Japan SEA Works Co., Ltd.

Japan SEA Works Co., Ltd. (日本海上工事株式会社) is a Japanese marine civil engineering and special survey company headquartered in Bunkyo, Tokyo. It was established on 4 June 1965 as a specialist survey firm skilled in cylindrical boring surveys, and two years later added a hydraulic asphalt division, forming the two-pillar structure that still defines its business. The company is a member of the Kajima and Kajima Road Group, and describes itself as having supported the safety and security of people's lives for more than 60 years through asphalt mats, coastal civil engineering, and survey operations. The company's signature technology is the asphalt mat, developed with proprietary know-how. According to the company, these mats are both tough and flexible, have withstood the tsunamis of repeated major earthquakes, and have demonstrated long-term durability of more than half a century. They are used for purposes including friction enhancement (KAM), scour prevention, suction prevention, and other applications that contribute to "resilience" of coastal structures. Beyond asphalt mats, Japan SEA Works provides asphalt mastic, NK Stoppers for joint waterproofing, high-durability epoxy adhesives such as KS Bond and KS Bond Type M, penetrating KS Primer and KS Primer II, and special concretes including Hydrocrete (underwater non-separating concrete) and NV Concrete (high-fluidity concrete), as well as surface protection such as FL Coat. Its survey business covers marine surveys, surveys of underground buried objects and cavities, and exploration for buried unexploded ordnance. Its coastal civil engineering works include public infrastructure and large-scale facility projects. Past major projects cited by the company include work related to the Honshu-Shikoku Bridge project, the Isahaya land reclamation closure works, nuclear power plant seawall works, marine structure reconstruction after the Great Hanshin-Awaji Earthquake, the Shikoku Electric Power Tachibana Bay Thermal Power Station outfall project, and marine structure reconstruction after the Great East Japan Earthquake, along with projects along coastlines throughout Japan. Japan SEA Works operates nationwide in Japan, with offices and worksites in Sapporo, Akita, Niigata, Chiba, Kyushu (Fukuoka), and Miyazaki, plus a Technical Research Laboratory in Chofu, Tokyo, within the Kajima Technical Research Institute. It also states that it has expanded overseas. Its stated corporate philosophy is to provide safety and security for the national land through proprietary technology and to contribute to comfortable living and a pleasant environment through its business. Looking ahead, the company positions itself around coastal disaster mitigation, national land resilience, and global warming countermeasures, and aims to contribute to environmental improvement through carbon-neutral initiatives. Its representative director and president is Kazutoshi Iyose (伊星 一俊).

Japan SEA Works Co., Ltd. was established on 4 June 1965 as a special survey company specializing in cylindrical boring surveys. Two years later, it added a hydraulic asphalt division, creating a two-division structure that formed the backbone of the company. From there it expanded into special concrete and high-durability epoxy adhesive businesses. The company is a member of the Kajima and Kajima Road Group, and has operated for more than 60 years, reaching its 60th anniversary on 4 June 2025. Over its history, the company has participated in major public works and large-scale projects. These include work related to the Honshu-Shikoku Bridge project, the Isahaya land reclamation closure works, nuclear power plant seawall works, marine structure reconstruction after the Great Hanshin-Awaji Earthquake, the Shikoku Electric Power Tachibana Bay Thermal Power Station outfall project, and marine structure reconstruction after the Great East Japan Earthquake, as well as projects along coastlines throughout Japan. Its proprietary asphalt mat technology has been a core business. According to the company, the mats are tough and flexible, have withstood the tsunamis of repeated major earthquakes, and have demonstrated long-term durability of more than half a century. In recent years, the company has focused on businesses that contribute to coastal disaster mitigation, national land resilience, and global warming countermeasures, and it aims to contribute to improving the living environment through carbon-neutral initiatives. It operates nationwide in Japan and has also expanded overseas.

• 2025

  Celebrated 60th anniversary.

• 1967

  Added a hydraulic asphalt division, forming a two-division structure.

• 1965

  Company established as a special survey company specializing in cylindrical boring surveys.

Specialist marine civil engineering and survey firm within the Kajima Group, positioned around proprietary asphalt mat technology for coastal disaster mitigation, national land resilience, and environmental sustainability.

• Asphalt mat

  Proprietary technology with long-term durability of over half a century, used for friction enhancement (KAM), scour prevention, suction prevention, and other applications contributing to resilience.

• Asphalt mastic

  Environmentally friendly and fully impermeable material.

• Hydrocrete

  Underwater non-separating concrete that is environmentally friendly and hardens without clouding water.

• NV Concrete

  High-fluidity concrete.

• KS Bond / KS Bond Type M

  High-durability epoxy adhesives for civil engineering.

• KS Primer / KS Primer II

  Penetrating primers.

• NK Stopper

  Joint waterproofing works.

• FL Coat

  Surface protection.

1. 1Japan SEA Works official websitekaijyokouji.co.jp
2. 2Company Information | Japan SEA Workskaijyokouji.co.jp
3. 3Company Outline and Office List | Japan SEA Workskaijyokouji.co.jp
4. 4Top Message and Corporate Philosophy | Japan SEA Workskaijyokouji.co.jp
5. 5Wikidata: Japan SEA Works Co., Ltd. (Japan)wikidata.org