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Blast furnace cements (CEM III) and alkali-activated slags are binders for concretes with several advantageous engineering properties, and their increased adoption in construction industry could contribute to reducing the CO2 emissions associated with cement production and use. However, the current knowledge about how these cements protect steel reinforcement in concretes against corrosion is very incomplete, which impedes their large-scale application. This knowledge gap is mainly due to the fact that these cements release sulfide and other reduced sulfur species into the concrete pore solution, the consequences of which for the state of the reinforcement and electrochemical measurements are not fully understood.
The present contribution first describes peculiarities of electrochemical measurements of steel in sulfide-containing cementitious materials and related solutions as reported in the literature and a recent report by EFC Working Party 11. It is demonstrated that the high sulfide concentrations in these systems lead to low open circuit potentials and low polarisation resistances, which may be incorrectly interpreted as indicating active corrosion of the steel.
Second, preliminary results of an ongoing project [funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 458297195] related to the passivation and corrosion initiation of steel in sulfide-containing solutions and mortars are presented. Eight mortars based on one alkali-activated blast furnace slag (BFS), three alkali-activated BFS/fly ash blends, one sodium sulfate-activated CEM III/C (‘hybrid cement’), one CEM III/C, one CEM III/B, and one CEM I (ordinary Portland cement, OPC) were produced, and their pore solutions expressed and analysed after 7, 14, 28, and 56 days of curing. The pH values of the solutions differed systematically, with the highest pH values recorded for the CEM I and the alkali-activated BFS/fly ash blends with a high proportion of fly ash, and the lowest pH recorded for the CEM III/B. The redox potentials of the solutions were between −500 mV and −340 mV vs. Ag/AgCl for the alkali-activated binders, approx. +10 mV vs. Ag/AgCl for the CEM I, and in between for the CEM III/B and the CEM III/C. As expected, the electrical conductivity was highest for the alkali-activated binders. These results are explained by the chemical compositions of the pore solutions of the mortars.
Finally, a test set-up to investigate the behaviour of steel in sulfide-containing solutions and the changes on subsequent oxygen and/or chloride addition is introduced. Preliminary electrochemical measurements of steel in sulfide-containing solutions are presented and discussed in the context of the above-mentioned data from the literature and the compositions of the pore solutions of the studied mortars.
Since geothermal wells are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are in many cases extreme in terms of corrosion due to the chemical composition of hydrothermal fluids and temperatures. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities. During operation of a geothermal research facility in Groß Schönebeck copper and lead effects have been found downhole. Occurring mechanisms and measures to prevent precipitation or scaling needed to be investigated as well as potential influences of such precipitates on corrosion resistance of metallic materials used for equipment.
This contribution deals with the evaluation of the corrosion behavior of carbon steel and corrosion resistant alloys in copper and/or lead containing artificial geothermal water, simulating the conditions in the Northern German Basin.
The behavior of these materials in an artificial geothermal water obtained by electrochemical measurements and exposure tests are presented. While carbon steel exhibits precipitation and deposition, higher alloyed material shows different response to such species and a higher resistance in saline geothermal water.
Basing on these results the suitability of the investigated corrosion resistant alloy is given for use in such conditions, whereas carbon steel creates difficulties due to its susceptibility to Cu- and Pb-precipitation.
Significant Cu-deposition and precipitation only occurred in combination with carbon steel. High-alloyed materials prevent the disturbing Cu-agglomeration. Pb-deposition and precipitation only occurred in combination with carbon steel. No negative Pb-effect could be observed in combination with high-alloyed steels. High alloyed corrosion resistant alloys are suitable and shall be chosen for future design of the piping system, either in massive or in cladded form, to prevent unwanted interactions with brine components.
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).
Corrosive geothermal brines are a major challenge to geothermal power-plants. For cost reasons, plant designers favorize low alloyed steels, e.g., carbon steel, which are susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic and saline properties. To solve such problem, coatings or inhibitors would be a protective solution as an alternative to the use of high alloyed materials.
This study investigated a coating system consisting of polyaniline/silicon dioxide basing on locally available resources. Protection against corrosion of carbon steel is shown by long-term exposure and electrochemical tests of coated carbon steels, performed in an artificial acidic and saline geothermal brine, comparable to real conditions at a site in Indonesia.
Therefore, an integrated coating system is presented for corrosion protection, combining the electro-chemical functionality of polyaniline and the physical advantages of silica.
The screening of coatings shows that the modification by adding individual pigment was not sufficient to protect carbon steel even during a short-term exposure, indicated by the discoloration after only seven days of exposure.
Electrochemical tests indicated that the coating cathodically protects carbon steel or slows down the corrosion reaction.
A long-term exposure test confirmed that the PANI/SiO2 modified coating successfully protects the carbon steel in the Sibayak artificial geothermal water at 150 °C for 6 months.
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 - Simonkollite.
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.