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Luís Pedro Esteves Internal Curing in Cement-Based Materials Universidade De Departamento De Engenharia Civil Aveiro 2009

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Luís Pedro Esteves Internal Curing in Cement-Based Materials Universidade De Departamento De Engenharia Civil Aveiro 2009 Universidade de Departamento de Engenharia Civil Aveiro 2009 Luís Pedro Esteves Internal curing in cement-based materials Universidade de Departamento de Engenharia Civil Aveiro 2009 Luís Pedro Esteves Internal curing in cement-based materials Dissertação apresentada à Universidade de Aveiro para cumprimento dos requisitos necessários à obtenção do grau de Doutor em Engenharia Civil, realizada sob a orientação científica do Dr. Paulo Barreto Cachim, Professor Associado do Departamento de Engenharia Civil da Universidade de Aveiro e do Dr. Victor Miguel C. de Sousa Ferreira, Professor Associado do Departamento de Engenharia Civil da Universidade de Aveiro. Beside other problematic, it was often astonishing to run after thoughts. As an ancient philosophy doctor pointed out: “The greater the attempt that is made to study the nature or behaviour of a photon or a particle, the greater will be the uncertainty or error of the measurements.” Heisenberg summarised this in his uncertainty principle, the concept being demonstrated by means of idealized “thought” experiments. If it is permitted for me to say, I would add: (…), provided that it can not be seen or felt. O júri PRESIDENTE: Reitora da Universidade de Aveiro VOGAIS: Doutor Ole Mejhede Jensen, Professor Catedrático da Technical University of Denmark. Doutor Klaas van Breugel, Professor Catedrático da Delft University of Technology. Doutor Aníbal Guimarães da Costa, Professor Catedrático da Universidade de Aveiro. Doutor José Luís Barroso de Aguiar, Professor Associado com Agregação da Universidade do Minho. Doutor Paulo Barreto Cachim, Professor Associado da Universidade de Aveiro (Orientador). Doutor Victor Miguel Carneiro de Sousa Ferreira, Professor Associado da Universidade de Aveiro (Co-Orientador). Acknowledgments This thesis is written to fulfil the requirements for the Portuguese degree of Doctor of Philosophy in Civil Engineering at Aveiro University. It is focused on the internal curing of cement-based materials, with concern on the study of autogenous phenomena and volume change at early-age. The experimental work was developed in approximately three years, comprising material testing at Aveiro University under the supervision by Paulo Cachim and Victor Ferreira, which is greatly acknowledged, and a short-term experimental framework at the main concrete laboratory of the electrical power plant at EDP, which was kindly granted by Armando Camelo. The assistance during the material testing by the technical staff at EDP is greatly acknowledged. Approximately one third of the Ph.D. work was conducted as guest researcher at Technical University of Denmark. This was made possible by Ole Mejlhede Jensen. No conference participations were possible during this period, due to professional obligations at Porto Engineering Institute, where I do lecture since April 2004, in the Civil Engineering Department. Two standard journal publications and one contribution for edited book have emerged from the preliminary results developed in the first year of the PhD work[1-3]. Other publications are expected in 2009, as a result of the findings presented in this document and from work that will follow. Particularly, in section 3.4, the simulation of the absorption kinetics in augmented reality and the graphical representation of polymer particles were performed in conjunction with Gonçalo Henriques. The author wishes to acknowledge his assistance in this work. A fairly chaotic strategy was taken during the last two and a half years of intensive work to explain the observations presented in the following chapters. It seemed that it was more important to pursuit fundamental research rather than running empirical or applied research to add-up text about history of cement and concrete research. It is then fair to say that inductive thinking was preferred at some point, rather then the deductive mode of thinking. “The findings may be a little chaotic, as cement!” keywords Internal curing, high performance concrete, autogenous deformation, superabsorbent polymers, fine aggregate particles abstract The development of high performance concrete in the early 80 revealed that this particular branch of cement-based materials is highly sensible to curing problems. It is well known the consequences of autogenous phenomena in high performance systems, namely the early-age cracking. This is seen as the major limitation on the further development of new materials with superior durability. Recent developments have returned internal curing methods as mean to mitigate such phenomena, where this thesis finds it space in time. Internal curing of cement-based materials by superabsorbent polymers is further analysed, with emphasis on the consequences of the volume-changes in plain Portland and SF-modified cement based systems at early age. Some limitations in the use of superabsorbent polymers are encountered, being concluded that the physical and chemical nature of superabsorbent polymers may significantly affect the efficiency of internal curing. In addition, the mechanisms of internal curing are discussed in more depth, from where it transpires that beyond the mechanisms with physical or chemical ground, significant mechanical effects do exist. Several techniques are used in the course of the investigation, which aimed, beside the characterisation of certain material properties, to pursue the open questions left by the international community, in respect with the fundamental mechanisms that may explain the autogenous phenomena. Examples of that are the hydration studies at a microscopic scale, rather than macroscopic. Furthermore, a new technique of internal curing is proposed, which is based on the use of very fine aggregate particles, as mean of partial mitigation of autogenous shrinkage. So far, this technique has not been reported in the research community as mean of mitigation, but the extent of internal curing that may potentially be obtained from this concept encounters several limitations. The significance of this technique in preventing microcracking is yet to be proved, but it is concluded that fine aggregate particles may be beneficial in reducing the restraint effects, and thus, reducing the potential for cracking events. The combined use of superabsorbent and fine aggregate particles may have as a consequence the development of concrete with nanocracking, rather than micro, during a period where the “culture” in the concrete technology is putting considerable effort in getting more intimate with the durability aspects of cement-based materials. keywords Cura interna, betão de elevado desempenho, deformação autogénea, polímeros super absorventes, agregados finos Portuguese summary O desenvolvimento de betões de elevado desempenho, durante o início da década de 80, revelou que este tipo particular de materiais com base em cimento é susceptível a problemas de cura. São bem conhecidos os efeitos dos fenómenos autogéneos em sistemas de elevado desempenho com base em cimento, nomeadamente a fissuração em idade jovem. Esta é, aliás vista como a maior limitação no desenvolvimento de novos materiais com durabilidade superior. Desenvolvimentos recentes de métodos de cura interna provaram ser uma boa estratégia de mitigação dos efeitos da auto-dissecação destes sistemas, onde a presente tese ganha o seu espaço no tempo. Este estudo centra-se essencialmente em sistemas de elevado desempenho com base em cimento com cura interna através de partículas superabsorventes, dando particular importância à alteração de volume em idade jovem. Da análise mais aprofundada deste método, resultam algumas limitações na sua aplicabilidade, especialmente em sistemas modificados com sílica de fumo. Conclui-se que a natureza física e química dos polímeros superabsorventes pode afectar significativamente a eficiência da cura interna. Em adição, os mecanismos de cura interna são discutidos mais profundamente, sendo que para além dos mecanismos baseados em fenómenos físicos e químicos, parecem existir efeitos mecânicos significativos. Várias técnicas foram utilizadas durante o decorrer desta investigação, com o objectivo, para além da caracterização de certas propriedades dos materiais, de perseguir as questões deixadas em aberto pela comunidade internacional, relativamente aos mecanismos que fundamentam a explicação dos fenómenos autogéneos. Como exemplo, são apresentados os estudos sobre hidratação dos sistemas para avaliação do problema numa escala microscópica, em vez de macroscópica. Uma nova técnica de cura interna emerge da investigação, baseada na utilização de agregados finos como veiculo para mitigar parcialmente a retracção autogénea. Até aqui, esta técnica não encontra par em investigação anterior, mas a extensão da cura interna ou a eficácia na mitigação baseada neste conceito encontra algumas limitações. A significância desta técnica em prevenir a micro fissuração é um aspecto que está ainda em aberto, mas pode concluir-se que os agregados finos podem ser benéficos na redução dos efeitos da restrição localizada no sistema, reduzindo o risco de micro fissuração. A utilização combinada de partículas finas de agregado e polímeros super absorventes pode ter como consequência betão sem microfissuração, ou pelo menos com nanofissuração. CONTENTS 1. INTRODUCTION ............................................................................................................................... 21 1.1. SCOPE ..........................................................................................................................................
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