Tokyo Institute of Technology: Research Group Initiates First-Ever In-Situ Measurement of Mechanical Properties of Hardened Cement Mortar in Deep Sea

Ube Industries, Ltd., the Port and Airport Research Institute, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Tokyo Institute of Technology, and Tokyo University of Marine Science and Technology today announced that a joint research group has established a method for evaluating the mechanical properties of hardened cement mortar and initiated the first-ever in-situ data measurement. The research project aims to contribute to the construction of deep-sea infrastructure. By collecting data on the hydraulic pressure arising inside of hardened cement mortar at a site on the deep-sea floor, the research is expected to yield useful data for the future development of infrastructure materials for deep-sea applications and the establishment of design methodologies for deep-sea structures.

The research is reported in a paper published in the Journal of Advanced Concrete Technology, Volume 19, which was released online on March 26, 2021.

Left: Measurement apparatus next to cement mortar specimen at a water depth of approximately 3,500 meters (Copyrighted image courtesy of JAMSTEC) Right: Remotely operated vehicle ROV Kaiko Mk-IV, used to install the cement mortar specimen

Research Details
The purpose of the research is to elucidate the mechanical propertiesof hardened cement mortar due to the effects of high hydraulic pressure over both a short and long period of time. Conventionally, a submersible is used to recover the cement mortar specimens deployed on the deep-sea floor, and the changes in the mortar specimen are measured after retrieval However, this method leaves open the possibility that pressure change from deep sea to sea surface on retrieval causes the changes in the cement mortar specimen, potentially preventing an accurate understanding of phenomena arising in the deep sea. Furthermore, testing that utilizes a water tank to simulate the high hydraulic pressure in the deep sea cannot reproduce the phenomena to the degree that they would arise in an actual structure, or the effects of actual currents and attachment of marine organisms.

The researchers established a method that enables continuous in-situ measurement of water pressure and strain arising in a cement mortar specimen on the deep-sea floor. The researchers can then pinpoint only the phenomena actually arising in the deep sea, thereby ensuring accurate data for analysis and interpretation.

In July 2020, the research group deployed a cement mortar specimen and measurement apparatus at a water depth of approximately 3,500 meters in the northeastern rim of the Nankai Trough, located about 70 kilometers from the tip of the Izu Peninsula. The specimen will be recovered in fiscal 2021 and researchers will analyze the data.

Research Group Initiates First-Ever In-Situ Measurement of Mechanical Properties of Hardened Cement Mortar in Deep Sea

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