Electrochemical study of corrosion inhibition of steel reinforcement in alkaline solutions containing phosphates based components Naceur Etteyeb Æ Leila Dhouibi Æ Mercedes Sanchez Æ Cruz Alonso Æ Carmen Andrade Æ Ezzeddine Triki Received: 27 January 2006 / Accepted: 22 August 2006 / Published online: 16 March 2007 Ó Springer Science+Business Media, LLC 2007 Abstract The aim of this study is to investigate the viability of use of sodium phosphate (Na 3 PO 4 : SP), tetra- sodium pyrophosphate (Na 4 P 2 O 7 : TSPP) and hydroxye- thylidene-diphosphonic acid (C 2 H 8 O 7 P 2 : HEDP) as a non-toxic corrosion inhibitors of steel bars in alkaline media which simulate the electrolyte in the concrete pores. The effectiveness of these phosphate compounds as cor- rosion inhibitors was investigated by measuring the cor- rosion potentials, the polarization curves, the corrosion current densities, and the electrochemical impedance spectroscopy of steel bars immersed for 30 days in satu- rated Ca(OH) 2 solutions with and without chlorides. At the completion of the tests, the mass losses were determined in order to verify the reliability of the electrochemical results. The results showed that phosphate compounds form a protective layer on the steel surface when immersed in alkaline solution without chlorides. In the presence of chloride ions, the SP acts as an anodic inhibitor and reduces the corrosion activity on steel. The HEDP shows lower efficiency, probably due to the decrease of the pH and to the high [Cl – ]/[inh] ratio used. Results obtained by electrochemical and gravimetric methods are in quite reasonable agreement. Introduction Concrete usually provides to reinforcing steel an excellent corrosion protection. The high alkaline environment in concrete results in the formation of a tightly adhering film, which passivates and protects steel from corrosion. Chloride ions are considered to be the major cause of premature corrosion of steel reinforcement. To minimize the corrosion processes a number of procedures can be assessed. The literature reports several ways to decrease or to prevent reinforcement corrosion. Among them, the use of corrosion inhibitors has been an envisaged solution [1–7]. Two approaches are generally used to evaluate the efficiency of inhibitors for concrete application; one uses simulated pore solution testing [8], and the other uses actual concrete or mortar specimens [9–11]. Both methods are some times used in conjunction. The approach in simulated pore solutions usually employed a saturated calcium hydroxide solution [12, 13] with or without alkaline addition. This methodology allows to evaluate rapidly the inhibitor efficiency and to determine in the simplified system the mechanisms of inhibition. But further tests in mortar and concrete are needed because the possible interaction of the inhibitor with the solid phases of the cement paste would modify or alter the concrete properties. Electrochemical tech- niques are usually employed to assess the corrosion pro- cess. Inorganic inhibitors, such as sodium phosphate (Na 3 PO 4 : SP), and sodium monofluorophosphate (Na 2 PO 3 F: MFP) were tested as corrosion inhibitors for concrete [14–17]. Those previous works have demon- strated that sodium phosphate (SP) inhibits pitting corro- sion of steel in pore solution if its concentration equals the N. Etteyeb  L. Dhouibi  E. Triki (&) Unite ´ de Recherche: Corrosion et Protection des Me ´talliques, ENIT, B. P. 37, Tunis-Belvedere 1002, Tunisia e-mail: ezzeddine.triki@enit.rnu.tn L. Dhouibi e-mail: dhouibiala@yahoo.fr M. Sanchez  C. Alonso  C. Andrade Institute of Construction Science Eduardo Torroja (CSIC), Madrid 28033, Spain 123 J Mater Sci (2007) 42:4721–4730 DOI 10.1007/s10853-006-0880-3