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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Mechanical activation of clay : a novel route to sustainable cementitious binders

Tole, Ilda January 2019 (has links)
EU Sustainable Development Strategy planned to achieve improvement of life-quality by promoting sustainable production and consumption of raw materials. On November 2018, EU Commission presented a long-term strategy, aiming among others a climate-neutral economy by 2050. Cement production is contributing to 6-10% of the anthropogenic CO2 emissions. Thus, several strategies for total or partial replacement of Portland cement in concrete production have been developed. The use of supplementary cementitious materials (SCM) and alkali-activated materials (AAM) is considered the most efficient countermeasure to diminish CO2 emissions. The broadening of knowledge with particular attention to the sustainable goals is the primary requirement to be fulfilled when novel materials are investigated. This study aims to develop a novel clay-based binder that can be used as a sustainable alternative to produce SCM as well as AAM. Clay is a commonly occurring material, with large deposits worldwide. However, natural clay has a low reactivity and various compositions, depending, e.g. on the weathering conditions. The present research aims exactly at enhancing the reactivity of natural clays occurring in Sweden subjecting them to mechanical activation in a planetary ball mill. Ball milling (BM) is considered a clean technology able to enhance the reactivity of crystalline materials without resorting to high processing temperatures or additional chemicals. BM was able to induce amorphization in clay minerals and to transform the layered platy morphology to spherical shape particles. The efficiency of the process was strictly related to the used process parameters. Higher ball to processed powder (B/P) ratio, longer time of grinding and higher grinding speeds increased the degree of the obtained amorphization. However, an undesired extensive caking and agglomeration occurred in certain setups. The potential of activated clay as a SCM was investigated in specific case studies. The measured compressive strength results showed a direct correlation between the enhanced amorphization degree of the mechanically activated clay and the increased strength values. The pozzolanic activity was induced and enhanced after the mechanical activation of the clay. The reactivity was assessed by the strength activity index (SAI). Furthermore, preliminary tests have shown that the alkali activation of the processed clays produced solidified matrixes with considerable strength.
12

Environmental Impact of Concrete Structures - with Focus on Durability and Resource Efficiency

Al-Ayish, Nadia January 2017 (has links)
Concrete is essential for the construction industry with characteristic properties that make it irreplaceable in some aspects. However, due to the large volumes consumed and the energy intense cement clinker production it also has a notable climate impact. In order to reach the international and national sustainability goals it is therefore important to reduce the climate impact of concrete structures. There are many ways to influence the environmental impact of concrete and a detailed analysis is one of the actions that could push the industry and the society towards a sustainable development. The purpose of this research is to evaluate the environmental impact of concrete structures and the built environment and to highlight the possibilities to reduce that impact with choice of concrete mix and innovative design solutions. A life cycle assessment (LCA) was carried out to analyze the environmental impact of two thin façade solutions with innovative materials and to evaluate influences of different greenhouse gas reducing measures on concrete bridges. The influence of supplementary cementitious materials (SCM) in terms of climate impact and durability was also analyzed. The results indicate that SCMs have a twofold effect on the climate impact of reinforced concrete structures. Not only do they reduce the greenhouse gases through cement clinker replacement but also by an improvement of durability regarding chloride ingress. Currently, this is not considered in the regulations, which makes it difficult to foresee in LCA at early design stages. The results also show great possibilities to reduce the climate impact through different measures and design alternatives and the need for further development of products and solutions. / <p>QC 20171002</p>
13

Alkali-silica reaction in concrete containing recycled concrete aggregates

Adams, Matthew P. 09 January 2012 (has links)
Using recycled concrete aggregate (RCA) as a replacement for natural aggregate in new concrete is a promising way to increase the overall sustainability of new concrete. This has been hindered, however, by a general perception that RCA is a sub-standard material due to the lack of technical guidance, specifically related to long-term durability, on incorporating RCA into new concrete. The goal of this research project was to determine whether current testing methods could be used to assess the potential alkali-silica reactivity of concrete incorporating RCA. The test methods investigated were ASTM C1260 and ASTM C1567 for assessing natural aggregate susceptibility to alkali-silica reactivity (ASR), and the ability of supplementary cementitious materials (SCMs) to mitigate ASR, respectively. Seven different RCA sources were investigated. It was determined that ASTM C1260 was effective in detecting reactivity but expansion varied based on RCA processing. Depending on the aggregate type and the extent of processing, up to a 100% increase in expansion was observed. Replicate testing was performed at four university laboratories to evaluate repeatability and consistency of results. The authors recommend modification to the mixing and aggregate preparation procedures, when testing the reactivity of RCA using ASTM C 1260. This study also investigated the efficacy of replacing portland cement with supplementary cementitious materials (SCMs), known to mitigate alkali-silica reaction (ASR) in concrete with virgin aggregates, to control ASR in concrete incorporating reactive RCA. The SCMs investigated as part of this study included: fly ash (class F), silica fume, and metakaolin. The results of modified alkali-silica reactivity tests, ASTM C1260 and ASTM C1567 (AMBT), are presented for two different recycled concrete aggregates when using 100% portland cement, binary blends of portland cement and fly ash, and ternary blends of portland cement, fly ash and metakaolin or silica fume. The results indicate that SCMs can effectively mitigate ASR in concrete made with RCA. A 40% replacement of portland cement with class F fly ash was able to reduce expansions to below 0.10% in the AMBT for concrete containing 100% of a highly reactive recycled concrete aggregate. A ternary blend, however, of portland cement with a class F fly ash and metakaolin was most effective for both RCAs tested in this study. Higher levels of mitigation may be required for some RCAs, compared to the level required to mitigate ASR in concrete made with their original natural aggregates, depending on the age and composition of the RCA. / Graduation date: 2012
14

Investigation of alternative supplementary cementitious materials and a new method to produce them

Weihrauch, Michael 30 August 2022 (has links)
Zementklinker ist der Hauptbestandteil von Zement und verbraucht zu dessen Herstellung signifikante Mengen von natürlichen Ressourcen und trägt gleichzeitig zu seiner sehr ungünstigen Treibhausgasbilanz bei. In dieser Arbeit wird gezeigt, dass Zementersatzstoffe mit spezifischen Eigenschaften aus Abfallstoffen wie Kieswaschschlämmen, Strassenwaschschlämmen und Gipskartonplatten ohne Leistungseinbußen auf Produktseite, bei geringeren Temperaturen und geringerer CO2 Emission hergestellt werden können. Entsprechend den angestrebten Eigenschaften solcher zum Teil anthropogener Zementbestandteile wurden lokal verfügbare geeignete Abfallstoffe ausgewählt und thermisch aktiviert. Eine industriell anwendbare Methode zur Aktivierung solcher Stoffe bei Temperaturen von 700 °C – 850 °C wurde entwickelt und patentiert. Es basiert auf einem neu entwickelten Trocknungsverfahren und der Kombination von zwei Produktionslinien, um durch die Verknüpfung der Gasströme beider Systeme eine energieeffiziente thermische Behandlung von Abfallstoffen zu ermöglichen sowie auf umweltfreundliche Weise einen Zementersatzstoff herzustellen.:Table of Contents List of Tables List of Figures List of Abbreviations Glossary Chapter 1: Introduction 1.1 Motivation 1.2 Research hypotheses and objectives 1.3 Research methodology 1.4 Thesis outline Chapter 2: State of the art in SCM production 2.1 Supplementary cementitious materials 2.2 Classification of SCMs 2.2.1 Classification according to origin 2.2.2 Classification according to reaction behaviour 2.3 Chemical composition of SCMs 2.4 Formation of hydraulic or pozzolanic minerals in thermal processes 2.4.1 Cement clinker 2.4.2 Burnt oil shale 2.4.3 Fly ash 2.4.4 Calcined clay 2.5 Performance of composite cements 2.6 Calcining technologies 2.6.1 Flash calciner 2.6.2 Rotary calciner 2.7 Comparison of process technologies 2.8 Summary of Chapter 2 Chapter 3: Alternative SCMs and a new method for activation 3.1 Introduction 3.2 Target of alternative SCM 3.3 Waste materials 3.3.1 Aggregate washing sludge 3.3.2 Road cleaning sludge 3.3.3 Deconstruction gypsum 3.4 Producing alternative SCMs 3.5 Thermal activation of alternative SCMs 3.6 Limitations in current calcining technology 3.6.1 Difficult emission control 3.6.1.1 Particulate emission 3.6.1.2 Gaseous emission 3.6.2 Challenging material preparation 3.6.3 Demand for noble fuels 3.6.4 Difficult colour control 3.6.5 Strict temperature control 3.6.6 CO2 footprint of calciners 3.7 Proposed new method of calcination 3.7.1 Feed material handling 3.7.2 Thermal heat-exchange system 3.7.3 Clay calciner design 3.7.4 Grinding 3.8 Summary Chapter 3 Chapter 4: Theoretical Considerations 4.1 Material considerations 4.1.1 Composition of alternative SCM 4.1.2 Anticipated products and characteristics 4.2 Process considerations 4.2.1 System capacity 4.2.2 Material characteristics 4.2.3 Material receiving, crushing and handling 4.2.4 Thermodynamic modelling 4.2.4.1 Mass balance 4.2.4.2 Drying and cooling heat balance 4.2.4.3 Calcination heat balance 4.2.4.4 Gas balance 4.2.4.5 Impact on clinker kiln line 4.2.4.6 Impact of calcite on the gas balance 4.2.5 Calciner design 4.2.6 Colour control 4.2.7 Emission prediction 4.2.7.1 Emission during drying 4.2.7.2 Emission during calcination 4.2.8 CO2 footprint of produced material 4.2.9 Grinding requirements 4.3 Summary of Chapter 4 Chapter 5: Experimental tests and proof of concept 5.1 Introduction 5.2 Sampling and characterization 5.2.1 Kaolinitic AWS from France 5.2.2 Non-kaolinitic AWS from Switzerland 5.2.3 Road cleaning sludges from Switzerland 5.2.4 Deconstruction gypsum from Switzerland 5.2.5 Sample preparation and shipping 5.3 Drying screw conveyor testing 5.4 Calcination testing 5.4.1 Mineralogy of activated products 5.4.1.1 Non-kaolinitic SCM 5.4.1.2 Kaolinitic AWS from France 5.4.2 Colour 5.5 Crushing tests 5.6 Grinding tests 5.7 Mortar compressive strength testing 5.8 Water demand testing 5.9 Summary of Chapter 5 Chapter 6: Experimental results 6.1 Characteristics of activated materials 6.2 Concrete performance and colour 6.2.1 Thermally activated kaolinitic AWS from France 6.2.2 Thermally activated non-kaolinitic alternative SCM from Switzerland 6.3 Equipment dimensioning 6.3.1 Process mass flow 6.3.2 Heat-exchanging screws and thermal oil system 6.3.3 Rotary calciner dimensioning 6.3.4 Ball mill dimensioning 6.4 CO2 reduction 6.5 Summary of Chapter 6 Chapter 7: Conclusion and outlook 7.1 Conclusions 7.2 Outlook. Literature
15

Characterization of Quarry By-Products as a Partial Replacement of Cement in Cementitious Composites

Nguyen, Tu-Nam N. 21 August 2023 (has links)
Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to characterize the quarry by-products: particle size distribution, helium pycnometry, X-Ray diffraction, X-Ray fluorescence, scanning electron microscopy, and a modified ASTM C1897 Method A that utilizes isothermal calorimetry and thermogravimetric analysis. These various methods allowed for the determination of the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious system). The quarry by-products were classified as four granites, two limestones, and one greenstone. These quarry by-products were found to be non-pozzolanic and non-hydraulic. However, there are indications that there may be reactions with the various clays and feldspars in the quarry by-products with calcium hydroxide, which suggests a degree of reactivity that is not necessarily pozzolanic or hydraulic. / Master of Science / Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to determine the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious solution) of the materials. The quarry by-products were classified as four granites, two limestones, and one greenstone. In general, these quarry by-products were not found to be reactive as a supplementary cementitious material, although the data may suggest some degree of reactivity between calcium hydroxide and the clays and/or feldspars in the quarry by-products.
16

Chemo-mechanical characterization of microstructure phases in cementitious systems by a novel NI-QEDS technique / Caractérisation chimico-mécanique des phases microstructurales de systèmes cimentaires avec la technique novatrice NI-QEDS

Wilson, William January 2017 (has links)
Face à la finitude des ressources de la terre et de sa capacité d’absorption de la pollution, le développement d’écobétons pour un futur industrialisé durable représente un défi majeur de la science du béton moderne. En raison de sa nature hétérogène complexe, les propriétés macroscopiques du béton dépendent fortement des constituants de sa microstructure (ex. silicates de calcium hydratés [C–S–H], Portlandite, inclusions anhydres, porosité, agrégats, etc.). De plus, la nécessité d’une exploitation rapide et optimale des matériaux cimentaires émergents dans les applications industrielles demande de nos jours une meilleure compréhension de leurs particularités chimico-mécaniques à l’échelle micrométrique. Cette thèse vise à développer une méthode de pointe de couplage de la nanoindentation et de la spectroscopie quantitative aux rayons X à dispersion d'énergie (NI-QEDS), puis à fournir une caractérisation chimico-mécanique originale des phases microstructurales présentes dans les matrices réelles de ciments mélangés. La combinaison d’analyses NI-QEDS statistiques et déterministes a ainsi permis d’élargir la compréhension des systèmes avec ciment Portland et ajouts cimentaires (ACs) conventionnels ou alternatifs. Plus spécifiquement, l’étude des C–(A)–S–H (C–S–H incluant l’aluminium ou non) dans différents systèmes à base de ciments mélangés a montré des compositions différentes pour cet hydrate (variations dans les taux de Ca, Si, Al, S et Mg), mais ses propriétés mécaniques n’ont pas été significativement affectées par l’incorporation des ACs dans des dosages typiques. Les résultats présentés ont aussi démontré le rôle important des autres phases imbriquées dans la matrice de C–(A)–S–H, soit les inclusions anhydres dures (ex. le clinker et les ACs) et les autres hydrates tels que la Portlandite et les hydrates riches en aluminium (ex. les carboaluminates) avec des propriétés mécaniques plus élevées que celles des C–(A)–S–H. La thèse est basée sur cinq articles couvrant : (1) une analyse NI-EDS de systèmes incorporant des volumes élevés de pouzzolanes naturelles; (2) le développement de la méthode NI-QEDS; des analyses statistiques NI-QEDS (3) de systèmes avec cendres volantes et laitier, et (4) d’un système combinant ciment, calcaire et argile calcinée; et (5) une exploration déterministe NI-QEDS de systèmes conventionnels et alternatifs incorporant la poudre de verre, le métakaolin, le laitier ou la cendre volante. Finalement, en plus d’avancer les derniers modèles et méthodes micromécaniques, l’outil développé a fourni une perception chimico-mécanique originale des phases microstructurales et de leur arrangement. Le dévoilement de la signature chimico-mécanique de ces pâtes de ciments mélangés particulièrement complexes offre un savoir unique pour l’ingénierie des bétons de demain. / Abstract : Facing the limitedness of the earth’s resources and pollution absorption capacity, the development of eco-concrete for a sustainable industrialized future is one of the major challenges of modern concrete science. Due to its complex heterogeneous nature, the macro-scale properties of concrete strongly depend on the microstructure constituents (e.g., calcium-silicate-hydrates [C–S–H], Portlandite, anhydrous inclusions, porosity, aggregates, etc.). Moreover, the need for rapid and optimal exploitation of emerging binding materials in industrial applications urges today a better understanding of their chemo-mechanical features at the micrometer scale. This thesis aims at developing a state-of-the-art method coupling NanoIndentation and Quantitative Energy-Dispersive Spectroscopy (NI-QEDS), and providing an original chemo-mechanical characterization of the microstructure phases in highly heterogeneous matrices of real blended-cement pastes. The combination of statistical and deterministic NI-QEDS analysis approaches opened new research horizons in the understanding of Portland-cement systems incorporating conventional and alternative supplementary cementitious materials (SCMs). More specifically, the investigations of C–(A)–S–H (C–S–H including aluminum or not) in different blended-cement systems showed variable compositions for this hydrate (i.e., Ca, Si, Al, S and Mg contents), but the mechanical properties were not significantly affected by the incorporation of SCMs in typical dosages. The presented results also showed the important role of the other phases embedded in the C–(A)–S–H matrix, i.e., hard anhydrous inclusions (e.g., clinker and SCMs) and other hydrates such as Portlandite and Al-rich hydrates (e.g., carboaluminates) with mechanical properties higher than those of the C–(A)–S–H. The thesis is based on five articles focusing on: (1) the NI-EDS investigation of high-volume natural pozzolan systems; (2) the development of the NI-QEDS method; the statistical NI-QEDS analyses of (3) fly ash and slag blended-cement systems and of (4) a limestone-calcined-clay system; and (5) the deterministic NI-QEDS exploration of alternative and conventional systems incorporating glass powder, metakaolin, slag or fly ash. Finally, the developed tool not only advanced the latest micromechanical methods and models, but also provided original chemo-mechanical insights on the microstructure phases and their arrangement. Unveiling the chemo-mechanical signature of these highly-complex blended cement pastes further provided unique knowledge for engineering concretes for tomorrow.
17

Koldioxidutsläpp och energianvändning vid husbyggnad med betongstomme : En studie av två flerbostadshus inom projektet Sågklingan/Pilen i Västerås

Ivarsson, Benjamin January 2022 (has links)
Purpose:  The purpose is to investigate the use of concrete as a frame material and its effects on carbon dioxide emissions and energy use. Carbon dioxide emissions and energy use are examined from the production stage to the management stage 100 years in the future. In addition, investigate other material compositions in concrete to study the possibilities 0f lower carbon dioxide impact and energy use. Method: The methods used have included investigating one construction project involving two multi-family houses with the same conditions. The investigation conducted is primarily made through calculations of CO2 emission and energy use. Furthermore, a literary study has also been conducted focused on investigating what the impact concrete has on the environment and what different alternatives are available to reduce potential carbon dioxide emissions and energy use in house construction with a concrete frame. The study has focused on both the production phase and the management phase. The construction stage has been investigated primarily within the concrete production, enforcement and including transports. Whereas the management stage has been studied upon the energy use of the buildings and its effect on carbon dioxide emission.  The literature study deals with methods that can be associated with the case study but will also deal with other presumptive methods. Results: The study of the construction project shows that CO2 emission and energy use primarily comes from cement production within the production stage. Whereas, looking at the whole life cycle studied, the primary contributor to CO2 emissions and energy use over time is the management stage of the buildings. The result also shows that by using renewable steel as reinforcement can significantly effect the energy use, as well as, CO2 emission of the production phase. Conclusions: The cement production is one of the biggest causes of CO2 emissions and energy use in the production phase of the studied life cycle. While the management phase is the largest in terms of the total life cycle studied. Several methods are possible to decrease the use of energy use and CO2-emission in the production stage, and to combine those methods is an alternative that suggested
18

Use of Agricultural Wastes as Supplementary Cementitious Materials / Användning av jordbruksavfall som kompletterande cementmaterial

Marchetti, Ezio January 2020 (has links)
Global cement production is continuously increasing from 1990 till 2050 and growing particularly rapidly in developing countries, where it represents a crucial element for infrastructure development and industrialisation. Every tonne of ordinary Portland cement (OPC) produced releases, on average, about 800 kg of CO2 into the atmosphere, or, in total, the overall production of cement represents roughly 7% of all man-made carbon emissions. The present paper aims to deepen the re-use of agricultural solid waste materials as partial replacement of OPC, which can positively contribute to the sustainability of the concrete industry because of their availability and environmental friendliness. In particular, rice-husk ash (RHA) and oat-husk ash (OHA), burned under the right conditions, can have a high reactive silica content, representing very potential pozzolans. The mechanical and physical characteristics of both materials are investigated to evaluate the influence on concrete properties. Subsequently, using the environmental product declarations (EPDs) of the material used, a comparative environmental impact analysis between RHA concrete and ordinary concrete having the same resistance class, is presented. It is concluded that the use of RHA as supplementary cementitious material can serve a viable and sustainable partial replacement to OPC for the reduction of CO2 emissions and global warming potential. / Den globala cementproduktionen ökar från 1990 till 2050 och växer särskilt snabbt i utvecklingsländer, där den utgör en viktig del för infrastrukturutveckling och industrialisering. Varje ton vanligt portlandcement (OPC) släpper i genomsnitt ut cirka 800 kg koldioxid i atmosfären, och, totalt, representerar den totala cementproduktionen ungefär 7% av alla koldioxidutsläpp från mänsklig verksamhet. Det här examensarbetet syftar till att fördjupa kunskapen om och därmed i förlängningen återanvändningen av fasta avfallsmaterial från jordbruket som delvis ersättning av OPC, vilket kan bidra till hållbarheten i betongindustrin på grund av deras tillgänglighet och miljövänlighet. I synnerhet kan risskalaska (RHA) och havreskalaska (OHA), som bränns under rätt process, ha en hög reaktiv kiseldioxidhalt, vilket representerar mycket potentiella puzzolaner. De mekaniska och fysiska egenskaperna hos båda materialen har undersökts för att utvärdera deras inverkan på betongegenskaper. Därefter presenteras en jämförande miljökonsekvensanalys mellan RHA-betong och OPC-betong med samma motståndsklass med användning av miljövarudeklaration (EPD) för det använda materialet. Man drar slutsatsen att användningen av RHA som alternativt bindemedel (SCM) till OPC kan hjälpa till att minska koldioxidutsläppen och den globala uppvärmningspotentialen.
19

Použitelnost ložového popele z vitrifikovaného lignitového uhlí v kompozitních cementech. / Suitability of vitrified lignite bottom ash for composite cements.

Bayer, Petr January 2014 (has links)
Předložená magisterská práce se zabývá možným použitím vitrifikovaného lignitového lóžového popele jako náhrada slinku v kompozitních cementech. Byly zkoumány vlivy přidaného vitrifikovaného lóžového popele, jeho jemnosti, alkalických roztoků a jejich koncentrací. Byly připraveny kompozitní cementy v souladu s normou DIN EN 197 – 1. V těchto cementech bylo nahrazeno 30 % slinku vitrifikovaným lóžovým popelem. Konkrétně byly připraveny kompozitní cementy s vitrifikovaným lóžovým popelem o jemnosti 5549 cm2/g a 8397 cm2/g. Dále byly přidány alkalické roztoky hydroxidů a síranů vždy o dvou různých koncentracích, za účelem stimulace pucolánové a/nebo geopolymerní reakce. Mechanické vlastnosti připravených vzorků byly charakterizovány mechanickým testováním na prizmách s rozměry 40×40×160 mm, jak je specifikováno v normě DIN EN 196 – 1. Byla provedena nedestruktivní měření dynamického elastického modulu a destruktivní testovaní na pevnosti v tlaku a v ohybu. Distribuce velikosti částic a chemická analýza vstupních materiálů byla vykonána pomocí laserové granulometrie a rentgenové fluorescence. U zatvrdlých kompozitů bylo dále zkoumáno po 2 a 28 dnech hydratace fázové složení s využitím metody rentgenové difrakce a mikrostruktura s využitím skenovací elektronové mikroskopie. Výsledky ukázaly, že mechanické vlastnosti jsou nezávislé na množství přidaných alkálií stejně jako na jemnosti přidaného vitrifikovaného lóžového popele. Nicméně, znatelně nižší mechanické pevnosti byly pozorovány pro vzorky, které byly aktivovány hydroxidy, pravděpodobně kvůli brzké tvorbě silikátového hydrogelu. Vzorky aktivované sírany nedosáhly pevností jako referenční malta.
20

Influence of Nontraditional and Natural Pozzolans (NNPs) on the Mechanical and Durability Properties of Mortars and Concretes

Alberto Castillo (12323243) 29 April 2022 (has links)
<p>  </p> <p>Concrete is the second most consumed material in the world after water and is an essential element of constructed infrastructure. Over 14 billion m3 of concrete are being produced annually, resulting in a serious impact on the environment. The production of cement, which is the main component of concrete, is responsible for 5 – 8 % of global CO2 emissions. As a result, several global initiatives have been undertaken to achieve carbon neutrality by 2050. This carbon neutrality target coincides with the Paris Agreement's goal to limit global warming to 1.5 °C. A well-known, and successful strategy to reduce CO2 emissions in the concrete industry is to use supplementary cementitious materials (SCMs) as a partial replacement for cement. However, it is projected that in 2030 the demand for two of the most commonly used SCMs, fly ash and slag cement, will exceed their supply. Using nontraditional and natural pozzolans (NNPs) can help to close this supply gap, but there is a lack of knowledge regarding the reactivity and long-term performance of these materials.</p> <p>The purpose of this research was to perform experiments on several NNPs, some of which can be supplied in commercially viable quantities with the objective of evaluating their performance in cementitious systems (mortars and concretes) with the goal of accurately assessing their potential for use as alternative SCMs. The mortar study was performed using a total of 11 different NNPs, belonging to 4 distinctive groups and distributed as follows: 3 from the group of calcined clays (CCs) - CC1, CC2, and CC3, 3 from the group of natural pozzolans (NPs) - NP1, NP2 and NP3, 2 from the group of fluidized bed combustion (FBCs) ashes - FBC1 and FBC2, and 3 from the group of bottom ashes (GBAs) - GBA1, GBA2, and GBA3.</p> <p>The concrete study was performed on 4 different materials, one from each of the previously mentioned groups. The materials selected for concrete study were the worst-performing members of each group, as determined by the analysis of the test results obtained from mortars. These included CC2, NP3, FBC1, and GBA3 materials. This approach was adopted under the assumption that achieving adequate concrete characteristics with lowest-quality materials will all but assure satisfactory performance of concretes with higher-quality materials. </p> <p>The findings generated from this research indicate that several of the NNPs used in this study present a viable alternative to traditional SCMs. As an example, out of the 11 NNPS, 9 were found to conform to the requirements of the ASTM C618-19, the standard specification currently used to assess the suitability of coal fly ash and raw or calcined natural pozzolans for use in concrete. Results obtained from tests performed on mortars demonstrated that, when used at the replacement level of 25%, all 11 NNPs produced mixtures with characteristics similar to those obtained from the plain cement (OPC) mortar. For that reason, this level of replacement was selected to prepare concrete specimens. The results collected from concrete specimens showed that, when compared to plain concrete, mixtures with all 4 NNPs attained comparable (or improved) mechanical (compressive and flexural strength), durability (freeze-thaw resistance), and transport (formation factor and rate of water absorption) properties. As in the case of traditional SCMs, the mixtures with NNPs were found to require extended curing times to fully realize their property-enhancing potential associated with pozzolanic reactions. Overall, the best performing materials were those from the CCs group, followed by those belonging to, respectively, NPs, GBAs, and FBCs groups. </p>

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