Emanuele Rossi

Last Name

Rossi

First Name

Emanuele

ORCID

0000-0002-2104-3646

Organisational unit

09593 - Angst, Ueli / Angst, Ueli

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Publications 1 - 10 of 13

The Interdependent Roles of Chloride, Moisture and Dissolved Oxygen in Macro-voids at the Steel-Concrete Interface in Corrosion
Susanna, Governo; Rossi, Emanuele; Azad, Seren; et al. (2026)
Corrosion of steel in concrete is a key durability issue for reinforced concrete structures, leading to significant economic costs and safety risks. Research suggests that moisture within voids at the steel-concrete interface (SCI) plays a critical role in corrosion. However, experimental evidence clarifying this role remains limited. Here, we systematically investigated the influence of macro-voids at the SCI by exposing reinforced concrete specimens to different wet-dry cycles and to continuous submersion in chloride solution, thereby generating distinct moisture conditions within the interfacial voids. X-ray computed tomography (XCT) was used to monitor the evolution of the gas-liquid configuration inside these voids along with steel corrosion over 9 months. Under wet/dry cycles, corrosion initiated at lower chloride levels than under continuous immersion. XCT revealed that interfacial voids became fully saturated after prolonged immersion but remained partially saturated during wet/dry exposure. These findings are interpreted through the lens of corrosion science and gas-liquid interactions in porous materials. We suggest a mechanism in which the dissolution of pressurized gas bubbles trapped within interfacial voids leads to an increase in dissolved oxygen concentration near the void, thereby locally elevating the steel corrosion potential (E_corr). Together with chloride accumulation, which gradually lowers the pitting potential, this shift in E_corr enhances the likelihood for local corrosion initiation under wet-dry cycles. Overall, this study contributes to understanding how different water exposure conditions affect the local environment at the SCI, providing insight into the mechanistic links between interfacial void gas-liquid content and corrosion in reinforced concrete.
Chloride-induced corrosion of steel in concrete—insights from bimodal neutron and X-ray microtomography combined with ex-situ microscopy
Angst, Ueli; Rossi, Emanuele; Boschmann Käthler, Carolina; et al. (2024)
Materials and Structures
The steel–concrete interface (SCI) is known to play a major role in corrosion of steel in concrete, but a fundamental understanding is still lacking. One reason is that concrete’s opacity complicates the study of internal processes. Here, we report on the application of bimodal X-ray and neutron microtomography as in-situ imaging techniques to elucidate the mechanism of steel corrosion in concrete. The study demonstrates that the segmentation of the specimen components of relevance—steel, cementitious matrix, aggregates, voids, corrosion products—obtained through bimodal X-ray and neutron imaging is more reliable than that based on the results of each of the two techniques separately. Further, we suggest the combination of tomographic in-situ imaging with ex-situ SEM analysis of targeted sections, selected based on the segmented tomograms. These in-situ and ex-situ characterization techniques were applied to study localized corrosion in a very early stage under laboratory chloride-exposure conditions, using reinforced concrete cores retrieved from a concrete bridge. Several interesting observations were made. First, the acquired images revealed the formation of several corrosion sites close to each other. Second, the morphology of the corrosion pits was relatively shallow. Finally, only about half of the total 31 corrosion initiation spots were in close proximity to interfacial macroscopic air voids, and > 90% of the more than 160 interfacial macroscopic air voids were free from corrosion. The findings have implications for the mechanistic understanding of corrosion of steel in concrete and suggest that multimodal in-situ imaging is a valuable technique for further related studies.
X-ray computed tomography to observe the presence of water in macropores of cementitious materials
Rossi, Emanuele; Governo, Susanna; Shakoorioskooie, Mahdieh; et al. (2023)
RILEM Technical Letters
Corrosion of steel reinforcement in concrete is a common degradation mechanism occurring in infrastructures worldwide. Even though extensive research has been conducted over the last decades to accurately predict the influence of steel corrosion on concrete durability, a comprehensive understanding of several micro‐scale processes simultaneously involved in the corrosion mechanism is still lacking. The application of X‐ray Computed Tomography (X‐ray CT) can contribute to elucidate these processes, since this technique allows observing the internal status of specimens non‐destructively, over time, and with a spatial resolution in the range of μm. Nevertheless, the relatively low sensitivity of light elements (e.g., hydrogen and oxygen) to X‐ray CT may hinder the observation of solution within the cementitious matrix. This consideration is discussed in this letter. The results of this study show that the detection of solution in macropores (e.g., air voids) through X‐ray CT is not limited by the relatively low attenuation coefficient of the fluid per se, but more by the spatial resolution at which acquisitions are performed and by the dimensions of the porous volume where solution penetrates. The observations reported in this letter may open several opportunities to further study the influence of the moisture conditions of air voids on several degradation mechanisms of reinforced cementitious materials (e.g., steel corrosion, freeze‐thaw damage), which have been rarely investigated with X‐ray CT according to the literature. The application of these findings could significantly deepen the understanding of several micro‐scale processes that affect the durability of reinforced cementitious materials which still need to be elucidated, as further discussed in the present letter.
Provably Efficient Causal Model-Based Reinforcement Learning for Systematic Generalization
Mutti, Mirco; De Santi, Riccardo; Rossi, Emanuele; et al. (2023)
Proceedings of the 37th AAAI Conference on Artificial Intelligence
In the sequential decision making setting, an agent aims to achieve systematic generalization over a large, possibly infinite, set of environments. Such environments are modeled as discrete Markov decision processes with both states and actions represented through a feature vector. The underlying structure of the environments allows the transition dynamics to be factored into two components: one that is environment-specific and another that is shared. Consider a set of environments that share the laws of motion as an example. In this setting, the agent can take a finite amount of reward-free interactions from a subset of these environments. The agent then must be able to approximately solve any planning task defined over any environment in the original set, relying on the above interactions only. Can we design a provably efficient algorithm that achieves this ambitious goal of systematic generalization? In this paper, we give a partially positive answer to this question. First, we provide a tractable formulation of systematic generalization by employing a causal viewpoint. Then, under specific structural assumptions, we provide a simple learning algorithm that guarantees any desired planning error up to an unavoidable sub-optimality term, while showcasing a polynomial sample complexity.
In-situ Study of Corrosion of Steel in Concrete through X-ray Computed Microtomography
Governo, Susanna; Rossi, Emanuele; Shakoorioskooie, Mahdieh; et al. (2024)
Book of Abstracts
Pit Morphology Characterization in Chloride-Exposed Reinforced Concrete
Yilmaz, Deniz; Angst, Ueli; Rossi, Emanuele (2024)
Chloride-induced corrosion stands as one of the most prevalent mechanisms causing damage to reinforced concrete, leading to a rapid loss of steel cross-section. In the evaluation of load-bearing behavior in existing structures, chloride-induced corrosion is typically assumed to result in an idealized loss of cross-sectional area in the reinforcement. This simplification arises due to a lack of understanding of the corrosion pit morphology. However, addressing this knowledge gap regarding the pit morphology is crucial for assessing the durability and quantifying the remaining service life of reinforced concrete structures. In a preliminary step, the pit morphology of over 400 corrosion pits on six actual structures has been documented and analyzed. 168 pits in an early corrosion state were documented on specimens from previous laboratory experiments. Subsequently, ten concrete specimens, each embedded with one reinforcement bar, were fabricated and exposed to a chloride solution in a controlled laboratory environment. The objective was to compare the corrosion pit morphology observed in the lab setting with that found on actual structures. Corrosion initiation was monitored using potential measurements, while corrosion kinetics were tracked through Linear Polarization Resistance (LPR) measurements. The examination of the first specimen after three months of active corrosion revealed a similarity between the pit morphology observed in the lab specimens and that identified on real structures. Notably, corrosion pits exhibited a tendency to grow in width and length rather than in depth. The remaining specimens are scheduled for opening and in-depth analysis in the near future. The insights gained into corrosion pit morphology in chloride-exposed reinforced concrete will contribute significantly to refining the calculation of the actual limit state of structures. This understanding will ultimately enhance the maintenance practices of reinforced concrete structures exposed to chlorides, offering benefits from both an economic and ecological standpoint.
Detection of water ingress in voids in cementitious materials through X-ray Computed Tomography
Rossi, Emanuele; Governo, Susanna; Shakoorioskooie, Mahdieh; et al. (2024)
Book of Abstracts
Insights on the precipitation of corrosion products precipitation in interfacial macro-pores: similarities between reinforced concrete and archeological artifacts embedded in soil
Rossi, Emanuele; Granget, Elodie; Governo, Susanna; et al. (2024)
The corrosion mechanism of metals embedded in opaque porous materials is highly influenced by, among other factors, the porous network of the medium and the conditions at the medium-metal interface, such as the local moisture conditions and the pH of the electrolyte at which corrosion occurs. Even though significant research has been conducted to elucidate the mechanisms of metallic corrosion in porous media (i.e., steel in concrete, archeological artefacts in soil, etc.), the opacity of the matrices and the complexity of the interfacial micro-scale processes involved when corrosion occurs and propagates often hinder the formulation of conceptual and analytical models that can tackle this problem from a fundamental perspective. In this context, studying certain inter-related mechanisms has been only possible since recently through advanced experimental techniques, such as bimodal X-ray and neutron computed tomography (X/n CT). As a collaboration within the CORINT Sinergia project, this study reports on the application of X/n CT and SEM analysis to investigate how corrosion products precipitate in macro-pores at the metal-media interface in the case of steel in concrete and of a roman archaeological iron nail embedded in soil. Even though the interfacial conditions may be considerably different in the two systems (e.g., pH of the electrolyte, size range of the porous network, ageing, etc.), a very similar precipitation pattern is visible. When favorable conditions for metallic dissolution in the proximity of an interfacial macro-pore are present, corrosion products precipitation occurs firstly as a dense layer along the edges of the void. Precipitation of consequent layers of corrosion products takes place growing inwards in the void volume. Microscopy analysis suggests that phase transformation of the different corrosion products compounds occurs over time and, most likely, depending on the local chemical conditions. These observations, as well as the implications that this growth pattern may have on corrosion propagation, will be comprehensively discussed.
Precipitation of corrosion products in macroscopic voids at the steel–concrete interface: observations, mechanisms and research needs
Mundra, Shishir; Rossi, Emanuele; Malenica, Luka; et al. (2025)
Materials and Structures
Macroscopic voids at the steel–concrete interface and their degree of saturation with an aqueous electrolyte are known to play an important role in the corrosion of steel in reinforced concrete. Irrespective of the exposure conditions and testing parameters, in the majority of studies corrosion products have been reported to consistently precipitate in a unique pattern within these macroscopic voids, preferentially along the void walls and growing inward. The underlying mechanisms governing corrosion product precipitation in macroscopic voids and their effects on long-term durability remain unclear. Through in-situ X-ray computed tomography observations, thermodynamic and kinetic considerations, and numerical modelling of water transport within macroscopic voids, here, we provide plausible hypotheses of the processes responsible for the precipitation of corrosion products along the walls of the voids. Understanding the mechanisms of corrosion product precipitation can offer insights into the development of stresses in and around the macroscopic interfacial void and the durability of reinforced concrete structures. This contribution also discusses opportunities for different avenues for research to elucidate several multiscale processes that influence the durability of reinforced concrete.
FIB-SEM of the steel-concrete interface to elucidate micro-scale corrosion processes
Rossi, Emanuele; Schmid, Thilo; Mundra, Shishir; et al. (2024)

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