Corrosion of Steel in Concrete: Some Fundamental Aspects of Concrete with Added Silica

Abstract

Silica, which is a waste product of the ferrosilicon industry, has been used as an additive to concrete. This silica-fume material consists of minute spherical silica particles with pozzolanic properties. In this study, steel embedded in concrete (waterxement = 0.55 to 0.60) with and without added silica has been exposed to seawater at 20 C for two years. During the exposure period, polarization studies and chloride analyses have been performed. A diffusion model for chloride penetration into the concrete gives an apparent diffusion coefficient of 6 × 10−9 cm2/s for a concrete with 16% added silica compared to 1.5 × 10−7 cm2/s for the similar concrete without added silica. The corrosion rates calculated from polarization studies showed that the corrosion of steel in concrete will be insignificant at a total chloride concentration in concrete of less than 0.30% (dry weight of concrete). The corrosion rates with and without added silica were not significantly different at any given total chloride concentration in the concrete. The initial resistivity of a concrete with 8% added silica will be around 2 × 106 ohm-cm compared to 4 × 103 ohm-cm for the similar concrete without added silica.