Publicação
Continuous characterization of stiffness of cement-based materials: experimental analysis and micro-mechanics modelling
| Resumo: | The structural performance and durability of reinforced concrete structures are strongly influenced by the material properties of concrete. Concrete’s characteristics endure strong evolution since casting, passing from a solid suspension to a structural material. Therefore, it is extremely important to understand and predict the structural behaviour of concrete since the beginning of the hardening process for a good structural design, particularly in regard to the development of self-induced stresses (due to heat of hydration and shrinkage). Apart from these issues related to structural design, relevant urges are brought about by the necessity of shortening construction schedules, both due to pressures by society, as well as due to economic and sustainability concerns. In view of these motivations, there are enough reasons to justify the importance of having experimental methods that allow continuous monitoring of the evolution of mechanical properties of concrete since very early ages, both in laboratory environment and “in-situ”. In such concern, several methods experimental have been proposed throughout the years, particularly in regard to the evaluation of the E-modulus of concrete. However, the most widespread methods still present limitations/complexities which make them inadequate for the wider intents mentioned above. Thus a new experimental method called EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) was proposed in 2009, which is based on the modal identification of a composite beam (acrylic and concrete) during the curing period of concrete, allowing the continuous measurement of concrete E-modulus since casting. Despite the good results obtained during the first implementation prior to this thesis, the EMM-ARM is still lacked extensive validation and presented several laminations that needed to be overcome. Following the encouraging results obtained in the first application of EMM-ARM, the work reported in this thesis intended to achieve an improved robust tool based on EMM-ARM to provide early information of the cementitious materials stiffness, readily available for application on behalf of both scientists and practitioners. In pursuit of that goal, relevant changes were introduced in EMM-ARM, particularly in concern to the geometry and materials involved in the EMM-ARM mould, as well as to the modal identification of technique. These changes allowed overcoming the identified constraints and to significantly improve the usability and robustness of the method. This thesis also presents a systematic study of the application of EMM-ARM compared to competing methods that mechanical characterization of cementitious materials at early ages with mutual validation objectives. This systematic study allowed proving that the results of EMM-ARM are metrologically robust and also to clearly identify the strengths and limitations of EMM-ARM. After the optimization and validation of EMM-ARM the method was applied in different conditions such as: (i) different isothermal curing temperatures in the range 10-40ºC; (ii) the implementation in a construction site; and (iii) non-isothermal conditions. This research also permitted demonstrating that EMM-ARM can be used to characterize a wide range of materials that undergoes chemical hardening such as structural epoxy adhesives. In addition, a new version of EMM-ARM for monitoring the concrete viscoelasticity during the fresh state was suggested. The thesis ends with a foray into the microstructural simulation of the stiffness evolution of cementitious materials by taking advantage of the unprecedented quantitative experimental information obtained with EMM-ARM. The stiffness evolution of cement pastes, simulated by μic/AMIE, developed at EPFL (École polytechnique fédérale de Lausanne) was validated through comparison with EMM-ARM results. |
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| Autores principais: | Granja, José Luís Duarte |
| Assunto: | Engenharia e Tecnologia::Engenharia Civil |
| Ano: | 2016 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The structural performance and durability of reinforced concrete structures are strongly influenced by the material properties of concrete. Concrete’s characteristics endure strong evolution since casting, passing from a solid suspension to a structural material. Therefore, it is extremely important to understand and predict the structural behaviour of concrete since the beginning of the hardening process for a good structural design, particularly in regard to the development of self-induced stresses (due to heat of hydration and shrinkage). Apart from these issues related to structural design, relevant urges are brought about by the necessity of shortening construction schedules, both due to pressures by society, as well as due to economic and sustainability concerns. In view of these motivations, there are enough reasons to justify the importance of having experimental methods that allow continuous monitoring of the evolution of mechanical properties of concrete since very early ages, both in laboratory environment and “in-situ”. In such concern, several methods experimental have been proposed throughout the years, particularly in regard to the evaluation of the E-modulus of concrete. However, the most widespread methods still present limitations/complexities which make them inadequate for the wider intents mentioned above. Thus a new experimental method called EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) was proposed in 2009, which is based on the modal identification of a composite beam (acrylic and concrete) during the curing period of concrete, allowing the continuous measurement of concrete E-modulus since casting. Despite the good results obtained during the first implementation prior to this thesis, the EMM-ARM is still lacked extensive validation and presented several laminations that needed to be overcome. Following the encouraging results obtained in the first application of EMM-ARM, the work reported in this thesis intended to achieve an improved robust tool based on EMM-ARM to provide early information of the cementitious materials stiffness, readily available for application on behalf of both scientists and practitioners. In pursuit of that goal, relevant changes were introduced in EMM-ARM, particularly in concern to the geometry and materials involved in the EMM-ARM mould, as well as to the modal identification of technique. These changes allowed overcoming the identified constraints and to significantly improve the usability and robustness of the method. This thesis also presents a systematic study of the application of EMM-ARM compared to competing methods that mechanical characterization of cementitious materials at early ages with mutual validation objectives. This systematic study allowed proving that the results of EMM-ARM are metrologically robust and also to clearly identify the strengths and limitations of EMM-ARM. After the optimization and validation of EMM-ARM the method was applied in different conditions such as: (i) different isothermal curing temperatures in the range 10-40ºC; (ii) the implementation in a construction site; and (iii) non-isothermal conditions. This research also permitted demonstrating that EMM-ARM can be used to characterize a wide range of materials that undergoes chemical hardening such as structural epoxy adhesives. In addition, a new version of EMM-ARM for monitoring the concrete viscoelasticity during the fresh state was suggested. The thesis ends with a foray into the microstructural simulation of the stiffness evolution of cementitious materials by taking advantage of the unprecedented quantitative experimental information obtained with EMM-ARM. The stiffness evolution of cement pastes, simulated by μic/AMIE, developed at EPFL (École polytechnique fédérale de Lausanne) was validated through comparison with EMM-ARM results. |
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