Speaker
Description
The advancement of deep-sea technologies, including subsea carbon storage, offshore wind energy, and seabed resource extraction, requires durable cementitious materials capable of supporting infrastructure exposed to extreme environmental stressors. This study investigates the durability and physicochemical stability of high-alumina calcium aluminate cement (AC) pastes under in-situ deep-sea oceanic conditions. Prismatic specimens (40 mm × 40 × 160 mm) of AC and Portland cement (PC) were submerged for one year at depths of approximately 1000 and 2000 meters in the Nankai Trough, Japan, where the water temperature (approximately 2 °C) and salinity (35 PSU) remained stable. Replicate specimens were exposed to laboratory immersion in seawater under ambient pressure and temperature to serve as a reference. Post-exposure analysis was conducted using scanning electron microscopy with energy-dispersive X-ray spectroscopy, electron probe microanalysis, and X-ray diffraction. PC paste specimens showed full-depth chloride ingress and severe surface degradation with alkali dissolution and extensive ettringite formation. In contrast, AC specimens exhibited minimal deterioration. Chloride ingress in AC was limited to approximately 10 mm from the specimen surface, while sulfate ingress was confined to the outer surface region. The primary hydrate phase, i.e., amorphous aluminum hydroxide, remained stable due to its low solubility in low temperature seawater. Slight expansion and cracking were observed. Fluorescence imaging confirmed that pressurized seawater fully infiltrated the AC specimen within one month, accelerating ion transport compared to ambient pressure conditions. However, strong chemical binding of chloride ions into calcium aluminate hydrates restricted chloride ingress. Furthermore, AC mortar was successfully applied in a pioneering deep-sea construction demonstration, connecting precast components at approximately 1000 m depth using a two-component injection system operated by a manned submersible. This study demonstrates that high-alumina AC exhibits exceptional chemical resistance, stability, and structural resilience under deep-sea exposure, offering a viable material for subsea infrastructure applications.
Affiliations
Kagawa University, 4-8-27 Ban-cho, Takamatsu, Kagawa, 7600017, takahashi.keisuke@kagawa-u.ac.jp
Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Kanagawa, 2390826
Tohoku University, 6-6-06 Aramaki Aoba, Sendai, Miyagi, 9808579
Imperial College London, South Kensington, London, SW7 2AZ
| Keywords | High-alumina, deep sea, durability, in-situ exposure, phase change |
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