The research conducted in this study was concerned with the development of low-cost continuous production of carbon fiber/aluminum composites. Two coatings, alumina and zirconia, were applied to the fibers to protect against interfacial degradation. They were applied using a sol-gel method and common metal salts. The fibers were infiltrated with molten aluminum using an ultrasound sonicator. The resultant composites were well-infiltrated and were tested in tension to determine their mechanical properties. Strengths were only 15-35% of the theoretical values predicted by the rule of mixtures. The composite microstructure revealed a sizable void fraction and that the fibers within the composites did not contain any coating on their surface. It was hypothesized that this was a result of few exposed graphite plane edges on the fiber surface, causing poor adhesion of the oxide coating to the fiber surface. To improve adhesion, an amorphous carbon coating was applied to the fiber surface, but still the oxide coatings were removed from the fibers upon infiltration. It was found, however, that the carbon coating on its own did strengthen the interface between the fiber and the aluminum.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.

Current research on thermal effects on guideways has addressed many aspects of the behavior of guideways using two-dimensional models. The two-dimensional models are acceptable for existing guideway designs, in which cross sectional shapes are uniform along the length of the guideway. However, three-dimensional models are necessary for a modular design, in which the track structures that interact with Maglev vehicles are made separately and are assembled into the support structure, and in which the cross sectional shapes are not uniform. A three-dimensional numerical model of the thermal environment, in which the effect of partial shading is taken into account, is implemented for the study of guideway behavior under various thermal environments. The numerical model of the thermal environment is calibrated to the experimental results under the thermal environment at Austin, Texas, and is extrapolated to predict the behaviors of guideways under the thermal environment in Las Vegas, Nevada, which is one of the candidate sites for the implementation and deployment of the high speed Maglev transportation system. This study addresses the suitability of a modular steel guideway design under such a thermal environment. Characteristics of the behavior of guideways under various thermal environments are identified, and the behavior of guideways under the effect of partial shading is summarized. / text

Αντικείμενο της παρούσας διδακτορικής διατριβής αποτελεί η θεωρητική και υπολογιστική προσομοίωση της πτήσης ατμοσφαιρικής καθόδου υψηλών ταχυτήτων, με ιδιαίτερη έμφαση στις υπερυπερηχητικές ταχύτητες και την αεροδυναμική και θερμοδυναμική ανάλυσή της. Η μεθοδολογία που ακολουθείται έχει ως κύριο σκοπό την πρόβλεψη του ίχνους επιστροφής υπερυπερηχητικών οχημάτων στη Γη, με δεδομένο οι ταχύτητες πτήσης να φτάνουν τα 15000 m/s (αριθμός Mach ~ 40) και οι θερμοκρασίες ανακοπής τους 15000 Κ. Στην εργασία αυτή ακολουθείται μεθοδολογική προσέγγιση και συστηματική βιβλιογραφική έρευνα στον επιστημονικοτεχνικό τομέα της αεροδυναμικής υπερθέρμανσης, που υφίστανται Υπερυπερηχητικά Οχήματα (Υ/Ο), κατά την πτήση τους στην ατμόσφαιρα. Η ανάλυση της υπερυπερηχητικής ροής, των θερμικών φορτίων και οι μέθοδοι θερμοθωράκισης των Υ/Ο αναπτύσσονται τις τελευταίες δεκαετίες και εξελίσσονται συνεχώς, αλλά μέχρι και σήμερα (2008), προκύπτουν αστοχίες, κυρίως κατά την επανείσοδό τους στην ατμόσφαιρα από το διάστημα. Για την προσομοίωση της υπερυπερηχητικής πτήσης καθόδου στην ατμόσφαιρα γίνεται μελέτη και ανάλυση των θερμοχημικών ιδιοτήτων και παραμέτρων, οι οποίες χαρακτηρίζουν τα ροϊκά πεδία στις υψηλές ταχύτητες και υψηλές θερμοκρασίες. Ο προσδιορισμός των μεταβαλλόμενων ροϊκών συνθηκών, των θερμοδυναμικών ιδιοτήτων και μεγεθών μεταφοράς θα συμβάλλει στις θεωρίες μοντελοποίησης και υπολογισμού της υψηλής θερμικής καταπόνησης, της σύστασης του υπέρθερμου αέρα και της υψηλής θερμοκρασίας του στην εξωτερική επιφάνεια του θερμομονωτικού τοιχώματος οχημάτων υψηλών ταχυτήτων, κατά την πτήση τους στην ατμόσφαιρα της Γης. Στα πλαίσια αυτά αναπτύσσονται υπολογιστικοί αλγόριθμοι προσομοίωσης και επιτυχούς πρόβλεψης του ατμοσφαιρικού ίχνους καθόδου οχημάτων υπερυπερηχητικής μεταφοράς. Τα βασικά αεροδυναμικά χαρακτηριστικά των ανωστικών οχημάτων στις υψηλές ταχύτητες υπολογίζονται με κατάλληλη προσαρμογή της κλασσικής Νευτώνειας Ροής στις υψηλές ταχύτητες και επιβεβαιώνονται με πειραματικά δεδομένα αεροδυναμικών μετρήσεων σε αεροσήραγγες υψηλών ταχυτήτων της NASA. Επιπλέον στη διατριβή ενσωματώνονται μοντέλα προσομοίωσης των ιδιοτήτων συμπεριφοράς του υπέρθερμου αέρα ως πραγματικού αερίου σε συνθήκες θερμοδυναμικής ισορροπίας σε ακραίες ροϊκές συνθήκες (υψηλές ταχύτητες, υψηλές πιέσεις και χαμηλές πυκνότητες). Πιο συγκεκριμένα γίνεται ανάλυση της μεταβαλλόμενης σύστασης και των ιδιοτήτων του αέρα (θερμοδυναμικά μεγέθη και μεγέθη μεταφοράς) στις πολύ υψηλές θερμοκρασίες του υπέρθερμου ροϊκού πεδίου. Η μελέτη αυτή θα οδηγήσει στην εξαγωγή ενός νέου μοντέλου υπολογισμού της μεταφερόμενης θερμικής ροής στην περιοχή ανακοπής υπερυπερηχητικών οχημάτων, το οποίο επιβεβαιώνεται τόσο με διεθνώς αναγνωρισμένα θερμικά μοντέλα (όπως αυτό των Fay-Riddell) όσο και με υπολογιστικές προσομοιώσεις άλλων ερευνητών. Η μεθοδολογία που ακολουθείται θα αποτελέσει τη βάση για την εξαγωγή ενός νέου θεωρητικού μοντέλου υπολογισμού της θερμοκρασίας του αέρα στην επιφάνεια του θερμοθώρακα του υπερυπερηχητικού οχήματος. Η αποτελεσματικότητα της προτεινόμενης μεθοδολογίας, με το συνδυασμό κινηματικής και αεροθερμοδυναμικής ανάλυσης σε ενιαίο υπολογιστικό αλγόριθμο, αποδεικνύεται και ενισχύεται μέσω της εφαρμογής των ανωτέρω μοντέλων προσομοίωσης σε βαλλιστικό (διαστημικός θαλαμίσκος Απόλλων) και ανωστικό (Σύστημα Διαστημικής Μεταφοράς, γνωστό ως Διαστημικό Λεωφορείο Space Shuttle) υπερυπερηχητικό όχημα. Τα αποτελέσματα της προτεινόμενης μεθόδου συγκρίνονται, αξιολογούνται και πιστοποιούνται με παρόμοια από διεθνώς αναγνωρισμένα υπολογιστικά συστήματα και πειραματικά δεδομένα μετρήσεων σε υπερυπερηχητικές αεροσήραγγες οχημάτων υψηλών ταχυτήτων. Μέσα στις επόμενες δεκαετίες, η εξέλιξη των υπερυπερηχητικών συστημάτων μεταφοράς θα είναι ραγδαία και ιδιαίτερα ελκυστική από τεχνολογικής πλευράς με ελπιδοφόρα μηνύματα για "γήϊνες" μετακινήσεις με υψηλές ταχύτητες σε σύντομους χρόνους, αλλά και πιθανές μετοικήσεις ανθρώπων-αστροναυτών σε άλλους πλανήτες του ηλιακού συστήματος. Έτσι η παρούσα διδακτορική διατριβή, αξιοποιώντας τις προόδους που έχουν συντελεστεί τα τελευταία χρόνια, εκτιμάται ότι συμβάλλει ουσιαστικά στο ακόμα υπό εξέλιξη – για τα ελληνικά δεδομένα πρωτόγνωρο – επιστημονικό πεδίο της Υπερυπερηχητικής Αεροθερμοδυναμικής, και στην ανάπτυξη μεθοδολογίας για τον αεροθερμοδυναμικό σχεδιασμό υπερυπερηχητικών οχημάτων. Το προτεινόμενο σύνθετο μοντέλο κινηματικής και θερμοδυναμικής υπολογιστικής ανάλυσης και η μεθοδολογία που ακολουθείται έχει ισχύ και εφαρμογή στην πλειονότητα των περιπτώσεων των υπερυπερηχητικών πτήσεων στη γήινη και, με κατάλληλες προσαρμογές, σε οποιαδήποτε πλανητική ατμόσφαιρα. Βεβαίως, η προτεινόμενη μεθοδολογία έχει περιθώρια εξέλιξης και ανάπτυξης, προκειμένου να βελτιωθεί η απόδοσή της με την εισαγωγή και νέων στοιχείων, αλλά και να διευρυνθεί το φάσμα των δυνατών εφαρμογών της. / The object of the present doctoral thesis constitutes the theoretical and calculating simulation of high-speed atmospheric flightmotion, with particular emphasis in hypersonic speeds and aerodynamic and thermodynamic analysis. The methodology that is followed has as main aim the prediction of return flight trace of hypersonic vehicles in Earth’s ground, assuming the speeds of flight to reach the 15000 m/s (Mach number ~ 40) and stagnation temperatures the 15000 K. In this work are followed methodological approach and systematic bibliographic research in the scientific field of aerodynamic overheating that suffers Hypersonic Vehicles(H/V) at their flight in Earth’s atmosphere. The analysis of hypersonic flow, thermal loads and new methods for thermal protection systems of H/V are developed the last decades and are evolved continuously, but until today (2008) resulting failures mainly at their reentry in atmosphere from the interval. For the simulation of the atmospheric hypersonic flight motion become study and analysis of thermodynamic properties and parameters, that characterize the flow fields in high speeds and high temperatures. The determination of altered flow conditions, thermodynamic properties and transport magnitudes will contribute in the theories of modelling and high thermal strain calculations, in the constitution of overheating air and it’s high temperature determination in the external surface of heat insulation wall of high-speed vehicles at their flight in Earth’s atmosphere. In this work are developed calculating algorithms of simulation for the successful prediction of atmospheric flight motion of hypersonic transport vehicles. The basic aerodynamic characteristics of lifting vehicles in high speeds are calculated with suitable adaptation of classic Newtonian Flow in high speeds and are confirmed with experimental data of aerodynamic measurements in high speed wind-tunnels of NASA. Moreover in this thesis are incorporated models for the simulation of properties of overheating air behaviour as real gas in thermodynamic balance in extreme flow conditions (high speeds, high pressures and low densities). Particularly becomes analysis of the altered constitution and properties of air (thermodynamic magnitudes and transport magnitudes) in very high temperatures on hypersonic flow field. This study will lead to the export of a new model for the transported thermal stagnation region calculations of hypersonic vehicles, which is confirmed so much with internationally recognized thermal models (as that of Fay-Riddell) and with calculating simulations of other researchers. The methodology that is followed will constitute the base for the export of a new theoretical model for high temperature air calculations in thermal protection systems surface of hypersonic vehicles. The effectiveness of proposed methodology, with the combination kinematic and aerothermodynamics analysis in united calculating algorithm, is proved and confirmed via the application of above simulation models on ballistic (Apollo Command Module) and lifting (Space Transportation System, known as Space Shuttle) hypersonic vehicles. The results of proposed method are compared, evaluated and certified with similarly by internationally recognized calculating systems and experimental data of measurements in hypersonic wind-tunnels for high speed vehicles. In the next decades, the development of hypersonic transportation systems will be rapid and particularly attractive from technological side with hopeful messages for “earthy” transfers with high speeds in short times, but also likely persons-astronaut missions in other planets of solar system. Thus the present doctoral thesis, developing the progress that has taken place in the past few years, is appreciated that it contributes substantially in still under development - for the Greek data unusual - scientific field of Hypersonic Aerothermodynamics, and in the growth of methodology for the aerothermodynamic construction of hypersonic vehicles. The proposed complex model of kinematic and thermodynamic calculating analysis and it’s methodology that is followed have influence and application in the majority of cases of hypersonic flights in earthy and, with properly adaptations, in anyone planetary atmosphere. Of course, the proposed methodology has margins of development and growth in order to improve her efficiency with the import of also new elements and also extended the spectrum of her possible applications.

O refinamento dos poros, associado à reação pozolânica e ao efeito filer, reduz a permeabilidade do concreto com cinza de casca de arroz (CCA), o que pode antecipar a sua degradação em altas temperaturas. A literatura mostra que o concreto reidratado em água pode recuperar substancialmente a sua resistência inicial, porém, os estudos sobre a reidratação ao ar e sobre a influência do modo de resfriamento na reidratação são escassos. A pesquisa desenvolvida teve como principal objetivo avançar na análise experimental de concretos convencional e com CCA em altas temperaturas e na reidratação. Na etapa exploratória se avaliou a influência da temperatura de exposição, da adição mineral, do ambiente de acondicionamento, da taxa de aquecimento e do tempo de exposição na resistência à compressão e módulo de elasticidade. Na etapa principal se avaliou a influência do modo de resfriamento, da adição e da idade de reidratação na resistência residual. Complementarmente se utilizou o ensaio de velocidade de pulso ultrassônico (VPU) para avaliar o grau de microfissuração e correlacionar a VPU com as propriedades mecânicas residuais. Na etapa exploratória concluiu-se que a adição, a temperatura, a taxa de aquecimento e o tempo de exposição influenciaram significativamente os resultados. O concreto com CCA cristalina apresentou pior desempenho em altas temperaturas. O concreto com CCA amorfa apresentou desempenho ligeiramente inferior ao concreto convencional em 200°C, devido ao efeito da poro-pressão. No entanto, ambas as CCA podem ser alternativas viáveis considerando sustentabilidade. Na etapa principal, o resfriamento brusco com água provocou maior redução na resistência devido aos gradientes térmicos, porém, permitiu maior recuperação logo nos primeiros sete dias de reidratação. Apesar da recuperação parcial, a resistência ao fim de 154 dias foi inferior a 40% do valor inicial. Nas análises térmicas e de DRX foi possível observar nos concretos resfriados com água a recristalização dos aluminatos de cálcio, do C-S-H e da portlandita, em maior grau no concreto convencional. Foi possível observar correlações fortes entre as variáveis de resposta na etapa exploratória, porém, o mesmo não ocorreu na etapa principal, devido à fissuração e presença de água nos poros. / The pore refinement, associated with the pozzolanic reaction and the filler effect, reduces the permeability of blended concrete with rice husk ash (RHA), which can anticipate its degradation at high temperatures. The literature shows that concrete rehydrated with water can recover substantially its initial strength, but studies on rehydration in air and on the influence of the cooling method on rehydration are scarce. The main objective of this research was to evaluate the performance at high temperatures and in rehydration of conventional and blended concretes with RHA. In the exploratory stage, the influence of exposure temperature, mineral admixture, conditioning environment, heating rate and exposure time on residual strength and modulus of elasticity of heated concrete was evaluated. In the main stage, the influence of cooling method, mineral admixture and time of rehydration in an unsaturated environment on residual strength of concrete was evaluated. The ultrasonic pulse velocity test (UPV) was used to evaluate the degree of micro cracking of concrete and to correlate the UPV with residual strength and modulus. In the exploratory stage it was concluded that mineral admixture, temperature, heating rate and time of exposure significantly influenced the results. In general, concrete with partially crystalline RHA presented the worst performance at high temperatures. Concrete with amorphous RHA presented worse performance than conventional concrete only at 200°C, due to the pore-pressure effect. Despite these results, RHA can be a viable option considering sustainability and high temperatures performance. In the main stage, the rapid cooling with water caused a greater reduction in strength, due to thermal gradients, however, caused a greater strength recovery in the first seven days of rehydration. Despite this partial recovery, the final strength of both concretes after 154 days of rehydration was less than 40% of the initial value. In water-cooled concretes thermal and XRD analyzes show recrystallization of the calcium aluminates, C-S-H and portlandite, to a greater degree in conventional concrete. In the exploratory stage it was possible to observe strong correlations between the independent variables; however, the same did not occur in the main stage, due to cracking and to the presence of water in the pores.

Made available in DSpace on 2016-12-08T17:19:24Z (GMT). No. of bitstreams: 1 Heloiza Doering Gasparin.pdf: 4558205 bytes, checksum: e414bcfd7c4434aa73fcdf59cdf98ff2 (MD5) Previous issue date: 2014-12-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This investigation study shows the effects of high temperatures and exposure time on the mechanical properties of one perlitic gray cast iron commonly applied to diesel engine cylinder heads. The effects were evaluated in samples which come from three different cast irons, FC300 class, with different percentages of molybdenum and different hardening mechanisms. Two of them have different amounts of molybdenum and the third did not have significant amounts of molybdenum, however, have refined graphite. The high temperature rupture tensile tests were performed on specimens with 10mm diameter, machined from bars 30mm diameter. The tests were performed at room and high temperature (200°C, 300°C, 350°C, 400°C, 450°C, 500°C and 550°C). The exposure times at elevated temperatures, after material heat homogenization, were 0min (default), 60min and 90 minutes. Samples with highest percentage of molybdenum (0.27 wt%) had the best mechanical properties for high temperature conditions. At room temperature, the material with refined graphite had higher strength resistance values when compared to the other two materials. The mechanical properties evaluated by measurements of microhardness, yield strength (0.2%) and specific strain complement the behavior analysis of these properties at elevated temperature. According to the obtained results, the stress strength decreases with the temperature incrementing. This is attributed to the pearlite matrix decomposition occurrence as a result of the carbon diffusion process. The Carbon from cementite goes by diffusion to the graphite, which is the responsible for the increase graphite percentage in the material. Metallographic analyzes indicate the occurrence of this phenomenon. Increases in high-temperature exposure time also contributed to the perlite degeneration. All microstructural evaluation were made by analysis of cementite and graphite percentage, graphite size for different test temperatures and different times of exposure to high temperature. 16 / Este trabalho de pesquisa apresenta os efeitos de elevadas temperaturas e do tempo de exposição sobre as propriedades mecânicas do ferro fundido cinzento de matriz perlítica, material comumente aplicado a cabeçotes de motor a diesel. Foram avaliados três ferros fundidos da classe FC300, com diferentes percentuais de molibdênio e diferentes mecanismos de endurecimento. Dois dos materiais possuem diferentes teores de molibdênio e o terceiro contém teores de molibdênio desconsideráveis, no entanto, possui grafita refinada. Ensaios de tração até ruptura a quente foram realizados em corpos de prova com diâmetro de 10 mm, usinados de um pino bruto de 30 mm de diâmetro. Os ensaios de tração foram realizados a frio (temperatura ambiente) e a quente (200°C, 300°C, 350°C, 400°C, 450°C, 500°C e 550°C). Os tempos de exposição a elevadas temperaturas, após homogeneização térmica do material, foram de 0 (padrão), 60 e 90 minutos. As amostras com o maior percentual de molibdênio (0,27% em peso) apresentaram melhores propriedades mecânicas para as condições de elevada temperatura. À temperatura ambiente, o material com grafita refinada teve valores de resistência à tração mais elevados em relação aos outros dois materiais. As propriedades mecânicas de microdureza, tensão de escoamento 0,2% e deformação específica complementaram a análise do comportamento destas propriedades à elevada temperatura. De acordo com os resultados obtidos, a redução na resistência mecânica com a elevação da temperatura é atribuída à ocorrência de decomposição da perlita, como resultado da difusão do carbono vindo da cementita migrando à grafita, que é o responsável pelo aumento da quantidade de grafita no material. As análises metalográficas evidenciaram a ocorrência deste fenômeno. Aumentos no tempo de exposição a temperaturas elevadas também contribuíram para a degeneração da perlita. Toda avaliação microestrutural se deu por análise de percentuais 14 de grafita, cementita e tamanho da grafita a diferentes temperaturas de ensaio, bem como diferentes tempos de exposição à elevada temperatura.

A thesis submitted to the Faculty of Engineering in fulfilment of the requirements for the degree of Master of Technology in Mechanical Engineering 2005 / The objective of this project was to monitor the high temperature creep behaviour of 441 stainless steel. Two different alloys of 441 were investigated; the main difference between them being the Niobium content. Particularly imporlant to the project was how the Niobium content and grain size affected the creep resistance of the material. Creep tests were performed using purpose built constant load creep test rigs. Initially the rigs were not suitable for the testing procedures pertaining to this project. This was due to persistent problems being experienced with regards the reliability and reproducibility of the rigs. After various modifications were made the results produced from the rigs were consistent. Creep test data was used in order to determine the mechanism of creep that is operative within the material (at a predetermined temperature) under a predetermined load. Particular attention was paid to the resulting stress exponents. in order to identify the operative creep mechanism. The identification of the operative creep mechanisms was also aided by microscopical analysis. This analysis was also necessary to monitor how the grain size had altered at various annealing temperatures. Heat treatment was used as a method to alter the high temperature strength and microstructure of the material. Heat treatments were performed at various temperatures in order to determine the ideal temperature to promote optimum creep resistance of 441. All heat treatments were performed in a purpose designed and built high temperature salt bath furnace. The commissioning of the salt bath formed part of the objectives for this project. Sag testing was also conducted, using purpose built sag test rigs. It was necessary to design and manufacture a sag test rig that could be comparable to the industry accepted method of sag testing known as the two-point beam method, as this method is believed to produce inconsistent results. Conclusions have been drawn from the results of the data and from previous research on the subject matter.

O refinamento dos poros, associado à reação pozolânica e ao efeito filer, reduz a permeabilidade do concreto com cinza de casca de arroz (CCA), o que pode antecipar a sua degradação em altas temperaturas. A literatura mostra que o concreto reidratado em água pode recuperar substancialmente a sua resistência inicial, porém, os estudos sobre a reidratação ao ar e sobre a influência do modo de resfriamento na reidratação são escassos. A pesquisa desenvolvida teve como principal objetivo avançar na análise experimental de concretos convencional e com CCA em altas temperaturas e na reidratação. Na etapa exploratória se avaliou a influência da temperatura de exposição, da adição mineral, do ambiente de acondicionamento, da taxa de aquecimento e do tempo de exposição na resistência à compressão e módulo de elasticidade. Na etapa principal se avaliou a influência do modo de resfriamento, da adição e da idade de reidratação na resistência residual. Complementarmente se utilizou o ensaio de velocidade de pulso ultrassônico (VPU) para avaliar o grau de microfissuração e correlacionar a VPU com as propriedades mecânicas residuais. Na etapa exploratória concluiu-se que a adição, a temperatura, a taxa de aquecimento e o tempo de exposição influenciaram significativamente os resultados. O concreto com CCA cristalina apresentou pior desempenho em altas temperaturas. O concreto com CCA amorfa apresentou desempenho ligeiramente inferior ao concreto convencional em 200°C, devido ao efeito da poro-pressão. No entanto, ambas as CCA podem ser alternativas viáveis considerando sustentabilidade. Na etapa principal, o resfriamento brusco com água provocou maior redução na resistência devido aos gradientes térmicos, porém, permitiu maior recuperação logo nos primeiros sete dias de reidratação. Apesar da recuperação parcial, a resistência ao fim de 154 dias foi inferior a 40% do valor inicial. Nas análises térmicas e de DRX foi possível observar nos concretos resfriados com água a recristalização dos aluminatos de cálcio, do C-S-H e da portlandita, em maior grau no concreto convencional. Foi possível observar correlações fortes entre as variáveis de resposta na etapa exploratória, porém, o mesmo não ocorreu na etapa principal, devido à fissuração e presença de água nos poros. / The pore refinement, associated with the pozzolanic reaction and the filler effect, reduces the permeability of blended concrete with rice husk ash (RHA), which can anticipate its degradation at high temperatures. The literature shows that concrete rehydrated with water can recover substantially its initial strength, but studies on rehydration in air and on the influence of the cooling method on rehydration are scarce. The main objective of this research was to evaluate the performance at high temperatures and in rehydration of conventional and blended concretes with RHA. In the exploratory stage, the influence of exposure temperature, mineral admixture, conditioning environment, heating rate and exposure time on residual strength and modulus of elasticity of heated concrete was evaluated. In the main stage, the influence of cooling method, mineral admixture and time of rehydration in an unsaturated environment on residual strength of concrete was evaluated. The ultrasonic pulse velocity test (UPV) was used to evaluate the degree of micro cracking of concrete and to correlate the UPV with residual strength and modulus. In the exploratory stage it was concluded that mineral admixture, temperature, heating rate and time of exposure significantly influenced the results. In general, concrete with partially crystalline RHA presented the worst performance at high temperatures. Concrete with amorphous RHA presented worse performance than conventional concrete only at 200°C, due to the pore-pressure effect. Despite these results, RHA can be a viable option considering sustainability and high temperatures performance. In the main stage, the rapid cooling with water caused a greater reduction in strength, due to thermal gradients, however, caused a greater strength recovery in the first seven days of rehydration. Despite this partial recovery, the final strength of both concretes after 154 days of rehydration was less than 40% of the initial value. In water-cooled concretes thermal and XRD analyzes show recrystallization of the calcium aluminates, C-S-H and portlandite, to a greater degree in conventional concrete. In the exploratory stage it was possible to observe strong correlations between the independent variables; however, the same did not occur in the main stage, due to cracking and to the presence of water in the pores.

O concreto leve de alto desempenho (CLAD), com argila expandida nacional, é um material alternativo para as concentrações brasileiras, considerando as características climáticas do país e baixo custo do material. Mas atualmente, existe pouca informação disponível sobre a produção e aplicação deste concreto com agregados leves, adições e aditivos nacionais. O objetivo desta dissertação é analisar o comportamento estrutural, por intermédio de ensaios mecânicos (resistência à compressão, resistência à tração por compressão diametral e módulo de deformação) do CLAD, sob ação de altas temperaturas. Para tanto, realiza-se uma análise comparativa da resistência mecânica do concreto em estudo, constituído por agregados leves de argila expandida, com o concreto convencional CAD (concreto de alto desempenho), composto por agregados de brita basáltica, determinando-se assim as respectivas resistências mecânicas, após terem sido expostos a temperaturas externas de até 800 graus centígrados. Através da análise dos resultados obtidos experimentalmente, pode-se comprovar a viabilidade do CLAD, produzido com argila expandida, comparativamente ao CAD, sob à ação de altas temperaturas. / The high performance lightweight aggregate concrete (HPLC), with national expanded clay, is an alternative material for the Brazilian constructions, considering the climatic characteristics of the country and low cost of the material. But now, little available information exists about the production and application of this concrete with lightweight aggregate, additions and addictive national. The aim of this dissertation is to analyze the structural behavior, by mechanical tests (compressive strength, splitting tensile strength and deformation modulus) of HPLC, under action of high temperatures. For so much, it takes place a comparative analysis of the mechanical resistance of the concrete in study, constituted by lightweight aggregate of expanded clay, with the conventional concrete HPC (high performance concrete), composed by crushed basalt coarse aggregate, determining the respective mechanical strength, after they have been exposed to external temperatures of up to 800°C. Through the analysis of the results obtained experimentally, it can be proven the viability of HPLC, produced with expanded clay, comparatively to HPC, under to the action of high temperatures.