Inibição de corrosão em concreto armado: eficiência e comportamento do sistema tiouréia/molibdato de sódio

Abstract

Rebar corrosion in reinforced concrete structures is a big issue to technical studies, because it has, besides the maintenance costs, indirect costs which affect bridges and building users. Corrosion inhibitors are chemical substances that added to concrete reduce or retard rebar corrosion. In this thesis we described the behavior of sodium molybdate and thiourea used as corrosion inhibitors (CI) for concrete mixes submitted to chloride medium. Calcium hydroxide solution, cement paste, mortar and concrete were used to understand corrosion inhibitors effects on their properties. Dosage study was performed using solutions, with and without the CI, applying cyclic voltammetry and steady-state polarization. Effects on cement paste and concrete were studied using four different dosages of the proposed CI and two commercial products, two different cements and silica fume as supplementary cementitious material. Concretes mixes were tested by workability, compression strength and resistance to chloride penetration, using ASTM C 1202 and ASTM C 1543. ASTM G 109 was used as standard to determine CI efficiency on corrosion inhibition and two techniques were used to determine concrete electrical resistivity: electrochemical impedance spectroscopy and conductivimetry. The proposed inhibitors showed, in 2% sodium molybdate and 0,67% thiourea, slight effects on concrete properties and good effects on improving the resistance to chloride penetration and to corrosion due chloride ions.