scholarly journals Evolution of the Reaction and Alteration of Mudstone with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive-Transport Modelling

Minerals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1026
Author(s):  
Keith Bateman ◽  
Shota Murayama ◽  
Yuji Hanamachi ◽  
James Wilson ◽  
Takamasa Seta ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Chemical Properties ◽  
Reactive Transport Modelling ◽  
Transport Modelling ◽  
General Sequence ◽  
Long Term Performance ◽  
Term Performance ◽  
Physical And Chemical ◽  
Flow Experiments

The construction of a repository for geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially high [Na] and [K], evolving to a Ca-rich fluid, and finally returning to the groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a mudstone, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the mudstone with the cement leachates resulted in small changes in pH with the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions. As the system evolves, secondary C-(A-)S-H phases re-dissolve and are replaced by secondary carbonates. This general sequence was successfully simulated using reactive transport modelling.

Development of a reactive transport code MC-CEMENT ver. 2 and its verification using 15-year in situ concrete/clay interactions at the Tournemire URL

Clay Minerals ◽  
2013 ◽  
Vol 48 (2) ◽  
pp. 185-197 ◽  
Author(s):  
T. Yamaguchi ◽  
M. Kataoka ◽  
T. Sawaguchi ◽  
M. Mukai ◽  
S. Hoshino ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Chemical Properties ◽  
Bentonite Buffer ◽  
Alkaline Environments ◽  
Radioactive Waste Repositories ◽  
Long Term Performance ◽  
Term Performance ◽  
Waste Repositories

AbstractHighly alkaline environments induced by cement-based materials are likely to cause the physical and/or chemical properties of the bentonite buffer materials in radioactive waste repositories to deteriorate. Assessing long-term alteration of concrete/clay systems requires physicochemical models and a number of input parameters. In order to provide reliability in the assessment of the long-term performance of bentonite buffers under disposal conditions, it is necessary to develop and verify reactive transport codes for concrete/clay systems. In this study, a PHREEQC-based, reactive transport analysis code (MC-CEMENT ver. 2) was developed and was verified by comparing results of the calculations with in situ observations of the mineralogical evolution at the concrete/argillite interface. The calculation reproduced the observations such as the mineralogical changes in the argillite limited to within 1 cm in thickness from the interface, formation of CaCO3 and CSH, dissolution of quartz, decrease of porosity in the argillite and an increase in the concrete. These agreements indicate a possibility that models based on lab-scale (∼1 year) experiments can be applied to longer time scales although confidence in the models is necessary for much longer timescales. The fact that the calculations did not reproduce the dissolution of clays and the formation of gypsum indicates that there is still room for improvement in our model.

The Migration of Radionuclides with Ground Water. A Discussion of the Relevance of the Input Parameters used in Model Calculations

1981 ◽  
Vol 11 ◽  
Author(s):  
Bror Skytte Jensen
Keyword(s):  
Radioactive Waste ◽  
Ground Water ◽  
Chemical Processes ◽  
Model Calculations ◽  
Input Parameters ◽  
Long Term Performance ◽  
Term Performance ◽  
Physical And Chemical ◽  
Take All

The plans for the disposal of radioactive waste leave very little time for testing long term performance of a repository so the evaluation of the hazards involved in the operation relies heavily on model calculations. It is therefore of utmost importance that these model calculations take all important parameters into account and are based on a thorough understanding of the possible physical and chemical processes in which the migrating species take part.

Long-term geochemical evolution of the near field repository: Insights from reactive transport modelling and experimental evidences

2008 ◽  
Vol 102 (3-4) ◽  
pp. 196-209 ◽  
Author(s):  
David Arcos ◽  
Fidel Grandia ◽  
Cristina Domènech ◽  
Ana M. Fernández ◽  
María V. Villar ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Near Field ◽  
Geochemical Evolution ◽  
Reactive Transport Modelling ◽  
Transport Modelling

Acoustic Emission Monitoring of Cement-Based Structures Immobilising Radioactive Waste

2007 ◽  
Author(s):  
L. M. Spasova ◽  
M. I. Ojovan ◽  
M. Hayes ◽  
H. Godfrey
Keyword(s):  
Acoustic Emission ◽  
Radioactive Waste ◽  
Mechanical Performance ◽  
Cement Matrix ◽  
Properties Of Materials ◽  
Long Term Performance ◽  
Term Performance ◽  
Physical And Chemical ◽  
Non Destructive

The long term performance of cementitious structures immobilising radioactive waste can be affected by physical and chemical processes within the encapsulating materials such as formation of new phases (e.g., vaterite, brucite), degradation of cement phases (e.g., CSH gel, portlandite), degradation of some waste components (e.g., organics), corrosion of metallic constituents (aluminium, magnesium), gas emission, further hydration etc. The corrosion of metals in the high pH cementitious environment is of especial concern as it can potentially cause wasteform cracking. One of the perspective non-destructive methods used to monitor and assess the mechanical properties of materials and structures is based on an acoustic emission (AE) technique. In this study an AE non-destructive technique was used to evaluate the mechanical performance of cementitious structures with encapsulated metallic waste such as aluminium. AE signals generated as a result of aluminium corrosion in a small-size blast furnace slag (BFS)/ordinary Portland cement (OPC) sample were detected, recorded and analysed. A procedure for AE data analysis including conventional parameter-based AE approach and signal-based analysis was applied and demonstrated to provide information on the aluminium corrosion process and its impact on the mechanical performance of the encapsulating cement matrix.

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