Browsing by Author "Carvajal, A. M."

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    Analysis of the Relation between Accelerated Carbonation, Porosity, Compressive Strength and Capillary Absorption in Concrete, in the Search of a New Control Method by Durability
    (2009) Carvajal, A. M.; P, Maturana; Pino, C.; Poblete, J.
    Carbonation of concrete is the second reason of corrosion on reinforced concrete structures. This has led to study the methods that might be useful for defining, from the phase of project, the conditions that a certain concrete must have, besides resisting mechanically, to be resistant to external attacks like it is the effect of the CO2 of industrial environments.
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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: 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.