The Effect of Leaching on the Pore Structure of Cement-Based Grouts for Use in Nuclear Fuel Waste Disposal

1990 ◽  
Vol 212 ◽  
Author(s):  
M. Onofrei ◽  
M. N. Gray ◽  
D. Breton ◽  
G. Ballivy
Keyword(s):  
Pore Structure ◽  
Total Porosity ◽  
Cementitious Materials ◽  
X Ray ◽  
Diffusion Characteristics ◽  
Deep Geological Disposal ◽  
Porosity And Permeability ◽  
Nuclear Fuel Waste ◽  
And Diffusion

ABSTRACTResearch on the longevity of cement-based grout materials for sealing a deep geological disposal vault is an important aspect of the Canadian and other nuclear waste management programs. These studies include assessments of the chemical durability of cement grouts, and the effects of leaching and phase transformation on the long-term hydraulic and diffusion characteristics of grouts.This paper presents the results of laboratory studies carried out to assess the effects of leaching of cement phases on the pore structure of hardened grouts. Measurements of mercury intrusion and scanning electron microscopy with energy dispersive x-ray analysis, have been used to investigate the changes in pore structure of both a reference grout (90% Type 50 cement, 10% silica fume, water-to-cementitious materials ratio between 0.4 and 0.7) and ALOFIX-MC (a fine cement product of Japan), as a function of leaching time.The work discussed here reveals that the porosity of hardened grout does change during leaching, but within limits that depend on grout composition and initial porosity. The results confirm that the materials have the potential to self-seal and maintain their performance for longer periods than those currently predicted by longevity models.Our studies of the porosity and permeability of grouts suggest that pore size distribution rather than total porosity is the more important parameter in determining longevity.

scholarly journals Relationship between Pore Structure and Chloride Ion Diffusivity in Cementitious Materials

2018 ◽  
Author(s):  
Yuya Sakai
Keyword(s):  
Pore Structure ◽  
Cement Paste ◽  
Pore Diameter ◽  
Chloride Ion ◽  
Total Porosity ◽  
Cementitious Materials ◽  
The Other ◽  
Diffusion Test ◽  
Other Hand ◽  
And Diffusion

In this study, literature on pore structure and chloride ion diffusivity was collected to investigate the correlation of pore structure indicators with diffusivity. Good correlation between total porosity and chloride ion diffusivity was found when the samples did not contain admixture materials and diffusion test was conducted without acceleration. Pore diameter indicators did not correlate with diffusivity. The diffusivity of cement paste was reduced by admixture materials compared to that without admixture materials even if the total porosity is the same. On the other hand, the diffusivity of concrete was not reduced by admixture materials.

scholarly journals Plutonium Migration during the Leaching of Cemented Radioactive Waste Sludges

Geosciences ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 31
Author(s):  
Kathleen A. Law ◽  
Stephen Parry ◽  
Nicholas D. Bryan ◽  
Sarah L. Heath ◽  
Steven M. Heald ◽  
...  
Keyword(s):  
Oxidation State ◽  
Fission Products ◽  
Surface Oxidation ◽  
State Standards ◽  
X Ray ◽  
Macro Scale ◽  
Deep Geological Disposal ◽  
The Uk ◽  
X Ray Absorption

One of the most challenging components of the UK nuclear legacy is Magnox sludge, arising from the corrosion of Mg alloy-clad irradiated metallic U fuel that has been stored in high pH ponds. The sludges mainly comprise Mg hydroxide and carbonate phases, contaminated with fission products and actinides, including Pu. Cementation and deep geological disposal is one option for the long-term management of this material, but there is a need to understand how Pu may be leached from the waste, if it is exposed to groundwater. Here, we show that cemented Mg(OH)2 powder prepared with Pu(IV)aq is altered on contact with water to produce a visibly altered ‘leached zone’, which penetrates several hundred microns into the sample. In turn, this zone shows slow leaching of Pu, with long-term leaching rates between 1.8–4.4 × 10−5% of total Pu per day. Synchrotron micro-focus X-ray fluorescence mapping identified decreased Pu concentration within the ‘leached zone’. A comparison of micro-focus X-ray absorption spectroscopy (µ-XAS) spectra collected across both leached and unleached samples showed little variation, and indicated that Pu was present in a similar oxidation state and coordination environment. Fitting of the XANES spectra between single oxidation state standards and EXAFS modeling showed that Pu was present as a mixture of Pu(IV) and Pu(V). The change in Pu oxidation from the stock solution suggests that partial Pu oxidation occurred during sample ageing. Similarity in the XAS spectra from all samples, with different local chemistries, indicated that the Pu oxidation state was not perturbed by macro-scale variations in cement chemistry, surface oxidation, sample aging, or the leaching treatment. These experiments have demonstrated the potential for leaching of Pu from cementitious waste forms, and its underlying significance requires further investigation.

Pozzolanic Reaction of Supplementary Cementitious Materials and Its Effects on the Strength of Mass Concrete

2010 ◽  
Vol 168-170 ◽  
pp. 505-511 ◽  
Author(s):  
Hua Shan Yang ◽  
Kun He Fang ◽  
Sheng Jin Tu
Keyword(s):  
Cementitious Materials ◽  
Pozzolanic Reaction ◽  
Supplementary Cementitious Materials ◽  
Mass Concrete ◽  
X Ray Diffraction ◽  
X Ray ◽  
Slag Powder ◽  
Phosphorous Slag ◽  
Better Than

The present study aims to investigate the opportunity to largely substitute low heat Portland cement of mass concrete with supplementary cementitious materials. The pozzolanic reaction of two types of supplementary cementitious materials, phosphorous slag powder and fly ash , were determined by X-ray diffraction, differential thermal analysis–thermogravimetry and scanning electron microscopy from 28 to 90 days. The properties of mortar and mass concrete containing 30% of supplementary cementitious materials were also investigated. Results showed that supplementary cementitious materials could decrease the amount of calcium hydroxide, fill the capillary pores, thus making the mortar and mass concrete more compact and durable. Long-term strength of mass concrete containing 30% of supplementary cementitious materials were comparable (or even better) than the control concrete (without supplementary cementitious materials) at constant workability, while the Young’s modulus was lower than the control concrete.

scholarly journals Effect of long-term irrigation and tillage practices on X-ray CT and gas transport derived pore-network characteristics

Soil Research ◽  
2019 ◽  
Vol 57 (6) ◽  
pp. 657
Author(s):  
Karin Müller ◽  
Nicola Dal Ferro ◽  
Sheela Katuwal ◽  
Craig Tregurtha ◽  
Filippo Zanini ◽  
...  
Keyword(s):  
Gas Transport ◽  
Greenhouse Gas Emission ◽  
Structural Characteristics ◽  
Network Connectivity ◽  
Total Porosity ◽  
Pore Network ◽  
Transport Parameters ◽  
X Ray ◽  
Tillage Practices

The gas transport parameters, diffusivity and air-filled porosity are crucial for soil aeration, microbial activity and greenhouse gas emission, and directly depend on soil structure. In this study, we analysed the effect of long-term tillage and irrigation practices on the surface structure of an arable soil in New Zealand. Our hypothesis was that topsoil structure would change under intensification of arable production, affecting gas exchange. Intact soil cores were collected from plots under intensive tillage (IT) and direct drill (DD), irrigated or rainfed. In total, 32 cores were scanned by X-ray computed tomography (CT) to derive the pore network >30µm. The cores were then used to measure soil-gas diffusivity, air-permeability and air-filled porosity of pores close to the resolution of the X-ray CT scans, namely ≥30µm. The gas measurements allow the calculation of pore-network connectivity and tortuosity parameters, which were compared with the CT-derived structural characteristics. Long-term irrigation had little effect on any of the parameters analysed. Total porosity tended to be lower under IT than DD, whereas the CT-derived porosity was comparable. Both the CT-derived mean pore diameter (MPD) and other morphological parameters, as well as gas measurement-derived parameters, highlighted a less developed structure under IT. The differences in the functional pore-network structure were attributed to SOC depletion and the mechanical disturbance through IT. Significant correlations between CT-derived parameters and functional gas transport parameters such as tortuosity and MPD were found, which suggest that X-ray CT could be useful in the prediction of gas transport.

scholarly journals Effects of OH− activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 267-278 ◽  
Author(s):  
Takuma Sawaguchi ◽  
Manabu Tsukada ◽  
Tetsuji Yamaguchi ◽  
Masayuki Mukai
Keyword(s):  
Dissolution Rate ◽  
Cementitious Materials ◽  
Ion Concentration ◽  
Bentonite Buffer ◽  
Deep Geological Disposal ◽  
Long Time ◽  
Alkaline Conditions ◽  
The Difference ◽  
High Level

AbstractThe highly alkaline environment induced by cementitious materials in a deep geological disposal system of high-level radioactive waste is likely to alter montmorillonite, the main constituent of bentonite buffer materials. Over long time periods, the alteration may cause the physical and/or chemical barrier functions of the buffer materials to deteriorate. In order to evaluate the long-term alteration behaviour, the dissolution rate, RA (kgm−3 s−1), of compacted pure montmorillonite (Kunipia-F) was investigated experimentally under conditions of hydroxide ion concentration of 0.10—1.0 mol dm−3 at temperatures of 50—90°C. The dissolution rate data, including those from a previous study at 130°C, were formulated as a function of the activity of hydroxide ions, aOH− (mol dm−3), and temperature, T (K), and expressed as RA = 104.5·(aOH−)1.3·e−55000/RT by multiple regression analysis, where R is the gas constant. The dissolution rate of montmorillonite was greater in the compacted montmorillonite than in the compacted sand-bentonite mixtures. The difference can be explained by considering the decrease in aOH− in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in aOH− is achieved somehow.

Relationships Between Structural, Functional, and X-Ray Microcomputed Tomography Parameters of Pervious Concrete for Pavement Applications

2017 ◽  
Vol 2629 (1) ◽  
pp. 51-62 ◽  
Author(s):  
Anush Konayakanahalli Chandrappa ◽  
Krishna Prapoorna Biligiri
Keyword(s):  
Pore Structure ◽  
Surface Area ◽  
Three Dimensional ◽  
Pervious Concrete ◽  
X Ray ◽  
Computed Microtomography ◽  
Porosity And Permeability ◽  
One Step ◽  
Positive Correlations ◽  
The Individual

Several countries have begun using pervious concrete (PC) pavements to reduce the adverse effects of impermeable surfaces resulting from high-impact development. Pore parameters and their relationship to other PC properties are not yet fully understood; however, this information is essential for rational designs of PC pavements. This study investigated the strength, functional, and permeability properties of 18 PC mixtures and used X-ray computed microtomography methods to determine the three-dimensional pore parameters and their relationships, which were thought to affect PC properties. The major findings of this study included the observation that the failure mode in compression was of the shear brittle type, in which the failure plane was inclined at 45° to the ground, and impact abrasion resistance was higher for larger-sized aggregates and was chiefly attributable to the individual aggregate particles debonding. Permeability was more sensitive at low hydrostatic pressure than at higher pressures. The sphericity and compactness of pores had positive correlations with each other, unlike the relationship between surface area and sphericity. The tortuosity calculated for six of the PC mixtures was less than one; this finding was attributed mainly to the single-sized pore structure. Tortuosity increased with an increase in porosity and permeability and decreased with increasing surface area and pore radius. This research should move the current understanding of PC pore structure one step forward and, therefore, will be helpful in modeling PC in a rational manner.

Physical Properties and Diffusion Characteristics of CVD-Grown TiSiN Films

2001 ◽  
Vol 697 ◽  
Author(s):  
Dalaver Anjum ◽  
Katharine Dovidenko ◽  
Serge Oktyabrsky ◽  
Eric Eisenbraun ◽  
Alain E. Kaloyeros
Keyword(s):  
Diffusion Barrier ◽  
Photoelectron Spectroscopy ◽  
Chemical Vapor ◽  
Flow Rate Ratio ◽  
X Ray ◽  
Transmission Electron ◽  
Diffusion Characteristics ◽  
Thick Barrier ◽  
Specific Electrical Resistivity ◽  
And Diffusion

AbstractTiSiN films grown by chemical vapor deposition were characterized to evaluate the properties relevant to the application as a diffusion barrier in Cu-based interconnects. The films were grown using TiI4 + SiI4 + NH3 + H2 chemistry at substrate temperature, 370°C, and SiI4 - to-TiI4 precursor flow rate ratio of 30. The combined results from x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) revealed that the bulk of Ti32Si21N42 films were predominantly consisted of a mixture of cubic TiN and amorphous SiNx phases. The specific electrical resistivity of the films was about 2000 μΩcm which is a few times higher than that of sputtered TiSiN films having similar composition and thicknesses. The 40 nm-thick barrier appeared to be thermally stable against Cu diffusion at the annealing temperatures up to 550°C. Breakdown of this diffusion barrier occurred at 600°C and was accompanied by the formation of Cu3Si protrusions at the TiSiN/Si interface.

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