Critical Chloride Content for the Corrosion of Steel Fibres in Artificial Concrete Pore Solutions


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Title: Critical Chloride Content for the Corrosion of Steel Fibres in Artificial Concrete Pore Solutions

Author(s): M. Raupach and C. Dauberschmidt

Publication: Special Publication

Volume: 212


Appears on pages(s): 165-180

Keywords: chloride; corrosion; cirtical chloride content; fibre; pore solution; steel; wire

Date: 6/1/2003

Reinforcing steel in concrete is normally protected against corrosion due to the high pH-value of the pore solution of the concrete. When a critical chloride concentration in the concrete is exceeded at the steel surface the passive layer is destroyed and corrosion of the steel starts. This critical chloride content for the corrosion of black steel is strongly dependent on the pH-value of the pore solution: the higher the concentration of OH--ions the higher the critical chloride content. For steel fibres, earlier investigations have shown, that they do not corrode in concrete even in presence of high chloride contents. Therefore it could be assumed, that the critical corrosion-inducing chloride content of steel fibres in concrete is distinctly higher than that of conventional reinforcing steel. To verify this assumption the corrosion-inducing chloride content of steel fibres has been investigated in artificial chloride-containing pore solutions at different pH-values. Five different types of steel fibres, one lashing (or tying) wire and one as reference reinforcing steel were investigated at 3 different pH-value ranges. The concentration of chloride within the pore solution was gradually increased in time steps of 12 h. The beginning of corrosion was determined by electrical current as well as potential measurements. Furthermore, additional investigations were carried out with intermediate products of the fibre production (steel wires with different diameters) to investigate whether the critical chloride content of the wires depends on the diameter of the fibres. The investigations show that steel fibres in artificial chloride-containing pore so- lutions have a significant increased resistance against chloride-inducing corrosion compared to conventional reinforcing steel for high pH-values. With decreasing diameter of wires the critical chloride content increases gradually.