Browsing by Author "Campillo, Igor"
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Item Effect of nanosilica additions on belite cement pastes held in sulfate solutions(2007-12) Dolado, Jorge S.; Campillo, Igor; Erkizia, Edurne; Ibáñez, José A.; Porro, Antonio; Guerrero, Ana; Goñi, Sara; Tecnalia Research & Innovation; ECOEFICIENCIA DE PRODUCTOS DE CONSTRUCCIÓN; TRAZABILIDAD CIRCULARFly Ash Belite Cement (FABC) pastes with and without nanosilica additions have been prepared and maintained in sulfate solutions (Na2SO 4 0.5M) for 180 days. The mechanical performance and the changes in microstructure have been monitored at 28, 90, and 180 days by compressive strength, X-ray diffraction (XRD), and 29Si MAS NMR measurements. We have found that, unexpectedly, and contrary to what happens in Ordinary Portland Cements (OPC), the addition of nanosilica particles induces an initial decline in the compressive strength of the samples. Only in samples maintained for a long time (180 days) does the nanosilica addition improve the mechanical properties. Our XRD and 29Si NMR experiments have revealed that although nanosilica additions trigger the consumption of Belite phases, this is not always accompanied by formation of longer calcium-silicate-hydrate (C-S-H) gel structures. Only at a long time (180 days), and due to a mechanism that seems to be controlled by the pH of the samples, do the nanosilica additions lead to high-polymerized C-S-H gels.Item Extraordinary transmission surfaces as superstrate(2009) Beruete, Miguel; Navarro-Cía, Miguel; Falcone, Francisco; Sorolla, Mario; Campillo, Igor; Rodríguez-Seco, J. E.; Perea, E.; Núñez-Manrique, I. J.; POWER SYSTEMS; DIGITAL ENERGY; Equipos ElectrónicosIn this work we explore in the microwave regime the modification of the radiation pattern of a commercial horn antenna when 1 and 4 stacked subwavelength hole arrays are placed as a superstrate. We report a clear enhancement of the E-plane while the H-plane remains almost unaltered when either 1 or 4 layers are inserted. We link the results with the current density excited in the output face of the perforated structure along with the backward propagation supported by the Extraordinary Transmission Metamaterial.Item Small changes can make a great difference(2010-01-12) Gaitero, Juan J.; Campillo, Igor; Mondal, Paramita; Shah, Surendra P.; Tecnalia Research & InnovationFour different types of commercially available silica nanoparticles were added to ordinary portland cement pastes to study their effects. The subsequent multiscale characterization of the material revealed that the addition of the nanoparticles induced a pozzolanic reaction that increased the amount of calcium silicate hydrate (C-S-H) gel in the paste to the detriment of portlandite. This had important implications for the hydration kinetics and the microstructure of the paste, including an increase in the initial hydration rate. A reduction of the overall porosity was also observed. The C-S-H gel of the pastes with nanosilica also showed some particular features, such as greater aluminum content and longer silicate chains. This was especially relevant because nanoindentation measurements and atomistic calculations showed that this was bound to an improvement in the mechanical properties of the C-S-H gel itself. Finally, the sum of all these factors resulted in pastes with 30% more compressive strength, which proved that, effectively, small changes can make a great difference.