Structural characterisation via C-14-PMMA impregnation technique : Method and application development

The C-14 polymethyl methacrylate (C-14-PMMA) impregnation technique is used to analyse the spatial distribution of porosity. As such, this work focuses on two interlinked aims: to further develop the C-14-PMMA impregnation technique, particularly the polymerisation and autoradiography steps; and to further develop its application extending it from granitic materials to fine-grained structures such as clays as well. To achieve these aims, method development focused on making the C-14-PMMA impregnation technique more flexible and suitable to a wide variety of conditions while maintaining its robustness. As such, we investigated the use of thermally degrading initiators and other impregnants. Thus, we examined the use of thermally degrading initiators as a way of completing the entire sample handling procedure in a laboratory without necessitating transportation to irradiation facilities, which are currently rare. Furthermore, we studied the use of a water-soluble comonomer, 2-hydroxyethyl methacrylate (HEMA), to allow for the possibility of impregnating water-saturated matrices in future, the focus of articles I and II. The second aim focused on the application-related development for the C-14-PMMA impregnation technique and tailoring the methodology to suit the different applications. Towards this end, we compared our results with those obtained via previously used methodologies and other measurement techniques. As such, the C-14-PMMA impregnation technique can be linked to multiple other techniques, providing comprehensive information on the materials studied. In this study, we examined the mineral porosities of rock at the centimetre scale using C-14-PMMA autoradiography (AG) and at the micrometre scale using scanning electron microscopy (SEM) imaging with the aim of studying the effect of the mineral structure on the spatial distribution of porosity. This is detailed in article III. We also studied the fixation of a contrast agent that does not require pressurised intrusion used to image the connected porosity of crystalline rock through SEM and X-ray tomography. In this case, impregnation with methyl methacrylate (MMA) served to fix the contrast agent in place. This research is described in article IV. Our results from the method development studies show that polymerisation can be reliably accomplished within crystalline rock using thermally degrading initiators with no notable drawbacks. We also found that clay rock could be impregnated and the impregnant could be polymerised with the same initiators as well. The two-monomer mixtures (100% C-14-labelled methyl methacrylate (C-14-MMA) and a mixture of 75% HEMA and 25% C-14-MMA) yielded fairly similar results and were consistent with reference values. The application development studies show that valuable information may be gained by combining the spatial distribution of the porosity with spatial information on the mineral structures. The contrast agent for SEM and X-ray tomography was successfully fixed in place by impregnation and polymerisation, and the contrast improved through both imaging techniques.C-14-polymetyylimetakrylaatti (C-14-PMMA)-impregnointitekniikkaa käytetään huokoisuuden paikkakohtaisen jakautumisen määritykseen senttimetrien kokoisissa kivinäytteissä. Tässä työssä on ollut kaksi toisiinsa sidottua päämäärää. Ensimmäinen on tekniikan kehitys, erityisesti polymeroinnin ja kuvantamisen suhteen. Toisena päämääränä on ollut uusien sovelluksien käyttöönotto. Kiteisten kivien lisäksi myös hienojakoisten materiaalien, esimerkiksi savien, huokoisuuksia on määritetty ja näiden kivien erikoispiirteet on otettu huomioon menetelmäkehityksessä. Näiden päämäärien saavuttamiseksi pyrittiin menetelmäkehityksessä lisäämään C-14-PMMA-impregnointitekniikan joustavuutta tinkimättä kuitenkaan luotettavuudesta. Tutkimus painottui lämpöherkkien initiaattoriyhdisteiden ja vaihtoehtoisten akrylaattien käyttöönottoon. Lämpöherkkien initiaattoreiden käyttöönotto sallii koko näytteenkäsittelyn tapahtuvan samassa laboratoriossa ilman tarvetta siirtää näytettä säteilytyslaitokseen, jotka ovat yhä harvinaisempia. Tämän lisäksi tutkimme vesiliukoisen 2-hydroksietyyli metakrylaatin (HEMA) käyttöä vesisaturoitujen näytematriisien huokoisuusmäärityksiä ajatellen. Tutkimuksen toinen päämäärä, huokoisuuden määrittäminen erilaisissa sovelluksissa ja eri määritysmenetelmien yhdistäminen C-14-PMMA menetelmällä saataviin tuloksiin, keskittyi impregnointitekniikan kuvantamisosuuden räätälöintiin eri sovelluksia varten. Tässä työssä on C-14-PMMA impregnointitekniikan rinnalla käytetty kahta eri tekniikkaa materiaalien rakenteen 2D ja 3D kuvantamiseksi. Mineraalien huokoisuudet määritettiin C-14-PMMA tekniikalla ja niiden alkuainekoostumukset pyyhkäisyelektronimikroskopiaa (SEM) ja energiadispersiivistä rötgenspektroskopiaa käyttäen selvittääksemme huokoisuuden ja mineraalikoostumuksensuhdetta. Tutkimme myös SEM- ja röntgentomografia-kuvantamisen herkkyyden parantamista näytteisiin imeytetyllä kontrastinvahvistimella, joka ei vaadi paine-avusteista imeytysmenettelyä. Tämä kontrastinvahvistin tunkeutui diffuusiolla ensiksi näytteen sisään ja sen jälkeen kiinnitettiin paikalleen imeyttämällä metyylimetakrylaattia ja polymeroimalla se näytteen huokosiin. Tulokset menetelmänkehityksestä osoittivat, että polymerointi voidaan toteuttaa luotettavasti kiteisessä kivessä käyttäen lämpöherkkiä initiaattoriyhdisteitä, ilman merkittäviä haittapuolia. Tulosten perusteella voitiin myös todeta, että savikivi voidaan impregnoida, ja impregnantti polymeroida samoilla initiaattoriyhdisteillä kuin kiteisen kiven tapauksessa. Kaksi käytettyä akrylaattiseosta (100 % C-14-leimattu metyylimetakrylaatti (C-14-MMA) ja seos, jonka koostumus oli 75 % HEMA: ja 25 % C-14-MMA) johtivat kumpikin samanlaisiin tuloksiin ja olivat vertailukelpoisia huokoisuuksien viitearvojen kanssa. Hyödyllistä tietoa saatiin yhdistämällä tulokset paikkakohtaisesta huokoisuudesta (C-14-PMMA impregnointitekniikka), mineraalikoostumuksesta (SEM-EDS) ja huokoisuuden rakenteesta (Röntgentomografia). SEM:ssa ja röntgentomografiassa käytetty kontrastinvahvistin saatiin onnistuneesti kiinnitettyä käytetyllä impregnointi- ja polymerointimenettelyllä ja erotuskykyä saatiin parannettua kummassakin kuvantamistekniikassa

Sealing, healing and fluid flow in clay rocks : Insights on episodic flow events in fault zones

The porosity distribution and mineralogical changes in a clay-rich fault core from the Tournemire underground research laboratory are analyzed to determine the mechano-chemical processes in a small-scale vertical strike-slip fault. The results display significant spatial variations in porosity and mineralogy along different gouge zones due to a polyphased tectonic history combined with complex paleo-fluid migrations. Porosity values increase from the center of the gouges to their borders indicating diffusive sealing/healing effects and past hydrothermal activities. The healing and thus the strengthening of the fault is marked by an increase of calcium content, which is concurrent with lower porosities around the gouge zone. Chemical mapping in the gouges reveal clay alteration, iron zonality and the presence of zinc sulphide as well as barium sulphate inside the gouge, further suggesting past hydrothermal activity. Finally, even though the observed porosity variations only occur in subcentimeter-thick gouge bands, the higher porosity sections are pathways for fluid flow during fault activity. © 5th International Conference on Fault and Top Seals 2019. All Rights Reserved.Peer reviewe

Diffusion and Sorption Studies of Cs, Sr and Co in Intact Crystalline Rock

Three cationic tracers, Sr2+, Co2+ and Cs+ were tested with a modified electromigration device by applying 2V, 3V and 4V voltage gradients over an intact Grimsel granodiorite rock sample. An ideal plug-flow model and an advection-dispersion model were applied to analyze the breakthrough curves. Matrix characterization by C-14-PMMA autoradiography and scanning electron microscopy showed that in the centimeter scale of Grimsel granodiorite rock, the interconnected matrix porosity forms a well-connected network for diffusion. Micrometer-scale fissures are transecting biotite and chlorite minerals, indicating sorption of the studied cations. The ideal plug-flow model indicated that the effective diffusion coefficients (De values) for Sr2+, Co2+ and Cs+ tracer ions within the Grimsel granodiorite rock were 3.20 × 10−13 m2/s, 1.23 × 10−13 m2/s and 2.25 × 10−12 m2/s, respectively. De values were also derived from the advection-dispersion model, from which 2.86 × 10−13 m2/s, 1.35 × 10−13 m2/s and 2.26 × 10−12 m2/s were calculated. The diffusion speed for the tracers was in the sequence of Cs+ > Sr2+ > Co2+ that is in the same sequence as their diffusion in diluted water. The distribution coefficients (Kd values) calculated from the models covered the range of two magnitudes (from 10−7 m3/kg to 10−5 m3/kg). The result indicated that the sorption process of the studied elements did not reach equilibrium during the electromigration process, mainly due to the too much acceleration of the migration speed by the voltage gradients applied over the rock sample

Diffusion and Sorption Studies of Cs, Sr and Co in Intact Crystalline Rock

Three cationic tracers, Sr2+, Co2+ and Cs+ were tested with a modified electromigration device by applying 2V, 3V and 4V voltage gradients over an intact Grimsel granodiorite rock sample. An ideal plug-flow model and an advection-dispersion model were applied to analyze the breakthrough curves. Matrix characterization by C-14-PMMA autoradiography and scanning electron microscopy showed that in the centimeter scale of Grimsel granodiorite rock, the interconnected matrix porosity forms a well-connected network for diffusion. Micrometer-scale fissures are transecting biotite and chlorite minerals, indicating sorption of the studied cations. The ideal plug-flow model indicated that the effective diffusion coefficients (De values) for Sr2+, Co2+ and Cs+ tracer ions within the Grimsel granodiorite rock were 3.20 × 10−13 m2/s, 1.23 × 10−13 m2/s and 2.25 × 10−12 m2/s, respectively. De values were also derived from the advection-dispersion model, from which 2.86 × 10−13 m2/s, 1.35 × 10−13 m2/s and 2.26 × 10−12 m2/s were calculated. The diffusion speed for the tracers was in the sequence of Cs+ > Sr2+ > Co2+ that is in the same sequence as their diffusion in diluted water. The distribution coefficients (Kd values) calculated from the models covered the range of two magnitudes (from 10−7 m3/kg to 10−5 m3/kg). The result indicated that the sorption process of the studied elements did not reach equilibrium during the electromigration process, mainly due to the too much acceleration of the migration speed by the voltage gradients applied over the rock sample

Porosity distribution in a heterogeneous clay-rich fault core by image processing of 14C-PMMA autoradiographs and Scanning Electron Microscopy

Shale formations are considered by a number of countries as the most suitable media to dispose of high-level radioactive waste. This is mainly due to the impermeable, self-sealing, chemical reducing, and sorption properties that tend to retard radionuclide migration. However, shale formations can also contain highly connected fault zones with permeabilities that can differ of several orders of magnitudes with respect to the undeformed host rock. The objective of this work is to use the 14C-PMMA autoradiography method combined with SEM-EDS measurements to understand the porosity variations in and around fault gouges and to define their relationship to mechano-chemical processes. The studied samples were taken from a low permeability shale in a small-scale vertical strike-slip fault at the Tournemire underground research laboratory. Results display significant variations in porosity and mineralogy along the studied gouge zone due to polyphased tectonics and paleo-fluid circulations.Shale formations are considered by a number of countries as the most suitable media to dispose of high-level radioactive waste. This is mainly due to the impermeable, self-sealing, chemical reducing, and sorption properties that tend to retard radionuclide migration. However, shale formations can also contain highly connected fault zones with permeabilities that can differ of several orders of magnitudes with respect to the undeformed host rock. The objective of this work is to use the 14C-PMMA autoradiography method combined with SEM-EDS measurements to understand the porosity variations in and around fault gouges and to define their relationship to mechano-chemical processes. The studied samples were taken from a low permeability shale in a small-scale vertical strike-slip fault at the Tournemire underground research laboratory. Results display significant variations in porosity and mineralogy along the studied gouge zone due to polyphased tectonics and paleo-fluid circulations.Peer reviewe

Impact of a 70°C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

International audienceRadioactive wastes in future underground disposal sites will induce a temperature increase at the interface between the cementitious materials and the host rock. To understand the evolution of Portland cement in this environment, an in situ specific device was developed in the Underground Research Laboratory in Tournemire (France). OPC cement paste was put into contact with clayey rock under water-saturated conditions at 70°C. The initial temperature increase led to ettringite dissolution and siliceous katoite precipitation, without monosulfoaluminate formation. After one year of interaction, partial decalcification and diffuse carbonation (calcite precipitation) was observed over 800 μm in the cement paste. At the interface, a layer constituted of phillipsite (zeolite), tobermorite (well-crystallised C-S-H), and C-(A)-S-H had formed. Globally, porosity decreased at both sides of the interface. Geochemical modelling supports the experimental results, especially the coexistence of tobermorite and phillipsite at 70°C, minerals never observed before in concrete/clay interface experiments

Recombinant Spider Silk Protein and Delignified Wood Form a Strong Adhesive System

Funding Information: This work was performed within the project “Strong Composite” supported under the umbrella of ERANET Cofund ForestValue, funded by Academy of Finland projects #308772, #317395, #326345, and #333238. The authors are grateful for the support by the FinnCERES Materials Bioeconomy Ecosystem, the Bioeconomy Infrastructure, and the OtaNano─Nanomicroscopy Center (Aalto-NMC) at Aalto University. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society.For developing novel fully biological materials, a central question is how we can utilize natural components in combination with biomimetic strategies in ways that both allow feasible processing and high performance. Within this development, adhesives play a central role. Here, we have combined two of nature's excellent materials, silk and cellulose, to function as an adhesive system. As an initial step in processing, wood was delignified. Without lignin, the essential microstructure and alignment of the wood remain, giving a strong scaffold that is versatile to process further. A recombinant spider silk protein was used as a fully biological and water-based adhesive. The adhesive strength was excellent with an average value of 6.7 MPa, with a maximum value of up to 10 MPa. Samples of different strengths showed characteristic features, with high tear-outs for weaker samples and only little tear-out for strong samples. As references, bovine serum albumin and starch were used. Based on the combined data, we propose an overall model for the system and highlight how multiple variables affect performance. Adhesives, in particular, biobased ones, must be developed to be compatible with the overall adherend system for suitable infiltration and so that their mechanical properties match the adherend. The engineering of proteins gives an unmatched potential for designing adhesive systems that additionally have desired properties such as being fully water-based, biologically produced, and renewable.Peer reviewe