International Concrete Abstracts Portal

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.

Fracture mechanics parameters, mainly Fracture toughness K1c and Critical ef- fective crack extension (Aacc), may be used to monitor deterioration of concrete members subjected to sulfate attack, specially Delayed ettringite formation. Concrete beams containing cements with different contents of C3A, gypsum and granulated blast furnace slag were casted and submitted to Fu's accelerated curing method (1), to trigger delayed ettringite formation. Then all specimens were immersed in 23 +- 1 oC saturated lime water for a period of 3 and 6 months, measuring the changes experienced in both Fracture Toughness and Critical Effective Crack Extension, following the Bazant-RILEM recommended practice. Additional sets of beams were tested to monitor Longitudinal Resonance Frequency, Ultrasonic Pulse Velocity and Length Change. X-ray Diffraction and Scanning Electron Microsope studies were carried out to confirm the presence of Delayed Ettringite Formation. At the present paper a brief introduction of Fracture Mechanics applied to concrete is included and test results up to date are presented.

During the production of the precast concrete tunnel lining segments (at low at- mospheric pressure steam curing) for the Adler Tunnel, a new system with simultaneous curing and protective coating was successfully applied for the first time (1996 and 1997). The segments are exposed to aggressive groundwater and high loads. As a follow-up of the Adler Tunnel the same system was used for tunnel sections of the Singapore Metro (1998 and 1999) and Metro Caracas (2002). The straight forward method with only a few production steps, consist of high- performance concrete with silica fume and a protective coating for excellent curing and for additional protection against aggressive environment. The coating consist of an aqueous epoxy resin dispersion, applied immediately after stripping on the whole hot concrete surface of 40 to 50 oC in a single operation with a layer thickness of 0.1 to 0.2mm. The results of microscopic analysis, water permeability and compressive strength, on covercrete of those segments, are considerably better than on uncoated segment concrete, which were cured by covering the segments with insulation matting after stripping.

Cathodic protection is used world-wide to protect reinforced concrete structures against reinforcement corrosion. Cathodic protection systems can generally be divided into impressed current systems and systems working with sacrificial anodes. The Zinc-Hydrogel Anode is one of these sacrificail anode systems. This paper presents investigation on the effectiveness of the Zinc-Hydrogel Anode to control rinforcement corrosion. The aim of this investigation was to find out how parameters like reinforcement content and position of the anode are affecting the effectiveness. As a result it was found, that the protection current density and the polarisation of the reinforcement are highly affected by both parameters.

Some of the edge beams of the Fiskebek bridge in Denmark were cast using a number of concrete types with varying contents of silica fume (0%, 10%, 17%, 20%, and 50% by mass of cement), fly ash (0%, 40%, 45% by mass of cement) and polypropylene fibres (1.25% vol., 1.75% vol.). The edge beams were cast and placed on the bridge in 1980 - 81. Investigations over the years cover visual inspections, freezing and thawing tests, detailed chloride profiles (after 13 and 21 years of in-situ exposure and in the laboratory), compressive strength tests (at 28 days and 20 years after casting) and petrographic analysis on thin sections (at time of casting, 3, 6, 13 and 20 years after casting). The paper presents the results covering among others the correlation between the diffusion coefficient, silica fume content and equivalent water-cement ratio. In addition the results from determination of the number of micro cracks, silica fume content, equivalent water-cement ratio and compressive strength are presented.