents (VSP, VSPF). Additionally, it may be possible to secure frost resistance by increasing the air volume after plasticization to 5% or more, or by using a post-added admixture that includes an air-entraining agent.

To treat decontamination equipment sludge generated from contaminated water at the Fukushima Daiichi Nuclear Power Station using alkali-activated materials (AAM), we solidified barium sulfate powder (BS) and potassium hexacyanocobalt(II)-ferrate(II) powder (FCN) with AAM, and investigated appropriate compositions that meet standards of properties. First, solidified bodies were produced while controlling the H₂O/base ratio, Si/Al molar ratio, and Na/Si molar ratio. When the base materials consisted of metakaolin and blast-furnace slug, several appropriate compositions were identified, and two concentrations of solutions were found to produce solidified bodies that meet standards of properties. Next, using solutions with these concentrations, we produced solidified bodies while controlling the amounts of BS, BS+FCN, and H₂O. The maximum usable amount of BS+FCN in appropriate compositions was greater than the maximum usable amount of BS when used alone.

In this study, we investigated a method to visualize the stress state of a GFRP sheet we developed, focusing on the phenomenon in which the GFRP sheet changes in appearance from a transparent state to a white turbidity state under stress. Tensile and bond tests were conducted on the GFRP sheet. In the tensile test, the weft fibers became turbid in response to tensile stress. In the bond test, the warp fibers became turbid before debonding, and the weft fibers became turbid after debonding. We conducted verification experiments and inferred that the mechanism behind the opacification was the generation of cracks inside the fiber bundles due to tensile stress acting in the direction perpendicular to the fiber bundles. Digital image analysis was used to calculate the turbidity rate from the turbidity area of the GFRP sheet, and a high correlation between the opacity rate and strain was found in both the tensile and bond tests.

Surface protection methods are primarily employed to mitigate sulfuric acid-induced deterioration in sewerage facilities. While laboratory-scale accelerated testing has been conducted to examine the sulfuric acid resistance of surface protective coatings, little research has been done in actual facilities, and the mechanism of sulfuric acid penetration and structural deterioration remains unclear. This study investigated the effects of surface protective coatings in actual facilities with approximately 20 years of service to shed light on the long-term deterioration mechanism. A series of analyses revealed that, in environments where sulfuric acid is present, the acid can penetrate the protective coating material and gradually deteriorate the underlying concrete. Furthermore, the pH drop caused by sulfuric acid was observed to extend beyond the neutralization depth zone, affecting the structural integrity of the hardened concrete.

In extrusion-based 3D concrete printing technology, a reinforcement method for 3D printed mortar is required because mortar generally has low tensile strength and cannot be used on its own for members subjected to tensile stress. In this study, continuous fiber reinforced mortar was printed by extruding continuous reinforcing steel fiber simultaneously with the mortar, and beam specimens with continuous fibers oriented in the axial direction were fabricated. The structural performance of the specimens was investigated by conducting bending tests, and the experimental results were compared with numerical calculations to evaluate the effect of reinforcement with continuous fibers. The results showed that the mortar beams reinforced with continuous fibers exhibited increased flexural capacity equivalent to the calculated values.