Action of Hydraulic Pressure on Portland Cement Mortars - Current Understanding and Related Progress of the First-Ever In-Situ Deep Sea Tests at a 3515 m Depth
Keisuke Takahashi, Yuichiro Kawabata, Mari Kobayashi, Shinpei Gotoh, Shun Nomura, Takafumi Kasaya, Mitsuyasu Iwanami
Abstract
In order to realize the utilization of cement-based materials in the special extreme environment, the deep sea, the authors have launched a project targeted at creating a technology platform with in-situ methods and systems for monitoring and evaluating cement-based materials located at deep ocean bottom sites. The first in-situ test in the world with a view to investigating the time-dependence of the volumetric stability and microstructure of Portland cement mortar following its long-term exposure to deep-sea conditions is currently underway at a 3515-m depth in the Nankai Trough. This paper reviews previous studies about the influences of deep-sea hydraulic pressure on cement-based materials, verifies the action of short-term hydraulic pressure using Portland cement mortars on a laboratory scale, and introduces the ongoing progress of in-situ deep-sea tests. Results from laboratory tests indicate that dimensional changes were provoked by liquid water infiltration and confinement while under short-term hydraulic pressure, however, time-dependent behavior under stresses such as creep has not appeared. Weight gain, changes in pore-size distribution, compressive strength and bending strength of the cement mortar were monitored after pressurization and depressurization processes.