A cadeia produtiva da construção civil exerce grande influência na macroeconomia de um país. Em contrapartida, este setor destaca-se pelo consumo indiscriminado de matérias-primas não renováveis, processos produtivos ineficientes, além de uma grande quantidade de resíduos gerados. A reciclagem de materiais de construção desempenha um papel importante para a sustentabilidade visto que se tem a conservação dos recursos naturais e a redução de áreas para aterro. O foco principal dessa pesquisa é o estudo de resíduos de construção e demolição, mais especificamente os agregados graúdos reciclados de concreto (AGRC). O objetivo principal desta tese foi analisar a influência dos principais parâmetros que regem a variabilidade de concretos produzidos com agregados graúdos reciclados de concreto (AGRC), visando a transferência tecnológica. O programa experimental foi dividido em seis etapas. Nas etapas iniciais, estudou-se o resíduo de concreto, analisando a sua origem, os métodos de ensaios, para por fim realizar a caracterização dos materiais. Nas etapas intermediárias, fez-se um estudo para entender o efeito da variação granulométrica durante o processo de produção do concreto com fins estruturais. E nas etapas finais foram feitos estudos quanto à condição de saturação do AGRC. Com os resultados pode-se concluir que com um eficiente controle dos parâmetros de variabilidade do AGRC é possível produzir concretos com fins estruturais, visando dessa forma a transferência tecnológica. / The construction industry supply chain has a great influence on country macro economy. In contrast, there is the indiscriminate consumption of non-renewable raw materials, production processes inefficient, plus a large amount of waste generated. The construction materials recycling plays an important role for the sustainability since it is the conservation of natural resources and reducing landfill areas. The main focus of this research is the study of construction and demolition waste, specifically recycled coarse aggregate concrete (AGRC). The main objective of this thesis is to analyze the influence of the main parameters governing the variability of concrete made with recycled coarse aggregate concrete (AGRC), aiming at technology transfer. The experimental program was divided into nine steps. In the early stages, concrete residue was studied, their origin and test methods were analyzed, and to end materials were characterized. In the intermediate stages, a study was made to understand the effect of varying particle size during the production process of structural concrete. And in the final stages studies were made in AGRC saturation condition. With the results it can be concluded that with an efficient control of AGRC variability parameter it is possible to produce concrete with structural objectives, aiming thereby to technology transfer.

A cadeia produtiva da construção civil exerce grande influência na macroeconomia de um país. Em contrapartida, este setor destaca-se pelo consumo indiscriminado de matérias-primas não renováveis, processos produtivos ineficientes, além de uma grande quantidade de resíduos gerados. A reciclagem de materiais de construção desempenha um papel importante para a sustentabilidade visto que se tem a conservação dos recursos naturais e a redução de áreas para aterro. O foco principal dessa pesquisa é o estudo de resíduos de construção e demolição, mais especificamente os agregados graúdos reciclados de concreto (AGRC). O objetivo principal desta tese foi analisar a influência dos principais parâmetros que regem a variabilidade de concretos produzidos com agregados graúdos reciclados de concreto (AGRC), visando a transferência tecnológica. O programa experimental foi dividido em seis etapas. Nas etapas iniciais, estudou-se o resíduo de concreto, analisando a sua origem, os métodos de ensaios, para por fim realizar a caracterização dos materiais. Nas etapas intermediárias, fez-se um estudo para entender o efeito da variação granulométrica durante o processo de produção do concreto com fins estruturais. E nas etapas finais foram feitos estudos quanto à condição de saturação do AGRC. Com os resultados pode-se concluir que com um eficiente controle dos parâmetros de variabilidade do AGRC é possível produzir concretos com fins estruturais, visando dessa forma a transferência tecnológica. / The construction industry supply chain has a great influence on country macro economy. In contrast, there is the indiscriminate consumption of non-renewable raw materials, production processes inefficient, plus a large amount of waste generated. The construction materials recycling plays an important role for the sustainability since it is the conservation of natural resources and reducing landfill areas. The main focus of this research is the study of construction and demolition waste, specifically recycled coarse aggregate concrete (AGRC). The main objective of this thesis is to analyze the influence of the main parameters governing the variability of concrete made with recycled coarse aggregate concrete (AGRC), aiming at technology transfer. The experimental program was divided into nine steps. In the early stages, concrete residue was studied, their origin and test methods were analyzed, and to end materials were characterized. In the intermediate stages, a study was made to understand the effect of varying particle size during the production process of structural concrete. And in the final stages studies were made in AGRC saturation condition. With the results it can be concluded that with an efficient control of AGRC variability parameter it is possible to produce concrete with structural objectives, aiming thereby to technology transfer.

Os rejeitos de construção e demolição representam, atualmente, grande volume de material desperdiçado no canteiro de obra e fábricas de pré-moldados de concreto. A necessidade da reciclagem para o desenvolvimento auto-sustentável, de materiais produzidos a partir dos rejeitos de construção, é de grande importância sob o impacto ambiental, além de proporcionar economia aos construtores e produtores de artefatos de cimento. Ensaios de concretos e argamassas, utilizando agregado reciclado, resultam bom desempenho mecânico e são relativamente mais leves quando comparados aos respectivos materiais utilizando agregados naturais. A fabricação de blocos de concreto com função estrutural, produzido com agregados reciclados de fração entre 2,4 mm e 9,5 mm, combinada à fração miúda de agregados naturais, possibilitam a execução de edifícios de pequena altura. A utilização da fração miúda reciclada, na preparação de argamassas de assentamento e revestimento, apresenta comportamento eficiente ao conjunto alvenaria-argamassa. A caracterização dos agregados, o estudo de traço, a análise do desempenho físico e mecânico dos blocos, prismas e paredes de alvenaria estrutural, bem como correlações de eficiência e análise da influência da argamassa de assentamento e de revestimento em relação à resistência de aderência à tração, é uma necessidade para o conhecimento e utilização deste material / The building and demolition rejects represent, nowadays, a great amount of wasted material in buildings and plants of pre-molded of concrete. The necessity of recycling for the self-supporting development of materials produced from the building rejects, is of great importance under the enviromental impact, and besides it provides savings for the builers and producers of concrete goods. Tests with concrete and mortar, utilizing recycled aggregate, show a good mechanical performance and they are lighter when compared to the respective materials using natural aggregate. The fabrication of concrete blocks with structural function, produced with recycled aggregate of fraction between 2,4 mm and 9,5 mm, combined to the small fraction of natural aggregate, make possible the construction of low height buildings. The application of the recycled small fraction, in the preparation of foundation and revetment mortar, shows efficient employed with the set masonry-mortar. The aggregate characterization, the study of the proportion of ingredients for concrete, the analysis of the physical and mechanical performance of the blocks, prisms and walls of structural masonry, as well the correlations of efficiency and analysis of the influence of foundation and revetment mortar, relating to the resistence of adherence to traction, are necessities for the knowledge and utilization of this material

La valorisation de déchets de démolition en tant que granulats à béton présente un double objectif de préservation des ressources naturelles et de désengorgement des sites de stockage. Les granulats recyclés de béton présentent la particularité de contenir du mortier résiduel qui influence certaines de leurs propriétés et, par voie de conséquence, celles des bétons dans lesquels ils sont utilisés. Cette thèse a pour but de développer l’utilisation de bétons de granulats recyclés en remplacement total des matériaux naturels. Elle a été réalisée en partenariat industriel avec l’entreprise CHRYSO.Une étude approfondie des propriétés des granulats recyclés de béton sur plusieurs lots (plateforme industrielle et laboratoire) a conduit à l’identification puis à l’analyse des spécificités de ces matériaux comparés aux matériaux naturels. La validité des protocoles expérimentaux a été testée, et de nouveaux protocoles ont été proposés axés sur ces spécificités. Les granulats recyclés présentent une absorption plus élevée, une résistance à l’abrasion plus faible, une distribution granulaire plus étalée et une circularité moindre que les granulats naturels. La granulométrie, la proportion d’éléments fins et l’absorption d’eau des sables recyclés sont des caractéristiques dépendantes d’une part, du prélèvement des granulats recyclés et d’autre part, de la robustesse des protocoles expérimentaux. Une réactivité des éléments fins a été démontrée pour les lots issus de laboratoire, mais son influence sur les propriétés des bétons peut être considérée de second ordre lorsque les éléments fins sont constitutifs du sable. Enfin, l’absorption et la morphologie des granulats recyclés sont dépendantes de la classe granulaire étudiée. Des corrélations entre les propriétés morphologiques/géométriques et l’absorption ont été démontrées. A l’issue de l’analyse de ces propriétés, des corrections ou adaptations aux modèles prévisionnels de performances ont été proposées. La faisabilité de réalisation de bétons de granulats recyclés de béton avec remplacement total des matériaux naturels (BGRB à 100%) a ensuite été démontrée. Pour de tels matériaux, la conservation des éléments fins inférieurs à 63μm est conseillée car nécessaire à l’obtention d’un squelette granulaire correct.Afin de compenser la perte d’ouvrabilité et de résistance mécanique observée avec l’utilisation des granulats recyclés de bétons, une recherche d’adjuvant a été menée et a conduit au choix de superplastifiants de la famille des polycarboxylates. Les interprétations proposées permettent de mieux comprendre la formulation des bétons de granulats recyclés de béton et des mortiers de bétons équivalents (MBE). Ainsi, la complexité des cinétiques d’absorption et de désorption d’eau conduit à une discussion autour de la notion d’eau efficace ; la différence de morphologie des granulats recyclés implique une correction du squelette granulaire ; enfin la fragilité des granulats recyclés à l’abrasion pose la question de sa prise en compte dans la détermination du squelette granulaire optimal.Enfin, une analyse comparative des impacts environnementaux des bétons de granulats recyclés de bétons ouvre des perspectives intéressantes. / Promoting the use of demolition waste as recycled aggregates presents a double objective: first to preserve natural resources and secondly to relieve storage site. In regards to natural aggregates, recycled aggregates contain mortar that influences theirs properties and those of concrete in which they are used. The objective of this thesis is to develop the use of 100 % recycled aggregates in concrete. This study was realised in patnership with the company CHYRSO. Properties of recycled concrete aggregates collected from several sources were studied to identify and analyse their specificities ; results were compared to natural ones. Normalised methods were modified in order to be applied on recycled aggregates and new methods were also proposed. Recycled aggregates present higher water absorption, lower mechanical strength, spreader granular distribution and a less circular shape compared to natural aggregates. The granulometry of recycled sand, fines content and the water absorption are properties that depend on the sampling and the robustness of protocols used. A reactivity of fines obtained from materials made at the laboratory have been established, meanwhile their influence on concrete properties is considered as minor. Finally, the absorption and morphology of recycled aggregate depend on the granular fraction. Correlation between morphological and mechanical properties with water absorption have been demonstrated. After analysing these properties, correction were proposed on mechanical performance forecasting models. It was also shown that the use of fines in recycled aggregate concretes provides better mechanical properties. For such materials, keeping aggregates less than 63μm is advisable because it provides correct granular skeletton. In order to balance the loss of workability and mechanical strength observed with the use of recycled aggregates, studies were carried with several superplasticisers. Polycarboxylates were identified as appropriate superplasticisers. Interpretations facilitate understanding of concrete formulation and concrete equivalent mortar formulation made with recycled aggregates. Thus, the complexity of absorption and desorption kinectics lead to a discusion around effective water definition. The difference between the morphology of recycled aggregates and natural ones involved a correction of the granular skeletton; finally, their weakness during mechanical test modifies the granular skeletton and need to be taken into consideration.Finally, studies on environmental impacts of recycled aggregates concrete were done and compared with those of natural aggregates concrete. This study starts interesting perspectives.

A cadeia produtiva da construção civil exerce grande influência na macroeconomia de um país. Em contrapartida, este setor destaca-se pelo consumo indiscriminado de matérias-primas não renováveis, processos produtivos ineficientes, além de uma grande quantidade de resíduos gerados. A reciclagem de materiais de construção desempenha um papel importante para a sustentabilidade visto que se tem a conservação dos recursos naturais e a redução de áreas para aterro. O foco principal dessa pesquisa é o estudo de resíduos de construção e demolição, mais especificamente os agregados graúdos reciclados de concreto (AGRC). O objetivo principal desta tese foi analisar a influência dos principais parâmetros que regem a variabilidade de concretos produzidos com agregados graúdos reciclados de concreto (AGRC), visando a transferência tecnológica. O programa experimental foi dividido em seis etapas. Nas etapas iniciais, estudou-se o resíduo de concreto, analisando a sua origem, os métodos de ensaios, para por fim realizar a caracterização dos materiais. Nas etapas intermediárias, fez-se um estudo para entender o efeito da variação granulométrica durante o processo de produção do concreto com fins estruturais. E nas etapas finais foram feitos estudos quanto à condição de saturação do AGRC. Com os resultados pode-se concluir que com um eficiente controle dos parâmetros de variabilidade do AGRC é possível produzir concretos com fins estruturais, visando dessa forma a transferência tecnológica. / The construction industry supply chain has a great influence on country macro economy. In contrast, there is the indiscriminate consumption of non-renewable raw materials, production processes inefficient, plus a large amount of waste generated. The construction materials recycling plays an important role for the sustainability since it is the conservation of natural resources and reducing landfill areas. The main focus of this research is the study of construction and demolition waste, specifically recycled coarse aggregate concrete (AGRC). The main objective of this thesis is to analyze the influence of the main parameters governing the variability of concrete made with recycled coarse aggregate concrete (AGRC), aiming at technology transfer. The experimental program was divided into nine steps. In the early stages, concrete residue was studied, their origin and test methods were analyzed, and to end materials were characterized. In the intermediate stages, a study was made to understand the effect of varying particle size during the production process of structural concrete. And in the final stages studies were made in AGRC saturation condition. With the results it can be concluded that with an efficient control of AGRC variability parameter it is possible to produce concrete with structural objectives, aiming thereby to technology transfer.

A reciclagem de resíduos de construção e demolição (RCD) é uma prática utilizada desde a Antigüidade, quando cidades destruídas pela guerra e por catástrofes naturais eram reerguidas dos próprios escombros. Hoje, ela é utilizada em larga escala em vários países da Europa e nos EUA. No Brasil, onde a preocupação com o destino desses resíduos é bem mais recente, poucos municípios se preocupam com o gerenciamento dos RCD. Os efeitos disso são visíveis: os resíduos ainda são depositados irregularmente em terrenos baldios, vias públicas, várzeas, córregos e até mesmo em áreas de proteção ambiental, causando a proliferação de vetores nocivos à saúde, enchentes e diversos prejuízos ao meio-ambiente. Assim, este trabalho tem como objetivo propor soluções que busquem a minimização desse impacto ambiental por meio da utilização dos RCD como agregados na fabricação de blocos de concreto. Os testes em laboratório e a comparação dos resultados obtidos com os das práticas convencionais provam a viabilidade da utilização dos resíduos, tanto em termos ambientais quanto econômicos, além de garantir que o emprego dos RCD atenda a todas as normas vigentes. Com isso, reafirmou-se o compromisso com a preservação ambiental, pois a reciclagem desse tipo de entulho, além de ajudar a removê-lo da paisagem urbana, ainda gera diferenciais consideráveis em termos de economia de energia e de recursos naturais não-renováveis que seriam utilizados como matérias-primas, reduzindo a poluição do ar, da água, do solo, desafogando aterros sanitários, e visando atingir o desenvolvimento sustentável. / Recycling of construction and demolition refuses (CDR) is a has been practiced since ancient history, when cities that were destroyed by war and natural disasters were rebuilt from their own ruins. Today, it is used in large scale in many countries in Europe and in the USA. In Brazil, where the concern with the destination of this kind of refuses is much more recent, few cities have planned and executed CDR management to this day. The side effects of this situation are plainly visible: the refuses have been continually and irregularly deposed in unused areas, thoroughfares, riversides, creeks and even in environmental protection areas, causing the proliferation of health-affecting problems, flooding and many other damages to the environment. Therefore, this study has the main goal of proposing solutions that can lessen the environmental impact by using CDR as aggregate in the manufacturing of concrete blocks. The lab tests and the comparing of the results obtained with those measured with the conventional techniques prove the viability of reutilizing these refuses, both in environmental and economical terms, as well as assuring that the use of CDR follows all the current regulations. With this, the compromise with environmental preservation is reinforced, since the recycling this type of refuse, beside helping to remove it from the urban landscape, generates considerable gains in saving energy and the non-renewable natural resources that would be used as raw material, lessening air, water and soil pollution, releasing the burden on landfills, always aiming at achieving sustainable development.

Orientador: Osvaldo Luís Manzoli / Resumo: Este trabalho apresenta uma proposta de análise numérica do concreto com agregados reciclados (CAR). A ferramenta desenvolvida facilita a avaliação do comportamento mecânico do material, verificando a viabilidade de sua utilização para fins estruturais. Considerando que no Brasil o emprego atual do material ainda é bastante limitado em comparação com outros países, o CAR pode vir a ser utilizado mais ampla e adequadamente, trazendo vantagens de caráter estrutural, econômico, e principalmente ambiental. Em termos de modelagem do CAR, a ocorrência de particularidades em nível mesoscópico exige um modelo em escala mais refinada para representar as propriedades alteradas do agregado reciclado (AR), de modo que foi desenvolvido um gerador de agregados reciclados para representar sua composição variada. Os mecanismos de falha que ocorrem nas interfaces características do agregado reciclado e da matriz de concreto introduzem não linearidade ao problema mecânico. Para que haja a representação dessa não linearidade, a estratégia de modelagem proposta recorre ao emprego da técnica de fragmentação de malha de elementos finitos juntamente com um modelo constitutivo de dano. Essa técnica de fragmentação baseia-se no emprego de elementos finitos com alta razão de aspecto, os quais poderão ser utilizados para representar as fases adicionais desse material compósito, correspondentes às diferentes zonas de transição interfaciais (ZTIs) intrínsecas do CAR em mesoescala, e consequentemente, cam... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This research presents a numerical analysis proposal for recycled aggregate concrete (RAC), whose recycled aggregates are obtained from the crushing of concrete waste. The developed tool facilitates the mechanical behavior evaluation of the RAC, verifying the feasibility of its use for structural purposes. Considering that in Brazil the current use of the material is still quite limited in comparison with other countries, the RAC could be used more widely and properly, bringing structural, economic and mainly environmental advantages. Due to the occurrence of mesoscopic specificities, the RAC modeling requires a more refined scale model to represent the altered properties of recycled aggregate, so that a recycled aggregate generator was developed to represent its variable composition. The failure mechanisms that occur at the several interfaces of the recycled aggregate (RA) and concrete matrix introduce nonlinearity to the mechanical problem. In order to represent this nonlinearity, the proposed modeling strategy uses the finite element mesh fragmentation technique together with robust and stable damage constitutive model. This fragmentation technique is based on the use of finite elements with high aspect ratio, which can be used to represent the additional phases of this composite material, corresponding to the different mesoscale RAC intrinsic interfacial transition zones (ITZs), as well as potential pathways for the propagation of fractures. A constitutive model based on ... (Complete abstract click electronic access below) / Mestre

Det pågår just nu ett arbete inom byggindustrin att allt mer gå över till en cirkulär ekonomi för att hushålla på världens naturliga resurser. För betongtillverkningen innebär det att försöka ersätta naturballast med återvunnen betong som ballast. Men för tillfället finns det lagkrav som förhindrar att naturballast helt ska kunna ersättas av återvunnen betong som ballast. Det är för att det finns vissa fysikaliska egenskaper, så som att porositeten ökar, som gör att de mekaniska egenskaperna blir sämre när naturballast ersätts med återvunnen betong som ballast. Detta examensarbete utfördes genom experimentella studier. Undersökningen utfördes i mekanik- och betonglaboratorium på Högskolan i Borås. Det utfördes en storskalig gjutningsserie där betongavfall från Ulricehamns Betong AB (UBAB) och Hedareds Sand & Betong AB (HEDA) prövades som ballastersättare till 50 och 100 %. För samtliga försök uppmättes både sättmått och betongens mekaniska egenskaper. Resultaten från betong med återvunnen betong som ballast (RAC) jämfördes med referensbetongen. Referensbetongen är baserad på ett känt- och beprövat originalrecept från UBAB respektive HEDA. Betongen med återvunnen betong som ballast är baserad på modifieringar som gjorts på referensrecept. Målet med studien var att undersöka hur återvunnen betong som ballast i betongblandningen påverkar betongens mekaniska egenskaper så som tryckhållfasthet, spräckhållfasthet och elasticitetsmodul. De testerna utfördes på gjutna cylindrar efter 28 dygn, tryckhållfastheten var också testad efter 7 dygn. Böjdraghållfasthet testades på balkar efter 28 dagar. Sedan utvärderades dessa resultat för att se hur de mekaniska egenskaperna förändras när en större del återvunnen betong som ballast används i recepten. Resultaten varierar litegrann för de olika provningarna. Denna studie styrker tesen att minskningen av tryckhållfastheten, efter 28 dagars härdning, som sker när återvunnen betong som ballast (RCA) används är inom intervallet 5–24 %. Provningarna av elasticitetsmodulen uppvisar liknande tendenser som tidigare forskning då betongen blir lite mindre styv när naturballast (NA) ersätts av RCA. Den styrker även tidigare forskning där böjdraghållfastheten är större vid ökade RCA-mängder. Då det för HEDA-recepten uppvisades en ökning med 9 procentenheter när all NA ersattes med RCA. Spräckhållfastheten uppvisade samma tendenser som böjdraghållfastheten. Det resultatet är däremot inte i linje med vad som har visats i tidigare forskning, då spräckhållfastheten har i de studierna minskat vid högre ersättningsandelar. / Work in the construction industry is currently underway to move to a circular economy to preserve the world’s natural resources. For concrete production this means trying to replace natural aggregate with recycled concrete aggregate. But for the time being there are standard allows that prevent natural aggregate from being completely replaced by recycled concrete aggregate. This is because there are certain physical properties, such as an increase in porosity, which have a negative impact on the mechanical properties when natural aggregate is replaced with recycled concrete aggregate. This thesis is carried out through experimental studies. The study was carried out in the mechanical and concrete laboratory at the University of Borås. Large scale castings were done where concrete waste from Ulricehamns Betong AB (UBAB) and Hedareds Sand & Betong AB (HEDA) were tested as aggregate replacers. For all experiments, both the measurement dimensions and the mechanical properties of the concrete was measured. The results from the recycled aggregate concrete were compared with the reference concrete. The reference concrete is based on an industrially active recipe from UBAB and HEDA. The Recycled Aggregate Concrete (RAC) is based on modifications made on reference recipes. The aim of this study was to investigate how recycled concrete aggregate in the concrete mix affects the mechanical properties of the concrete, such as compressive strength, splitting tensile strength and the modulus of elasticity. They were performed on cylinders at 28 days, the compressive strength was also performed at 7 days. The flexural strength was also tested. Those tests were performed on beams. Then these results were evaluated to see how the mechanical properties change when a greater replacement ratio is used in the recipes. The results vary slightly for the different tests. This study confirms that the decrease in compressive strength, after 28 days hardening, that occurs when Recycled Concrete Aggregate (RCA) is used is within the range 5–24%. The tests of the modulus of elasticity show similar tendencies as previous research because the concrete becomes a little less stiff when Natural Aggregate (NA) is replaced by RCA. It also corroborates previous research where the flexural strength is greater with increased RCA amounts. When the HEDA prescriptions showed an increase of 9 percentage when all NA was replaced with RCA. The splitting tensile strength exhibited the same tendencies as the flexural strength. On the other hand, this result is not in line with what has been shown in previous research, as the splitting tensile strength in those studies has decreased at higher replacement ratios.

[pt] Nas últimas décadas, o setor da construção tem procurado mitigar os efeitos da sua atividade desenvolvendo novas formulações de materiais mais sustentáveis. Diversos estudos têm analisado a viabilidade do uso de agregado reciclado a partir de resíduos de construção e demolição, em substituição ao agregado natural. As normas internacionais restringem o uso de agregados reciclados em concreto estrutural, geralmente limitando-se a agregados reciclados compostos apenas por fragmentos cimentícios. Entretanto, a utilização de agregado reciclado com certo teor de fragmentos cerâmicos simplificaria o processo de separação antes da reciclagem, tornando-a mais viável e barata. Neste trabalho, observou-se que mesmo a substituição de 100 por cento do agregado natural por agregado reciclado misto não causou impacto significativo nas propriedades do concreto fresco e endurecido. Os resultados experimentais também mostraram que o Modelo do Empacotamento Compressível pode ser aplicado com sucesso para a dosagem de concretos produzidos com agregado reciclado misto até a classe de resistência C50. Por fim, os resultados à flexão de vigas curtas de concreto armado mostraram que as prescrições da norma brasileira ABNT NBR 6118:2014 para concretos convencionais também podem ser aplicadas a vigas de concreto com agregado reciclado misto com até 15 por cento de fragmentos cerâmicos. / [en] In the last decades, the construction sector has tried to mitigate the adverse effects of its activity by developing new formulations for more sustainable materials. Several studies have analyzed the feasibility of using recycled aggregate from construction and demolition waste in concrete to replace natural aggregate. International standards restrict the use of recycled aggregates in structural concrete, usually limiting to recycled aggregates composed only of cement-based fragments. However, using recycled aggregate with a certain content of ceramic fragments would simplify the separation process before recycling, making it more feasible and cheaper. In this work, it was observed that even replacing 100 percent of the natural aggregate with mixed recycled aggregate did not cause a significant impact on fresh and hardened concrete properties. The experimental results also showed that the Compressible Packing Model could be successfully applied for the mix design of mixed recycled aggregate concrete up to strength class C50. Finally, the results regarding the flexural behavior of short reinforced concrete beams showed that the prescriptions of the Brazilian standard ABNT NBR 6118:2014 for the bending behavior of conventional concrete beams could also be applied to beams made with concrete with mixed recycled aggregate up to 15 percent of ceramic fragments.

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute of the Libyan Government