A method for determining the necessity of maintenance of cement treated soil in coastal areas based on the possibility of producing magnesium hydroxide layer

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04600
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Yamaguchi University
• Principal Investigator: Hara Hiroyuki 山口大学, 大学院創成科学研究科, 准教授 (00588709)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 土質安定処理 / セメント / 劣化抑制 / 水酸化マグネシウム / カルシウム溶出 / pH

Outline of Final Research Achievements

In this study, it was investigated that conditions for producing protective sediments, mainly magnesium hydroxide, generated at surface of cement-treated soil in seawater environment, and the following results were obtained. 1) The protective sediments were deposited when the pH at surface of cement treated clay specimen was maintained above 10 for a certain period. 2) It was shown that the region where the precipitation of protective sediments can be determined by the pH of the cement-treated soil and the magnesium concentration in seawater. 3) The effect of suppressing deterioration of the protective sediments were maintained under repeated dry-wet conditions, but it may disappear in a permeable conditions.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

セメントや石灰を土に添加する固化処理工法は，軟弱地盤対策として広く活用されている．しかし，セメント処理土は海水の化学的浸食によってその性質が劣化することが指摘されている．一方で，セメント処理土に白色の保護物質が生成される場合があり，これが生成されると劣化の進行が極端に遅延される．本研究では，未だ不明瞭であった保護物質の生成条件を解明し，さらにセメント処理土のpHと接触する海水のMgイオン濃度によって生成される領域を示すことができた．保護物質生成の有無は現場におけるセメント処理土の維持管理の要否を判定する重要な指標の一つとなり得る．