Browsing by Author "Vera, R."

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    Concrete Carbonation in Ibero-American Countries DURACON Project: Six-Year Evaluation
    (2015) Troconis de Rincon, O.; Montenegro, J. C.; Vera, R.; Carvajal, A. M.; Mejia de Gutierrez, R.; Del Vasto, S.; Saborio, E.; Torres-Acosta, A.; Perez-Quiroz, J.; Martinez-Madrid, M.; Martinez-Molina, W.; Alonso-Guzman, E.; Castro-Borges, P.; Moreno, E. I.; Almeraya-Calderon, F.; Gaona-Tiburcio, C.; Perez-Lopez, T.; Salta, M.; de Melo, A. P.; Martinez, I.; Rebolledo, N.; Rodriguez, G.; Pedron, M.; Millano, V.; Sanchez, M.; de Partidas, E.
    Concrete carbonation data from 16 test sites in 9 countries (Bolivia, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal, and Venezuela) were compared to identify concrete performance due to carbonation at natural exposure conditions after almost six years of exposure. This research is part of the DURACON project ("Effect of the environment on reinforcement durability"), a long-term Ibero-American project intended to correlate the influence of urban and marine meteorochemical parameters on the performance of reinforced concrete structures. Environmental parameters were measured following the ISO 9223 standard. Concrete was physically characterized by the results of compressive strength, elastic modulus, total and effective porosity, and water absorption resistance (Fagerlund method) laboratory tests. Concrete specimens (with and without steel reinforcement bars-rebars) were prepared for electrochemical and physical/mechanical/chemical tests using materials available in each country. Concrete composition was kept similar between specimens by following strict preparation protocols. Two water/cement (w/c) ratios were used: 0.45 w/c ratio concrete had a minimum cement content of 400 kg/m(3); and 0.65 w/c ratio concrete had a minimum 28-day compressive strength of 210 kg/cm(2). Materials were type I Portland cement, siliceous sand, and crushed rock as coarse aggregates (13-mm maximum nominal size). After six years of exposure, corrosion potentiality and probability analysis of the reinforcement at the different sites indicated the concrete prepared in Venezuela to have the highest probability of experiencing carbonation-induced reinforcement corrosion. The concrete prepared at the Cali, Colombia, site had the lowest probability. Carbonation aggressiveness was found to be highest at tropical sites, with the Venezuela sites exhibiting the most aggressive conditions among the participating countries.
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    Corrosion products of reinforcement in concrete in marine and industrial environments
    (ELSEVIER SCIENCE SA, 2009) Vera, R.; Villarroel, M.; Carvajal, A. M.; Vera, E.; Ortiz, C.
    The corrosion products formed on embedded steel in concrete under simulated marine and industrial conditions and natural marine environment were studied. A 0.50 water/cement ratio concrete was used concrete 3.5% NaCl and 180 g L(-1) of H(2)SO(4) with 70 ppm of chloride ions solutions were used to simulate the synthetic medium. The initial electrochemical variables of the steel and pH, chlorides and sulfates profiles were measured according to the concrete depth. The morphology of the corrosive attack was determined electron microscopy (SEM), and the composition of the corrosion products was determined via scanning zer and an X-ray diffractorneter (XRD). The protective power of the corrosion products was evaluated through anodic polarization curves in a saturated Ca(OH)(2) Solution. The results from XRD and SEM show that all the resulting corrosion products correspond to lepidocrocite, goethite and magnetite mixtures: moreover, akaganeite was also identified under natural and simulated marine environments. Siderite was only detected in samples exposed to a natural marine environment. Concerning the protective nature of the corrosion products, these show lower performance in a simulated industrial environment, where the corrosion rate of the steel is up to 1.48 mu m year(-1). (C) 2008 Elsevier B.V. All rights reserved.
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    Diagnosis and rehabilitation of real reinforced concrete structures in coastal areas
    (MANEY PUBLISHING, 2012) Carvajal, A. M.; Vera, R.; Corvo, F.; Castaneda, A.
    A diagnosis and rehabilitation study of two reinforced concrete structures located in coastal areas in two different climates is presented. Building 1 was constructed in the north of Chile in 1949, at a distance of 600 m from the coastline, in a seismic zone. Cracks, steel corrosion, loosening of concrete cover and slab deformations have been identified. Building 2 was constructed in Habana City, Cuba, in 1973. It is located at <100 m from the shore. The structure of building 1 shows severe localised damage: loosening of reinforced cover and intense reinforcement bar corrosion due to high deposits of sea salts. High chloride and sulphate content in the concrete mass, low compressive strength in walls and slabs, high level of steel corrosion and zones with the existence of rust instead of steel were reported. A structural rehabilitation project to ensure an increase in service life is not possible. On the contrary, in case of building 2, a possible rehabilitation procedure is recommended. Elimination of chloride contaminated concrete and the use of special mortar is an option, and electrochemical chloride extraction and incorporation of sacrificial anodes is another. An important conclusion is made: the use of chloride and sulphate contaminated aggregates is more dangerous than the penetration of these two contaminants from the external environment for buildings constructed in coastal zones.
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    DURACON : Influencia de la acción del medio ambiente en la durabilidad del concreto. Parte 2. Resultados de Chile después de 5 años de exposición
    (2009) Vera, R.; Villarroel, María; Delgado, Diana; Carvajal Guerra, Ana María; De Barbieri, F.; Troconis, O.
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    DURACON: Effect of the Environment on Reinforced Concrete Durability. Results of Chile after 5 years of Exposure
    (PONTIFICIA UNIV CATOLICA CHILE, ESCUELA CONSTRUCCION CIVIL, 2009) Vera, R.; Villarroel, M.; Delgado, D.; Carvajal, A. M.; De Barbieri, F.; Troconis, O.
    This study presents the results obtained in Chile under the international project "Influence of Environmental Action in the durability of concrete, DURACON" that joins 11 countries (Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal and Venezuela) that began in 2002. The project considers the exposure of reinforced concrete specimens for at least 5 years at stations located in the marine environment (Valparaiso-PUCV) and urban (PUC-Santiago). The concrete specimens were designed with w/c 0.45 and 0.65 and characterized by determining the compressive strength and tensile strength, elastic modulus, resistivity, capillary absorption, absorption and total porosity. The corrosion of steel was evaluated by corrosion potential and corrosion current and depth of carbonation in the concrete to determine the critical onset corrosion.
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    Effect of the marine environment on reinforced concrete durability in lberoamerican countries: DURACON project/CYTED
    (2007) de Rincon, O. Troconis; Sanchez, M.; Millano, V.; Fernandez, R.; de Partidas, E. A.; Andrade, C.; Martinez, I.; Castellote, M.; Barboza, M.; Irassar, F.; Montenegro, J. C.; Vera, R.; Carvajal, A. M.; de Gutierrez, R. M.; Maldonado, J.; Guerrero, C.; Saborio-Leiva, E.; Villalobos, A. C.; Tres-Calvo, G.; Torres-Acosta, A.; Perez-Quiroz, J.; Martinez-Madrid, M.; Almeraya-Calderon, F.; Castro-Borges, P.; Moreno, E. I.; Perez-Lopez, T.; Salta, M.; de Melo, A. P.; Rodriguez, G.; Pedron, Miguel; Derregibus, M.
    This work presents some of the results from the project: "Effect of the environment on reinforcement durability" (DURACON) in its first two-years period, which investigates the influence of urban and marine meteorochemical parameters on the performance of reinforced concrete structures. The results presented in this investigation are from 21 marine test sites only (no urban environments are included), distributed among I I countries (Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal and Venezuela). The environment was evaluated using ISO Standard 9223 and the concrete was characterized by measuring compressive strength, elastic modulus, total and effective porosity, chloride permeability according to ASTM standards, as well as the effective porosity and resistance to water absorption using the Fagerlund method. To that effect, concrete specimens (with and without reinforcement) were prepared for electrochemical and physical/mechanical/chemical tests using the existing materials in each participating country, following strict procedures which enabled the preparation of similar concrete samples. Two water/cement (w/c) ratios (0.45 and 0.65) were selected, where the concrete with 0.45 w/c ratio had to have a minimum cement content of 400 kg/m(3) and the one with 0.65 w/c ratio a compressive strength of 210 kg/cm(2). Type I Portland cement, siliceous sand, and crushed rock as coarse aggregates (13-mm maximum nominal size) were used. After a one-year exposure, the results of the corrosion potentiality and probability analysis of the reinforcement in the different test stations showed that, for marine atmospheres, the most aggressive environment to induce steel corrosion was at Portugal's Cabo Raso station, and the least aggressive one was at Chile's Valparaiso station. These results are comparable with the ones found using electrochemical measurements, after a two-year exposure. (C) 2007 Elsevier Ltd. All rights reserved.
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    Mapa de corrosión atmosférica de Chile : resultados después de un año de exposición
    (2012) Vera, R.; Puentes, M.; Araya, R.; Rojas, P.; Carvajal Guerra, Ana María
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    Supplementation, stocking rates, and economic performance of lamb production systems in the Mediterranean-type region of Chile
    (2006) Aguilar, C.; Vera, R.; Allende, R.; Toro, P.
    A simulation model was developed and validated to analyze the bioeconomic performance of alternative technologies applied to lamb production systems in the Mediterranean-type rangelands of Central Chile. The model includes consideration of climatic events that affect pasture growth, the nutritive value of the forage on offer, and animal performance as affected by energy and protein intake of directly grazed native pastures and supplements.
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    Technical efficiency and viability of organic dairy sheep farming systems in a traditional area for sheep production in Spain
    (2011) Toro-Mujica, P.; Garcia, A.; Gomez-Castro, A. G.; Acero, R.; Perea, J.; Rodriguez-Estevez, V.; Aguilar, C.; Vera, R.
    The technical efficiency and viability of organic dairy sheep farming systems were investigated in Castilla-La Mancha, a Spanish region with a tradition of sheep rearing. The thirty one farms sampled, had an average of 359 ha, 508 sheep and 1.9 work units (WU); the reproductive rate was 1.5 lambs per ewe and year and the human productivity reached 303 sheep/Wu. There was however a high degree of variation among farms. Although the average level of technical efficiency was 66%, 74% of farms sampled operated at medium or low rates of technical efficiency. Differences in technical efficiency were largely due to the consumption of feeding supplements and productivity. A total of 45% of the farms was classified as non-viable. It was concluded that strategies for improving competitiveness and the use of resources are specific to each level of efficiency. The most efficient farms must increase their size; moderately efficient farms need to focus their efforts on improving the management of resources to enhance results. Improving competitiveness of the less efficient farms requires an increase of productivity; a better balance between the use of feeding supplements and the sheep productive capacity. (C) 2011 Elsevier B.V. All rights reserved.
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    Use of supplements and variation in the stocking rate in cow-calf systems on temperate pastures in Chile: a simulation approach
    (CSIRO PUBLISHING, 2009) Catrileo, A. R.; Toro, P. M.; Aguilar, C. D.; Vera, R.
    A simulation model was developed to evaluate the productive and economic effect of the variation in feed practices and stocking rate of a cow-calf system in Chile. Winter supplementation at grazing, stocking rate and economic aspects of the system were analysed. The supplementation of straw v. pasture hay at two different stocking rates was evaluated in the temperate pasture zone in La Araucania, Chile. Data were simulated using a decision support tool to help analyse the system. Simulations with the model involved 20 replicates of a factorial combination of two stocking rates (1.0 and 1.4 cows/ha) with differences in the initial weight ('light' v. 'heavy' with weights of heifers, primiparous and multiparous cows being 340 v. 380, 400 v. 450 and 440 v. 480 kg, respectively), at the same grazing pressure ( kg liveweight/ha), two winter supplements ( oat straw v. pasture hay) and two levels ( 6 v. 8 kg straw, and 5.1 v. 6.8 pasture hay). The model was validated with data collected from an experiment conducted with permanent pastures and a beef cattle cow-calf system from 1984 to 1989. The results indicate that there was a significant (P<0.01) effect of a cow's weight on the calves at 180 days, and on their reproductive performance, with the heavier cows increasing their calving rate by 20% relative to the lighter group. The stocking rate and the type and amount of supplement, however, did not influence (P>0.05) the weight of female and male calves at the time of sale. Finally, supplementation with pasture hay, as opposed to oat straw, incurred a larger (P<0.01) mean cost at an equivalent level of provision of metabolisable energy. Although difficult to analyse under real conditions, the economic and productive benefits of various feed practices and stocking rates were successfully evaluated in the present study using simulation tools.