Abstract

The environment in which the concrete structure is inserted has a great influence on its durability and its service life. Thus, the present work aims to study of the performance of 5 types of concretes of same compressive strength (35 MPa at the age of 28 days) and considers kinetic and thermodynamic aspects of the corrosion induced by chlorides. The 5 types of concretes studied were produced with the use of mineral additions in partial replacement on cement mass (10% of silica fume, 30% of fly ash and 20% of metakaolin), besides the control situation (without mineral addition). The water-to-cementitious materials ratio was different for the concretes ranging from 0.30 to 0.55. Specifically, for the concrete with fly ash, two water/binder ratios were studied (0.30 and 0.40) with the goal of verifying if there are or not significant differences on properties of corrosion with little change of water quantity in the mix. The chloride attack consisted by 308 days (44 weekly cycles) in immersion in aggressive solution rich in chlorides and subsequent drying in a laboratory environment. During this period, the corrosion potentials (Ecorr) and corrosion rate (icorr) from polarization resistance (Rp) of steel bars were monitored. As a general result, it was possible to compare the performance of concretes at the same class of compressive strength to denote which systems have the longest durability in view of attack by chloride. The results have shown that the concretes produced with mineral additions did not show steel bar corrosion, thus configuring major service life for them. Control concrete presented depassivation of reinforcing steel, Ecorr more electronegative and higher icorr over time.

Abstract

This research aims to compare corrosion parameters obtained by linear polarization technique and Tafel extrapolation method in steel bars embedded in concrete. It was analyzing the intervention of mineral additions, such as metakaolin (10%) in binary concrete mixtures and silica fume (9% ) and nano silica (1%) in ternary concrete mixtures of water/binder ratio of 0.4 and 0.6 after induction of corrosion by wetting and drying cycles in a solution containing chlorides. Thus, the corrosion potential (Ecorr), polarization resistance (Rp) and corrosion rate (icorr) were measured. As a main result, a good correlation (R² of 0.82 and 0.96) was obtained with the values of polarization resistance (Rp) and corrosion rate (icorr), obtained by Rp and by Tafel slope, respectively. Binary and ternary concretes mixtures showed higher performance than reference concretes. Reference concrete with w/ratio of 0.6 showed a high corrosion rate.