Electrochemical Behaviour of Steel in Dense Silica-Cement Mortar


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Title: Electrochemical Behaviour of Steel in Dense Silica-Cement Mortar

Author(s): Carolyn M. Preece, Hans Arup, and Thomas Frolund

Publication: Special Publication

Volume: 79


Appears on pages(s): 785-796

Keywords: electrical steels; sil cement resista ica. pastes; corro nce; mortars ion; electrical properties; material porosity; reinforcing

Date: 5/1/1983

A study has been made of the ability of a highly dense silica-cement mortar to protect steel reinforcement from corrosion. Corrosion of the steel is an electrochemical process in which the cement pore water acts as the electrolyte. The cement must, therefore, allow (i) passage of electrical current, (ii) diffusion of oxygen and other species from the environment to the steel and (iii) transport of the corrosion products away from the steel. The properties of the cement which are of interest are, thus, its electrical resistivity, its porosity and the chemistry of the pore water, particularly the pH. However, it is the combination of these properties which determines the corrosion rate and, as yet, not enough informatiou is available to allow a direct prediction of the corro-sion rate. Consequently, electrochemical polarization measurements have been made in order to determine the actual corrosion behaviour. In the electrochemical experiments, a steel rod embedded in the mortar is held at a constant potential with respect to a reference electrode and the current flowing between the embedded rod and an external steel electrode is measured. By repeating the process for different values of the potential, it is possible to extrapolate the data to the corrosion potential, thereby giving a direct estimate of the free corrosion rate. These experiments have been carried out in different environments (anaerobic solutions, NaCl solutions, H2C03 solutions, etc.) and the results are discussed in terms of the properties of the silica-cement mortar. Despite the Pozzolanic reaction in the cement, it appears to provide excellent protection to steel reinforcement.