Browsing by Author "Dolado, J. S."
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Item 3D computational simulation of calcium leaching in cement matrices(2014-10-01) Gaitero, J. J.; Dolado, J. S.; Neuen, C.; Heber, F.; Koenders, E. A.B.; Tecnalia Research & Innovation; ECOEFICIENCIA DE PRODUCTOS DE CONSTRUCCIÓNCalcium leaching is a degradation process consisting in progressive dissolution of the cement paste by migration of calcium atoms to the aggressive solution. It is therefore, a complex phenomenon involving several phases and dissolution and diffusion processes simultaneously. Along this work, a new computational scheme for the simulation of the degradation process in three dimensions was developed and tested. The toolkit was used to simulate accelerated calcium leaching by a 6M ammonium nitrate solution in cement matrices. The obtained outputs were the three dimensional representation of the matrix and the physicochemical properties of individual phases as a consequence of the degradation process. This not only makes it possible to study the evolution of such properties as a function of time but also as a function of the position within the matrix. The obtained results are in good agreement with experimental values of the elastic modulus in degraded and undegraded samples.Item Aluminum incorporation to dreierketten silicate chains(2009-03-05) Manzano, H.; Dolado, J. S.; Ayuela, A.; Tecnalia Research & InnovationThis work explores, from a theoretical viewpoint, the aluminum incorporation into silicate chains with dreierketten conformation relevant in the cementitious calcium-silicate-hydrate (C-S-H) gel and in other minerals, such as wollastonite and hillebrandite. To this end, we have investigated by means of ab initio calculations both the stability and the formation of aluminosilicate chains. Our results show that only certain aluminosilicate chains are stable, namely, those whose tetrahedra length m obey the m ) 3n - 1 rule with n ) 1, 2, 3,..., in agreement with experiments. Moreover, our detailed analyses explain why Al ions prefer the bridging sites and introduce new insights on the growth process.Item Brownian cluster dynamics with short range patchy interactions: Its application to polymers and step-growth polymerization(2014-07-14) Prabhu, A.; Babu, S. B.; Dolado, J. S.; Gimel, J. C.; Tecnalia Research & InnovationWe present a novel simulation technique derived from Brownian cluster dynamics used so far to study the isotropic colloidal aggregation. It now implements the classical Kern-Frenkel potential to describe patchy interactions between particles. This technique gives access to static properties, dynamics and kinetics of the system, even far from the equilibrium. Particle thermal motions are modeled using billions of independent small random translations and rotations, constrained by the excluded volume and the connectivity. This algorithm, applied to a single polymer chain leads to correct static and dynamic properties, in the framework where hydrodynamic interactions are ignored. By varying patch angles, various local chain flexibilities can be obtained. We have used this new algorithm to model step-growth polymerization under various solvent qualities. The polymerization reaction is modeled by an irreversible aggregation between patches while an isotropic finite square-well potential is superimposed to mimic the solvent quality. In bad solvent conditions, a competition between a phase separation (due to the isotropic interaction) and polymerization (due to patches) occurs. Surprisingly, an arrested network with a very peculiar structure appears. It is made of strands and nodes. Strands gather few stretched chains that dip into entangled globular nodes. These nodes act as reticulation points between the strands. The system is kinetically driven and we observe a trapped arrested structure. That demonstrates one of the strengths of this new simulation technique. It can give valuable insights about mechanisms that could be involved in the formation of stranded gels.Item C-A-S-H gels formed in alkali-activated slag cement pastes. Structure and effect on cement properties and durability(2014) Puertas, F.; Palacios, M.; Manzano, H.; Dolado, J. S.; Rico, A.; Rodriguez, J.; Tecnalia Research & InnovationThe development of alternatives to traditional Portland cement produced with more eco-efficient processes (lower energy consumption and CO2 gas emissions) is an item on climate change and innovation agendas. Alkaline cements and concretes are an effective alternative to traditional cements. The structure of the C-S-H gel in Portland cements consists mostly of 14-nm tobermorite (with a chain length of five) and jennite (2-link chain). The mechanical properties of C-S-H gels can be explained in terms of the three types of packing found in these gels: low density (LD), high density (HD) and ultra-high density (UHD). The main reaction product in alkali-activated slag (AAS) cements is a C-A-S-H gel, which adopts different structures depending on the nature of the alkaline activator. When the activator is a NaOH solution (4 % Na2O by slag weight), the C-A-S-H gel formed has an intermediate structure between 14-nm tobermorite with a chain length of five links and 11-nm tobermorite with 14 links. When the activator is a waterglass solution (4 % Na2O by slag weight), traits characteristic of 14-nm tobermorite with 11-link chains and 11-nm tobermorite with a chain length of 14 co-exist in the structure of the C-A-S-H gel formed. This densely packed structure (with three HD states) yields excellent mechanical properties. Like the C-A-S-H gels obtained in NaOH (4% Na2O)-activated AAS paste, the C-A-S-H gels forming in AAS gels activated with waterglass have no UHD states. The structure and composition of these C-A-S-H gels determine strength development in AAS mortars and concretes as well as their resistance to aggressive chemicals.Item Comment on "A waveguide slit array antenna fabricated with subwavelength periodic grooves Appl. Phys. Lett. 91 143512 (2007)"(2008) Beruete, M.; Falcone, F.; Sorolla, M.; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYItem Comments on "a high-gain antenna consisting of two slot elements with a space larger than a wavelength"(2010) Beruete, M.; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Falcone, F.; Sorolla, M.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYItem Do cement nanotubes exist?(2012-06-26) Manzano, H.; Enyashin, A. N.; Dolado, J. S.; Ayuela, A.; Frenzel, J.; Seifert, G.; Tecnalia Research & InnovationUsing atomistic simulations, this work indicates that cement nanotubes can exist. The chemically compatible nanotubes are constructed from the two main minerals in ordinary Portland cement pastes, namely calcium hydroxide and a calcium silicate hydrate called tobermorite. These results show that such nanotubes are stable and have outstanding mechanical properties, unique characteristics that make them ideally suitable for nanoscale reinforcements of cements.Item Dual-band low-profile corrugated feeder antenna(2006-02) Diaz, Miguel Beruete; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Falcone, Francisco; Ayza, Mario Sorolla; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYA dual-operating-band planar horn antenna having very low profile is presented in this paper. By opening a subwavelength aperture into a corrugated conducting plate, good return losses and a narrow radiated beam in each of the two desired operating frequency bands can be measured. This behavior is very similar to that observed in optical wavelengths where enhanced transmission was measured through apertures etched in metallic corrugated plates. Here, the double-corrugated structure has been scaled into the microwave frequency range and the excitation has been done by a conventional closed metallic waveguide placed in the rear part of the structure. In this way, a new concept of a very low profile feeder is proposed with potential wireless applications.Item Elastic properties of the main species present in Portland cement pastes(2009-03) Manzano, H.; Dolado, J. S.; Ayuela, A.; Tecnalia Research & InnovationThe elastic properties of the most important phases present in cement pastes have been studied by force field atomistic methods. Calculations reproduce the mechanical properties of crystalline species alite, belite and portlandite fairly well. The elastic properties of amorphous calcium-silicate-hydrate (C-S-H) gel are also explained in terms of the commonly used structural models 1.4 nm tobermorite and jennite, once the intrinsic porosity and the silicate chain length are concurrently considered through the appropriate micromechanical models. The findings conclude that bringing the atomic structure into contact with the mechanical properties of C-S-H gel may modify the actual view of the gel.Item Enhanced microwave transmission and beaming using a subwavelength slot in corrugated plate(2004-12) Beruete, M.; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Sorolla, M.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYEnhanced microwave transmission and beaming through a subwavelength slot placed into a corrugated conducting plate is experimentally observed compared with the case of the single isolated slot. This phenomenon is similar to that happening for optical wavelengths where surface plasmons model is employed to describe the metal. This letter shows that the phenomenon is also present in the microwave range where perfect conductor model applies. Enhanced subwavelength transmission and beaming stimulates new research for future applications.Item Enhanced microwave transmission using a subwavelength slot in corrugated plate(2005) Beruete, M.; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Sorolla, M.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYThe new phenomenon related with enhanced microwave transmission and beaming through a subwavelenght slot placed into a corrugated conducting plate has been experimentally observed, in the microwave range, compared with the case of the single isolated slot. It is very similar to that happening for optical wavelengths where surface plasmons model is employed to describe the metal. The phenomenon is also present in the microwave range where perfect conductor model applies. Future applications in antennas can be possible.Item Enhanced millimeter wave transmission through quasioptical subwavelength patterned structures(2004) Beruete, M.; Sorolla, M.; Campillo, I.; Dolado, J. S.; Martín-Moreno, L.; García-Vidal, F. J.; Tecnalia Research & InnovationWe show that the phenomenon of extraordinary transmission though arrays of subwavelength holes is also present in the microwave range as it occurs in the optical regime. Following simulations of the influence of the number of holes, a prototype has been designed and fabricated in an Aluminum plate. By using a Millimeter Wave Quasioptical Vector Network Analyzer in the range between 40 GHz and 110 GHz, measurements of the transmission response has been performed. A resonant total transmission at wavelengths close to the period of the array appear in the spectra. Moreover, an structure consisting of a single narrow slit flanked by a finite array of grooves is now under consideration. All these structures operating in the subwavelength regime are opening the possibility of exciting future applications.Item Enhanced millimeter wave transmission through quasioptical subwavelength perforated plates(2005-06) Beruete, Miguel; Sorolla, Mario; Campillo, I.; Dolado, J. S.; Martín-Moreno, Luis; Bravo-Abad, J.; García-Vidal, F. J.; Tecnalia Research & InnovationIn this paper, we show that the phenomenon of extraordinary transmission through arrays of subwavelength holes, present in the optical regime, is also present in the millimeter wave range. After presentation of the theoretical foundations of the enhanced transmission, measurements of the transmission response have been performed on different samples by using a millimeter wave quasioptical vector network analyzer in the range between 45 and 110 GHz. The prototypes have been fabricated in Aluminum plates with several thickness and different hole diameters drilled by using a laser machine. Good agreement between theory and experiment is obtained, with clear signals of the existence of resonant transmission at wavelengths close to the period of the array. Possible applications in frequency selective surfaces and near-field imaging are envisaged.Item Enhanced millimeter-wave transmission through subwavelength hole arrays(2004-11-01) Beruete, M.; Sorolla, M.; Campillo, I.; Dolado, J. S.; Martín-Moreno, L.; Bravo-Abad, J.; García-Vidal, F. J.; Tecnalia Research & InnovationWe explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.Item Ettringite strengthening at high pressures induced by the densification of the hydrogen bond network(2012-08-02) Manzano, H.; Ayuela, A.; Telesca, A.; Monteiro, P. J.M.; Dolado, J. S.; Tecnalia Research & InnovationEttringite is a rare mineral with high-water content, more than half of its weight, and a relevant secondary product in Portland cement. Using density functional theory, we simulate the crystal structure and properties of ettringite under pressure. Our calculations predict a change in slope for all the lattice parameters versus pressure at about 2.5 GPa. Above such pressure, the elastic properties show a drastic increase of nearly 80% in the bulk modulus. This finding is explained in terms of a concurrent amorphization and densification of the hydrogen bond network. At low pressures, ettringite can be compressed substantially without significant repulsion in the hydrogen bond network. At high pressures, the hydrogen bonds become stiff, and their contribution to the total repulsion is then important. These changes are also supported by the evolution on the electronic density of ettringite with pressure.Item High calcium coal fly ash as raw material for synthesizing new low-energy cements(American Concrete Institute, 2004-05-01) Goni, S.; Guerrero, A.; Lorenzo, M. P.; Moragues, A.; Campillo, I.; Dolado, J. S.; Malhotra, V.Mohan; Tecnalia Research & InnovationStudies on the viability of high calcium fly ash from coal combustion are being conducted in our laboratory to produce a new kind of low-energy cement. The process presents important environmental advantages, such as a reduction of C02 emission compared to that produced by the conventional technology of portland cement manufacture. Furthermore, the processing temperature is also considerably reduced. The low-energy cement shows potential for good hydraulic activity for application in construction. The changes of fly ash composition were followed by X-Ray Diffraction (XRD), F f Infrared (FTIR) spectroscopy and BET surface area analysis.Item Improvement of initial mechanical strength by nanoalumina in belite cements(2007-04) Campillo, I.; Guerrero, A.; Dolado, J. S.; Porro, A.; Ibáñez, J. A.; Goñi, S.; Tecnalia Research & Innovation; TRAZABILIDAD CIRCULARThe development of new environmentally friendly and energy efficient cements such as belite cements are being promoted due the environmental problems related to CO2 emissions in the manufacture of Portland cement. Although long-term hydrated belite cements show comparable and even better mechanical strength to ordinary Portland hydrated cements, they have low initial mechanical strength, which limits their applicability. In this work we analyse the potential of nanomaterials for activation of the initial strength of belite cements. Different nanoparticles are added to belite cement and both the microstructure modification of the resulting paste and the mechanical properties at early ages are studied. Our results show that the addition of nanoparticles can overcome the drawbacks of this type of eco-efficient cements making them competitive to OPC.Item Increase of the transmission in cut-off metallic hole arrays(2005-02) Beruete, M.; Sorolla, M.; Campillo, I.; Dolado, J. S.; Tecnalia Research & InnovationIn this letter, the phenomenon of extraordinary transmission through arrays of subwavelength holes in the microwave range is demonstrated. It is also shown that the magnitude of the transmission is strongly dependent on the number of holes in the sample. Prototypes have been designed and fabricated in an Aluminum plate. The transmission response is measured with a millimeter wave quasi-optical vector network analyzer in the range between 40 and 70 GHz. These measurements show a resonant total transmission at wavelengths close to the period of the array which depends strongly on the number of resonant holes. These results can give rise to interesting applications such as frequency selective surfaces and other quasi-optical structures.Item Low profile antenna feeders based of enhanced microwave transmission through a narrow slot on a corrugated plane(2006-05) Beruete, M.; Campillo, I.; Dolado, J. S.; Rodríguez-Seco, J. E.; Perea, E.; Falcone, F.; Sorolla, M.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYIn this work, several antenna prototypes based on the Extraordinary Optical Transmission phenomenon are developed. They all share in common the property of being all-metallic, flat and low profile. The radiation of a central slot is boosted by texturing the output metallic plane. Enhancement depends directly on the number of grooves carved. Thus, a rich variety in the farfield response can be obtained changing the number of corrugations. Among the prototypes a dual-operating-band planar horn antenna with low profile is presented. It is also seen that by giving the structure rotational simmetry the gain can be increased, resulting in the high-gain Bull's-Eye antenna. Other approaches related with the perturbation profile are under development. The behavior of the current prototypes is very similar to those reported in optics. In this way, a new concept of a very low profile feeder is proposed with potential wireless applications.Item Low-profile corrugated feeder antenna(2005) Beruete, M.; Campillo, I.; Dolado, J. S.; Rodriguez-Seco, J. E.; Perea, E.; Falcone, F.; Sorolla, M.; Tecnalia Research & Innovation; POWER SYSTEMS; DIGITAL ENERGYA very low-profile planar rectangular horn antenna made of a subwavelength aperture surrounded by two grooves on the conducting plate is presented. This structure exhibits good return losses and radiated beam. Its operation is based upon enhanced transmission and beaming through apertures in metallic corrugated plates. Here, the corrugated structure is designed to operate in microwaves and, moreover, a waveguide flange, which has been properly mechanized in the rear part of the structure, is employed for excitation. A new very low-profile planar feeder with reduced size is introduced that could be properly scaled for potential wireless applications.
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