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Agar gel pads have been used for electrochemical measurements for some time. For zinc in particular, a standard method for measuring the stability of the corrosion product layer is being established. The main interpretation factor is the corrosion product layer resistance RL, as it is easy to determine and interpret. A high corrosion product layer resistance indicates a high level of protection. However, it is not yet known how low the corrosion product layer resistance is for freshly produced zinc samples. As zinc is highly active, it reacts immediately with the environment to form a corrosion product layer, which affects the corrosion product layer resistance. The addition of zinc acetate to the agar gel pads prevents the formation of a surface layer and destroys existing ones.
This makes it possible to measure an almost corrosion product-free zinc surface. This is important in defining the range of corrosion product layer resistance for a protective surface.
It is well known that cement manufacture, including CaCO3 calcination and clinker formation, is associated with substantial energy consumption and significant greenhouse gas emissions. Alkali-activated binders (AAB) and concretes made from them can significantly contribute to reducing CO2 emissions caused by the construction industry. However, to what extent and for how long concretes made from AAB can protect the steel in reinforced concrete components from corrosion is still unclear. Unlike PC-based binders, AABs are made by reacting alkaline solutions with solid precursors such as fly ash and ground granulated blast furnace slag (GGBFS). Therefore, steel reinforcement corrosion mechanisms in AAMs differ from PC-based binders. The present study aims to evaluate the corrosion behavior of steel rebar in alkali-activated materials (AAMs) synthetic pore solution with different chemical concentrations representing different GGBFS and Flay Ash based binders by performing electrochemical tests to measure the corrosion rate and corrosion potential of steel rebar. This information can be used to improve the design of AAMs in order to ensure a longer service life for these materials.
The safe storage of radioactive material in nuclear waste repositories is a major task of our societies. The sealing function of such repositories is depending on the ability of the applied construction materials to form and maintain a geotechnical barrier with the surrounding rock. Corrosion of the construction material can lead to leakage of radioactive compounds and must therefore be avoided or minimized. Since concretes based on conventional Portland cement have not been found suitable in this context, alternative binders must be evaluated.
One such class of binders are hybrid cements, which are blends of low fractions of Portland cement or Portland clinker and high fractions of supplementary cementitious materials, such as blast furnace slag and fly ash, activated by an alkali salt. Besides a low heat of hydration and a sufficient early compressive strength [1], chemical similarities with ancient Roman concrete suggest an excellent durability in saline environments [2], which makes these cements potentially suitable for applications in nuclear waste repositories in evaporite rock, such as the Morsleben repository in Germany.
In the present study, two previously designed and characterized [3] hybrid cements, an alkali-activated slag/fly ash blend, and an OPC paste were studied regarding their resistance against corrosion in an aggressive saline solution. The saline solution was designed by the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) [Association for Facility and Reactor Safety] as a reference representing a solution forming as the result of contact of surface water with evaporite rock. The cement pastes were exposed to the saline solution up to 70 days and characterized by X-ray diffraction, thermogravimetric analysis and spatially resolved X-ray fluorescence spectroscopy. In addition, thermodynamic modelling was performed to simulate the alterations of the phase assemblage with increasing exposure to the saline solution and, thus, provide indications on the long-term durability of the cement pastes.
The experimental results revealed a correlation between the Portland clinker content of the cements and the resistance of the cement pastes against attack by the saline solution. This outcome was related to the formation of portlandite when sufficient clinker was available, which maintained the pore solution pH at ~12.5, and thus prevented the dissolution of cementitious phases. Once portlandite was consumed, C-N-A-S-H and ettringite dissolved and released calcium, aluminium, and hydroxide ions in the solution, maintaining the pH at ~10. In this pH range, the formation Cl-AFm phases was observed. At lower pH values, i.e., extended exposure durations, gypsum was the major corrosion product. The pH-dependent dissolution and formation of phases lead to pronounced zonation in the exposed cement pastes. Thermodynamic modelling indicated that the dissolved silicon from C-N-A-S-H reacts with magnesium ions in the saline solution to form M-S-H, and that long-term exposure eventually leads to a material rich in amorphous silica and brucite.
Corrosion monitoring of reinforced concrete structures:The DGZfP specification B12 Collaboration
(2023)
Corrosion monitoring of reinforced or prestressed concrete structures has becomeincreasingly important in recent years. Areas of application include componentsthat are no longer accessible after completion or where potential fieldmeasurements cannot be carried out due to existing coatings. Corrosion monitoringcan also be used to monitor the progress of corrosion in corroding systems, e.g. to prove the success of repair measures according to repair principle 8 in accordancewith EN 1504‐9 or repair method 8.3 in accordance with the DIBt repair guideline.It also could be used to prove the functionality of cathodic corrosion protectionsystems in accordance with ISO 12696. Despite the increasing importance ofcorrosion monitoring, no guidelines orrecommendations existed until 2018. Thisgap was closed by the English version of specification B12,“Corrosion Monitoringof Reinforced and Prestressed Concrete Structures,”of the German Society for Non‐Destructive Testing, which was published in 2021. This article introducesspecification B12 by explaining the basicmeasurement principles and illustratingthe potential of corrosion monitoring in new and existing buildings.
The corrosion behavior of galvanized steels and zinc components under atmospheric exposure depends mostly on the corrosion product‐based cover layer formation under the prevailing conditions. The use of agar‐based gel electrolytes makes it possible to use electrochemical methods to obtain a characteristic value from these cover layers that describe their current and future protective capacity. It is shown here that different states of galvanized steel can be distinguished very well under laboratory conditions and that this method is also suitable for use under practical conditions. Based on the characteristic values and assuming future time of wetness, it is very easy to draw up a forecast for the future corrosion rate, which provides plausible values.