Sorption Mechanism of Carbon-14 by Hardened Cement Paste

1995 ◽  
Vol 412 ◽  
Author(s):  
K. Noshita ◽  
T. Nishi ◽  
M. Matsuda ◽  
T. Izumida
Keyword(s):  
Electrostatic Force ◽  
Cementitious Materials ◽  
Hardened Cement ◽  
Sorption Mechanism ◽  
Carbon 14 ◽  
Adsorption Sites ◽  
Radioactive Waste Repositories ◽  
Waste Repositories ◽  
Positively Charged

AbstractCarbon-14 sorption by cementitious materials should be enhanced to ensure the long term safety of radioactive waste repositories. The sorption mechanism of inorganic C- 14 (CO32- was investigated using batch sorption experiments and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Ordinary Portland cement (OPC) did not contain enough SiO2 compared with its CaO content to produce sufficient numbers of C-14 adsorption sites. The C-14 distribution coefficient (Kd) was increased from 2,000 to 7,000 mL/g by adding SiO2 to OPC.

An Assessment of the Long-Term Durability of Concrete in Radioactive Waste Repositories

1985 ◽  
Vol 50 ◽  
Author(s):  
A. Atkinson ◽  
D. J. Goult ◽  
J. A. Hearne
Keyword(s):  
Reinforced Concrete ◽  
Radioactive Waste ◽  
Concrete Slab ◽  
Laboratory Studies ◽  
Preliminary Assessment ◽  
Reinforced Concrete Slab ◽  
Radioactive Waste Repositories ◽  
Waste Repositories ◽  
Durability Of Concrete

AbstractA preliminary assessment of the long-term durability of concrete in a repository sited in clay is presented. The assessment is based on recorded experience of concrete structures and both field and laboratory studies. It is also supported by results of the examination of a concrete sample which had been buried in clay for 43 years.The enoineering lifetime of a 1 m thick reinforced concrete slab, with one face in contact with clay, and the way in which pH in the repository as a whole is likely to vary with time have both been estimated from available data. The estimates indicate that engineering lifetimes of about 103 years are expected (providing that sulphate resisting cement is used) and that pH is likely to remain above 10.5 for about 106 years.

scholarly journals Composition and selected properties of low pH mortars and concretes for radioactive waste repositories

2020 ◽  
Vol 322 ◽  
pp. 01033
Author(s):  
An Cheng ◽  
Wei-Ting Lin ◽  
Sao-Jeng Chao ◽  
Hui-Mi Hsu
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Spent Nuclear Fuel ◽  
Cementitious Materials ◽  
Low Ph ◽  
Engineering Properties ◽  
Filling Materials ◽  
Radioactive Waste Repositories ◽  
Waste Repositories

Conventional cementitious materials as tunnel supporting materials are utilised in the construction of the final repository for spent nuclear fuel. However, the use of cementitious material releases alkaline ions from pH12 to pH13 plumed into groundwater. Such a high pH is detrimental to the performance of the bentonite functioning, which may possibly enhance the dissolution and alteration of the fracture buffer and filling materials. Instead, low-pH cementitious materials are being developed for use in geological repositories. This study is aimed at evaluating the usability of low-pH cementitious materials containing 40% silica fume or composites blended with 20% silica fume and 40% fly ash. Engineering properties were analysed and verified through experimental research using the flow, compressive strength, pH measurement and hydraulic conductivity. Test results show that the replacement level with 40% of silica fume or 20% of silica fume and 40% of fly ash was suitable for the mixture of low-pH cementitious. Compared to the compressive strength and water permeability of ordinary cementitious, those of low-pH cementitious enhanced better engineered performances at the age of 91 days. The information is contributed us to establish the long-term durability and environmental requirements of disposal repositories in Taiwan.

scholarly journals Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experiment

2009 ◽  
Vol 60 (5) ◽  
pp. 431-436 ◽  
Author(s):  
Igor Stríček ◽  
Vladimír Šucha ◽  
Peter Uhlík ◽  
Jana Madejová ◽  
Igor Galko
Keyword(s):  
Crystal Size ◽  
Exchange Capacity ◽  
Layer Charge ◽  
Size Distributions ◽  
Geochemical Environment ◽  
Mineral Stability ◽  
Experimental Alteration ◽  
Radioactive Waste Repositories ◽  
Waste Repositories

Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experimentBentonite is a basic component of most concepts of multibarrier systems in underground radioactive waste repositories. It is important to determine the bentonite stability under the conditions close to the future real situation. The paper brings the detailed mineral and structural analyses of smectites from the bentonitic material exposed to the long term Mock-Up-CZ experiment. The compacted barrier blocks and residual filling contained 85 % of bentonite from the Rokle deposit, 10 % of quartz sand and 5 % of graphite. They were exposed to temperatures of up to 90 °C for almost 4 years. Quantitative mineral analyses, crystal size distributions, FTIR spectra, as well as cation exchange capacity and layer charge density show high mineral stability of the Rokle bentonite under the conditions of Mock-Up-CZ experiment. Small changes in the crystal sizes and slight change in the layer charge as a consequence of the experimental alteration could be linked to the hydration and the variation of the geochemical environment of the experiment.

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.

Mineralogical Analyses of Old (78 and 98 Years) Concrete

2011 ◽  
Author(s):  
Tomoko Ishii ◽  
Hitoshi Owada ◽  
Hiroyuki Sakamoto ◽  
Masahito Shibata ◽  
Kumi Negishi
Keyword(s):  
Cementitious Material ◽  
Fresh Groundwater ◽  
Groundwater Environment ◽  
Dissolution Tests ◽  
Radioactive Waste Repositories ◽  
Rotary Kilns ◽  
Waste Repositories ◽  
Cement Factories

Because Ca-dissolution from cementitious material is considered a source of long-term alteration of the performance of radioactive waste repositories, much research including dissolution tests has been conducted on this topic. These studies have introduced models such as Atkinson’s model [1] to calculate the leaching of cementitious material. These models have been used to verify that the results of many studies do represent the alteration of cementitious minerals and the composition of the leachate. They have also been used to make numerous estimates of long-term mineralogical alteration in repositories, such as cement-clay interaction in cementitious barrier systems, and to evaluate the change in repository performance. However, immersion tests using bulky cementitious material have often indicated that the actual alteration of cementitious material might be slower than the rates calculated by these models. This difference may be due to a change of mass-transport characteristics, either in the bulky cementitious material or at the interfaces with other materials. In this study, a mineralogical analysis was conducted on two types of old concrete. Drilled cores from the foundations of rotary kilns at two cement factories were collected beneath the groundwater level. Both concrete structures were made from Japanese ordinary Portland cement (OPC), which is similar to European type 1 cement. One structure had been set into a fresh groundwater environment for 78 years (78-F), and the other had set sunk into a saline environment for 98 years (98-S).

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