Shishir Mundra

Last Name

Mundra

First Name

Shishir

ORCID

0000-0001-6559-8814

Organisational unit

09593 - Angst, Ueli / Angst, Ueli

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Publications 1 - 10 of 43

Fundamentally understanding carbonation-induced corrosion of steel in environmentally friendly concretes
Albert, Cristhiana; Mundra, Shishir; Isgor, O. Burkan; et al. (2024)
Revista ALCONPAT
The fundamental understanding of the kinetics of carbonation-induced corrosion, considering the role of the concrete pore solution, pore structure, and moisture content, is discussed in this paper. Open questions and promising approaches to clarify them are also discussed. Based on this knowledge, corrosion propagation can be properly included in the service life design of reinforced concrete structures, reconciling the goals for both sustainable and durable structures. One of the primary solutions is employing environmentally friendly cements with lower clinker content, such as those containing supplementary cementitious materials. However, concretes produced with some of these cements are vulnerable to fast carbonation. While traditional approaches focus on preventing concrete carbonation and corrosion initiation, evidence shows that corrosion rates of steel in carbonated concrete do not necessarily compromise durability.
Transformation of 2-Line Ferrihydrite to Goethite at Alkaline pH
Furcas, Fabio E.; Lothenbach, Barbara; Mundra, Shishir; et al. (2023)
Environmental Science & Technology
The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH ≥ 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis, and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life, t1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 h at pH = 14.0. The calculated-first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log10 k = log10 k0 + a·pH3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow redissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.
The influence of silica on the formation of corrosion products in cementitious systems
Furcas, Fabio Enrico; Mundra, Shishir; Lothenbach, Barbara; et al. (2024)
Chloride binding by layered double hydroxides (LDH/AFm phases) and alkali-activated slag pastes: an experimental study by RILEM TC 283-CAM
Gluth, Gregor J.G.; Mundra, Shishir; Henning, Ricky (2024)
Materials and Structures
Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM ‘Chloride transport in alkali-activated materials’ significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS.
Transformation of 2-line ferrihydrite to goethite at alkaline pH
Furcas, Fabio E.; Lothenbach, Barbara; Mundra, Shishir; et al. (2023)
arXiv
The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH >= 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life,t_1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 hours at pH = 14.0. Calculated first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log_10 k = log_10 k_0 + a*pH^E3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow re-dissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.
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.
Kinetics of iron (hydr)oxide precipitation in cementitious materials
Furcas, Fabio E.; Mundra, Shishir; Lothenbach, Barbara; et al. (2023)
Further Reduction of CO2-Emissions and Circularity in the Cement and Concrete Industry, 16th International Congress on the Chemistry of Cement 2023 - ICCC2023
The accumulation of corrosion products throughout the concrete pore network may lead to the development of internal stresses and spalling of the concrete cover, thus facilitating further structural detonation. To gain a more profound understanding of this self-sustaining sequence of events, both the type of corrosion product(s) as well as their rate of formation within the chemical environment characteristic to cementitious materials must be investigated. By employing a combination of time-resolved TGA, XRD, XAS and ICP studies, we show that the formation of the thermodynamically stable end member goethite (α-FeOOH(s)) is preceded by rapid precipitation of 2-line ferrihydrite (2l-Fe(OH)3(s)) at alkaline pH. Over time, dissolution of the amorphous intermediate prompts re-crystallisation of goethite from solution. Here, precipitation rates scale with the H+ activity. Kinetic rate laws deduced from the progression of aqueously dissolved iron and the amount of solid phase(s) present at any time can lead to better reactive transport models that predict the service life of reinforced concrete structures more accurately.
Thermodynamic modeling: Success in cement science – Untapped potential in corrosion research
Furcas, Fabio E.; Lothenbach, Barbara; Mundra, Shishir; et al. (2025)
RILEM Technical Letters
For more than a century, the corrosion of steel in concrete has prevailed as a complex and yet poorly understood phenomenon, with many durability design approaches relying on phenomenological or semi-empirical service life models. The increasing societal demand to maintain aging infrastructure, the development of new cementitious binders and the push towards an environmentally more benign and circular concrete economy exacerbate the need for a more comprehensive scientific understanding of the underlying physicochemical processes, particularly in the absence of long-term empirical data. This manuscript retraces the history of thermodynamic modeling in cement and concrete research, examining early concepts, the barriers to adoption, and the pivotal role of modern Gibbs free energy minimisation solvers towards its broad level of acceptance within the scientific community. We further examine the current use of thermodynamic modeling techniques in corrosion science, emphasizing the limitations of classical potential-pH stability diagrams and addressing the widespread misconception that thermodynamics and kinetics are opposing concepts. Finally, we explore the opportunity to leverage the recent developments in the field of cement science and adopt thermodynamic modeling techniques in corrosion research, thereby addressing open questions related to the corrosion of steel in concrete.
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.
Characterising the microstructure of corrosion products precipitated in interfacial macro voids using FIB-SEM
Rossi, Emanuele; Mundra, Shishir; Angst, Ueli (2026)
RILEM Bookseries ~ Proceedings of the RILEM Spring Convention and Conference 2025, Volume 2
In an attempt to accurately predict the implications of steel corrosion on the long-term durability of reinforced concrete structures, the literature still reveals a lack of understanding of several multi-scale processes occurring at the steel-concrete interface (SCI) relevant to steel reinforcement corrosion. Among other open questions, recent studies have highlighted the need to elucidate in depth aspects such as the microstructure, pore structure, and phase assemblage of the SCI, as well as the characteristics of the corrosion products precipitating therein. To this end, this study reports on the application of Focused Ion Beam – Scanning Electron Microscopy (FIB-SEM) on one polished section of corroding reinforced concrete specimen to investigate potential to characterize the micro-scale porosity and the micro-structure of corrosion products precipitated in interfacial macropores (e.g., voids) and within the surrounding concrete matrix. The obtained spatial resolution (i.e., pixel size of 20 nm) allowed for the observation of the porous network of the concrete matrix around the interfacial void, as well as that of the corrosion products phases precipitated along the walls of the void. Through the performed FIB-SEM analysis, distinct layers of corrosion products, differentiated by morphology and chemical composition, were found at the walls of the void, filling the void inwards. The potential of this technique to elucidate several open questions is discussed, and ongoing and future work in line with this study is finally described.

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