The Effect of Silica Fume on Corrosion of Steel Reinforcement-A Review

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Title: The Effect of Silica Fume on Corrosion of Steel Reinforcement-A Review

Author(s): M. Maage

Publication: Special Publication

Volume: 199

Issue:

Appears on pages(s): 477-496

Keywords: carbonation; chlorides; concrete; corrosion; electrical resistivity; literature review; oxygen diffusion; pH in pore water; sil-ica fume

Date: 6/1/2001

Abstract:
The practical application of silica fume started in the late seventies. At that time and the following years, opinions on the effect of silica fume on reinforcement corrosion varied quite a lot. Since then a lot of research has been carried out and the results of many years of practical experience are known. The corrosion process of reinforcement steel in concrete may be divided into two stages: the initiation period and the propagation period. Silica fume affects both the two stages. In the initiation period, carbonation is going on or chlorides are transported into the concrete. The carbonation process results in reduced pH values allowing corrosion to start. Silica fume may be expected to reduce the resistance against carbonation due to reduced amount of calcium hydroxide. On the other hand, silica fume will also improve the resistance against CO? ingress. A concentration of chlorides higher that the threshold value at the steel surface may result in reinforcement corrosion. Silica fume reduces the chloride binding capacity of the binder, leaving more chlorides to attack the steel, but again silica fume will also improve the resistance against chloride ingress. In the propagation period, the electrical resistivity of the concrete and oxygen diffusion are the governing factors for corrosion rate. The first is very much increased by silica fume, the second more debatable. Based on literature review, all important factors for the initiation period and the propagation period are discussed. As far as possible, consensus for each factor is given and an overall conclusion for the effect of silica fume on reinforcement corrosion is given. The overall conclusion is that silica fume has both positive and negative effects on the different factors governing the steel reinforcement corrosion. However, the positive factors are dominating by far over the negative factors.