197 research outputs found
Celmisia brevifolia Cheeseman 1925
No full text<p> <b>11.</b> <i>Celmisia brevifolia</i> Cockayne ex Cheeseman (1925: 938).</p> <p> Type:—NEW ZEALAND. South Island, Plateau of the Old Man Range in herb-moor, 1500 m. alt., 27 March 1919, <i>L. Cockayne 1970</i> (lectotype K 77065 [image!] designated here; isolectotype WELT SP45774!).</p> <p> <b>Notes:—</b> Cheeseman (1925) described <i>C. brevifolia</i> and cited several syntypes that include plants with quite different leaf appearances regarding shape and indumentum. Plants from the Old Man Range (<i>L. Cockayne 1970</i>, see typification) and some from Mt Pisa (<i>L. Cockayne 1978</i>, K 77064 [image!], WELT SP45775!, SP45776!), both in Central Otago, have leaves obovate and pseudopetiolate, upon which Allan (1961: 618) wrote: “Neither type locality nor type is indicated, but Central Otago plants included by Cheeseman are fairly uniform […]”. Another syntype from Mt. Pisa (SP46497!) and one collected at Mt Ernest in northwest Otago (AK 34925!) have leaves that vary from obovate, obovate-oblong, oblanceolate-oblong, to almost linear-oblong, approaching <i>C. angustifolia</i>. Additional syntypes (AK 9707!, 9708!, AK 9709!, 9710!, AK 9706!, WELT SP46498!) coming from the Two Thumb Range in South Canterbury, have a conspicuous white arachnoid indumentum covering most of the adaxial surface (note that the syntypes mentioned above and the typical <i>C. angustifolia</i> are glabrous on the adaxial surface) and leaves oblanceolate-oblong to linearoblong, almost identical to <i>C. angustifolia</i> from its typical area (Torlesse Range, see typification of <i>C. angustifolia</i>).</p> <p> Plants from the Old Man Range are quite uniform in leaf shape and are representative of the taxon commonly recognized as <i>Celmisia brevifolia</i> that occurs mainly in Central Otago (Allan 1961, Mark & Adams 1973) as indicated above.Therefore, I have chosen the material from this locality (<i>L. Cockayne 1970</i>) as a lectotype. Besides, this specimen corresponds to a branch with leaves and one scape with a complete involucre, morphological features that allow its appropriate identification.</p> <p> Cheeseman ascribed the name <i>C. brevifolia</i> to Cockayne, however, according to the ICN Art. 46.5 and 46.6 (Turland <i>et al</i>. 2018), the author can be cited either as <i>C. brevifolia</i> Cheeseman or as <i>C. brevifolia</i> Cockayne ex Cheeseman.</p>Published as part of <i>Saldivia, Patricio, 2023, Nomenclature and typifications in Celmisia (Asteraceae: Astereae): The New Zealand endemic subgenera Caespitosae, Glandulosae, and Lignosae, pp. 31-45 in Phytotaxa 591 (1)</i> on pages 35-36, DOI: 10.11646/phytotaxa.591.1.3, <a href="http://zenodo.org/record/7784168">http://zenodo.org/record/7784168</a>
Magnesium-based glasses prepared by sol-gel processing for use as supplementary cementitious materials
No full textAbstract
For decades, supplementary cementitious materials (SCMs) have been utilized as clinker substitutes as one of the strategies to mitigate the CO2 emissions associated with Portland cement production. However, traditional SCMs (e.g., coal fly ash, silica fume, and blast furnace slag) are being phased out, as they are insufficient to enable high volume clinker substitution. Therefore, alternative SCMs are actively being sought to meet market demand. Synthetic glasses may be a potential source of SCMs due to their pozzolanic activity and tunable properties. The chemical composition of glasses determines their pozzolanic activity, with Ca-based glasses being predominantly studied owing to their high reactivity. However, this leads to the same inherent CO2 emissions as for cement, originating from the production of CaO from CaCO3.
This thesis investigates Mg-based silicate glasses synthesized via the sol-gel method, tuning their composition for higher pozzolanic activity. The feasibility of using Mg-based silicate glasses as SCMs was studied through three main pathways:
(1) Development of a binary Mg-Si sol-gel glass system: The impact of varying Mg concentrations on the glass reactivity was assessed (Publication Ⅰ).
(2) Introduction of Fe into the Mg-Si system: Varying concentrations of Fe3+/ Fe2+ were incorporated into Mg-Si glasses, investigating changes in reactivity (Publications Ⅱ, Ⅲ).
(3) Assessment of cementitious performance: The pozzolanic activity of Mg-based glasses was evaluated, and their impact on the properties and performance of cementitious systems was studied (Publication Ⅳ).
The research revealed the high elemental solubility of the synthetic glasses, indicating their high reactivity, and demonstrated pozzolanic activity exceeding that of conventional SCMs such as fly ash slag. These findings provide a preliminary assessment of the potential for using Mg silicate glasses as novel SCMs with the aim of reducing CO2 emissions. Original papers Jiang, C., Ramteke, D. D., Li, J., Sliz, R., Sreenivasan, H., Cheeseman, C., & Kinnunen, P. (2023). Preparation and characterization of binary Mg-silicate glasses via Sol-Gel route. Journal of Non-Crystalline Solids, 606, 122204. https://doi.org/10.1016/j.jnoncrysol.2023.122204 https://doi.org/10.1016/j.jnoncrysol.2023.122204 Self-archived version Jiang, C., Santos, H. S., Yliniemi, J., Lindén, J., Ramteke, D. D., Illikainen, M., Cheeseman, C., & Kinnunen, P. (2024). Fe-bearing magnesium silicate glasses for potential supplementary cementitious applications. Frontiers in Materials, 11, 1509403. https://doi.org/10.3389/fmats.2024.1509403 https://doi.org/10.3389/fmats.2024.1509403 Self-archived version Jiang, C., Yliniemi, J., Santos, H. S., Lindén, J., Ramteke, D.D., Cheeseman, C., & Kinnunen, P. (2024). Optimizing Fe(II)/Fe(III)-bearing magnesium silicate glasses for applications in supplementary cementitious materials. Manuscript submitted for publication. Jiang, C., Santos, H. S., Ahmad, L., Yliniemi, J., Cheeseman, C., & Kinnunen, P. (2025). Properties of Fe-bearing Mg silicate glasses as novel supplementary cementitious materials. Manuscript submitted for publication. Tiivistelmä
Jo vuosikymmenten ajan sementin seosaineita (SCM) on käytetty klinkkerin korvikkeina tavoitteena vähentää portlandsementin tuotannossa syntyviä CO2-päästöjä. Perinteisten SCM-materiaalien, kuten lentotuhkan, silikajauheen ja masuunikuonan, saatavuus ei kuitenkaan riitä mahdollistamaan korkeaa klinkkerin korvausastetta. Siksi on tarpeen kehittää uusia SCM-materiaaleja markkinoiden tarpeiden täyttämiseksi. Synteettiset lasit voivat olla potentiaalinen vaihtoehto niiden potsolaanisen aktiivisuuden ja säädettävien ominaisuuksien ansiosta. Lasien kemiallinen koostumus määrittää niiden potsolaanisen aktiivisuuden, ja enimmäkseen on tutkittu Ca-pohjaisia laseja niiden korkean reaktiivisuuden vuoksi. Tämä johtaa kuitenkin samoihin luontaisiin CO2-päästöihin kuin sementin tuotannossa, koska CaO:ta tuotetaan CaCO3:sta.
Tämä väitöskirja tutkii Mg-pohjaisia silikaattilaseja, jotka tuotetaan sol-gel-menetelmällä, jossa lasien koostumusta säädetään korkeamman potsolaanisen aktiivisuuden saavuttamiseksi. Mg-pohjaisten silikaattilasien käyttökelpoisuutta SCM-materiaaleina tutkittiin kolmen pääasiallisen lähestymistavan kautta:
(1) Binaarisen Mg-Si sol-gel-lasin kehitys: Eri Mg-pitoisuuksien vaikutuksia lasin reaktiivisuuteen arvioitiin (julkaisu I).
(2) Fe:n lisääminen Mg-Si-järjestelmään: Mg-Si-laseihin lisättiin eri pitoisuuksia Fe3+/Fe2+:aa, ja niiden vaikutusta reaktiivisuuteen tutkittiin (julkaisut II, III).
(3) Sementtimäisen suorituskyvyn arviointi: Mg-pohjaisten lasien potsolaanista aktiivisuutta arvioitiin, ja niiden vaikutusta seostettujen sementtien ominaisuuksiin ja suorituskykyyn tutkittiin (julkaisu IV).
Tutkimus paljastaa synteettisten lasien korkean alkuaineliukoisuuden, mikä viittaa niiden korkeaan reaktiivisuuteen, sekä osoittaa, että niiden potsolaaninen aktiivisuus ylittää perinteiset SCM:t, kuten lentotuhkan ja kuonan. Nämä havainnot tarjoavat alustavan arvion Mg-silikaattilasien potentiaalista uusina SCM-materiaaleina, joiden tavoitteena on CO2-päästöjen vähentäminen. Osajulkaisut Jiang, C., Ramteke, D. D., Li, J., Sliz, R., Sreenivasan, H., Cheeseman, C., & Kinnunen, P. (2023). Preparation and characterization of binary Mg-silicate glasses via Sol-Gel route. Journal of Non-Crystalline Solids, 606, 122204. https://doi.org/10.1016/j.jnoncrysol.2023.122204 https://doi.org/10.1016/j.jnoncrysol.2023.122204 Rinnakkaistallennettu versio Jiang, C., Santos, H. S., Yliniemi, J., Lindén, J., Ramteke, D. D., Illikainen, M., Cheeseman, C., & Kinnunen, P. (2024). Fe-bearing magnesium silicate glasses for potential supplementary cementitious applications. Frontiers in Materials, 11, 1509403. https://doi.org/10.3389/fmats.2024.1509403 https://doi.org/10.3389/fmats.2024.1509403 Rinnakkaistallennettu versio Jiang, C., Yliniemi, J., Santos, H. S., Lindén, J., Ramteke, D.D., Cheeseman, C., & Kinnunen, P. (2024). Optimizing Fe(II)/Fe(III)-bearing magnesium silicate glasses for applications in supplementary cementitious materials. Manuscript submitted for publication. Jiang, C., Santos, H. S., Ahmad, L., Yliniemi, J., Cheeseman, C., & Kinnunen, P. (2025). Properties of Fe-bearing Mg silicate glasses as novel supplementary cementitious materials. Manuscript submitted for publication. Academic dissertation to be presented with the assent of the Doctoral Programme Committee of Technology and Natural Sciences of the University of Oulu for public defence in the Wetteri auditorium (IT115), Linnanmaa, on 25 April 2025, at 12 noonAbstract
For decades, supplementary cementitious materials (SCMs) have been utilized as clinker substitutes as one of the strategies to mitigate the CO2 emissions associated with Portland cement production. However, traditional SCMs (e.g., coal fly ash, silica fume, and blast furnace slag) are being phased out, as they are insufficient to enable high volume clinker substitution. Therefore, alternative SCMs are actively being sought to meet market demand. Synthetic glasses may be a potential source of SCMs due to their pozzolanic activity and tunable properties. The chemical composition of glasses determines their pozzolanic activity, with Ca-based glasses being predominantly studied owing to their high reactivity. However, this leads to the same inherent CO2 emissions as for cement, originating from the production of CaO from CaCO3.
This thesis investigates Mg-based silicate glasses synthesized via the sol-gel method, tuning their composition for higher pozzolanic activity. The feasibility of using Mg-based silicate glasses as SCMs was studied through three main pathways:
(1) Development of a binary Mg-Si sol-gel glass system: The impact of varying Mg concentrations on the glass reactivity was assessed (Publication Ⅰ).
(2) Introduction of Fe into the Mg-Si system: Varying concentrations of Fe3+/ Fe2+ were incorporated into Mg-Si glasses, investigating changes in reactivity (Publications Ⅱ, Ⅲ).
(3) Assessment of cementitious performance: The pozzolanic activity of Mg-based glasses was evaluated, and their impact on the properties and performance of cementitious systems was studied (Publication Ⅳ).
The research revealed the high elemental solubility of the synthetic glasses, indicating their high reactivity, and demonstrated pozzolanic activity exceeding that of conventional SCMs such as fly ash slag. These findings provide a preliminary assessment of the potential for using Mg silicate glasses as novel SCMs with the aim of reducing CO2 emissions.Tiivistelmä
Jo vuosikymmenten ajan sementin seosaineita (SCM) on käytetty klinkkerin korvikkeina tavoitteena vähentää portlandsementin tuotannossa syntyviä CO2-päästöjä. Perinteisten SCM-materiaalien, kuten lentotuhkan, silikajauheen ja masuunikuonan, saatavuus ei kuitenkaan riitä mahdollistamaan korkeaa klinkkerin korvausastetta. Siksi on tarpeen kehittää uusia SCM-materiaaleja markkinoiden tarpeiden täyttämiseksi. Synteettiset lasit voivat olla potentiaalinen vaihtoehto niiden potsolaanisen aktiivisuuden ja säädettävien ominaisuuksien ansiosta. Lasien kemiallinen koostumus määrittää niiden potsolaanisen aktiivisuuden, ja enimmäkseen on tutkittu Ca-pohjaisia laseja niiden korkean reaktiivisuuden vuoksi. Tämä johtaa kuitenkin samoihin luontaisiin CO2-päästöihin kuin sementin tuotannossa, koska CaO:ta tuotetaan CaCO3:sta.
Tämä väitöskirja tutkii Mg-pohjaisia silikaattilaseja, jotka tuotetaan sol-gel-menetelmällä, jossa lasien koostumusta säädetään korkeamman potsolaanisen aktiivisuuden saavuttamiseksi. Mg-pohjaisten silikaattilasien käyttökelpoisuutta SCM-materiaaleina tutkittiin kolmen pääasiallisen lähestymistavan kautta:
(1) Binaarisen Mg-Si sol-gel-lasin kehitys: Eri Mg-pitoisuuksien vaikutuksia lasin reaktiivisuuteen arvioitiin (julkaisu I).
(2) Fe:n lisääminen Mg-Si-järjestelmään: Mg-Si-laseihin lisättiin eri pitoisuuksia Fe3+/Fe2+:aa, ja niiden vaikutusta reaktiivisuuteen tutkittiin (julkaisut II, III).
(3) Sementtimäisen suorituskyvyn arviointi: Mg-pohjaisten lasien potsolaanista aktiivisuutta arvioitiin, ja niiden vaikutusta seostettujen sementtien ominaisuuksiin ja suorituskykyyn tutkittiin (julkaisu IV).
Tutkimus paljastaa synteettisten lasien korkean alkuaineliukoisuuden, mikä viittaa niiden korkeaan reaktiivisuuteen, sekä osoittaa, että niiden potsolaaninen aktiivisuus ylittää perinteiset SCM:t, kuten lentotuhkan ja kuonan. Nämä havainnot tarjoavat alustavan arvion Mg-silikaattilasien potentiaalista uusina SCM-materiaaleina, joiden tavoitteena on CO2-päästöjen vähentäminen
Developing supplementary cementitious materials from waste London clay
No full textMajor tunnelling projects in London have generated enormous amounts of excavated clay, and there will be even larger production of excavated London clay in the next few years. This research focuses on investigating the technical feasibility of processing excavated London clay into a supplementary cementitious material (SCM) suitable for the use in concrete.
Excavated London clay was calcined at a range of temperatures between 600 and 1000 °C for 2 hours. The as-received and calcined London clay samples were characterized using techniques including XRF, XRD, FTIR, TGA/DTG, ICP, SEM, nitrogen adsorption, laser diffraction, isothermal conduction calorimetry and pycnometry. London clay is a complex mix of various types of clay and non-clay minerals, such as kaolinite (30.2 wt.%), illite (11.9 wt.%), montmorillonite (41.3 wt.%), chlorite, pyrite, goethite, feldspar and quartz (16.6 wt.%). Calcining excavated London clay resulted in oxidation, dehydration, dehydroxylation, amorphization and recrystallization, causing significant compositional and structural changes to clay and non-clay minerals. The degree of change depended on the calcining temperature. At 600 °C, kaolinite was entirely dehydroxylated, and the removal of octahedral hydroxyls led to a collapse of the 1:1 layered structure. As a result, metakaolin was formed. In contrast, the dehydroxylation of illite and montmorillonite started below 600 °C but finished at around 800 °C. Additionally, the two clay minerals did not suffer significant loss in crystallinity from complete dehydroxylation. The collapse of the 2:1 layered structure of illite and montmorillonite took place only when the calcining temperature was 900 °C and above. It was also observed that the recrystallization of spinel occurred above 950 °C.
The assessment of pozzolanic reactivity for calcined London clays was performed using the strength activity index (SAI) test, Frattini test, portlandite consumption test and the Chapelle test. The results showed that excavated London clay can be transformed into a SCM by calcining, and the optimum calcining temperature is 900 °C. The decrease at 950 °C can be attributed to the occurrence of spinel recrystallization.
London clay calcined at 900 °C was used to produce concrete at replacement levels up to 30 wt.% and three water-to-binder ratios (0.3, 0.4, 0.5). A CEM-I replacement of up to 30 wt.% showed no detrimental effect on workability or the compressive strength of concrete. In addition, the concrete with 30 wt.% of CEM-I substituted by calcined London clay and a w/b ratio of 0.3 had greater strength than control concrete after 28 days curing. At a replacement of 20 wt.% and a w/b ratio of 0.4, the concrete containing calcined London clay had similar 90-day compressive strength to those incorporating pulverised fuel ash, ground granulated blastfurnace slag and silica fume.
Carbon emission estimation showed that a 30 wt.% substitution of CEM-I by calcined London clay in concrete produces 27% less CO2 emission compared to 100 wt.% CEM-I.
This study has demonstrated that it is technically feasible to use calcined London clay as a supplementary cementitious material for use in concrete.Open Acces
A Regulatory Switch Alters Chromosome Motions at the Metaphase-to-Anaphase Transition
No full textSummaryTo achieve chromosome segregation during mitosis, sister chromatids must undergo a dramatic change in their behavior to switch from balanced oscillations at the metaphase plate to directed poleward motion during anaphase. However, the factors that alter chromosome behavior at the metaphase-to-anaphase transition remain incompletely understood. Here, we perform time-lapse imaging to analyze anaphase chromosome dynamics in human cells. Using multiple directed biochemical, genetic, and physical perturbations, our results demonstrate that differences in the global phosphorylation states between metaphase and anaphase are the major determinant of chromosome motion dynamics. Indeed, causing a mitotic phosphorylation state to persist into anaphase produces dramatic metaphase-like oscillations. These induced oscillations depend on both kinetochore-derived and polar ejection forces that oppose poleward motion. Thus, our analysis of anaphase chromosome motion reveals that dephosphorylation of multiple mitotic substrates is required to suppress metaphase chromosome oscillatory motions and achieve directed poleward motion for successful chromosome segregation
Cement-based materials with hydrophobic micro-textured surface
No full textThe use of hydrophobic additives is a relatively new development within the field of durability
design of concrete structures. This approach relies mainly on chemical modification of the
cement paste matrix. Another promising, but less well-studied approach is by adopting the
Cassie-Baxter mechanism. This can be achieved by creating a suitable micro texture on the
surface of the cementitious material, which traps air when in contact with water leading to the
separation between water and solid. The focus of this study is to develop concretes with
hydrophobic micro textured surfaces and to study the properties and durability of such
concretes. Hydrophobic Precipitated Calcium Carbonate (HPCC) made by dry ball milling
calcium carbonate and stearic acid is used to enhance hydrophobicity of the textured surfaces.
The effects of HPCC on the wettability and mass transport properties of cementitious materials
were investigated. By adopting soft lithography, micro textures on hydrophobic lotus and taro
leaves were transferred onto the surfaces of cementitious samples. Furthermore, research on
developing hydrophobic surfaces using a fine microgrid to mimic the micro texture of
hydrophobic plant leaves was undertaken. The hydrophobicity of micro textured surfaces was
enhanced by adding HPCC into cementitious mixture or by coating the surface with
Polydimethylsiloxane (PDMS). Water contact angle measurements were carried out to
determine the effect of surface micro textures on wettability and imbibition experiments were
carried out to determine the effect they have on water transport properties. Optical microscopy
was used to observe the formation and evolution of air trapped between the micro texture.
Furthermore, their durability and hydrophobicity when exposed to a range of conditions were
investigated. Changes in morphology due to continuous hydration, atmospheric carbonation
and abrasion, and wettability of deteriorated textured surfaces were investigated.
The research was successful in developing cementitious materials with micro textured
surfaces that displayed hydrophobicity, high water contact angle and strong adhesion between
droplets and substrate. The addition of HPCC to both micro textured and non-textured
samples showed decreasing wettability with increasing HPCC content. For example, taro
textured cementitious samples containing 16% HPCC had a water contact angle of 143˚,
compared to 123˚ for taro textured samples without HPCC. Furthermore, micro textured
samples containing 16% HPCC showed around 40% reduction in water sorptivity while the
textured samples with PDMS coating showed a reduction of 70% compared to non-textured
samples. The decrease in water absorption is mainly due to formation of trapped air cushions
when the sample is submerged underwater. However, samples containing less than 8% HPCC do not form such air cushion, and therefore, are less effective in decreasing water absorption.
This indicates that the performance of micro textures is related to HPCC content.
Durability studies showed that abrasion and efflorescence could affect the morphology of
textured surfaces and increase their wettability. In contrast, the influence of continuous
hydration and carbonation was negligible. Replacing 10% wt. of cement with silica fume can
prevent efflorescence and increase the abrasion resistance of surface textures, which yielded
a more durable textured surface. PDMS coating on micro textured surfaces was resistant to
cyclic wetting and elevated temperature of 50˚C, indicating that the coating was stable and
capable of providing long-term protection to cementitious materials. Overall, this research has
shown that the combination of hydrophobic treatments (HPCC / PDMS coating) and microtextured surfaces is a promising approach to deliver innovative hydrophobic concrete for
durable structures.Open Acces
Control of clogging in permeable concrete pavements
No full textThis thesis aims to improve the understanding of clogging and the effects this has on permeable concrete, and to develop new permeable concretes that are more durable and resistant to clogging without the need for frequent maintenance.
Permeable concrete, also known as pervious concrete, is used to reduce urban flooding as it allows water to flow through normally impermeable infrastructure. It is prone to clogging by particulate matter and predicting the long-term performance of permeable concrete is challenging as there is currently no reliable means of characterising clogging potential. New methods were developed to study clogging and define clogging potential. The tests involved applying flowing water containing sand and/or clay in cycles, and measuring the change in permeability. Three methods were used to define clogging potential based on measuring the initial permeability decay, half-life cycle and number of cycles to full clogging. We show for the first time strong linear correlations between these parameters for a wide range of samples, indicating their use for service-life prediction.
The problem which leads to clogging in existing permeable concrete is the pore network that is highly tortuous, with variable cross-section and random interconnectivity. As a result, it is important to develop new permeable concretes that have uniform pore structures with tortuosity of 1. This thesis reports on the development of cementitious materials that can be poured on-site, or provided as pre-cast elements, forming a low tortuosity connected porosity microstructure so that surface water is effectively transferred from one side of the permeable pavement to the other, with minimal risk of clogging.
High-strength clogging resistant permeable pavement (CRP) was prepared by introducing direct channels of varying size and number into self-compacting mortar. In all cases, permeability and compressive strength proved to be far higher than conventional permeable concrete. More significantly, not a single sample became clogged despite extensive cyclic exposure to flow containing sand and/or clay. We show for the first time a high strength clogging resistant permeable pavement capable of retaining sufficient porosity and permeability for storm-water infiltration throughout the service life while having a high compressive strength to utilise permeable pavement in heavy loading applications. This innovative system will help alleviate urban flooding and contribute towards a more sustainable urbanisation.
In order for the new design to be considered a truly successful innovation it is necessary to examine means by which the work done in a laboratory setting can be utilised in a large-scale commercial setting. Several methods have been investigated. While each of these methods has benefits and limitations, collectively they constitute a valid range of possible approaches for potential in-situ and pre-cast delivery of CRPs on a large scale.Open Acces
Role of informal sector recycling in waste management in developing countries
No full textWILSON, David C. VELIS, Costas. CHEESEMAN, Chris. Role of informal sector recycling in waste management in developing countries. Department of Civil and Environmental Engineering, Centre for Environmental Control and Waste Management, Imperial College, London, 2005 Many thousands of people in developing country cities depend on recycling materials from waste for their livelihoods. With the focus of the Millennium Development Goals on poverty reduction, and of waste strategies on improving..
Role of materials development in resource efficiency
No full text1st Spanish National Conference on Advances in Materials Recycling and Eco-Energy
Madrid, 12-13 November 2009Peer reviewe
Fructose the odd man out. Why is the genomic control of intestinal GLUT5 expression different?
No full textDevelopment of novel low pH Magnesium Silicate Hydrate (M-S-H) cement systems for encapsulation of problematic nuclear wastes
No full textThere are more than 100,000 tonnes of nuclear waste currently stored in the UK, waiting for final disposal. Composite cements consisting of Portland cement (PC) and blast furnace slag (BFS) have a good track record in encapsulation of a range of nuclear wastes. However, the pH of this system is relatively high (~13.3) for encapsulating wastes that containing trace levels of aluminium, as this can react under high pH conditions. The aim of this research was to develop novel cement systems with lower pH (~10) for encapsulating wastes containing aluminium metal and Magnox swarf.
The hydration of magnesium oxide to form brucite produces a pH around 10 and this is a favourable pH for aluminium passivation. A range of reactive fillers were investigated and silica fume (SF) found to be the most suitable to achieve the desired pH. Identification of the hydrated phases in MgO/SF samples showed that magnesium silicate hydrate (M-S-H) gel is the main hydration product. Brucite (Mg(OH)2) also forms in the early stages of hydration but then reacts with SF to produce additional M-S-H gel. The system has been improved by addition of sodium hexameta-phosphate (Na-HMP) as a dispersant, magnesium carbonate to control the early pH and sand to minimise the drying shrinkage. The physical, chemical and mechanical properties of the improved MgO/ SF system have been investigated and compared with the control PC/BFS system.
Magnox swarf and aluminium 1050 (Al) supplied by National Nuclear Laboratory (NNL) were used as metal wastes. These metals were encapsulated in the control PC/ BFS system and the optimised MgO/ SF system. The interaction between the metals and the two cement systems has been investigated by monitoring H2 generation, studying the microstructure by SEM and the crystalline phases by XRD. Al strips were firmly bound into the optimised MgO/ SF system and no H2 gas was detected during the test period. The corrosion of Al is very limited in the optimised MgO/SF system compared to the control system. Magnox swarf was found to show similar corrosion behaviour when encapsulated in both the control system and the optimised MgO/SF system. The M-S-H gel forming cement system developed in this research is novel and may have potential for encapsulating certain types of problematic legacy wastes generated from the nuclear industry
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