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Insights into the water retention behaviour of GMZ bentonite pellet mixture.

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Title: Insights into the water retention behaviour of GMZ bentonite pellet mixture.
Authors: Liu, Zhang-Rong1 (AUTHOR), Ye, Wei-Min1,2 (AUTHOR) ye_tju@tongji.edu.cn, Cui, Yu-Jun3 (AUTHOR), Zhu, He-Hua1,2 (AUTHOR), Wang, Qiong1,2 (AUTHOR), Chen, Yong-Gui1,2 (AUTHOR)
Source: Acta Geotechnica. Oct2021, Vol. 16 Issue 10, p3145-3160. 16p.
Subjects: Radioactive waste repositories, Porosity, Pore size distribution, Bentonite, Radioactive wastes, Engineering systems
Abstract: Bentonite pellets are recognized as good buffer/backfill materials for sealing technological voids in high-level radioactive waste (HLW) repository. Compared to that of a traditional compacted bentonite block, one of the most important particularities of this material is the initially discrete pellets and the inevitable heterogeneous porosity formed, leading to a distinctive water retention behaviour. In this paper, water retention and mercury intrusion porosimetry (MIP) tests were conducted on pellet mixture (constant volume), single pellet (free swelling) and compacted block (constant volume) of GMZ bentonite, water retention properties and pore structure evolutions of the specimens were comparatively investigated. Results show that the water retention properties of the three specimens are almost similar to each other in the high suction range (> 10 MPa), while the water retention capacity of pellet mixture is lower than those of the compacted block and single pellet in the low suction range (< 10 MPa). Based on the capillary water retention theory (the Young–Laplace equation), a new concept 'saturated void ratio' that was positively related to water content and dependent on pore size distribution of the specimen was defined. Then, according to the product of saturated void ratio and water density in saturated void, differences of water retention properties for the three specimens at low suctions were explained. Meanwhile, MIP tests indicate that as suction decreases, the micro- and macrovoid ratios of pellet mixture and compacted block decrease as the mesovoid ratio increases, while all the void ratios of single pellets increase. This could be explained that upon wetting, water is successively adsorbed into the inter-layer, inter-particle and inter-pellet voids, leading to the subdivision of particles and swelling of aggregates and pellets. Under constant volume condition, aggregates and pellets tend to swell and fill into the inter-aggregates or inter-pellets voids. While under free swelling condition, the particles and aggregates in a single pellet tend to swell outward rather than squeezing into the inter-aggregate voids, leading to the expansion of the pores and even formation of cracks. Results including the effects of initial conditions (initial dry density and fabric) and constraint conditions (constant volume or free swelling) on the water retention capacity and pore structure evolution reached in this work are of great importance in designing of engineering barrier systems for the HLW repository. [ABSTRACT FROM AUTHOR]
Copyright of Acta Geotechnica is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Insights into the water retention behaviour of GMZ bentonite pellet mixture.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Liu%2C+Zhang-Rong%22&quot;&gt;Liu, Zhang-Rong&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Ye%2C+Wei-Min%22&quot;&gt;Ye, Wei-Min&lt;/searchLink&gt;&lt;relatesTo&gt;1,2&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; ye_tju@tongji.edu.cn&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Cui%2C+Yu-Jun%22&quot;&gt;Cui, Yu-Jun&lt;/searchLink&gt;&lt;relatesTo&gt;3&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Zhu%2C+He-Hua%22&quot;&gt;Zhu, He-Hua&lt;/searchLink&gt;&lt;relatesTo&gt;1,2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Wang%2C+Qiong%22&quot;&gt;Wang, Qiong&lt;/searchLink&gt;&lt;relatesTo&gt;1,2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Chen%2C+Yong-Gui%22&quot;&gt;Chen, Yong-Gui&lt;/searchLink&gt;&lt;relatesTo&gt;1,2&lt;/relatesTo&gt; (AUTHOR)
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  Data: &lt;searchLink fieldCode=&quot;JN&quot; term=&quot;%22Acta+Geotechnica%22&quot;&gt;Acta Geotechnica&lt;/searchLink&gt;. Oct2021, Vol. 16 Issue 10, p3145-3160. 16p.
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– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Bentonite pellets are recognized as good buffer/backfill materials for sealing technological voids in high-level radioactive waste (HLW) repository. Compared to that of a traditional compacted bentonite block, one of the most important particularities of this material is the initially discrete pellets and the inevitable heterogeneous porosity formed, leading to a distinctive water retention behaviour. In this paper, water retention and mercury intrusion porosimetry (MIP) tests were conducted on pellet mixture (constant volume), single pellet (free swelling) and compacted block (constant volume) of GMZ bentonite, water retention properties and pore structure evolutions of the specimens were comparatively investigated. Results show that the water retention properties of the three specimens are almost similar to each other in the high suction range (&gt; 10 MPa), while the water retention capacity of pellet mixture is lower than those of the compacted block and single pellet in the low suction range (&lt; 10 MPa). Based on the capillary water retention theory (the Young–Laplace equation), a new concept &#39;saturated void ratio&#39; that was positively related to water content and dependent on pore size distribution of the specimen was defined. Then, according to the product of saturated void ratio and water density in saturated void, differences of water retention properties for the three specimens at low suctions were explained. Meanwhile, MIP tests indicate that as suction decreases, the micro- and macrovoid ratios of pellet mixture and compacted block decrease as the mesovoid ratio increases, while all the void ratios of single pellets increase. This could be explained that upon wetting, water is successively adsorbed into the inter-layer, inter-particle and inter-pellet voids, leading to the subdivision of particles and swelling of aggregates and pellets. Under constant volume condition, aggregates and pellets tend to swell and fill into the inter-aggregates or inter-pellets voids. While under free swelling condition, the particles and aggregates in a single pellet tend to swell outward rather than squeezing into the inter-aggregate voids, leading to the expansion of the pores and even formation of cracks. Results including the effects of initial conditions (initial dry density and fabric) and constraint conditions (constant volume or free swelling) on the water retention capacity and pore structure evolution reached in this work are of great importance in designing of engineering barrier systems for the HLW repository. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: &lt;i&gt;Copyright of Acta Geotechnica is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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        Value: 10.1007/s11440-021-01249-y
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        Text: English
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        StartPage: 3145
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      – SubjectFull: Radioactive waste repositories
        Type: general
      – SubjectFull: Porosity
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      – SubjectFull: Pore size distribution
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      – TitleFull: Insights into the water retention behaviour of GMZ bentonite pellet mixture.
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              Text: Oct2021
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