INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Testing phosphate ions as corrosion inhibitors for construction steel in mortars
Autor/es:
L. YOHAI; M.B. VALCARCE; M. VÁZQUEZ
Lugar:
Troia
Reunión:
Simposio; 11th Intenational Symposium on Electrochemical Methods in Corrosion Resarch; 2015
Resumen:
Reinforced concrete is widely used in the construction industry. Among the most frequent failures, those related to reinforcing steel bar (rebar) corrosion are at the top of the list. Various procedures are frequently employed to minimize rebar corrosion. Corrosion inhibitors are a common choice since thay can be cost-effective and are easy to apply. However, aggressive service environments and contaminated aggregates may accelerate deterioration and failure. Recently, we carried out an investigation in simulated pore solution showing that phosphate ions behave as mixed-type corrosion inhibitors, protecting steel against corrosion in chloride-contaminated environments. The purpose of this investigation is to extend that study, analyzing the effectiveness of phosphates as inhibiting agents but now for steel bars embedded in mortars. The study was performed using cylindrical mortar test specimens (2.8 cm in diameter by 8 cm high) containing one rebar segment and leaving a 1 cm mortar cover. Three mix designs that were selected for this study. Mix A had no admixed chlorides and was used as reference. Mix designs B and C were contaminated with 1% in weight of chlorides /weight of cement. Mix C also incorporated 7% Na3PO4. After setting for 48 h, the samples were cured for 7 days immersed in water during 720 days. Three specimens of each group were then immersed in aerated saline solutions 3.5 % of NaCl (% w/V). The corrosion potential (Ecorr), the polarization resistance (Rp) and the electrochemical impedance spectra were recorded regularly. Additional specimens with the same composition but without rebars were casted in parallel. These were used to evaluate porosity and chloride profiles. The porosity (evaluated following ASTM C-642) resulted in a value typical of standad quality material (17.6 ± 0.6 %.) The presence of phosphate ions as inhibitors has no effect on the Ecorr values and suggest mixed-type inhibition. Mix C remains passive until 180 days of exposure, with Rt > 100 kΩ cm2. At longer times, Rt decreases in time but the inhibition percentage is always higher than 95% when evaluates by impedance spectra. Using Rp, this value stays higher than 70%. These are promising results suggesting that phospates could be used as green inhibitors in reinforced concrete.