Testing phosphate ions as corrosion inhibitors for construction steel in mortars

L. YOHAI; M.B. VALCARCE; M.VÁZQUEZ

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 202 p. 316 - 324

0013-4686

The purpose of this investigation is to analyze the effectiveness of phosphates as inhibiting agents forsteel bars embedded in mortars. Three mix designs were selected for this study: mix A had no admixedchlorides and was used as reference; mix designs B and C were contaminated with 1% in weight ofchlorides/weight of cement and mix C also incorporated 7% Na3PO4.12 H2O. After setting for 48 h, thesamples were cured for 7 days immersed in water. Three specimens of each group were then immersed inaerated saline solutions 0.5 mol L1 NaCl during 720 days. The corrosion potential(Ecorr), the polarizationresistance (Rp) and the electrochemical impedance spectra were recorded regularly. After 720 days ofimmersion one set of mortars was anodically polarized and another set cathodically polarized. After that,Raman spectra of corrosion products were registered. Additional specimens were used to evaluateporosity and chloride profiles. The presence of phosphate ions as inhibitors has no effect on Ecorr valuesand suggests mixed-type inhibition. Mix C remains passive until 180 days of exposure, withRt> 100 kVcm2. At longer times, Rt decreases in time but the inhibition percentage is always higherthan 95% when evaluated by impedance spectra. Using Rp, inhibition stays above 70%. Anodic andcathodic polarization curves, together with corrosion potential values, suggestthat phosphates behave asa mixed-type inhibitor.