Many highway and hydraulic structures in North America have been reported to be affected by alkali aggregate reaction (ASR). It is anticipated that most of these structures will be demolished as they approach the end of their service lives. Recycling demolished concrete as aggregates in new concrete is an option that not only reduces the amount of construction demolition waste (CDW) disposed in landfills but also lessens the consumption of non-renewable resources such as natural aggregates. However, the use of recycled concrete aggregate (RCA) in new concrete requires detailed research to make sure that the durability of the recycled material is not compromised, especially if the RCA had been previously affected by ASR. In this research project, coarse recycled concrete aggregate (RCA) is reclaimed and processed from distinct members (i.e. foundation blocks, bridge deck and columns) of an ASR-affected overpass after nearly 50 years of service. RCA concrete mixtures incorporating 50 and 100% replacement are manufactured and stored in conditions enabling further ASR development. Mechanical (i.e. Stiffness Damage Test - SDT) and microscopic (Damage Rating Index - DRI) analyses are performed at a fixed “secondary” induced expansion of 0.12%. Results show that the overall performance of the ASR-affected recycled mixtures depends upon the “past” condition of the RCA particles. Moreover, the DRI was able to capture the “past” and “secondary” induced expansion and damage of affected RCA while the SDT only detected the “secondary” distress development. Lastly, an adapted version of the DRI was proposed to further evaluate the overall damage of recycled concrete along with properly displaying “past” and “secondary” induced distress.

No description available.

Thesis (MScEng) --University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis deals with the development of a new process for the production of Direct Reduced Iron (DRI), intended for use specifically by small scale Electric Arc Furnace (EAF) based steel mills, who require small volumes of DRI. The term development as used here is taken to include such aspects as conceptual design, theoretical verification and initial practical testing. The rise of EAF steelmaking brought about the metamorphosis of steel scrap from a waste product into a valuable raw material. Scrap prices rose steeply during the period 1995 to 2009 compelling EAF steelmakers, wishing to have more control over the cost of their input material, to seek for scrap supplements or alternatives. DRI has become an accepted and sought after supplement, or even complete alternative, to steel scrap. Adding DRI to an EAF charge has a range of advantages, including the dilution of tramp elements and possible cost benefits, but it does have negative effects. These include the lowering of the scrap to liquid metal yield and an increase in power consumed. The effect of charging DRI to a small EAF is quantified. The maximum DRI that may be added to the burden whilst still maintaining the present steelmaking volume, is shown to be as high as 50% if charged continuously, and the maximum price payable for DRI, is shown to be approximately 80% of base grade scrap price. Finally other requirements unique to small scale EAF operators are considered in order to prepare a schedule of requirements for a DRI plant specifically for small scale EAF steel mills. A review of published information on existing DRI production technology, processes and plants is undertaken is establish the fit of existing processes to the requirements set. Initially the thermodynamics and kinetics of iron ore reduction and coal gasification, specifically downdraft gasification are reviewed. Thereafter existing processes are reviewed. Shaft based processes and rotary kiln based processes are identified as possible suitors to the requirements. Limitations of these processes, specifically heat transfer in rotary kilns and the pressure drop over a reduction shafts are investigated. Finally a typical process in each of the main process classes is adjudicated against the set requirements. None is found to match the set requirements. A new process is proposed that is claimed to better suit to small scale operation. The uniqueness of the process is embodied in the combination of existing technologies of downdraft gasification and iron ore reduction in a shaft, in a single reactor. The process consists of two shafts, one placed above the other. Iron ore is charged into the top shaft, called the pre-heat shaft, where it is pre-heated and lightly reduced to wustite with gas from the bottom shaft, called the reduction shaft. The pre-heated ore is then charged together with coal into the reduction shaft. Gasification air is drawn into the top of the reduction shaft where the coal is gasified in a downdraft gasifier, generating reduction gas which reduces the ore as the gas moves concurrently with the iron ore. The exit gas is cleaned and pumped to the pre-heat shaft where it combusted with air to pre-heat the iron ore in the pre-heat shaft. The concept is analysed thermodynamically using amongst others, FactSage, and is shown to be thermodynamically viable. To test the concept process concept practically, an extremely small pilot plant with a production rate of 2kg DRI/h, consisting of only a gasifier/reduction shaft, was designed and constructed using reduction rate data obtained from literature supplemented with data obtained from thermogravimetric analysis of CO reduction of lump Sishen hematite. Pilot Plant trials were performed using various reductant sources. The degree of metallizaion was analysed using visual inspection of cut and polished samples compared to calibrated standards. Analysis of the results indicate that coal rate and production rate influence the degree of reduction positively and negatively. The conclusions arrived at include the fact that the process is thermodynamically viable, that it was possible to reduce iron ore in a simplified pilot plant, and that the process was found to be stable and controllable. It is recommended that a larger scale pilot plant, embodying the full proposed flow sheet be erected to test the process more completely. / AFRIKAANSE OPSOMMING: Die tesis handel oor die the ontwikkeling van ‘n nuwe proses vir die vervaardiging van sponsyster. Die proses is beoog spesifiek vir gebruik deur kleinskaalse Elektriese Boogoond (EBO) gebaseerde staal aanlegte, wat kleiner hoeveelhede sponsyster benodig. Die term ontwikkeling soos hier gebruik word aanvaar om aspekte soos konseptuele ontwerp, teoretiese verifikasie en aanvanklike toetsing te behels. Die vinnige groei van EBO staalvervaardiging het skroot getransformeer van weggooiproduk tot waardevolle grondstof. Die prys van skroot het skerp gestyg gedurende die periode 1995 to 2009. EBO gebaseerde staal produsente, in ‘n poging om meer beheer te hê oor die koste van hul insetmateriaal, het hul in ‘n toenemende mate tot skrootalternatiewe gewend. Sponsyster het ‘n aanvaarde en gewaardeerde byvoeging, en selfs alternatief tot staalskroot geword. Die byvoeging van sponsyster by die lading van ‘n tipiese EBO het besliste voordele, maar het dit ook nadelige effekte. Die voordele sluit die verdunning van reselemente en moontlike kostevoordele in, terwyl van die nadele die verlaging van die skroot tot vloeistaal opbrengs, en ‘n verhoging in kragverbruik, is. Die effek van die byvoeging van sponsyster tot ‘n EBO lading word gekwantifiseer. Daar word getoon dat die maksimum hoeveelheid sponsyster wat by ‘n EBO lading gevoeg kan word terwyl die hoeveelheid staal geproduseer konstant gehou word, ongeveer 50% is indien die sponsyster kontinue gelaai word, en die maksimum prys wat vir die sponsyster betaal kan word, word bereken op ongeveer 80% van die prys van basisgraad skroot. Ander vereistes uniek aan kleinskaal EBO bedrywers word oorweeg ten einde ‘n lys van vereistes vir ‘n sponsysteraanleg, uniek aan kleinskaal EBO bedrywers, te kan bepaal. ‘n Oorsig van gepubliseerde inligting oor sponsysterproduksietegnologie word onderneem ten einde die passing van bestaande prosesse met die gestelde vereistes te kan bepaal. Nadat die termodinamika en kinetika van ysterertsreduksie en steenkoolvergassing be-oordeel is, word bestaande sponsysterprosesse beskou. Skag- en Roterende oond gebaseerde prosesse word as moontlik gepaste prosesse identifiseer. Hitte-oordrag en die drukval oor gepakte beddens, synde tipiese beperkings eie aan die twee prosesse, woord beskou. Tipiese prosesse in elk van die hoofklasse van prosesse word ten laaste be-oordeel aan die gestelde kriteria. Daar word bevind dat geeneen van die bestaande prosesse aan die vereistes voldoen nie. ‘n Nuwe proses, wat skynbaar die behoefte van kleinskaalse EBO gebaseerde staalprodusente beter bevredig, word voorgestel. Bestaande tegnolgie word in ‘n unieke opstelling geïntegreer. Reduksie word in ‘n reduksiekag gedoen as gevolg van die ooglopende massa- en hitte-oordragvoordele van ‘n skag. Reduksiegas word verkry van steenkoolvergassing in ‘n afstroomvergasser ten einde teerverwydering in ‘n naverwerkingsstap oorbodig te maak. Die uniekheid van die proses is beliggaam in die kombinasie van ‘n steenkoolvergasser en reduksieskag in ‘n enkele reaktor. Die proses bestaan uit twee skagte, een bo die ander. Ystererts word in die boonste skag, wat die voorverhitskag genoem word, gelaai. Hier word die erts voorverhit en moontlik lig gereduseer tot wustiet met gas van die onderste skag, wat die reduksieskag genoem word. Die voorverhitte erts word saam met steenkool in die reduksieskag gelaai. Vergassingslug, word in die reduksieskag gesuig waar die steenkool in ‘n afstroomvergasser vergas word. Hierdeur word reduksiegas gegenereer wat die erts verder reduseer soos dit saamstromend met die erts af beweeg. Die uitlaatgas word gesuiwer en na die voorverhitskag gepomp waar dit verbrand word om die erts te voorverhit. Die konsep is termodinamies analiseer met gebruikmaking van onder andere FactSage, en werkbaar bevind. ‘n Baie klein, vereenvoudigde proefaanleg, met ‘n produksievermoë van 2kg DRY/uur, bestaande uit slegs ‘n reduksiekag, is ontwerp en gebou met gebruikmaking van kinetika inligting uit die literatuur aangevul met inligting uit termogravimetriese analise van die CO reduksie van Sishen hematiet. Proefaanleglopies is uitgevoer met ‘n reeks reduktantbronne. Die metallisasiegraad is bepaal deur visuele inspeksie van gesnyde, gepoleerde monsters wat vergelyk is met gekalibreerde standaarde. Analise van die resultate toon dat die steenkoolkoers ‘n positiewe verband, en die produksiekoers ‘n negatiewe verband met die metallisasiegraad het. Die slotsom waartoe gekom is, is dat die proses termodinamies werkbaar is, dat reduksie van ystererts in ‘n vereenvoudigde proefaanleg bewerk kon word, en dat die prose stabiel en beheerbaar voorgekom het. Die aanbeveling word gemaak dat ‘n groter proefaanleg wat die volledige voorgestelde vloeiskema verteenwoordig, opgerig behoort te word, ten einde die proses meer volledig te kan toets.

<p>In a prospective randomised double-blind study eighty patients with MRI verified lumbar disc herniation and corresponding clinical findings underwent microscopic disc removal. The patients were peroperatively given systemic and local corticosteroids or placebo, and followed for 2 years. The hospital stay and time to return to full-time work was significantly shorter in the treatment group. Pain measured as worst pain during the last week was also lower in the corticosteroid group. The results indicate that peroperative treatment with corticosteroids reduces pain and improves the functional outcome in patients operated for lumbar disc herniations.</p><p>To evaluate whether thermal quantitative sensory testing (QST) is applicable in the study of sensory dysfunction in lumbar disc herniations 66 patients with disc herniations underwent thermal QST. We found that thermal QST reflects sensory dysfunction in patients with lumbar disc herniations. However, thermal QST seems to have a poor predictive value for identifying the anatomic location of a herniated lumbar disc.</p><p>Quantitative sensory testing (QST) was used to detect damage to the myelinated A-delta fibres (cold sense) and the unmyelinated C-fibres (warmth sense). Corticosteroids combined with surgery in lumbar disc surgery improved the normalisation for the warmth disturbance compared to the control group. </p><p>A prospective analysis was performed on the predictive value of preoperatively determined lumbar lordosis and flexion for pain and disability in patients treated by microscopic lumbar disc surgery. Preoperative hyperlordosis correlated to more pain postoperatively (p=0.004). In patients with hypoflexion there was an association between hyperlordosis and moderate or severe pain postoperatively (p<0.001). The same outcomes were found for DRI. The stiff and straight back indicates a good outcome of lumbar disc surgery concerning pain and disability. </p>

In a prospective randomised double-blind study eighty patients with MRI verified lumbar disc herniation and corresponding clinical findings underwent microscopic disc removal. The patients were peroperatively given systemic and local corticosteroids or placebo, and followed for 2 years. The hospital stay and time to return to full-time work was significantly shorter in the treatment group. Pain measured as worst pain during the last week was also lower in the corticosteroid group. The results indicate that peroperative treatment with corticosteroids reduces pain and improves the functional outcome in patients operated for lumbar disc herniations. To evaluate whether thermal quantitative sensory testing (QST) is applicable in the study of sensory dysfunction in lumbar disc herniations 66 patients with disc herniations underwent thermal QST. We found that thermal QST reflects sensory dysfunction in patients with lumbar disc herniations. However, thermal QST seems to have a poor predictive value for identifying the anatomic location of a herniated lumbar disc. Quantitative sensory testing (QST) was used to detect damage to the myelinated A-delta fibres (cold sense) and the unmyelinated C-fibres (warmth sense). Corticosteroids combined with surgery in lumbar disc surgery improved the normalisation for the warmth disturbance compared to the control group. A prospective analysis was performed on the predictive value of preoperatively determined lumbar lordosis and flexion for pain and disability in patients treated by microscopic lumbar disc surgery. Preoperative hyperlordosis correlated to more pain postoperatively (p=0.004). In patients with hypoflexion there was an association between hyperlordosis and moderate or severe pain postoperatively (p&lt;0.001). The same outcomes were found for DRI. The stiff and straight back indicates a good outcome of lumbar disc surgery concerning pain and disability.

Ce travail de thèse est consacré à la modélisation du procédé de réduction directe du minerai de fer, un procédé alternatif intéressant dans le contexte de la réduction des émissions de CO2 de la sidérurgie. Le four à cuve, réacteur central du procédé, est divisé en trois zones (réduction, transition et refroidissement). Le modèle mathématique mis au point pour simuler l’ensemble repose sur une description détaillée et fidèle des principaux phénomènes physico-chimiques et thermiques intervenant. C’est un modèle bidimensionnel, en régime permanent et multi-échelle. Le lit mobile est constitué de boulettes, elles-mêmes supposées composées de grains et de cristallites. Huit réactions chimiques hétérogènes et deux réactions chimiques homogènes sont prises en compte. Les équations de conservation locales de la masse, l'énergie et de la quantité de mouvement ont été résolues numériquement en utilisant la méthode des volumes finis. Ce modèle a été appliqué avec succès pour simuler le four à cuve de deux usines de réduction directe de capacités différentes. Les résultats obtenus renseignent sur le fonctionnement interne du four et mettent en évidence des zones aux performances inégales. Le modèle a ensuite été exploité, après l’ajout et le couplage d’un modèle du reformeur, pour des calculs paramétriques, en particulier lorsque les caractéristiques des gaz réducteurs sont modifiées. Enfin des pistes sont présentées pour optimiser une installation de réduction directe en augmentant la capacité de production et le degré de métallisation du produit / This thesis is dedicated to the modelling of the iron ore direct reduction process, an attractive alternative process for making steel in the context of the reduction in CO2 emissions. The shaft furnace, the core reactor of the process, is divided into three sections (reduction, transition and cooling). The mathematical model developed to simulate this reactor is based on a detailed and faithful description of the main physical-chemical and thermal phenomena involved. The model is a two-dimensional, steady state and multi-scale. The moving bed is comprised of pellets of grains and crystallites. Eight heterogeneous chemical reactions and two homogeneous chemical reactions were taken into account. The local mass, energy and momentum balances were solved numerically using the finite volume method. The model was successfully applied to simulate the shaft furnace of two direct reduction plants of different capacities. The results obtained provide new insights on the internal behaviour of the furnace and highlight zones of uneven performance. After the addition and coupling of a reformer model, the shaft furnace model was used for parametric calculations, in particular when considering changes in the composition of the reducing gases. Finally, new possibilities are presented for optimizing the direct reduction process, e.g. for increasing the production capacity and the degree of metallization of the produced iron

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

Concrete has proven to be, by far, one of the most reliable materials for the construction of critical infrastructure. However, despite its structural capacity, concrete members are susceptible to damage mechanisms that may decrease its performance and durability throughout its service life. One such mechanism is alkali-silica reaction (ASR), which takes place when unstable siliceous phases present in coarse or fine aggregates react with the alkali hydroxides from the concrete pore solution, generating a secondary product (i.e., ASR gel); this product swells upon moisture uptake from the surrounding environment, leading to cracking and expansion of the affected concrete. In severe cases of ASR-affected infrastructure, structural safety could become a problem, and thus requiring the demolition of affected members. It is, therefore, necessary to adopt effective protocols for the diagnosis and prognosis of aging infrastructure, to ensure its performance over time along with properly planning for rehabilitation strategies, whether required. This work presents a two-stage case study of the S.I.T.E. building at the University of Ottawa for the diagnosis and prognosis of ASR-affected members (i.e., columns) after nearly 20 years in service. The diagnosis phase was conducted with the aim of evaluating the cause and extent of distress and interpreting its impact on the performance of the affected structure. First, a visual inspection was conducted to evaluate potentially damaged members, in order to select the best location for core-drilling. Once ASR was confirmed through petrographic examination, specimens were evaluated through the multi-level assessment (i.e., coupling of microscopic and mechanical assessment). A range of damage was discovered among the examined columns (i.e., 0.03%, 0.05%, and 0.08% expansion). Moreover, evidence of developing freeze and thaw (FT) damage was discovered in columns with greater levels of expansion, raising future concerns regarding the durability and serviceability of members affected by this coupling of damage (i.e., ASR+FT). For the second stage of this project (i.e., prognosis), a novel ASR semi-empirical model was developed with the aim of predicting future ASR-induced expansion and damage in the S.I.T.E. building. The above model was developed and validated (using ASR exposure site data) through the coupling of existing chemo-mechanical macro-models, which were used to predict material behaviour on the structural scale, and novel mathematical relationships for the prediction of anisotropy in the columns. Moreover, the use of the multi-level assessment to predict the mechanical implications of predicted distress was found to enhance the model’s capacity for prognosis and demonstrated important potential for the accurate prediction of multi-level damage in the S.I.T.E. columns.

Steel has played an indispensable role in shaping our contemporary world  and will persist to play that role for the foreseeable future. However, the steel industry currently is responsible for 7% of the global CO2-emissions, primarily due to the conventional carbon-based reduction process of iron ore. Fossil-free steel manufacturing, such as hydrogen direct reduction,  could essentially make the  CO2-emissions from primary steel production obsolete. The product from hydrogen-based direct reduction of iron ore is H-DRI, which subsequently are molten in an EAF to produce crude steel. Due to H-DRI  being   a   novel   product,   its   thermophysical   properties   are   not   well documented,  which  are  essential  when  investigating  the  heating  and dissolution behavior.  When  feeding  H-DRI  to  an  EAF,  ferrobergs  may  form,  which  consist  of unmolten material that interrupts the continuous melting process. It is not established whether the heat transfer of the pellets or the heat transfer to the pellets is the leading cause of ferroberg-formation. Modelling the melting process in an EAF is considered near impossible, therefore a simplified heating model of H-DRI was required. In the present thesis, H-DRI pellets were examined with heating experiments in a lab-scale vertical tube furnace to 1500°C  while  the  surface- and center  temperatures  of  the  pellets were  measured.  The measured  surface  temperatures  were  applied  as  varying boundary  conditions  in COMSOL  Multiphysics  heat transfer simulations of  H-DRI  and H-HBI.  The  thermal conductivity  function  was  utilized  as  an  adjustable  parameter to  fit  the  theoretical center temperatures from the heat transfer simulations with the experimental center temperatures to acquire the temperature dependent effective heat conductivity and thermal diffusivity of H-DRI. By establishing an estimate correlation between the heat conductivity of H-DRI and H-HBI, the thermal conductivity and thermal diffusivity of H-HBI could also be obtained. The experiments together with the heat transfer simulations proved to be effective and yielded successful results of the effective heat conductivity and thermal diffusivity of H-DRI  and  H-HBI,  which  can  be  used  in  process  design,  future  models,  and simulations. Furthermore, it is unlikely that ferroberg-formation is caused by slow heat transfer of the H-DRI. It is more likely that it is due to slow heat transfer to the H-DRI. Therefore, the focus should be to increase the heat transfer to the H-DRI pellets while melting in an EAF to avoid ferrobergs. / Stål har haft en oumbärlig roll i att forma vår samtida värld och kommer att fortsätta att inneha  den  rollen  under  en  överskådlig  framtid.  Men  stålindustrin  ansvarar närvarande  för  7%  av  den  totala  globala  CO2-utsläppen,  främst  på  grund  av den konventionella kolbaserade reduktionsprocessen av järnmalm. Fossilfri ståltillverkning, som direktreduktion av järnmalm med vätgas, kan i princip göra CO2-utsläppen   från   primärståltillverkning föråldrat.   Produkten   från   vätgasbaserad direktreduktion  av järnmalm  är  H-DRI,  som  sedan  smälts  i  en  ljusbågsugn  för att producera  råstål. Eftersom  H-DRI  är  en  ny  produkt  så  är  dess  termofysiska egenskaper,  som  är väsentliga  när  man  undersöker  dess  uppvärmnings-  och smältbeteende, inte väl dokumenterat. Vid matning av H-DRI till en ljusbågsugn kan det bildas  ferroberg  som består  av  osmält  material  som  hindrar  den  kontinuerliga smältningsprocessen. Det är inte fastställt om det är värmeöverföringen i pelletsen eller värmeöverföringen  till pelletsen  som  är  den  främsta  orsaken  till  att  ferroberg bildas. Modellering  av  smältprocessen  i  en  ljusbågsugn  anses  nästintill  omöjlig, därför krävdes en förenklad uppvärmningsmodell av H-DRI. I detta examensarbete undersöktes H-DRI-pellets med uppvärmningsexperiment i en vertikal rörugn till 1500°C samtidigt som yt- och centrumtemperaturerna för pelletsen mättes. De uppmätta yttemperaturerna  användes  som  varierande  randvillkor  i  COMSOL Multiphysics värmeöverföringssimuleringar  av  H-DRI  och  H-HBI.  Den  termiska konduktiviteten användes som en justerbar parameter för att anpassa de teoretiska centrumtemperaturerna från värmeöverföringssimuleringarna med de experimentella centrumtemperaturerna  för  att  erhålla  den  temperaturberoende effektiva  termiska konduktiviteten och termiska diffusiviteten för H-DRI. Genom  att   fastställa   en uppskattad korrelation mellan värmeledningsförmågan för H-DRI och H-HBI, kunde även den termiska konduktiviteten och termiska diffusiviteten för H-HBI erhållas. Experimenten  tillsammans  med  värmeöverföringssimuleringarna  visade  sig  vara effektiva och gav framgångsrika resultat av den effektiva termiska konduktiviteten och termiska  diffusiviteten  hos H-DRI och H-HBI,  som  kan  användas  i  processdesign, framtida modeller och simuleringar. Det är osannolikt att ferrobergbildning orsakas av långsam värmeöverföring  i H-DRI, utan det är mer troligt att det beror  på långsam värmeöverföring till H-DRI. Därför bör fokus vara att öka värmeöverföringen till H-DRI pellets i en ljusbågsugn för att undvika ferrobergbildning.

H2 Green Steel AB was founded in 2020 to build a large-scale green steel factory in Boden, Norrbotten, Sweden. The factory consists of green hydrogen production, iron production and steel production. In 2030, the factory’s annual steel production will be 5 million tonnes annually. The objective of the thesis was to build a concept to improve a recommendation for a Hydrogenproduction site in an early stage of engineering. It included improving the understanding and basis for three criteria. The first criteria consisted of technical and customer requirements, seeing the requirements for the specific application of hydrogen as the critical factor. The second criteria consisted of further investigating how existing interfaces and utilities can be used in hydrogen production and building the basis for qualification. The third criteria consisted of adapting the concept to existing internal design tools by building it forward compatible. The thesis was initiated by bench-marking possible activities related to the recommendation acting as technical support and extensions to existing solutions. The research approach used was Design Research Methodology (DRM), held as the framework for execution. The result from the thesis delivers a database model built upon three linked packages providing a methodology of increased technical information, forward compatibility and a modular approach for design.