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• Equilibria of the chemical composition of the concrete pore solution. Part I: Comparative study of synthetic and extracted solutions

  A. Moragues, A. Macías, C. Andrade

  Cement and Concrete Research (1987). Vol. 17 (2), pp. 173-182

  
  

  Abstract

  A critical review is made on Frattini and Hansen's results on the equilibria of the different ions present in the aqueous solution of cement paste after mixing. These values are compared with those obtained from results of squeezed cement paste specimens drawing the conclusions that the cement paste solution is oversaturated in Ca(OH)2 just after mixing but the ions present in it are not in thermodynamic equilibrium because the solution is continuously evolving during early ages. Also the increase in the solubility of the Ca+2 ion because of the presence of SO4= is discussed and attributed to the increase in the ionic strength of the solution.

  Abstract
  A critical review is made on Frattini and Hansen's results on the equilibria of the different ions present in the aqueous solution of cement paste after mixing. These [...]

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• Galvanized steel behaviour in Ca(OH)2 saturated solutions containing SO4 ions

  A. Macías, C. Andrade

  Cement and Concrete Research (1987). Vol. 17 (2), pp. 307-316

  
  

  Abstract

  In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH of 13.3 ± 0.1 below which the Zn in contact with such a medium is passivated, but at pH values above this it corrodes continuously until it totally disappears. In this paper, the influence of the presence of SO4 ions on the electrochemical behaviour of the galvanized has been studied. It has been established that the precipitation of CaSO4 with takes place in the media studied makes that the pH never surpasses the value of 13.3 ± 0.1. This coincidence with the pH threshold previously reported for passivation of the galvanized bars allows conclude that the sulfates not only are innocuous with respect to the galvanized behaviour in media which simulate the concrete but they are beneficial.

  Abstract
  In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH of 13.3 ± [...]

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• Some unpublished results on the research in corrosion of steel in concrete

  C. Andrade

  Materials and Structures (1987). Vol. 20, pp. 153-159

  
  

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• Accuracy of different electrochemical laboratory techniques for evaluating corrosion rates of galvanized reinforcements

  A. Marias, C. Andrade

  (1987). Proceedings of the Fourth International Conference on Durability of Building Materials and Components Singapore, 4–6, pp. 516-522

  
  

  Abstract

  In the present paper the accuracy of three electrochemical laboratory techniques in order to evaluate the corrosion rate of galvanized rods inmersed in solutions which simulate the pore solution, is commented. The techniques used were: polarization resistance, electrochemical impedance and harmonic analysis. The corrosion intensity values obtained through these techniques were compared with the gravimetric ones. Values of constant B obtained through polarization curves and the harmonic analysis were compared.

  Abstract
  In the present paper the accuracy of three electrochemical laboratory techniques in order to evaluate the corrosion rate of galvanized rods inmersed in solutions which simulate [...]

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• Evaluation of steel durability in a construction system of reinforced mortar-polystyrene-mortar panels

  C. Andrade, J. Rodrigues

  (1987). Proceedings of the Fourth International Conference on Durability of Building Materials and Components, Vol. 4-6, pp. 623-630

  
  

  Abstract

  This paper sumarises the research into steel durability in reinforced sandwich panels made of mortar-polystyrene mortar, which is a new construction system for buildings. In this type of system the main risk of steel corrosion is that of the steel connectors, which cross the polystyrene, and the corrosion of the reinforced mesh, owing to the carbonatation of the mortar coating. The evaluation of different suplementary protection methods which increase expected service life in aggressive environments is also presented. The different tests carried out are described. The specimens were of small, medium and full size. The corrosion was monitored with electrochemical techniques (polarization resistance). The specimens were submitted to wet and dry cycles and some of them were carbonated. Galvanized, stainless and bare steel were tested. Also addition in the mix of calcium nitrite as an inhibitor was used. Results show that the steel connectors are not the weakest point of the system as previously thought. Finally, practical recomendations are given which allow a reasonable increase in the service life of the reinforced mortar-polystyrene-mortar system. The specifications are presented considerinng three levels of environmental aggressivity.

  Abstract
  This paper sumarises the research into steel durability in reinforced sandwich panels made of mortar-polystyrene mortar, which is a new construction system for buildings. [...]

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• Equilibria of the chemical composition of the pore concrete solution Part II: Calculation of the equilibria constants of the synthetic solutions

  A. Moragues, A. Macías, C. Andrade, J. Losada

  Cement and Concrete Research (1988). Vol. 18 (3), pp. 342-350

  
  

  Abstract

  The chemical composition of synthetic solutions used to simulate the pore concrete solution was analyzed in Part I. It was not possible to match the experimental results obtained from concentration measurements of the ions present in the solutions with the results obtained from calculations based on the values of pK of Ca(OH)2 and CaSO4. The inconsistency between the experimental values and the theoretical calculations was attributed to the elevated concentrations that exist, and, therefore, the elevated ionic strength.The errors that are committed when applying the Debye-Huckel theory make it imprecise for proper calculations at such high concentrations. As an alternative the use of “apparent constants” is proposed. These are calculated from the values of the concentrations directly measured in the solutions.

  Abstract
  The chemical composition of synthetic solutions used to simulate the pore concrete solution was analyzed in Part I. It was not possible to match the experimental results obtained [...]

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• Polypropylene Fibre Reinforced Concrete Air Permeability

  M. Sanjuan-Barbudo, A. Moragues, B. Bacle, C. Andrade

  MRS proceedings library (1991). Vol. 211 (71)

  
  

  Abstract

  The permeability of concrete to gases is of direct importance to the durability of concrete structures, because of carbon dioxide flowing through the concrete favour lime carbonation and reinforcing steel corrosion. Mortar with and without polypropylene fibres having water/cementitious ratios of 0.30, 0.35 and 0.40 and a cement/sand ratio of 1/1 were studied. Polypropylene dosage varied from 0.1 to 0.3% by volume of cement. The characterization of mortar permeability was made using cylindrical shaped samples (3 cm height and 15 cm diameter). These specimens were 28 days cured and then dried before the test. The addition of fibres results in a decrease of air permeability. Variation of the water/cement ratio is of lesser importance than fiber addition.

  Abstract
  The permeability of concrete to gases is of direct importance to the durability of concrete structures, because of carbon dioxide flowing through the concrete favour lime [...]

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• Quantitative measurement of the corrosion rate using a small counter electrode in the boundary of passive and corroded zones of a long concrete beam

  C. Andrade, Á. Macias, S. Feliu, J. González

  (1990). Corrosion Rates of Steel in Concrete, ed. N. Berke, V. Chaker, and D. Whiting (West Conshohocken, PA: ASTM International), pp. 134-142.

  
  

  Abstract

  Recently, in CORROSION-87, one paper was presented which, assuming the electrical model of the 'transmission line' to represent the nonuniform distribution of the current in a concrete beam, demonstrated the calculation of the instantaneous corrosion rate by unit of length of the rebar through mathematical equations. In the present contribution those equations are used in order to determine whether the equations enable distinction between the corroded zones of a rebar and those which remain passive. A concrete beam was fabricated, half of it by mixing chlorides with the cement (and therefore inducing a corrosion in the rebars) and the other half without admixtures (passivated zones of the rebars). The apparent polarization resistance was measured along the beam using a small counter electrode. Through the equations previously proposed, the corrosion rate was calculated. The results obtained confirm that the boundary between corroded and passivated zones can be clearly identified using these formulae. Finally, some comments are given on the relative activity of galvanic macrocells compared with the corrosion microcells.

  Abstract
  Recently, in CORROSION-87, one paper was presented which, assuming the electrical model of the 'transmission line' to represent the nonuniform distribution of the [...]

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• Initial effort to use the corrosion rate measurements for estimating rebar durability

  C. Andrade, C. Alonso, J. González

  (1990). Corrosion Rates of Steel in Concrete, ed. N. Berke, V. Chaker, and D. Whiting (West Conshohocken, PA: ASTM International), pp. 29-37.

  
  

  Abstract

  The approach presented here is an attempt to implement the values of corrosion intensity which have been measured in laboratory tests, in the framework of the service life prediction analysis for corroding structures. First of all, the model on service life suggested by Tuuti was considered, and only the propagation period model has been analyzed in this paper. In order to expand the proposal, different steps were covered: (1) the definition of an unacceptable level of deterioration, taking into consideration the levels suggested by the Comite Eurointernational du Beton (CEB) in its Bulletin No. 162, in order to define the urgency of intervention in a damaged structure; (2) the reduction in bar diameter or bar section was taken as the determining parameter in failure risk, assuming that this decrease in section occurs either in a generalized form or in the zones of the structure in which the load-carrying capacity may be significantly affected; and (3) the ranges of possible corrosion intensity values were introduced in Tuuti's model for calculating the reduction in bar section in function of the life of the structure. Some examples for bars of 10 and 20 mm Φ were presented. Finally, the limitations and the improvements of the proposal are discussed.

  Abstract
  The approach presented here is an attempt to implement the values of corrosion intensity which have been measured in laboratory tests, in the framework of the service life [...]

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• The behaviour of galvanized steel in chloride-containing alkaline solutions-I. The influence of the cation

  A. Macías, C. Andrade

  Corrosion Science (1990). Vol. 30 (4-5), pp. 393-407

  
  

  Abstract

  The behaviour of galvanized reinforced bars (rebars) in chloride-contaminated concrete is a very controversial matter not yet resolved. An extensive study of the behaviour of galvanized steel in alkaline solutions which simulate the aqueous phase present in concrete pores has been undertaken. This paper describes the modifications that the presence of chloride has on the corrosion behaviour of galvanized steel in alkaline solutions, as well as the influence of the accompanying cation. It was confirmed that the corrosion behaviour of galvanized steel in the presence of chlorides is controlled by the medium pH, which depends on the calcium or sodium salt which provides the chloride ions.

  Abstract
  The behaviour of galvanized reinforced bars (rebars) in chloride-contaminated concrete is a very controversial matter not yet resolved. An extensive study of the behaviour [...]

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