Showing papers by "Francisca Puertas published in 2007"

Comportamiento de morteros de escoria activada alcalinamente con adición de fibras de carbón

Abstract: The paper describes the effect of carbon fibre on alkaliactivated slag mortar (AAS) mechanical strength, volume stability and reinforcing steel corrosion, compared to its effect on the same properties in Portland cement (PC) properties. Mechanical strength and volume stability tests were performed as set out in the respective Spanish UNE standards. The corrosion rate of steel embedded in the specimens studied was determined from polarization resistance analysis. One of the findings of the study performed was that carbon fibre failed to improve AAS or CP mortar strength. As far as volume stability is concerned, the inclusion of carbon fibres in AAS with a liquid/solid ratio of 0.5 reduced drying shrinkage by about 50%. The effect of carbon fibre on PC mortars differed from its effect on AAS mortars. Studies showed that in the presence of carbonation, steel corrosion reached higher levels in carbon-fibre reinforced AAS mortars; the inclusion of 1% carbon fibre improved corrosion resistance perceptibly in these same mortars, however, when exposed to chloride attack.

Effect of polycarboxylate admixture structure on cement paste rheology

Abstract: El objetivo de este trabajo ha sido estudiar el efecto de las diferencias estructurales de cuatro aditivos basados en policarboxilatos y polieteres sobre las propiedades reologicas de pastas de cemento con diferente composicion quimica, mineralogica y con distintas adiciones activas (CEM I 42,5 R, CEM I 52,5 R, CEM I 52,5 N/SR, CEM II/AV 42,5R, CEM II/ B-L 32,5 R, CEM III/B 32,5R, BL I 52,5R y CAC - Norma EN 197-1:2000). Los resultados obtenidos sobre la fluidez de la pasta en el ensayo del ?Minislump? coinciden con la evolucion de los valores de los parametros reologicos (esfuerzo de cizalladura y viscosidad plastica) determinados a traves de un viscosimetro rotacional. Las caracteristicas estructurales de los aditivos que mas afectan al efecto fluidificante son el contenido de grupos carboxilatos (GC) y de grupos polieteres (GE). En relacion con las caracteristicas y composicion de los cementos, son factores fundamentales, la finura y las relaciones C3A/sulfato calcico y C3S/C3A. Asi, las pastas de CEM I 52,5N/SR son las que presentan una mayor modificacion de los parametros reologicos, mientras que las de BL I 52,5R son las que se ven modificadas en menor medida. Las pastas de CEM III/B 32,5R, con escoria granulada de horno alto, son las que presentan mayores incrementos de la fluidez mas acusados. Por ultimo, el efecto fluidificante del aditivo es mucho mas marcado en cementos de aluminato de calcio aunque presenta acusadas perdidas de fluidez con el tiempo.

Efecto de la temperatura de tratamiento de un caolín en la permeabilidad a cloruros en morteros

Abstract: The present paper discusses the results of chloride resistance tests conducted on ordinary Portland cement (OPC) mortars containing a Colombian kaolin pre-treated at temperatures of from 600 to 800 oC. The resulting metakaolin (MK) was added to OPC mortar mixes in proportions of 10 and 20% by cement weight. The mortars were compared for physical and chemical properties, including capillary absorption, chloride permeability and pore microstructure as assessed by mercury porosimetry. The best performance was recorded for the samples containing 20% of the material treated at 800 oC.