Creation of a Foundation Contributing to Blue Carbon Ecosystems and Biodiversity Through Tidal Flat Construction

Toyo Construction Co., Ltd. (Headquarters: Chiyoda-ku, Tokyo; President and Representative Director: Tatsuyoshi Nakamura), in collaboration with JFE Steel Corporation (Headquarters: Chiyoda-ku, Tokyo; President and Representative Director: Masayuki Hirose), will begin a demonstration experiment on April 1, 2026, in the Marushima area of the Amagasaki-Nishinomiya-Ashiya Port in Hyogo Prefecture. This experiment aims at the regeneration and creation of a foundation that contributes to blue carbon ecosystems and biodiversity through the construction of tidal flats. In this demonstration, dredged cohesive soil will be repurposed as material for shallows*1, tidal flats, and submerged breakwaters, advancing the development of technologies that contribute to carbon neutrality.

Background of the Demonstration Experiment In recent years, it has become increasingly difficult to secure soil disposal sites for the dredged cohesive soil discharged during the dredging of navigation channels and anchorages necessary to maintain and expand port functions. Therefore, the effective utilization of this soil has become a pressing issue.

Overview of the Demonstration Experiment Dredged cohesive soil has high moisture content and is soft, making it difficult to utilize effectively as-is. It requires strength improvement through processes such as dehydration or solidification. While modification by adding cement is common in solidification processes, this demonstration also aims to confirm the applicability of using calcia-modified materials*2 for tidal flat construction to suppress CO2 generation. Therefore, calcia-modified soil*3 will be used as the foundation material for the tidal flats, and calcia artificial stone*4 will be used for the submerged breakwaters. Calcia-modified soil is attracting attention as a material expected to have turbidity-suppressing effects and strength-improving effects on dredged soil, without adversely affecting marine organisms, and is anticipated to improve bottom sediment quality. Furthermore, the design considers the effective use of resources by employing recycled and renewable materials for the construction of the tidal flats. For instance, piles and mats made from bamboo, a renewable resource, will be used to reinforce against sliding at the lower part of the submerged breakwater of the tidal flat and for maintenance piers.

Future Prospects In this demonstration experiment, we plan to collaborate with a nearby university to investigate the settlement status of seaweed and seagrass on the stone and bamboo materials, and to survey the amount of atmospheric CO2 absorbed and sequestered as blue carbon by marine plants. In addition to verifying the manifestation of tidal flat effects such as biodiversity, we are also considering its use as a site for environmental education and environmental research once the tidal flat effects have been established.

Moving forward, we will continue to contribute to the realization of a sustainable society by advancing demonstration experiments and focusing on the development of technologies that contribute to the realization of a carbon-neutral society.

*1 Primarily shallow water areas facing the coast *2 A material produced by adjusting the composition and particle size of converter-type steelmaking slag generated as a by-product of steel manufacturing *3 A material whose physical and chemical properties have been modified by mixing calcia-modified material into soft dredged soil *4 A material created by mixing a binder such as ground granulated blast-furnace slag into calcia-modified soil to increase its strength to the level of stone, which is then crushed after solidification