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Evaluation of transport properties of cement-based materials subjected to water attack using non-destructive integrated CT-XRD method
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| Title: | Evaluation of transport properties of cement-based materials subjected to water attack using non-destructive integrated CT-XRD method |
| Other Titles: | 非破壊CT-XRD連成法を用いた水の作用を受けたセメント系材料の輸送特性の評価 |
| Authors: | TAN, Yingyao Browse this author |
| Issue Date: | 25-Mar-2024 |
| Publisher: | Hokkaido University |
| Abstract: | Concrete is used in underground radioactive waste disposal facilities due to its stable chemical properties to
fulfill the requirement of structural stability. However, these facilities are inevitably in contact with ground water
for a long time, which brings the danger of concrete structure being damaged by leaching. Leaching refers to the
process by which soluble compounds in the cement hydrated system are dissolved and carried away by water.
This process can increase the porosity and permeability of the concrete, making it more susceptible to further
leaching and the ingress of harmful substances. Therefore, it is of great significance to analyze the transport
properties of concrete under the impact of long-term leaching deterioration. However, as a heterogeneous material,
the different phases in concrete, including aggregates, bulk cement paste, the interfacial transition zone (ITZ) and
pores, have different responses to the leaching process, which together form the picture of the leaching process of
concrete. This response is firstly reflected in the change in transport of substances in different phase, that is, the
change in transport properties. Although research efforts have been made on evaluating leaching deterioration in
the past, quantitative analysis on transport properties considering the alteration of different phases from the
microscopic point of view is still needed.
This research aims to study the alteration of cement-based materials under leaching from a microscopic
perspective using non-destructive integrated CT-XRD method. Integrated CT-XRD technique using synchrotron
radiation X-ray source can provide high-precision three-dimensional geometric information and phase distribution
information of specimen non-destructively and simultaneously. The addition of random walk algorithm to the CT
image analysis made it possible to quantify transport properties of different phases in concrete. Among them, ITZ
is difficult to quantify due to its irregular and tiny geometric shape. To solve this problem, a reconstructed method
of CT images in adjacent aggregate region was originally proposed, which made the transport properties analysis
on ITZ possible.
In the experiments, a series of natural leaching tests under different conditions were conducted. The
dissolution front of portlandite was identified, enabling to separate the leached region and non-leached region in
the specimen after the leaching tests. Then, transport properties of different regions were analyzed, and
corresponding diffusion coefficients of calcium ions were calculated including in the ITZ. It is found that the
diffusion coefficient of calcium ion in the leached region was about 50 times larger than that of the non-leached
region, while it was about 10 times larger in ITZ as compared with the non-leached region. In this way, this study
successfully provided the changing diffusion coefficients in altered specimens due to leaching. The obtained
results were verified by simulating with the SiTraM2D software. Using the quantitative transport properties
obtained from CT-XRD method and random walk algorithm, the dissolution of portlandites in concrete after 10
years immersion was predicted. Results showed that the dissolution front ranged from 6.2 to 7.2 mm deep inward
the concrete, indicating non negligible effect of ITZ. In addition, it was implied that the diffusion of Sr2+ ion was
influenced by the carbonation as well as the portlandite dissolution. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第15849号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Examination Committee Members: | (主査) 教授 杉山 隆文, 教授 松本 高志, 教授 長井 宏平, 准教授 橋本 勝文 |
| Degree Affiliation: | 工学院（環境フィールド工学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/91970 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 工学院(Graduate School of Engineering)
学位論文 (Theses) > 博士 （工学）
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