The ports, airports and coastal infrastructures that have been in service for a long time are increasing, but financial resources and the number of engineers for facility maintenance are limited. As important port, airport, and coastal infrastructure functions should be maintained, the strategic maintenance, renewal, and other measures to maintain such functions are strongly required. Therefore, we are trying to establish methods for structure design and material selection which are excellent in terms of maintenance, and will develop techniques and technologies regarding various countermeasures for maintenance phase.

Concerning technology for inspecting and diagnosing port structures, we examined various inspection and diagnosis techniques and inspection systems.

We conducted exposure tests on concrete, steel and other materials to evaluate their long-term durability.

We examined methods of evaluating the applicability of sustainable materials to marine environments.

Study on the implementation and operation of inspection and diagnosis techniques for developing the evaluation of marine structure performance. To study the use of underwater drones as an alternative to visual inspections, we tested their effectiveness in a survey of anode wear. During the test, we deployed underwater drones to measure the electric currents discharged from anodes while also visually inspecting them, and found that underwater drones could be a viable alternative to the conventional inspection method involving professional divers. However, the test also indicated that the efficiency of water drone surveys greatly depends on the skill of the operator. Another study we conducted focused on a monitoring method using an IoT-based inspection and diagnosis system. As part of this study, we selected a pier to survey the concentration of its salt accumulation and perform numerical analysis of the wind conditions underneath it in order to investigate effective positions for installing sensors on the surrounding marine structures. The results revealed that the spatial distribution of the accumulated salt concentration across the bottom surface of the pier might have been affected by the winds.

Research and development on techniques to deal with external disturbances affecting inspection equipment operation. As part of our study on the use of ROVs to inspect the superstructures of piers, we developed a prototype of a stationary positioning system (i.e., thrust adjustment, countersteering, etc.) utilizing the positioning function already implemented in the ROVs, which is one of the techniques used to deal with external forces. We also took our ROV designed for inspecting pier superstructures to the Ajigawa and Taisho areas of Osaka Port to conduct on-site surveys of bottom surface of pier superstructures, and successfully tested the effectiveness of the aforementioned stationary positioning function as the ROV hovered in waves in the actual port environment. In this connection, our published report, Development of a Pier Superstructure Inspection Robot and a Diagnosis Assistance System, which included the findings from this study, won the 4th Infrastructure Maintenance Award for Excellence (jointly sponsored by the MLIT and six other Ministries) in January 2021.

Exposure test on concrete, steel, and other materials to evaluate their long-term durability.We set up a long-term exposure test facility to examine a method of predicting concrete corrosion induced by chlorine, the cathodic protection characteristics that affect steel bars in reinforced concrete, the concentrated corrosion mechanism of steel components, and the cathodic protection characteristics present near LWL. We also acquired data on the durability of various wood materials in this study.

Development of a performance evaluation method applicable to protective coating methods used on marine structures. We have been continuously performing exposure tests (for 36 years) at the Hazaki Oceanographical Research Station (HORS) to examine various coating methods for protecting steel piles in order to establish a method for predicting deterioration applicable to protective-coated steel structures. In addition, we worked on elucidating the deterioration mechanism of petrolatum-coated structures based on the findings from our accelerated weathering and indoor exposure tests along with the aforementioned exposure tests conducted at the HORS. In addition, we conducted a survey on the superstructure of a pier that had been surface-coated 18 years ago to evaluate the durability of the protective coating (surface coating method) applied to concrete structures and to test the effectiveness of our deterioration prediction method.

Examination of productivity improvement methods applicable to concrete structures at ports.To promote the utilization of precast concrete materials in port structure construction, we created test specimens mimicking joint sections of pier-superstructure beams consisting of precast sleeve tubes and steel-pipe piles in order to perform a peak-to-peak alternating load experiment and numerical analysis. In this examination, we found that such joint sections possessed a superior energy absorption capacity compared to the conventional type of pier superstructure joints while maintaining a similar level of load-bearing capability. In terms of the method of connection between sleeve tubes and main steel bars, the experiment indicated that the stress would mainly occur around the folded sections of those components, and that the stress that was transmitted to the sleeve tubes and RC beams was not affected by the diameter-to-thickness ratio of the steel-pipe piles. In addition, we started performing accelerated deterioration and outdoor exposure experiments on PCa test specimens created by the PC mild-press-joint method in order to evaluate the durability of component joints.

Study on the effectiveness of the design and implementation of concrete pavement at airports. Steel nets are typically installed on the concrete pavements at airports to prevent the spread of cracks and maintain the integrity of the rebar joints underneath them, while preventing foreign objects from falling into the cracks. However, the effectiveness of this design and implementation method was yet to be proven, so we conducted a study for this purpose. For this study, we constructed a test pavement and compared its areas with and without steel-net covering to see if it would make any difference in terms of crack formation and stress generation, etc., but the comparison showed no significant difference.

On this research topic, our studies encompass evaluation of various performance indices of concrete components that utilize recycled materials (i.e., applicability, durability, etc.), organization of information on the performance requirements of port structures made of concrete (mainly unreinforced) and examination of various evaluation methods for assessing their long-term durability, and evaluation of the applicability of ecofriendly materials (especially recycled materials), etc. (While prior research mainly focused on durability, we are conducting a more comprehensive examination including their environmental effects such as CO2 emissions.)