Perez-Nicolas, M. (María)

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    Study of NOx abatement by calcium alumniate cements modified by TiO2
    (Universidad de Navarra, 2014-04-11) Cruz-Yusta, M. (Manuel); Sanchez, L. (Luis); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Navarro-Blasco, I. (Iñigo); Balbuena, J. (José); Fernandez-Alvarez, J.M. (José María)
    Different percentages of TiO2 (1 to 10 wt.%) were incorporated into two different Calcium Aluminate Cements (iron rich – d-CAC – and iron lean – w-CAC–) which were cured under two curing conditions. The mild hydrothermal curing condition 2 was chosen so as to resemble the natural ageing of aluminate cements in which hydrated hexagonal phases are converted into more stable cubic ones. Fresh and hardened state properties were studied. NOx removal under UV illumination was assessed in TiO2-bearing mortar samples. NO conversion values were higher in w-CAC than in d-CAC. Retention of NO2 in w-CAC samples was also more successful than in d-CAC samples due to the presence of ferrite in the latter ones. The presence of ferrite in d-CAC was established by XRD, SEM and EDAX. The interaction of ferrite phases with TiO2 was monitored in both types of mortars and different behaviours were observed. In the d-CAC, the incorporation of TiO2 results in the appearance of two new iron containing phases: namely pseudobrookite and in a lesser extent ilmenite, at the expense of brownmillerite. These new phases yielded in an improve photocatalytic efficiency of d-CAC in the visible region of spectrum, as proved by Methyl Orange degradation tests.
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    Cal como sustrato para incorporación de agentes fotocatalíticos
    (Grupo de Investigación MIMED. Servicio de Publicaciones de la Universidad de Navarra, 2018-05-15) Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    Diferentes morteros de cal fueron modificados por la incorporación en masa de aditivos fotocatalíticosnanoestructurados (TiO2 o TiO2 dopado con hierro (Fe-TiO2) o vanadio (V-TiO2)). Las propiedades plásticas y endurecidas de estos morteros han sido evaluadas para estudiar la influencia de estos nanoaditivos. Los retrasos en la demanda de agua observados en las pastas de cal se atribuyeron al impedimento de la difusión de CO2 dentro de la pasta. El TiO2 y el TiO2 dopado no mostraron reactividad puzolánica alguna. El examen por microscopía electrónica de barrido de los morteros de cal mostró que las fases predominantes en la microestructura eran placas hexagonales de portlandita y las aglomeraciones gruesas escalenoédricas de calcita. Se encontró que el Fe-TiO2 se distribuía homogéneamente, mientras que el análisis EDS demostró la tendencia al aglomeramiento del V-TiO2. La capacidad de absorción de agua no se vio afectada por la incorporación de nanoaditivos, lo cual es una característica favorable para la aplicación de estos morteros.
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    Aditivos y adiciones para la mejora de morteros de cal
    (LNEC (Laboratório Nacional de Engenharia Civil, Lisboa), 2016-05-25) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    Los morteros de cal presentan una interesante capacidad de admitir aditivos fotocatalíticos sin detrimento de otras características: se mantienen adecuadas resistencias, la estructura porosa no se modifica de forma sustancial y no hay cambios aparentes de color o brillo. El TiO2 dopado presenta sensibilidad mejorada hacia la luz solar y es una interesante vía de aplicación. Los recubrimientos activos son una manera muy prometedora de mejorar las prestaciones de autolimpieza de los morteros de cal. El uso de aditivos dispersantes y/o de medios de dispersión adecuados puede mejorar notablemente la eficacia fotocatalítica de los morteros de cal tratados.
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    Behaviour of air lime-metakaolin mortars modified with polynaphthalene sulfonate as superplasticizer
    (Aristotle University of Thessaloniki, 2016-10-11) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
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    Atmospheric NOx removal: study of cement mortars with iron- and vanadium-doped TiO2 as visible light–sensitive photocatalysts
    (Elsevier, 2017-09-15) Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    Mortars made with Portland cement, two different calcium aluminate cements and air lime were chosen to incorporate photocatalytic additives, because they have large exposed surfaces that boost the photochemical oxidation (PCO) of atmospheric pollutants such as nitrogen oxides. TiO2 as reference catalyst, and two doped titania, Fe-TiO2 and V-TiO2, which were expected to increase the sensitivity of the additives towards the visible light, were studied. Cementing matrices, particularly air lime and high alumina cement mortars, yielded significant amounts of NO removal under the three illumination conditions studied (UV, solar and visible light), with high selectivity response for NO abatement (up to 60 to 80%) and low NO2 release. The presence of calcium carbonate has been shown to have a synergistic effect, enhancing the PCO of these mortars under different light sources.
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    Role of different superplasticizers on hydrated lime pastes and mortars
    (2015-10) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    The use of plasticizing admixtures in order to improve the handling of cement-based media has been extensively reported. High-range water reducers or superplasticizers (SPs) act reducing the water demand and enhancing the flowability of the fresh mortars, yielding workable materials. So far little attention has been devoted to the study of the performance of superplasticizers in lime-bearing pastes and mortars. The widespread use of hydrated lime and pozzolan-hydrated lime pastes for paints, consolidant products, soil treatments and the obtaining of repair mortars and grouts, especially for architectural monuments of the Cultural Heritage, supports the interest of these materials. In order to design suitable hydrated lime pastes and mortars, the use of compatible and effective SPs seems to be imperative.
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    Role of different superplasticizers on hydrated lime pastes and mortars
    (2015-10-13) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    The behaviour of different superplasticizers admixtures was assessed for hydrated lime pastes and mortars. Sometimes, air lime pastes and mortars were modified with two supplementary cementing materials (SCMs), namely nanosilica (NS) and metakaolin (MK). Two different polycarboxylate ethers, a lignosulfonate and a naphthalene condensed sulfonate superplasticizer were added to lime pastes and mortars and their effects on fresh-state properties as well as on the mechanical strengths were evaluated. A close relationship was found between the molecular architecture of the plasticizers and the flowability of the pastes. Zeta potential assessment allowed us to elucidate the main action mechanisms for these admixtures. In the case of polycarboxylate ethers, the large specific surface area of nanosilica led to a large SPs consumption as compared with metakaolin with lower surface area. However, polycarboxylate ethers in MK-lime samples were attached favourably to the C-S-H and aluminate hydrates, so that the dispersing action was greater with respect to NS-lime suspensions.
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    Obtaining of self-cleaning repair air lime mortars with photocatalysts
    (Aristotle University of Thessaloniki, 2016) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    The obtaining of self-cleaning mortars is very interesting to apply them in Built Heritage. Atmospheric pollutants, mainly carbonaceous particles and gases like NOx and SO2 can lead to severe aesthetic and functional damages in artworks. In the case of mortars and renders, the use of photocatalysts -usually based on TiO2- can be worthy of consideration. Photocatalysts, after being activated by light, are able to oxidize pollutants avoiding their deposition onto building materials. In this work, different air lime mortars modified upon the addition of TiO2-based photocatalysts were obtained and studied. Photocatalysts can be incorporated in bulk and the changes in fresh state properties were studied as well as the effect of the presence of the photocatalysts on the pore structure and mechanical resistance. Finally, the photocatalytic efficiency of these materials was carried out by means of a NOx abatement test. Results showed that the presence of the photocatalysts had a positive impact on the preservation of the lime mortars characteristics.
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    Study on the effectiveness of PNS and LS superplasticizers in air lime-based mortars
    (Elsevier, 2016-04-01) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    Polynaphtalenesulfonate (PNS) and lignosulfonate (LS) were tested as superplasticizers in pastes and mortars of pure air lime and air lime with a pozzolanic additive, nanosilica (NS). LS showed a better plasticizing effect than PNS: the flowability of the samples with LS as well as the slump retention over time was larger. LS strongly hindered carbonation due to its ability to form Ca2+ complexes. In mortars with NS, PNS was seen to interfere with the C-S-H formation, resulting in lower mechanical strengths. Adsorption isotherms and zeta potential showed that PNS was more adsorbed than LS onto lime and C-S-H particles. PNS acted mainly through electrostatic repulsion owing to its high anionic charge density and flat adsorption. However, LS was more efficient as superplasticizer in air lime media, steric hindrance being the main mechanism responsible for avoiding flocculation. Furthermore, LS yielded high compressive strengths in mortars with NS.
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    The use of a lignosulfonate superplasticizer in repair air lime-metakaolin mortars
    (Aristotle University of Thessaloniki, 2016) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
    A superplasticizing admixture of natural origin, lignosulfonate (LS), was incorporated to air lime mortars sometimes modified with a pozzolanic additive, metakaolin, to obtain a new range of repair mortars to be applied in Built Heritage. LS improved the flowability of the air lime samples and showed good slump retention over time: for example, after 150 minutes of the air lime pastes preparation, blends with LS lost only ca. 13% of the slump value. Experimental results showed that LS interfered with the carbonation due to its ability to form Ca2+ complexes. Adsorption isotherms and zeta potential measurements showed that LS was scarcely adsorbed onto lime and C-S-H particles. Due to its branchy structure, LS exhibited an adsorption mechanism leading to steric hindrance as the main responsible mechanism for avoiding flocculation. The presence of free LS molecules in the dispersion was seen to improve the plasticizing effect of this polymer. Flexural and compressive strengths as well as the durability in the face of freezing-thawing cycles of these mortars were also determined to assess the applicability of these repair mortars.