Aportaciones al estudio reológico de pastas y morteros de cemento portland

The concrete could be considered as a thick solid particles suspension in fine particles suspension. The rhealogy of the last one influences very hardly the concrete behaviour, so that the importance to realize an study concerning the mortars and pastes rheology. The first objective of this work has been to determine the more adequated rheometer to characterize this kind of samples, considering the difficulty of the rheologic study of high concentration suspensions who tends towards the development of shear phenomena in the walls of the sensor system. Between the equipments with placa-placa sensor, coaxial cylinders and helicoidal band shaker, the first ones were discarded due to the high relationship between particle diameter and measure cavity that makes de viscose properties scarcely repetitive, whereas the last set doesn′t present this problem, in view of which we choose to use it to the obtention of rheologic properties of the samples studied. Secondly, we have try to describe the viscose behaviour of different pastes and mortars with different agregates and relations water/cement. For this purpose some sweeping of shake speed were realized as well as tests at constant speed, relating the viscosity evolution with the setting time. The analyse of the rheologic behaviour is affected by the fact of applying a shake that conduces to the system break who tends towards to be structured during the setting time. This specificity concerning the time, joined with the heterogeneity of the samples, makes difficult to obtain results with a good repeatability. El hormigón se puede considerar como una suspensión de partículas sólidas gruesas en una suspensión de partículas finas. La reología de esta última influye sustancialmente sobre el comportamiento del hormigón, de ahí la importancia de realizar un estudio sobre la reología de pastas y morteros. El primer objetivo de este trabajo ha consistido en determinar el tipo de reómetro más adecuado para caracterizar este tipo de muestras, considerando la dificultad que conlleva el estudio reológico de suspensiones de concentración elevada que tienden a desarrollar fenómenos de deslizamiento en las paredes del sistema sensor. Entre los equipos con sensor placa-placa, con cilindros coaxiles y con agitador de cinta helicoidal, fueron desechados los primeros debido a la alta relación diámetro de partícula/hueco de medida que presentan y que hace que las propiedades viscosas sean escasamente repetitivas, mientras que el último aparato no presenta este problema, por lo que se optó por su utilización para la obtención de la