Properly proportioned, placed and cured concrete can be durable under most conditions. However, deterioration of concrete does occur under certain environments. One of the problems that affect the durability of hardened concrete is delayed ettringite formation (DEF) which is an important problem encountered in precast concrete industry where high temperature curing is applied. Although there had been many researches on DEF, there are still many uncertainties about its chemistry and mechanism. In this study, the effects of partial cement replacement by different mineral admixtures (trass, blast furnace slag and fly ash), SO3/Al2O3 molar ratio and specific surface area of cement on DEF were investigated. For this purpose, 9 groups of control cements were prepared with 3 different specific surface areas and 3 different SO3/Al2O3 molar ratios. Different amounts of mineral admixtures were blended with the control cements. High temperature curing was applied to the cement pastes and the expansions of these pastes were measured periodically for 240 days. v The experimental results obtained were interpreted for a comparative analysis of the effects of the afore-mentioned parameters.

ABSTRACT IMPROVEMENT OF BEARING CAPACITY OF A SOFT SOIL BY THE ADDITION OF FLY ASH &Ouml / ZDEMIR, Murat Aziz M.Sc., Department of Civil Engineering Supervisor : Prof. Dr. Erdal &Ccedil / OK&Ccedil / A Co-Supervisor : Assoc. Prof. Dr. Murat G&Uuml / LER May 2011, 119 pages Soft soils are not suitable for use in runway and highway construction due to their undesirable characteristics such as poor grading, low strength, excessive plasticity, tendency to shrink or swell. By stabilizing such soils with appropriate agents, their engineering properties can be improved. One of the stabilizing agents is Class C fly ash. This study aimed at investigation of bearing capacity improvement of a soft soil (from Elmadag area) by using Class C fly ash (from Soma Thermal Power Plant). In the experimental study, index properties of soft soil and fly ash stabilized samples are determined. Then modified Proctor compaction, soaked California Bearing Ratio, and Unconfined Compressive Strength characteristics of the samples are investigated. During the study, the stabilized soil samples are prepared at different fly ash contents, i.e., 0%, 3%, 5%, 7%, and 10%. The samples are subjected to soaked California Bearing Ratio tests after 0, 7, and 28 days of curing. In addition to California Bearing Ratio tests, Unconfined Compressive Strength tests with 0, 7, and 28 days of curing are performed samples. For comparison purpose, hydrated lime is also used instead of fly ash in Unconfined Compressive Strength tests at predetermined contents, i.e., 3%, 5%, and 7%. In order to observe microstructures of samples, Scanning Electron Microscope - Energy Dispersive X-ray analysis are performed. The results of the study show that bearing capacity of Elmadag soft soil can be improved substantially and swell can be reduced significantly by using Class C fly ash.

The use of backfill in underground mining is increasing due to need for systematic backfilling of mine openings and workings to avoid surface damage, increase safety and contribution to sustainable mining. This study is to investigate backfill materials and new methods suited for systematic selection and application of backfill in underground mines. Laboratory tests were carried out on physical, chemical and mechanical properties of different backfill materials and mixtures thereof. Special attention was paid to materials generated as by-products and other cheaply available materials e.g. fly ash and FGD-gypsum from power plants, natural and synthetic anhydrite. The different material mixtures investigated can be used as a technically and economically viable backfill for underground mines. In summary, the systematic selection of backfill materials from by-products, mine waste and tailings from the mineral processing of mining industry and other industries were suited as a backfill material for test field in China coal fires and recommended for underground potash mines in Thailand.

In der vorliegenden Arbeit wurde die Nähr- und Schadstoffdynamik flugaschebeeinflusster Waldböden der Dübener Heide bezüglich ihres aktuellen Zustandes und der zu erwartenden zukünftigen Entwicklung untersucht. In der Dübener Heide wurden jahrzehntelang große Mengen an Flugasche abgelagert, die die Eigenschaften des Bodens entscheidend und nachhaltig prägten. Selbst 15 Jahre nach dem abrupten Ende der Einträge kann eine Flugaschebeeinflussung noch immer deutlich nachgewiesen werden. Das Ökosystem hat sich an die durch die Flugasche veränderten Umweltbedingungen angepasst. Nach Wegfall der Einträge unterliegt das System nun allerdings wieder neuen Veränderungen, deren Auswirkungen auf die Bestände noch unklar sind. Als Grundlage für nachhaltige forstliche Planungen und ein angepasstes Naturparkmanagement wurden deshalb im Rahmen des ENFORCHANGE-Teilprojektes Bodenprozesse der aktuelle bodenchemische Zustand der Dübener Heide untersucht und Prognosen über die zukünftige Entwicklung abgeleitet. Für die Ermittlung des Ist-Zustandes wurden 12 Kernversuchsflächen ausgewählt, die entlang eines Entfernungsgradienten ausgehend vom angenommenen Hauptemittenten, Kraftwerk Zschornewitz, gelegen sind und die typischen Bodentypen und Bestände der Dübener Heide repräsentieren. 2 m tiefe Bodenprofile wurden angelegt und in Tiefenstufen beprobt. Die Bodenproben wurden mit Standardmethoden auf verschiedene bodenchemische Parameter untersucht. Die Ergebnisse wurden sowohl hinsichtlich der Überschreitung von Mittel-, Vorsorge- und Grenzwerten als auch bezüglich der Ausbildung von Tiefen- und Entfernungsabhängigkeiten beurteilt. Darüber wurden die eindeutig flugaschebeeinflussten Parameter und die am stärksten beeinflussten Tiefenstufen identifiziert. Diese Informationen wurden anschließend genutzt, um die Standorte statistisch in unterschiedlich stark flugaschebeeinflusste Gruppen einzuteilen. Weiterhin wurden aktuelle Potentiale und Risiken abgeschätzt und über den Vergleich mit Literaturdaten die vergangene Entwicklung beurteilt. Die Ergebnisse zum derzeitigen bodenchemischen Ist-Zustand der Dübener Heide können wie folgt zusammengefasst werden: Als eindeutig flugaschebeeinflusst sind der pH-Wert, die Basensättigung sowie die Gesamtgehalte der Metalle Aluminium, Eisen, Calcium, Magnesium, Cadmium, Cobalt, Nickel und Zink identifiziert worden. Für diese bodenchemischen Parameter liegen klare, abnehmende Gradienten mit zunehmender Entfernung vom Hauptemittenten vor. So sind die pH-Werte im Mittel in den emittentennahen Auflagen um 1,5 pH-Einheiten höher als bei den emittentenfernen Auflagen. Während die emittentenfernen Auflagen dabei bereits etwa über den standorttypischen pH-Wert verfügen, sind die der nahen Standorte noch deutlich durch die Flugasche angehoben. Ebenso liegen in den Auflagen der emittentennahen Standorte sehr hohe Basensättigungen um 90 % und gegenüber den fernen Standorten um etwa 20 - 400 % höhere Metall-Gesamtgehalte vor. Der pH-Gradient ist außerdem die Ursache dafür, dass Metalle mit pH-abhängigen Mobilitäten sehr deutlich ausgebildete Entfernungsgradienten in ihren verfügbaren Gehalten aufweisen, wobei die verfügbaren Gehalte im Gegensatz zu den Gesamtgehalten mit zunehmender Entfernung zum Emittenten ansteigen. Anhand der Gesamtgehalte lässt sich nachweisen, dass die Flugaschebeeinflussung vor allem die Auflagen betrifft. Der Transport ganzer Flugaschepartikel in den Mineralboden wird anhand der vorliegenden Ergebnisse als unbedeutend angesehen. Dagegen erfolgt aber eine Verlagerung gelöster Flugaschebestandteile mit dem Sickerwasser. Diese führt dazu, dass ein flugaschebedingter Einfluss auf die pH-Werte, die Basensättigungen und die verfügbaren Gehalte der Basenkationen teilweise noch in 30 cm Tiefe feststellbar ist. Im tieferen Mineralboden überwiegen dann aber andere Standortfaktoren. Für die Analyse des Flugascheeinflusses ist der Oh-Horizont am besten geeignet. Hier liegen die eindeutigsten und stärksten Gradienten von allen beeinflussten bodenchemischen Parametern vor. Der Of-Horizont ist dagegen bereits durch den Einfluss der Vegetation (Basenpumpe) teilweise überprägt. Entsprechend der aktuellen Werte der eindeutig flugaschebeeinflussten Parameter lassen sich die Standorte zu drei unterschiedlich stark beeinflussten Gruppen zusammenfassen. Diese Gruppen spiegeln den Entfernungsgradienten wider und wurden deshalb als nahe, mittlere und ferne Standorte bezeichnet. Die in der vorliegenden Arbeit gefundene Gruppierung weist aber Veränderungen gegenüber der anhand der Rauchschäden der Bestände vorgenommenen Einteilung der Dübener Heide in vier Rauchschadenszonen auf [LUX 1965b]. So wird heute der ehemals stark beeinflusste Standort Ochsenkopf-BDF (RSZ 1) nicht mehr den nahen, sondern den mittleren Standorten zugeordnet, während ein Teil ehemals mäßig beeinflusster Standorte (RSZ 3) mit früher gering geschädigten Standorten (RSZ 4) zu einer Gruppe zusammengefasst werden. Ein Vergleich mit vorhandenen Literaturdaten zur Dübener Heide zeigt, dass die Unterschiede zwischen den Zonen (z. B. im pH-Wert) mit der Zeit mehr und mehr abnehmen und Nährstoffe (wie Calcium) langsam ausgewaschen werden. Bezüglich der Potentiale und Risiken kann angegeben werden, dass abgesehen von Cadmium, welches in der gesamten Dübener Heide erhöhte Werte aufweist, der Großteil der untersuchten Standorte über standorttypische mittlere Werte und Gehalte verfügt. Nur an den nahen Standorten treten überdurchschnittlich hohe pH-Werte, Basensättigungen, Calcium-Gesamtgehalte und Vorsorgewertüberschreitungen bei den Gesamtgehalten von Cadmium und Zink auf. Die hohen pH-Werte dieser Standorte führen aber dazu, dass die mobilen Schwermetall-Gehalte derzeit noch niedrige Werte aufweisen und die positive Wirkung der verbesserten Nährstoffsituation überwiegt. Dabei nimmt der Standort Burgkemnitz eine Sonderrolle ein, da er selbst gegenüber dem ebenfalls nahen Standort Buchholz über extrem hohe Calcium-Gehalte und in Verbindung mit seiner sehr mächtigen Auflage auch über sehr hohe Elementvorräte verfügt. Aufgrund der bereits zu beobachtenden Wiederversauerung und Abnahme der Calcium-Gehalte sind besonders für die nahen Standorte eine Verschlechterung der Nährstoffsituation und eine zunehmende Mobilisierung der Schwermetalle zu erwarten. Als Grundlage für die Abschätzung der Wirkung zukünftiger Veränderungen auf das Waldökosystem und die Bestände wurden deshalb Prognosen über die Entwicklung der relevanten flugaschebeeinflussten Parameter in den Auflagen der Dübener Heide aufgestellt. Mit Hilfe dieser Prognosen sollten sowohl das zu erwartende Ausmaß der Veränderung als auch deren zeitlicher Rahmen besser einschätzbar werden. Für die Prognosen wurden Altdaten, aktuelle Messwerte und die Ergebnisse eines Freisetzungsexperimentes genutzt, um daraus Trends über die mittlere Entwicklung in den beim Ist-Zustand gefundenen Entfernungsgruppen ableiten zu können. Zusätzlich wurden die Einflüsse verschiedener, in der Prognose nicht berücksichtigter Faktoren diskutiert. Mit der vorliegenden Arbeit steht damit aus bodenchemischer Sicht erstmals ein umfassendes Werkzeug für die Bewertung zukünftiger Entwicklungen in der Dübener Heide zur Verfügung. Die aufgestellten Prognosen lassen für die Auflagen der Dübener Heide die folgenden Aussagen zu: Die pH-Werte werden weiter fallen, so dass sich bereits in wenigen Jahrzehnten signifikante pH-Unterschiede zwischen den mittleren und fernen Standorten nicht mehr feststellen lassen werden. Die nahen Standorte werden sich zwar noch am längsten durch erhöhte pH-Werte auszeichnen, aber in etwa 150 Jahren wird in der gesamten Dübener Heide wieder der standorttypische pH-Wert von etwa 3,0 vorliegen. Verbunden mit der Abnahme der pH-Werte werden auch die Basensättigungen zurückgehen. Etwa 50 Jahre lang können die nahen Standorte noch als mindestens basenreich (> 50 % Basensättigung [AG-BODEN 2005]) angesehen werden. Gegen Ende des betrachteten Zeitraums von 150 Jahren ist dann mit einem einheitlichen Niveau der Basensättigung von ca. 20 % (Grenze zwischen mittelbasisch und basenarm [AG-BODEN 2005]) in den Auflagen der Dübener Heide zu rechnen. Die Vorräte von Calcium und Magnesium werden nach und nach ausgetragen, wobei die Hauptursache dafür bei Calcium die Auswaschung aufgrund der Wirkung saurer Niederschläge, bei Magnesium der Ernteentzug ist. Mindestens 50 Jahre kann aber an den nahen Standorten noch von einer überdurchschnittlich guten Calciumversorgung ausgegangen werden. Stellenweise kann aber trotz der hohen Vorräte bereits in 30 Jahren die Magnesiumversorgung zum wachstumsbegrenzenden Faktor werden, da nur ein relativ kleiner Teil des Magnesiums freisetzbar zu sein scheint. Bezüglich des Risikos nachteiliger Wirkungen aufgrund zu hoher verfügbarer Schwermetall-Gehalte sind nur Cadmium und Zink von Bedeutung. Die verfügbaren Gehalte dieser Schwermetalle werden im Zuge der Wiederversauerung ansteigen. Gleichzeitig erfolgt aber auch eine Auswaschung der Gehalte, die dem Anstieg der verfügbaren Gehalte und damit dem Überschreiten der Vorsorgewerte entgegenwirkt. Eine Gefährdung der Waldbestände ist demnach kaum zu erwarten. Die Toleranz der Bäume gegenüber Cadmium und Zink sollte aber trotzdem für langfristige waldbauliche Planungen berücksichtigt werden. / In this study the dynamics of nutrients and pollutants within fly ash-affected forest soils of the Dübener Heide, Germany, were examined concerning their current state and the future development to be expected. In the Dübener Heide large amounts of fly ash were deposited over decades, which had a crucial and lasting impact on the soil properties. Even 15 years after the abrupt end of the immissions this influence can still be proven. The ecosystem has adapted itself to the environmental conditions changed by the fly ash. However, after the loss of further immissions the system is subject to changes once again with yet unknown consequences for the forest. As a basis for sustainable forest planning and an adapted nature park management the current soil-chemical state of the Dübener Heide was examined and prognoses for the future development were derived within the ENFORCHANGE subproject of soil processes. For the determination of the current state 12 sites, that are representative for the typical soil types and stands of the Dübener Heide, were selected which have increasing distances to the coal-fired power plant Zschornewitz, regarded as the main emitter. Soil profiles, two meters in depth, were set up and sampled in depth stages. The soil samples were analyzed for different soil-chemical parameters by means of standard methods. The results were judged regarding the exceeding of mean, critical and limiting values as well as the occurrence of dependencies on depth or distance. By that means parameters which are definitely influenced by the fly ash as well as the most strongly affected depth stages were identified. These information were used afterwards in order to statistically divide the sites into groups of different grade of fly ash-affection. Furthermore current potentials and risks were estimated, and the previous development was judged by comparison with literature data. The results for the current soil-chemical state of the Dübener Heide can be summarized as follows: The pH value, the base saturation and the total contents of the metals aluminium, iron, calcium, magnesium, cadmium, cobalt, nickel and zinc were identified as definitely fly ash-affected. Decreasing values of these soil-chemical parameters are clearly observable with increasing distance from the main emitter. So on average, the pH values of the forest floor horizons close to the emitter are greater by about 1.5 pH units than that of sites far from the emitter. Thereby the forest floor horizons far from the emitter already have approximately the typical pH value while pH values are sill raised by the fly ash at the closed-by sites. Very high base saturations around 90 % and total metal contents, that are higher by approximately 20 400 % compared with more distant sites are present in the forest floor horizons of sites close to the emitter, too. In addition, the pH gradient is the cause for the fact that the available contents of metals with pH-dependent mobility exhibit very clearly formed distance gradients, with the available contents rising with the distance to the emitter contrary to the total contents of the metals. By means of the total contents it can be proven, that the influence of the fly ash mainly concerns the forest floor horizons. The transport of whole fly ash particles into the mineral soil is regarded as insignificant on the basis of the available results. However, a displacement of solved fly ash components with seepage water takes place. This leads to the fact, that a fly ash-induced influence on the pH value, the base saturation, and the available contents of the base cations is partly detectable as far as 30 cm in depth. However, in still deeper mineral horizons different location factors predominate. For the analysis of the fly ash influence the Oa-horizon is the most suitable. Here the clearest and strongest gradients of all affected soil-chemical parameters are present. The Oe-horizon is additionally marked in parts by the influence of the vegetation (base pump) According to the current values of the definitely fly ash-affected parameters the sites can be divided into three groups with different grade of fly ash-affection. The distance gradients are reflected in these groups, and that is why the groups were termed closed-by, intermediate and distant sites. However, the grouping found in the current study exhibits changes compared with the grouping of the Dübener Heide into the four smoke damage zones [LUX 1965b] according to the damage done to the stands by the smoke. Thus, today the formerly strongly affected site Ochsenkopf-BDF (RSZ 1) is no longer assigned to the closed-by but instead to the intermediate sites, while a part of the formerly moderately affected sites (RSZ 3) is now combined into one group together with formerly only slightly damaged site (RSZ 4). A comparison with existing literature data from the Dübener Heide shows, that the differences between the zones (e.g. in pH value) decrease more and more with time, and that nutrients (like calcium) are slowly washed out. Concerning the potentials and risks it can be indicated that apart from cadmium, which exhibits increased values over the entire Dübener Heide, the majority of the examined sites has averaged values and contents typical for the location. Only at the closed-by sites pH values, base saturations, total contents of calcium above the average and violations of limits of precaution of cadmium and zinc occur. But the high pH values at these sites lead to the fact, that the mobile heavy metal contents exhibit still low values at present, and that the positive effect of the improved nutrient situation predominates. The site Burgkemnitz takes a special position, since it has extremely high calcium contents and in connection with its very thick forest floor horizon also very high element stocks even in comparison with the likewise closed-by site Buchholz. Due to the already observable acidification and the decrease in calcium contents a degradation of the nutrient situation and an increasing mobilization of the heavy metals are to be expected particularly for the closed-by sites. Therefore, as a basis for the estimation of the effect of future changes on the forest ecosystem and the stands prognoses for the development of the relevant fly ash-affected parameters in the forest floor horizons of the Dübener Heide were derived. With the help of these prognoses both the extent of the change to be expected and its time frame should become better assessable. For the prognoses literature data, measured values of the current study and the results of a release experiment were used in order to be able to derive from it trends for the averaged development within the different groups of sites found for the current state. Additionally the influences of different factors not considered for the prognoses were discussed. So with this, for the first time there is available a comprehensive tool for the evaluation of future developments in the Dübener Heide from soil-chemical point of view. The set up prognoses allow the following statements for the forest floor horizons of the Dübener Heide: The pH values will continue to fall, so that already in a few decades significant pH differences between the intermediate and the distant sites will not be determinable any more. The longest time the closed-by sites will be characterised by increased pH values, but in approximately 150 years a location typical pH value of about 3.0 will be present over the entire Dübener Heide again. Connected with the reduction of the pH values the base saturation will decrease, too. About 50 more years the closed-by sites can still be regarded as at least base rich (> 50 % base saturation [AG-BODEN 2005]). But towards the end of the considered time of 150 years it has to be reckoned on a uniform level of the base saturation of approximately 20 % (threshold between medium-basic and base-poor [AG-BODEN 2005]) in the forest floor horizons of the Dübener Heide. The stocks of calcium and magnesium will be gradually decreased, for what the main cause is leaching due to the effect of acid precipitations for calcium and harvest removal for magnesium. At least for 50 more years it can be assumed that the closed-by sites will have a calcium supply good above average. In parts, however, despite the high stocks the magnesium supply can already become the growth-limiting factor in 30 years, since only a relative small part of magnesium seems to be available for leaching. Only cadmium and zinc are of importance concerning the risk of unfavourable effects caused by too high contents of mobile heavy metals. The available contents of these heavy metals will rise as the result of increasing acidification. But at the same time leaching of the metals takes place what counteracts the rise of the available contents and thus the violation of the limits of precaution. According to this an endangerment of the forest stands is hardly to be expected. However, for long-term forest-structural planning the tolerance of the trees with respect to cadmium and zinc should be considered nevertheless.

Μεγάλο τμήμα της παραγόμενης ενέργειας στην Ελλάδα προέρχεται από την καύση λιγνίτη στην Βόρεια (Δυτική Μακεδονία) και Νότια (Πελοπόννησος) Ελλάδα. Η καύση του λιγνίτη έχει ως αποτέλεσμα την παραγωγή μεγάλων ποσοτήτων στερεών παραπροϊόντων, όπως η ιπτάμενη τέφρα (ΙΤ) και η τέφρα πυθμένα (ΤΠ), των οποίων η συνολική παραγωγή ανέρχεται σήμερα σε 14Mt ετησίως. Η ποσότητα των παραπροϊόντων αυτών αναμένεται να αυξηθεί τα επόμενα χρόνια εξ’ αιτίας της συνεχώς χαμηλότερης ποιότητας λιγνίτη που χρησιμοποιείται (χαμηλότερη θερμογόνος δύναμη). Ένα τμήμα της παραγόμενης ΙΤ (10-12%) στην Ελλάδα αξιοποιείται ως πρώτη ύλη στη παραγωγή τσιμέντου, ενώ η ΤΠ δεν απορροφάται μέχρι σήμερα από καμία εφαρμογή, κυρίως λόγω του υψηλού ποσοστού άνθρακα που περιέχει. Το αντικείμενο της παρούσας διατριβής είναι η αξιοποίηση, πρωτίστως, της ΤΠ και, μετέπειτα, της ΙΤ ως πρώτες ύλες στην παραγωγή τεχνητών ελαφροαδρανών για χρήση τους στην παραγωγή ελαφροσκυροδέματος. Για την παραγωγή των τεχνητών ελαφροαδρανών εφαρμόστηκε η διεργασία της πυροσυσσωμάτωσης σε σχάρα (grate sintering) έπειτα από σφαιροποίηση μιγμάτων των δύο τεφρών. Πραγματοποιήθηκε διερεύνηση των φυσικοχημικών χαρακτηριστικών των λιγνιτικών τεφρών (Κεφάλαιο 2) με σκοπό τον προσδιορισμό και την κατανόηση των χαρακτηριστικών τους, τα οποία αναμένεται να έχουν σημαντική επίδραση στην εφαρμογή της διεργασίας και στην ποιότητα του παραγόμενου προϊόντος. Επιπλέον, γίνεται αναλυτική αναφορά στα βασικά χαρακτηριστικά των διεργασιών σφαιροποίησης και πυροσυσσωμάτωσης (Κεφάλαιο 3). Για την εφαρμογή της επιλεγμένης διεργασίας παραγωγής τεχνητών ελαφροαδρανών πραγματοποιήθηκε σχεδιασμός μιγμάτων με διαφορετικές αναλογίες ΤΠ και ΙΤ (Κεφάλαιο 4). Ο περιεχόμενος άνθρακας της ΤΠ αποτελεί το καύσιμο της διεργασίας πυροσυσσωμάτωσης, ενώ η υψηλή περιεχόμενη υγρασία της ΤΠ αξιοποιείται ως το κύριο συνδετικό υλικό κατά την διάρκεια σφαιροποίησης για τον σχηματισμό σφαιριδίων. Οι διαφορετικές αναλογίες ΤΠ και ΙΤ αντιστοιχούν σε διαφορετικό ποσοστό στερεού καυσίμου στο μίγμα (προκύπτει από τις διαφορετικές vi αναλογίες), μία παράμετρος η οποία έχει επίδραση στην ολοκλήρωση της πυροσυσσωμάτωσης και στην ποιότητα του παραγόμενου (ελαφροαδρανούς) προϊόντος. Η πυροσυσσωμάτωση ολοκληρώθηκε με επιτυχία με ελάχιστο ποσοστό στερεού καυσίμου (περιεχόμενο άνθρακα ΤΠ) 6.5%κβ (Κεφάλαιο 5). Πραγματοποιήθηκε φυσικοχημικός χαρακτηρισμός όλων των προϊόντων της πυροσυσσωμάτωσης των μιγμάτων λιγνιτικών τεφρών της Μεγαλόπολης, και διαπιστώθηκε ότι το ποσοστό περιεχόμενου άνθρακα της ΤΠ είναι μια πολύ σημαντική παράμετρος για την παραγωγή ελαφροαδρανών υλικών. Ο σχηματισμός πορώδους δομής στο εσωτερικό των πυροσυσσωματωμένων πελλετών, στην οποία οφείλεται και το χαμηλό βάρος των παραγόμενων αδρανών, προκαλείται από την ταυτόχρονη εξέλιξη δύο διεργασιών: α) την παραγωγή αερίων σε υψηλές θερμοκρασίες και β) τον σχηματισμό ρευστής φάσης στην εξωτερική επιφάνεια της πελλέτας στο ίδιο χρονικό διάστημα (Κεφάλαιο 6). Οι αντοχές των πυροσυσσωματωμένων πελλετών οφείλονται σε αντιδράσεις και στον σχηματισμό νέων φάσεων είτε στερεών μέσω διάχυσης είτε ρευστών που προέρχονται από επιτήξεις στα όρια των κόκκων. Στην συνέχεια τα παραγόμενα ελαφροαδρανή χρησιμοποιήθηκαν για την παραγωγή δοκιμίων θερμομονωτικού και δομικού ελαφροσκυροδέματος και πραγματοποιήθηκε έλεγχος των θερμικών και μηχανικών τους ιδιοτήτων, αντίστοιχα (Κεφάλαιο 7). Τα αποτελέσματα δείχνουν ότι τα τεχνητά ελαφροαδρανή μπορούν να χρησιμοποιηθούν για την παραγωγή θερμομονωτικού και δομικού ελαφροσκυροδέματος. Η επιτυχής παραγωγή τεχνητών ελαφροαδρανών από μίγματα λιγνιτικών τεφρών Μεγαλόπολης αποτέλεσε και την βάση για δοκιμές πυροσυσσωμάτωσης των παραπροϊόντων αυτών με άλλα στερεά βιομηχανικά παραπροϊόντα όπως η ερυθρά ιλύς (ΕΙ), η οποία παράγεται από την επεξεργασία βωξίτη προς παραγωγή αλουμινίου (Κεφάλαιο 8). Για την διαπίστωση της συνεργασίας των δύο διαφορετικών παραπροϊόντων πραγματοποιήθηκε προσθήκη μέχρι και 30%κβ ΕΙ σε μίγματα λιγνιτικών τεφρών. Πραγματοποιήθηκε φυσικοχημική διερεύνηση των προϊόντων της πυροσυσσωμάτωσης και χρήση τους στην παραγωγή δοκιμίων σκυροδέματος. Τα αποτελέσματα δείχνουν ότι η αύξηση της προστιθέμενης ΕΙ στο μίγμα λιγνιτικών vii τεφρών της Μεγαλόπολης επιφέρει αύξηση στο βάρος των παραγόμενων αδρανών, ενώ μπορούν να χαρακτηριστούν ελαφροαδρανή τα προϊόντα πυροσυσσωμάτωσης μιγμάτων μέχρι και 20%κβ προσθήκης ΕΙ. Τα αποτελέσματα των μετρήσεων των μηχανικών αντοχών των δοκιμίων σκυροδέματος δείχνουν ότι η ΕΙ επιφέρει αύξηση στις αποκτώμενες αντοχές σε ποσοστό προσθήκης μέχρι και 15%κβ. Η εφαρμογή που προτείνεται σε αυτή την διατριβή για την παραγωγή τεχνητών ελαφροαδρανών υλικών από τα στερεά λιγνιτικά παραπροϊόντα του ΑΗΣ Μεγαλόπολης αποτελεί την πρώτη πρόταση για αξιοποίηση της ΤΠ στην Ελλάδα. Η πυροσυσσωμάτωση μιγμάτων των λιγνιτικών τεφρών μπορεί να οδηγήσει στην παραγωγή τεχνητών ελαφροαδρανών για χρήση τους στο δομικό και θερμομονωτικό ελαφροσκυρόδεμα ενώ ο περιεχόμενος άνθρακας της ΤΠ, ο οποίος αξιοποιείται ως το καύσιμο διεργασίας παραγωγής, αποτελεί σημαντική παράμετρο για την ποιότητα των τεχνητών ελαφροαδρανών. Επιπλέον, οι λιγνιτικές τέφρες της Μεγαλόπολης μπορούν να συνεργαστούν με άλλα στερεά βιομηχανικά παραπροϊόντα όπως η ΕΙ για την παραγωγή τεχνητών ελαφροαδρανών διαφορετικής ποιότητας. Επίσης, η συγκεκριμένη πρόταση αφορά στην μαζική αξιοποίηση της ΤΠ και πιθανή εφαρμογή έχει την δυνατότητα να απορροφήσει το μεγαλύτερο τμήμα του παραγόμενου αυτού παραπροϊόντος. / Large part of energy demand in Greece is covered by lignite combustion in West Macedonia and Peloponnesus. Lignite combustion results in production of, approximately, 14Mt/year of solid byproducts, such as fly ash (FA) and bottom ash (BA). The quantity of these byproducts is going to be increased in future because of the low quality of available lignite (lower calorific value). Part of FA (10-12%) produced in Greece is utilized as raw material in cement production while there is no application of BA, mainly because of its high carbon content. This study investigates a new method for utilization of BA, primarily, and FA, afterwards, as raw materials in the production of lightweight aggregates and further utilization of produced aggregates in lightweight aggregate concrete. A two stage process, pelletization and sintering, is applied in BA and FA mixtures. Physical and chemical analyses of Megalopolis lignite ashes are performed (Chapter 2) in purpose of characterization of process raw materials. Furthermore, fundamental theory of pelletization and grate sintering is presented (Chapter 3) in purpose of better understanding of process details. Mixtures of different BA/FA ratio are prepared for sintering tests (Chapter 4). Carbon contained in BA is utilized as the fuel of the process, while high water content of BA is utilized as the primary binding material during pelletization in purpose of pellets formation. Different BA/FA ratios represent different solid fuel percentages in sintering mixtures. This is an important parameter, which strongly affects the completion of the process and the quality of product. Successful completion of sintering process is achieved with minimum solid fuel content (BA carbon) 6.5wt% in mixture (Chapter 5). Physical and chemical characterization is performed for products of all different sintering mixtures. The results show that BA carbon content is an important parameter for the production of lightweight aggregates. Porous structure formation inside the sintered pellets, which is responsible for aggregates low weight, is caused by simultaneous development of two different processes: a) production of gases in high temperatures and, b) liquid (glassy) phase formation in the outer part of pellets in the same time period (Chapter 6). ix Formation of either solid state bonds, through diffusion, and/or glassy phase bonds at the points of particles mutual contact are responsible for pellet strength. Lightweight aggregates produced are used in the production of insulating and structural lightweight aggregate concrete specimens and thermal and mechanical tests are performed, respectively. According to tests results artificial lightweight aggregates can be used for insulating and structural purposes. The successful experimental results from the utilization of lignite solid byproducts in the production of LWA offered new opportunities for collaboration of these byproducts with other industrial solid residues, such as red mud (RM) which is produced during bauxite treatment for aluminum production (Chapter 8). In purpose of investigation of collaboration of these different byproducts sintering mixtures are prepared with low RM addition, up to 30wt%, in lignite ashes mixtures. Physical and chemical characterization is performed for products of all sintering mixtures and they are used for production of concrete specimens. Results show that increase of RM addition brings increase in aggregates weight, while aggregates formed by RM addition up to 20wt% can be considered as lightweight ones. The results of mechanical strength tests in concrete specimens show that RM addition up to 15wt% brings increase in aggregates strength. This is the first proposed method for utilization of lignite BA in Greece in the production of lightweight aggregates. Sintering of mixtures of lignite ashes results to the production of lightweight aggregates and the produced aggregates can be used for insulating and structural lightweight aggregate concrete. BA carbon content, which is utilized as the fuel of the process, is an important parameter for lightweight aggregate production and porous structure formation. Furthermore, Megalopolis lignite ashes can be treated in collaboration with other industrial solid byproducts, such as RM for the production of lightweight aggregates of different quality. Finally, the proposed method targets to massive utilization of BA produced in Megalopolis power station.

In recent decades, advances in low NOₓ coal combustion and increasingly strict CO₂ reduction mandates have changed power plant boiler operations quite significantly. As a result of these necessary efforts, the characteristics of fly ash generated at many power plants have also changed. In particular, increases in unburned carbon content have been observed with detrimental implications on the utility of these fly ashes in concrete applications. Over the same time period, the combustion of biomass for energy generation has received increased attention due to the potential benefits of reducing CO₂ emissions and improved sustainability when compared to fossil fuel combustion. Biomass is directly burned, gasified, or co-fired with coal to achieve this goal. Currently, close to 120 million metric tons of coal combustion by products are produced in the U.S. annually. As with coal combustion, production of energy from biomass combustion/gasification results in significant by-product generation that must either be productively reused or geologically disposed. While much research effort has been devoted to understanding the properties and potential productive reuse alternatives for coal combustion residuals, relatively little work has been done on the by-products of biomass combustion. This study investigated the properties and engineering behavior of sixteen ash samples that were produced in eleven different power plants. Specifically, three high carbon content Class F fly ashes, eight coal and biomass co-fired ashes, three pure biomass ash samples, and two high quality, low carbon content ash samples, one of which is commercially marketed (for reference) were chosen. The various ash samples were characterized by means of: electron microscopy; laser diffraction and dry sieve particle size analysis; loss on ignition and total organic carbon analysis; specific surface area analysis; as well as x-ray fluorescence and x-ray diffraction. The ash samples were also investigated for their potential engineering application in the fired clay brick industry, as low-cost adsorptive agents, and in alkali activated geopolymer synthesis for geotechnical and geoenvironmental applications. Results from physical and chemical characterization of the ash samples show no significant differences between pure coal ash and coal co-fired with biomass ash samples from the same power plant. However, there are significant morphological, chemical, and mineralogical differences between coal ash and pure biomass ash. Unlike pure coal ash, biomass ash is not composed primarily of aluminosilicate glass cenospheres but rather consists mainly of charred, fibrous woody remnants with elevated calcite content as compared to coal ash. Bench scale fired bricks produced by partial replacement of clay material with high carbon coal ash, co-fired ash, and pure biomass ash, respectively, was successful. Physical properties of a number of the mix designs exceeded the highest ASTM weathering grade requirements. As sorptive agents, high carbon concentrates from coal and co-fired ash samples, along with all the biomass ash samples, showed significant uptake of lead. The unaltered as- received ash samples (i.e. no acid or steam activation) showed only moderate arsenic (V) and selenium (VI) sorption capacity. Finally, solidification/stabilization by geopolymerization of high carbon content, co-fired ash with as little as 3 molar NaOH in the activator solution was successful, possibly paving the way for various geotechnical and geoenvironmental applications in ground improvement and soil/ash-pond stabilization.

Expansive soils are one of the most serious problems which the foundation engineer faces. Several attempts are being made to control the swell-shrink behavior of these soils. One of the most effective and economical methods is to use chemical additives. Fly ash and desulphogypsum, both of which are by-products of coal burning thermal power plants, are accumulating in large quantities all over the world and pose serious environmental problems. In this study, the expansive soil was stabilized using the fly ash and desulphogypsum obtained from &Ccedil / ayirhan Thermal Power Plant. Fly ash and desulphogypsum were added to the expansive soil from 0 to 30 percent. Lime was used to see how efficient fly ash and desulphogypsum on expansive soil stabilization were, and was added to the expansive soil from 0 to 8 percent. The properties obtained were chemical composition, grain size distribution, consistency limits, swelling percentage, and rate of swell. Fly ash, desulphogypsum, and lime added samples were cured for 7 days and 28 days, after which they were subjected to free swell tests. Swelling percentage decreased and rate of swell increased with increasing stabilizer percentage. Curing resulted in further reduction in swelling percentage and further increase in rate of swell. 25 percent and 30 percent fly ash and desulphogypsum additions reduced the swelling percentage to levels comparable to lime stabilization.

In recent years, scientific studies are carried out to find new refractory material. Having good mechanical properties under very high temperatures, refractories are widely used in industries like iron, steel, glass, cement and pottery. Researches are focused on monolithic refractory making because of their superior properties comparing to conventional firebrick refractories. Providing a mono-block body, having no joints makes the monolithic refractories more durable at elevated temperatures. Easier production and installation are two main points that people are choosing monolithic refractories, thus an economy is made. In this study, for monolithic refractory production, high alumina cement was used as binding material. It is known that the increase in alumina (Al2O3) content increases the high temperature resistance, so that crushed firebrick, having 85% Al2O3 was used as aggregate. Pozzolanic materials, which are silica fume, fly ash, ground granulated firebrick and ground granulated blast furnace slag, were added to improve physical and mechanical properties of mortar. With the addition of steel fibres, change in compressive strength and flexural strength was observed.Superplasticizer was used to understand its behaviour under high temperatures. Portland cement containing mortars were also prepared to make comparison with high alumina cement containing specimens. Specimens were prepared in 5x5x5 cm and 4x4x16 cm prisms. They were cured for one day at curing room, then heated to 105&deg / C and then heated to 1100&deg / C. Weight, size and ultrasound velocity change, compressive strength and flexural strength tests were done to determine physical and mechanical properties of the monolithic refractories, before and after heating. Heated and non-heated specimens were pulverized for microstructural investigation with X-Ray diffraction (XRD) method. Using high alumina cement with 50 &ndash / 60 % granulated blast furnace slag or granulated firebrick, by the weight of cement, and crushed firebrick as aggregate, a satisfactory monolithic refractory material was made. It was observed that, mechanical properties were decreased at the Portland cement used mortars after several times of heating and cooling cycles. Also, it was determined that the microstructure of the high alumina cement containing mortars did not deteriorate much at 1100&deg / C, as long as there was no change observed from the results.

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

Thallium is a highly toxic element that humans are exposed to mainly by consumption of drinking water and vegetables grown in soil with high thallium content but also through inhalation of particles in the air. Thallium is also present in fossil fuels, alloys, and in electronic utilities. The increasing use of the element and emissions from notably energy production has lead to a higher load on the surface of the Earth. This study aims at increasing the knowledge about the behaviour of thallium in aquatic environments. Focus has been on the redox chemistry of thallium in relation to its mobility, which is of great importance because Tl(I) and Tl(III) have very different properties in this respect. The relationship between Tl(I) and Tl(III) in surface waters from contaminated and uncontaminated environments was examined by ion chromatography connected on line to ICP-MS (inductively coupled plasma mass spectrometry). It was found in controlled systems that even though Tl(III) is thermodynamically unstable under fresh water conditions Tl(I) was oxidised in the presence of light and iron(III). This was also confirmed in field studies. When lake water samples were exposed to light, Tl(I) was oxidised and thallium was lost from the solution. The most likely explanation for this was adsorption of thallium to particle surfaces. The concentration of thallium in Swedish lakes and soil were measured. In unpolluted lakes the concentration ranges between 4.5-12 ng/l, the sediment concentration was 0.07-1.46 mg/kg. The anthropogenic load was found to have increased since the end of the Second World War although concentrations above background were found since the early industrialisation. In contaminated areas the concentration in soil ranges from 0.64-88 mg/kg, high concentrations were found in systems with alum shale and in soil exposed to runoff from a lead and zinc enrichment plant. The mobilisation of thallium from solid phases in contaminated areas was dependent on pH and about 50% of the leachable content was mobilised already at pH 5-6. Once it had been released to water it was highly mobile. These conditions suggest that in a large part of the Swedish environment a high mobility of thallium can be expected.