Corrosion inhibition of reinforcing steel in concrete

Abstract

CORROSION inhibition of reinforcing steel in concrete was studied using Dicyclohexylamine nitrite (DCHAN), Dicycl ohexy-lamine (DCHA), Dimethylethanolamine (DMEA), Try-n-butyl amine (TNBA), Sodium nitrite (SN), Sodium tetraborate (STB) and Sodium molybdate (SM). These substances were evaluated using electrochemical methods in solutions that simulate concrete environments (saturated calcium hydroxide solution (1.85 g/l)). Sodium chloride (3.5 wt %) was used as corrosion initiator. Experiments were carried out in absence of both corrosion initiator (NaCl) and corrosion inhibitor, in presence of corrosion initiator only and in presence of both initiator and inhibitor. Linear Polarization (LP) technique was used to determine polarization resistance and corrosion rate. Pitting corrosion testing was also carried out using cyclic anodic polarization technique. It is found that Ecorr of reinforcing steel moves towards more positive values with time until it attains a steady state on the fourth day whereupon it remains constant for the rest of the testing period. It is also found that the corrosion rate of samples, determined from LP experiments, is proportional to the chloride ion concentration. The highest corrosion rate of 0.027 mm/y is obtained at 21,000 ppm Cl-. The order of inhibition efficiency of the tested inhibitors after seven days testing is: DCHAN (95%) > SM (88 %) > TNBA (87 %) > DCHA (85%) = SN (85%) > STB (78%) > DMEA (75%). Results of pitting corrosion experiments show that only DCHAN and SN can resist this type of attack. The results were interpreted on the premise of inhibitor structure.