Materials and Structures

, Volume 36, Issue 8, pp 530–540 | Cite as

Studies on corrosion inhibition of steel reinforcement by phosphate and nitrite

  • L. Dhouibi
  • E. Triki
  • M. Salta
  • P. Rodrigues
  • A. Raharinaivo
Article

Abstract

This work deals with the effectiveness of sodium phosphates and nitrites used as inhibitors against steel corrosion in concrete reinforcement. First, concrete pore water was simulated with several alkaline solutions. Then, reinforced concrete specimens with inhibitors added in fresh concrete mix are immersed in chloride solution. The effectiveness of inhibitors was assessed by applying electrochemical techniques, namely Electrochemical Impedance Spectroscopy (EIS), Polarisation Curves (PC), and Open Circuit Potential (OCP) measurements. The final concrete condition was analysed with Scanning Electronic Microscopy (SEM), X-Ray Diffraction (XRD) and Infrared Spectroscopy (FT-IR).

In solutions simulating concrete contaminated with chloride, the influence of the inhibitors on the steel corrosion was assessed by (PC) and (EIS). The results obtained show that phosphate prevents pitting corrosion when its content is equal to chloride concentration, and that nitrite only contributes to increase the value of pitting potential. Corrosion rate is reduced with both inhibitors at the different contents tested.

For reinforced concrete specimens immersed in chloride solution, their conditions were assessed by applying EIS. The results indicate that after 1 year of immersion with the two inhibitors the corrosion rate decreased. Then, after 3 years of immersion no influence of inhibitors on the corrosion rate was observed. However a significant increase in concrete electrical resistance was observed when inhibitors were present. Visual examinations showed that all steel bars were corroded in the presence of chlorides.

Results from analytical tests done on the concrete after 3 years of immersion show that as far as the final concrete condition is concerned, the tested inhibitors did not change the type of compounds in concrete. But the final free chloride content remained higher than the critical chloride threshold. The results of FT-IR technique showed that nitrites are likely washed out of concrete during immersion in chloride solution and phosphates interfere with the equilibrium between CO3 2− and HCO3 in concrete.

The main conclusion of this study is: the efficiency of the tested inhibitors decreases with time, after two years of immersion in chloride solution.

Keywords

Nitrite Corrosion Rate Corrosion Product Electrochemical Impedance Spectroscopy Open Circuit Potential 

Résumé

Le présent travail concerne l'évaluation de l'efficacité du nitrite de sodium et du phosphate sodique contre la corrosion des armatures du béton. L'étude expérimentale a été menée en milieu simulant la solution interstitielle du béton et dans le béton durci additionné de l'inhibiteur lors de son malaxage. Plusieurs techniques ont été appliquées, électrochimiques telles que: la Spectroscopie d'Impédance Electrochimique (SIE), les Courbes de Polarisation (CP), et la mesure du potentiel de corrosion (PC), et analytiques, notamment la Microscopie Electronique à Balayage (MEB), la Diffraction des rayons X (DRX) et la Spectroscopie Infrarouge (IR).

En milieu simulant le béton contaniné par les chlorures, l'influence de l'inhibiteur sur la corrosion a été évaluée par (CP) et (SIE). Les résultats obtenus ont montré que les phosphates empêchent la corrosion par piqûre lorsque leur teneur est égale à la concentration en chlorure et que les nitrites anoblissent uniquement le potentiel de piqûration. La vitesse de corrosion est réduite avec les deux inhibiteurs.

Pour le béton durci additionné de l'inhibiteur et immerge en milieu chloruré, la résistance à la corrosion a été évaluée par SIE. Les résultats ont indiqué que pour des courtes durée d'immersion (une année), la vitesse de corrosion dimirue. A long terme (3 ans d'immersion), l'inhibiteur augmente la résistance électrique du béton mais son influence sur la corrosion s'estompe. L'observation visuelle des armatures montrent que celles-ci sont toutes corrodées.

Les résultats relatifs à l'analyse du béton de l'interface après 3 ans d'immersion, ont révélé que les inhibiteurs testés ne changent pas la nature chimique des produits d'hydratation du ciment durci. Cependant, la teneur des chlorures libres demeure supérieure à la concentration critique. Les résultats de la spectroscopie infrarouge stipulent que les nitrites sont susceptibles de sortir du béton durant son immersion en milieu chloruré et que les phosphates s'interferent avec l'équilibre entre CO3 2− et HCO3 dans le béton.

La conclusion principale de ce travail est qu'en présence des chlorures, l'efficacité de l'inhibiteur diminue à long terme (après 2 ans d'immersion).

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Copyright information

© RILEM 2003

Authors and Affiliations

  • L. Dhouibi
    • 1
  • E. Triki
    • 1
  • M. Salta
    • 2
  • P. Rodrigues
    • 2
  • A. Raharinaivo
    • 3
  1. 1.U.R. Corrosion et Protection des MétalliquesENITTunisTunisie
  2. 2.Laboratorio Nacional de Engenharia CivilDepartmento de Materiais de ConstruçãoLisboaPortugal
  3. 3.Laboratoire Central des Ponts et ChausséesParis cedex 15France

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