Desarrollo de materiales con retracción compensada a partir del óxido de calcio (cao)
- Autores: Cristina Fernández Rubio
- Directores de la Tesis: Sergio H. Pialarissi Cavalaro (dir. tes.), Ignacio Segura Pérez (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Juan Ramon Rosell Amigo (presid.), Ana Blanco Alvarez (secret.), Joan Formosa Mitjans (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería de la Construcción por la Universidad Politécnica de Catalunya
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
The shrinkage of concrete and the current methods to mitigate this phenomenon are mainly based on the realization of retraction joints approximately 24 hours after the mixing. These joints represent a critical point in the pavements due to the fact that they can trigger pathological processes. These processes go from the rupture of the lips of the joint to the filtration of substances that can be harmful to the concrete.
The different pathologies arising from the realization of the joints, as well as the concrete cracking of the concrete have raised the use of materials with compensated shrinkage in order to reduce the number of joints and mitigate the cracks that appear in the element. In this doctoral thesis the effect of the addition of CaO to the cemetícia mixture for the realization of compensated shrinkage concretes (SCC) has been studied.
The first line of research is based on the study of the chemical interaction between cement and lime, considering the variation of three main variables such as the ratio w/c, the percentage of lime added and the type of lime used. The results have shown that there is a synergy between cement and lime during hydration, as well as competition during the hydration of CaO with some of the phases present in the cement. Likewise, the addition of lime modifies the setting times of the different mixtures studied, generating mixtures that set in a shorter time than a cement paste without the addition of lime.
The second line of research has shown the impossibility of measuring the expansion process that occurs in this type of material during the first 24 hours after mixing by using standardized tests. The obtained results indicate that both the process of expansion and the generation of tensions occur, mainly, during this period of time. Due to this fact it has been necessary to propose new tests in order to characterize both processes. The method of the mixed mould has allowed to determine the influence of the addition of lime in mortars. Thus, maximum values of deformation generated by this addition have been obtained, as well as the stress values that these materials can achieve. In most cases it has been observed that the stress obtained is higher than that proposed in the literature. Any damage has been observed in the hardened specimen despite the stress values accomplished.
The third line of research has given rise to a simplified numerical model in which the expansion and stress curves generated by the material have been modelled since the few minutes after the mixtures. Through the application of the model it has been established that not all the added lime generates effective expansion in the material. Part of it is damped by hydrating in a plastic material. On the other hand, when introducing the deformation curve for the calculation of the tension generated in the real tests, a second damping has also been observed. This shows that the tension of the material cannot be obtained by direct multiplication of the deformation by the elastic module. In order to obtain de stress value is necessary to introduce a damping factor in the equation.
Finally, the real experiences carried out, mainly in slab-type elements, have allowed to observe the real behavior of the mixture in a situation of non-control of the production system of the mixture, as well as during transportation and dumping. No incompatibilities have been found between lime and the use of conventional reinforcement or fibers. On the other hand, the compression tests show that the concretes with the addition of lime are more resistant than the reference ones without lime.
