INVESTIGADORES
YOHAI DEL CERRO lucia
congresos y reuniones científicas
Título:
The role of chloride and phosphate ions on the corrosion of construction steel
Autor/es:
L. YOHAI; M. VÁZQUEZ; M.B. VALCARCE
Lugar:
Praga
Reunión:
Encuentro; 63th Annual Meeting of the ISE; 2012
Resumen:
Reinforced concrete is one of the most widely used building materials. Distinctive features such as low cost, availability and formability, as well as excellent structural and durability properties characterize one of the most important materials in the construction industry. However, aggressive service environments and contaminated aggregates accelerate deterioration and failure. Steel corrosion is one of the main factors that negatively influences the performance of reinforced concrete. To minimize the effect of corrosion, various techniques can be employed, such as cathodic protection, inhibitors dosage or the application of coatings to the external concrete surface or to the reinforcing steel bars. Nitrite ions are widely used as corrosion inhibitors although there are some environmental risks. As an alternative, this investigation evaluates sodium phosphate (Na3PO4) as corrosion inhibitor for construction steel. All the tests are carried out in a solution that simulates the composition of the pores in chloride-contaminated concrete. The sodium phosphate concentration being tested is 0.3 mol L-1 and the pH of the synthetic medium that simulates concrete is 13, while the phosphate/chloride ratio is kept at 1. Cyclic voltammograms, potentiodynamic reductions and anodic polarization curves complemented with micro-Raman spectroscopy were used to follow the performance of this inhibitor. The results are compared to those from weight-loss tests, after exposing the specimens during 90 days. The results show that chloride contamination increases the accumulation of corrosion products on the metallic surface and promotes pitting corrosion. Relevant parameters associated to pitting corrosion are shown in the table below. When phosphate ions are incorporated, pitting is inhibited. The changes in the composition of the surface layer in the presence of the contaminant, or the inhibitor, and of both the contaminant and the inhibitor together are investigated by micro Raman spectroscopy. It can be concluded that phosphate ions are good candidates to be used as corrosion inhibitors for steel in chloride-contaminated concrete. The role of phosphates in the improved protectiveness of the passive layer in chloride-rich solutions is interpreted on the basis of a mechanism that takes into account solubility products of iron (II) phosphates, which are much lower than those of the respective hydroxides. pH=13 ECORR / mVHg/HgO EPIT / mVHg/Hg EPIT-ECORR / mVHg/HgO OH- -208 ± 21 ----- ----- OH- + 0.3 mol/L Cl- -257 ± 40 6 ± 35 182 ± 81 OH- + 0.3 mol/L PO43- -337 ± 54 ----- ----- OH- + PO43- + Cl- -263 ± 34 ----- -----