%0 Journal Article %T Early hydration cement Effect of admixtures superplasticizers %A Puertas %A F. %A V芍zquez %A T. %J Materiales de Construccion %D 2001 %I Consejo Superior de Investigaciones Cient赤ficas %X Early hydration of portland cement with superplasticizer admixtures of different nature has been studied. These admixtures were: one based on melamine synthetic, other based on vinyl copolymer and other based on polyacrylate copolymers. The dosage of the formers were constant (1% weigth of cement) and for the third, the influence of admixture dosage was also evaluated, giving dosage values among 1-0.3%. The pastes obtained were studied by conduction calorimetry, XRD and FTIR. Also the apparent fluidity was determined by "Minislump" test. The main results obtained were: a) superplasticizers admixtures used, regardless of their nature and for the polycarboxilate one the dosage, retard the silicate hydration (specially, alite phase), b) The ettringite formation is affected by the nature of the admixture. c)A relationship between the dosage of admixture based on polycarboxilates and the time at the acceleration has been established. A lineal relation (y = 11.03 + 16.05x) was obtained. From these results is possible to know, in function of dosage admixture, the time when the masive hydration products and the setting times are produced. Also the total heat releases in these reactions is independent of the nature and dosage of admixture, saying that in all cases the reactions are the same. En el presente trabajo se ha estudiado la hidrataci車n inicial de un cemento portland aditivado con superplastificantes de diferente naturaleza. Dichos aditivos fueron: uno basado en melaminas sint谷ticas, otro en copol赤meros vinilicos y otro en policarboxilatos. La dosificaci車n de los dos primeros se fij車 constante en 1% en peso con relaci車n al cemento, mientras que para el tercero se evalu車, tambi谷n, la influencia de la dosificaci車n, tomando proporciones desde el 1% hasta el 0,3%. Las pastas obtenidas se estudiaron por: calorimetr赤a de conducci車n, DRX y FTIR. Tambi谷n se determin車 la fluidez de la pasta a trav谷s del ensayo del "Minislump ". Los resultados obtenidos han indicado que: a) Los aditivos superplastificantes utilizados, independientemente de su naturaleza y para el aditivo basado en policarboxilados de su dosificaci車n, retardan la hidrataci車n de los silicatos (especialmente de la fase alita), b) La formaci車n de etringita se ve afectada por la naturaleza del superplastificante. c) Se ha establecido la relaci車n existente entre la dosificaci車n del aditivo basado en policarboxilatos y el tiempo en el que aparece el m芍ximo de la se al de aceleraci車n. Obteni谷ndose una relaci車n lineal (y = 11,03 + 16,05x). A partir de estos resultados es posible, en funci車n de la dosificac %U http://materconstrucc.revistas.csic.es/index.php/materconstrucc/article/view/371/416