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Hydrogen-induced stress corrosion cracking (HSCC) is well known, and highly sensitive pre-stressing steels are normally not available on the market. But in the case of existing structures, it could be necessary to ensure their safety through special kinds of investigations. Those kinds of investigations are often not applicable in a non-destructive way.
Therefore, a once in a lifetime project was initiated.
In the course of the deconstruction of the "Bridge of the 20th anniversary of the GDR" at the Altstädter Bahnhof in Brandenburg a. d. Havel, new information on the initiation of hydrogen-induced stress cracks could obtained. The initial observation to do several investigations at this bridge are several meters long longitudinal cracks in the concrete web of the box girder above and below the tension duct. The BAM was commissioned by the Brandenburg State Road Administration to participate in a corresponding joint project which is financed by the Federal Ministry for Digital and Transport. The added value of the new information gained in this project goes beyond the specific structure. It describes unexpected new damage patterns that can be transferred to other structures with concentrated tendons (tendon block method and Baur-Leonhardt method) and were previously unknown in this form. These should be made known to other developers to enable them to initiate any necessary actions.
One of the major results is, the wire breaks observed at this bridge can be attributed to cracking as a result of HSCC and subsequent crack growth until breakage, due to cyclic loading from traffic and alternating restraint stresses. The probable trigger here was crevice corrosion processes at the contact points of the wires to the spacer plates in superposition with high tensile stresses due to prestressing after or with in grouting the duct. Tension wire breaks, which may have occurred before grouting and during prestressing, were not detected. The unfavorable gap situation at the spacer plates occurs over the entire cross-section of the prestressing channel and can thus affect each individual prestressing wire. Losses in the load-bearing capacity of the prestressed concrete structure can then be the result. A disadvantage of the prestressing block method in this respect is that a large number of individual wires can be affected at the same time (theoretically all wires), which can reduce the prestressing effect of the concentrated tendon accordingly. With the usual use of only one tendon per web, the possibility of load transfer to other tendons is thus not given (lack of redundancy).
Corrosion of reinforcement is one of the major reasons in questioning the sturdiness of building structures. The application of cathodic protection techniques plays a big role in controlling the corrosion process to ensure a longer service life of building structures. This systematic study compares the efficiency and durability of various discrete galvanic zinc anode systems available in the current market using different criteria for measuring efficiencies such as potential measurements, electrolyte resistance measurements and several polarization methods to determine the polarizability of the anodes. Results to validate the performance of long-time exposure of discrete zinc anodes in the concrete medium are already shown in 2021. Now the results of analyzing the phase boundary between mortar and anodes by using 3D computer tomography are shown, as also the field application at large-scale specimens where the potential distribution and the current were investigated.
Surface applied corrosion inhibitors (SACI) are widely used to mitigate corrosion process of steel reinforcement in concrete. But they remain controversial as to their effectiveness and the ability to compare materials from different manufacturers
and technologies. They are applied onto the surface of
hardened concrete and penetrate towards steel reinforcement. This paper discusses the corrosion inhibition performances of
dual-phase surface applied corrosion inhibitor and the efficiency of the corrosion inhibitor is assessed by selected testing procedures in BAM laboratories.
Due to the corrosion resistance of carbon steel, bridge constructions are currently protected against corrosion by applied coating systems. These coating systems need to be renewed after approximately 25 50 years. Galvanized constructions without any welding areas at the construction site could be prepared as grouted joints and can be used without any renewing for about 100 years.
In order to obtain a statement on the corrosion resistance of stainless steel against pitting corrosion, a well-tested measuring arrangement is required. For this purpose, the so-called ECISS test can be used to determine the critical chloride content. This makes it possible to assess the corrosion resistance of various stainless steels that have different chromium contents.
In the course of the deconstruction of the "Bridge of the 20th anniversary of the GDR" at the Altstädter Bahnhof in Brandenburg a. d. Havel, new information on the initiation of hydrogen-induced stress cracks was obtained. BAM was commissioned by the Brandenburg State Road Administration to participate in a corresponding joint project which is financed by the Federal Ministry for Digital and Transport. The added value of the new information gained in this project goes beyond the specific structure. It describes unexpected new damage patterns that can be transferred to other structures with concentrated tendons (tendon block method and Baur-Leonhardt method) and were previously unknown in this form. These should be made known to other developers to enable them to initiate any necessary actions.
Potential Mapping - What could we measure and what should we able to detect – guideline B03 of DGZfP
(2022)
“Electrochemical potential mapping according to guideline B3 of DGZfP (German Society for Non-Destructive Testing) is a recognized technique for the localization of corroding reinforcing steels.
Areas of corroding reinforcement steel can be located in a non-destructive manner by means of this procedure. Half‐cell potential measurements are used in order to detect chloride‐induced corrosion. However, it is not recommended in order to assess the risk of carbonation‐induced corrosion. For this purpose, determining the carbonation depth and the concrete cover appears more appropriate. The content of this specification exclusively refers to the application of mobile, local variable reference electrodes, which are only placed on the concrete surface while measuring. The technique distinguishes itself thereby from the range of corrosion monitoring systems with stationary installed reference electrodes and sensor systems, respectively, whereby it is possible to continuously track measurements within the area of the installed electrodes. However, these methods are not dealt with in this specification.”
Galvanic corrosion protection by embedded zinc anodes is an accepted technique for the corrosion protection of reinforcing steel in concrete. Galvanic currents flow between the zinc anode and the steel reinforcement due to the potential difference that is in the range of a few hundred mV. The ion distribution was studied on two steel reinforced concrete specimens admixed with 3 wt.% chloride/wt. cement and galvanically protected by a surface applied EZ-anode. On both specimens, a zinc anode was embedded and glued to the concrete surface by a geo-polymer-based chloride-free binder. At one specimen, the EZ-anode was operated for 2,5 years, the EZ-anode at the other specimen was not electrically connected to the reinforcement, this specimen serves as a reference. Both specimens have been stored under identical conditions. The ion distribution between the anode (EZ-anode) and cathode (steel reinforcement) was studied by laser-induced breakdown spectroscopy (LIBS) after 7 months, 12 months, and 2,5 years. Results of the LIBS studies on the specimen with activated EZ-anode after 7 months, 12 months, and 2,5 years and of the reference specimen after 2,5 years are reported. Results show that diffusion of ions contributes to the changes in the ion distribution but migration, especially of chlorides towards the EZ-anode is significant despite the weak electric field – several hundred millivolts - generated by the galvanic current. Results show that chloride ions accumulate near the zinc-anode as in water-insoluble zinc-hydroxy chlorides - Simonkolleit.