Ueli Angst


Last Name

Angst

First Name

Ueli

ORCID

0000-0002-2603-4757

Organisational unit

09593 - Angst, Ueli / Angst, Ueli

Search Results

Publications1 - 10 of 217
  • Stahlkorrosion in sauerstoffarmer Lösung und Effekt von Karbonaten
    Item type: Other Conference Item
    Angst, Ueli; Martinelli-Orlando, Federico (2021)
  • Moisture as a key factor in the corrosion of steel in carbonated low-clinker materials
    Item type: Conference Paper
    Albert, Cristhiana; Mundra, Shishir; Isgor, O. Burkan; et al. (2025)
    Low-clinker concretes, while environmentally sustainable, are more susceptible to carbonation, which is often directly associated with steel corrosion and decreased durability of reinforced concrete structures. This paradigm limits the potential of low-clinker cements to significantly reduce CO2 emissions in the cement industry. To address this problem, we propose to investigate the actual corrosion kinetics of steel in carbonated low-clinker concretes, with emphasis on their pore solution composition, pore structure, and moisture state. Our study evaluates corrosion rates of low-carbon steel in carbonated mortar mixes with cements containing 50% clinker replacement with various supplementary cementitious materials – including limestone, pozzolan, silica fume, slag, and calcined clay – at two water/binder ratios, 0.45 and 0.60. These diverse mixes exhibit a range of pore solution chemistries and pore structures, developed after long-term sealed curing (91 days) and accelerated carbonation (4% CO2). Electrochemical methods are used to assess the corrosion rate of steel under two extreme exposure conditions: (i) a dry state (60% RH), with negligible steel corrosion, and (ii) a saturated state, associated with the highest corrosion rates of the steel. Despite variations in corrosion behavior based on cement type and water/binder ratio, the moisture condition of the mortar was the key factor influencing the corrosion rate of steel in this study. This highlights the need for improved scientific understanding of the moisture state and moisture transport – particularly at the steel-concrete interface – in carbonated concrete produced with low-clinker cements. As a result, the durability design of reinforced structures might consider the concrete cover as a barrier to water ingress rather than only carbonation.
  • Modelling Effect of Coarse Aggregates on Oxygen Transport and Corrosion Products Precipitation in Reinforced Concrete
    Item type: Conference Paper
    Zhang, Zhidong; Angst, Ueli (2021)
    4th International Rilem Conference on Microstructure Related Durability of Cementitious Composites: Microdurability 2020
    The structure of concrete, in particular the microstructure of the steel-concrete interface (SCI), can significantly affect corrosion of rebars. To support corrosion, oxygen needs to diffuse from the ambient environment to the steel surface. Meanwhile, corrosion products transport through the SCI and precipitate in concrete. Transport properties of concrete play an important role in these two processes. However, the effect of the heterogeneous structure of concrete especially coarse aggregates on oxygen transport and corrosion products precipitation in reinforced concrete is rarely studied in the literature. This study employed a numerical model to investigate such effect. Simulation domains in 2D were created with different aggregate contents and sizes. The model included oxygen diffusion, ions diffusion and migration, corrosion products oxidation and precipitation. The simulation results showed that the presence of aggregates significantly reduces oxygen diffusion. It becomes more pronounced for high aggregate contents which lead to more corrosion products formed at the interface. Furthermore, results showed that the interfacial transition zone (ITZ) around aggregates can enhance oxygen diffusion.
  • Neuartige Inspektionsmethode für Winkelstützmauern
    Item type: Conference Paper
    Bircher, Lukas; Pfändler, Patrick; Angst, Ueli (2023)
    Beiträge zum 37. Christian Veder Kolloquium: Zustandserhebung, Bewertung und Sanierung von gealterten bzw. schadhaften geotechnischen Konstruktionen
  • Kinetics of electrochemical dissolution of metals in porous media
    Item type: Journal Article
    Stefanoni, Matteo; Angst, Ueli; Elsener, Bernhard (2019)
    Nature Materials
    Metals embedded in porous media interact electrochemically with the liquid phase contained in the pores. A widespread form of this, adversely affecting the integrity of engineered structures, is corrosion of steel in porous media or in natural environments. While it is well documented that the rate of this electrochemical dissolution process can vary over several orders of magnitude, understanding the underlying mechanisms remains a critical challenge hampering the development of reliable predictive models. Here we study the electrochemical dissolution kinetics of steel in meso-to-macro-porous media, using cement-based materials, wood and artificial soil as model systems. Our results reveal the dual role of the pore structure (that is, the influence on the electrochemical behaviour through transport limitations and an area effect, which is ultimately due to microscopic inhomogeneity of the metal/porous material interface). We rationalize the observations with the theory of capillary condensation and propose a material-independent model to predict the corrosion rate.
  • Direct Numerical Modelling Of Capillary Driven Multiphase Flow at the Embedded Steel - Porous Media Interface
    Item type: Other Conference Item
    Malenica, Luka; Zhang, Zhidong; Angst, Ueli (2024)
    Proceedings of the 9th World Congress on Momentum, Heat and Mass Transfer (MHMT 2024)
    Multiphase flow through porous materials is an important field of study in a broad range of applications. One of such applications is understanding and predicting corrosion mechanisms inside reinforced porous materials, such as soil or concrete, where air-water distribution at the steel surface is directly related to corrosion processes and has a great impact on durability of reinforced structures [1]. Prediction of water transport and retention throughout pore systems is generally based on traditional models relying on either Darcy scale modelling, such as Richards equation [2] or simplified pore scale modelling, such as bundle of capillary tubes or pore-network modelling [3]. However, such models are not capable of providing detailed insight into water distribution at the steel-porous media interface which is crucial to understanding of relevant degradation mechanisms such as corrosion. One approach that can overcome mentioned limitation of traditional models is direct numerical modelling of multiphase flow directly at pore scale [4]. Such an approach solves the full set of Navier-Stokes equations which accurately describes multiphase flow by directly resolving fluid-fluid interfaces and contact lines of fluid phases with solid boundaries, such as contact between air, water and solid (both porous skeleton and steel in our case). Moreover, these models are capable to account for complex microstructure heterogeneities of real pore structures obtained by pore-scale imaging, such as X-ray microtomography or FIB-SEM techniques. In this work, OpenFOAM based volume-of-fluid (VOF) solver is used to perform high-fidelity direct numerical simulations of gas-liquid multiphase flow inside different reinforced porous media, such as reinforced soil or concrete. Both synthetic and realistic (imaged-based) pore structures, as well as different material properties were studied. Even that direct numerical modelling approach cannot be used to predict flow over full scale of interest (mostly due to high computational cost and size limitations of pore-scale imaging), combining detailed resolution of fully dynamic pore-scale multiphase processes with realistic 3D geometries of pore space enables us deeper insight and consistent explanation of particular processes that are still not well understood.
  • Microstructural examination of carbonated 3D printed concrete
    Item type: Journal Article
    Aguilar Sanchez, Asel Maria; Wangler, Timothy; Stefanoni, Matteo; et al. (2022)
    Journal of Microscopy
    The recent interest in 3D printing with concrete has generated great interest on how inhomogeneities arise and affect performance parameters, in particular strength and durability. With respect to durability, of particular interest is how 3D printed layer interfaces can impact transport of species of interest, such as moisture, chlorides, or carbon dioxide in carbonation processes. This is of particular interest considering that the primary use case of 3D printed concrete has been as a lost formwork for a cast structural concrete, and thus it is of interest to determine the carbonation resistance. This study consists of a preliminary look at the microstructure after accelerated carbonation of a 3D printed concrete used as a lost formwork. Preferential carbonation is observed in the layer interfaces compared to the bulk of the printed filaments, possibly related to porosity from air voids or a locally high capillary porosity corresponding to the lubrication layer.
  • Modelling life cycle costs for edge beams of three Norwegian bridges
    Item type: Report
    Boschmann Käthler, Carolina; Angst, Ueli (2022)
    NPRA Reports
    For the planning of cost-effective infrastructure maintenance, it is important to assess the condition of structures and to estimate the optimum time, the extent and the type of repair needed to continue operating the structures safely. In this study, a novel approach is presented, which combines data from condition assessment of reinforced concrete structures (e.g. chloride profiles), predictive modelling (future chloride ingress) and experimentally determined chloride threshold values (Ccrit) on cores retrieved from the structures with a method recently developed at ETH Zurich, Switzerland. This approach is applied to three bridges in Norway.
  • On the Carbonation Dilemma and How to Escape from It
    Item type: Conference Paper
    Angst, Ueli (2023)
    RILEM Bookseries ~ International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures. SynerCrete 2023 - Volume 2
    There is a dilemma between designing cementitious binders with low greenhouse gas (GHG) emissions and at the same time attempting to satisfy carbonation test requirements. In fact, various studies have shown that with increasing clinker replacement, the carbonation rate increases. The established paradigm to ensure durability, particularly to avoid reinforcement corrosion related damage, is based on avoiding carbonation of the concrete, as carbonation is conceptually equated with corrosion. This view presents a major goal conflict, and has important consequences for the ambition to reduce GHG emissions from the cement and concrete industry. The requirement to avoid carbonation penalizes binders with high clinker replacements in comparison with Portland cement. To overcome this barrier and to unleash the full potential of low carbon binders, there is thus an urgent need to escape from this “carbonation dilemma”. This conference contribution discusses how new insight with regard to the mechanism of corrosion of steel in concrete presents an opportunity to resolve the mentioned dilemma. There is increasing evidence that the moisture at the steel surface is the more important factor to ensure durability than whether or not the concrete carbonates. This way of looking at durability is underpinned by the findings of a working group within RILEM TC 281-CCC as well as recent scientific laboratory studies. A review of this literature is presented and a vision of a possible escape route from the “carbonation dilemma” is sketched.
  • In-situ photometric reflectance measurements of carbon steel surfaces upon cathodic protection
    Item type: Other Conference Item
    Martinelli-Orlando, Federico; Angst, Ueli (2023)
    Cathodic protection (CP) is an electrochemical technique used to reduce corrosion rate of carbon steel to negligible values. CP has been used since almost 100 years to protect underground structures, e.g., soil buried pipelines. Despite the worldwide use of the technique, the working mechanism of CP is still under debate. On the one side, researchers suggest that the modification of the electrolyte in the vicinity of the steel surface (i.e., increase in pH and oxygen consumption) might promote the formation of a passive film that contributes to the protection mechanism by reducing the corrosion rate of steel to negligible values. On the other side, other researchers suggest that the protection mechanism achieved by the CP system can be explained based on corrosion kinetic considerations, with the iron dissolution reaction being reduced to negligible values. On both sides, experts based their reasoning on theoretical approaches or indirect measurements. Up to now, investigation regarding the modifications of the steel surface upon the application of cathodic protection is still missing. To fill this gap of knowledge, the aim of the work is to analyze the changes of the carbon steel surface with in-situ photometric reflectance measurements upon the application of CP. Carbon steel samples were immersed in a soil simulated solution and CP was applied for 30 minutes at different potentiostatic conditions. During the experiments, the increase in the absorbance in the UV region of the light upon the application of CP suggested the formation and growth of an oxide film at the carbon steel surface in presence of a cathodic current. The results obtained in this study are of main importance concerning the advancing in understanding cathodic protection mechanisms.
Publications1 - 10 of 217