Untersuchungen zum kritischen korrosionsauslösenden Chloridgehalt von Stahlfasern in künstlicher Betonporenlösung

Abstract

It is well known, that reinforcement steel in concrete is normally protected against corrosion due to the high pH-value of the pore solution of the concrete. This alkalinity leads to a passive layer on the steel surface, which prevents further corrosion. The passive layer can be destroyed by chloride ions diffusing into the concrete. The concentration of chloride in the concrete which leads to a destruction of the passive layer and therefore to corrosion of the steel is defined as the critical chloride content. Investigations in artificial concrete pore solutions show that the critical chloride content of black steel is strongly dependent on the pH-value of the solution: the higher the concentration of the OH - -ions the higher the critical chloride content. For steel fibres earlier investigations have shown, that steel fibres do not corrode in concrete even at high chloride contents. Therefore it could be assumed, that the critical corrosion-inducing chloride content of steel fibres in concrete is distinctly higher than of conventional reinforcing steel. To verify this assumption the corrosion-inducing chloride content of steel fibres is investigated in artificial chloride-containing concrete pore solutions at different pH-values. 5 different types of steel fibres, 1 lashing wire and as reference 1 reinforcing steel are investigated at 3 different pH-value ranges. The concentration of chloride within the pore solution is gradually increased in time steps of 12 h. The beginning of corrosion is determined by current as well as potential measurements. Furthermore additional investigations are carried out with intermediate products of the fibre production (steel wires with different diameters) to investigate if the critical chloride content of the wires is increasing gradually with decreasing diameter. The investigations show, that steel fibres in artificial chloride-containing pore solutions indicate an distinctly increased resistance against chloride-inducing corrosion compared with conventional reinforcing steel for high pH-values. With decreasing diameter of wires the critical chloride content increases gradually.