Publications by Emil Gallyamov

Mechanics of alkali-silica reaction in concrete across scales

Alkali-silica reaction occurs in concrete between the alkalis contained in the pore solution and silica in the aggregates. Generation of ASR products gives rise to the internal pressures that cause expansion and cracking. Due to its deleterious effect on concrete, ASR poses a major threat to the safety and operability of the concrete infrastructure worldwide.Recent experimental advances obtained in the scope of the multi-disciplinary Sinergia project entitled ``Alkali-silica reaction in concrete'' of Swiss research institutes shed new light on ASR. Being part of Sinergia, the research conducted in the scope of the present thesis had a goal to fill in the knowledge gap on the ASR mechanics. Therefore, analytical and numerical models facilitated by the novel experimental data have been developed.One of the Sinergia experimental studies showed that the initial ASR products accumulate between the crystal grains of aggregates. We are using this knowledge together with an estimate of the volumetric increase of a typical ASR product to evaluate the crack-growing potential of a single region filled with ASR products. This is done by employing a semi-analytical model of an expanding inclusion of nanometre-size encircled by a disk-shaped crack. The role of the expansion value and the inclusion's size and shape on the resulting crack length is investigated. The analytical findings are confirmed by a finite element model.Another experimental Sinergia study produced a time-series of X-ray tomograms of the ASR-affected concrete, which resolved the evolution of the deformation field, the crack growth and the accumulation of ASR products. This unique set of data is used in the current thesis to study the growth of ASR-crack networks and their role in the macroscopic behaviour of concrete. A novel cohesive elements-based meso-scale model capable of predicting the stable growth of numerous cracks is developed. Several hypotheses on the ASR-loading and cracking mechanismsare proposed and tested by including them in the model. Statistical comparison of the numerical and experimental crack networks provide new insights into ASR-cracking physics.The continuous-damage approach is adopted to improve the efficiency and stability of the meso-scale model. The physics of the model is enriched by accounting for the orthotropic behaviour of damaged elements and the self-contact in cracks. This development allows reproduction of the macroscopic expansion of the concrete samples under substantial uniaxial load, which was not feasible by the earlier isotropic-damage models. Moreover, the role of creep on the ASR in concrete is investigated by combining viscoelasticity with strain-softening.The last subject treated in this thesis is the macroscopic behaviour of ASR-affected structures. A computational multi-scale model of concrete is developed, validated and used to investigate the long-term behaviour of a real ASR-affected dam. The latter was facilitated by the availability of actual field measurements. This approach combines the meso-scale model with the orthotropic damage and the macro-scale model of the dam. The model allows us to relate the macroscopic expansion of concrete to its state at the meso-scale, which comprises the crack network, its openings and orientations, and expansions of individual ASR sites. Coupling of the mechanical model with the transient heat analysis permits to evaluate the role of temperature variations on the ASR expansion.

EPFL2022

Numerical Scheme for the Large-scale Geomechanical Simulations of CO2-storage

Emil Gallyamov

CO2 geological storage implies injecting supercritical carbon dioxide in deep geological formations. CO2 geological storage is currently the only available Negative Emission Technology with sufficient proven capabilities to significantly contribute to the removal of carbon dioxide from the atmosphere. The design and operations of a storage site are based on the combination of measurements and the use of physics-based computational models.

2022

Study on the internal crack network of the ASR-affected concrete by the tomography-based numerical model

Emil Gallyamov, Jean-François Molinari, Mahdieh Shakoorioskooie

In this paper, we present a novel finite element model to simulate alkali-silica reaction in a realistic concrete meso-structure. Application of the internal ASR loading leads to the evolution of multiple deviated cracks and corresponding macroscopic expansion. A particular crack-extension algorithm and a solution scheme provide numerical stability and allow to model complicated crack patterns while preserving the physics. The predictive validity of the model is demonstrated by matching an analytical solution of a loaded penny-shaped crack. The model is applied to the experimental dataset comprising the time-evolving X-ray tomograms of the ASR-affected concrete. Similar to the tomography data, the model results in an expanded concrete sample with a developed crack network. Two hypotheses on the crack loading and extension mechanisms are tested by comparing the crack statistics. Simulations with varying number of ASR sites and application of the uniaxial loading bring interesting insights. The latter concerns the role of the ASR-sites number, the individual loading amplitude and the difference in crack patterns.

PERGAMON-ELSEVIER SCIENCE LTD2022

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This paper aims to employ a 2D thermo-mechanical multi-scale ASR model for the analysis of a concrete gravity dam in Western Switzerland. Simulation results are com- pared to the ﬁeld measurements and observations. Analysis of the results reveals no eﬀect of temperature variation on the ASR advancement: ﬁeld displacements could have been reproduced by assigning a constant temperature within an entire dam cross-section. The diﬀerence in length between the upstream and the downstream faces is identiﬁed as the main source for the upstream drift at the level of the crest. Study of the structural eﬀects reveals ASR-related expansion anisotropy and cracks alignment being more pronounced along the upstream part and the foundation. If the former is explained by the transmission of the self-weight, the latter is attributed to the constraining eﬀect of the underlying rock.

2021

Meso-scale finite element modeling of Alkali-Silica-Reaction

Emil Gallyamov, Jean-François Molinari, Roozbeh Rezakhani

The Alkali-Silica Reaction (ASR) in concrete is a chemical reaction, which produces an expansive product, generally called “ASR gel”, and causes cracking and damage in concrete over time. Affecting numerous infrastructures all around the world, ASR has been the topic of much research over the past decades. In spite of that, many aspects of this reaction are still unknown. In this numerical-investigation paper, a three-dimensional concrete meso-structure model is simulated using the finite-element method. Coarse aggregates, cement paste, and ASR gel are explicitly represented. A temperature dependent eigen-strain is applied on the simulated ASR gel pockets to capture their expansive behavior. This applies pressure on the surrounding aggregates and the cement paste, leading to cracks initiation and propagation. Free expansion of concrete specimens due to ASR is modeled and validated using experimental data. Influence of different key factors on damage generation in aggregates and paste and macroscopic expansion are discussed.

2021

Multi-scale model of a dam affected by alkali-silica reaction

Mauro Corrado, Emil Gallyamov, Jean-François Molinari

2021

Predicting damage in aggregates due to the volume increase of the alkali-silica reaction products

Emil Gallyamov, Barbara Lothenbach, Jean-François Molinari

Volume increase between the reactants and the products of alkali silica reaction could reach up to 100%. Taking place inside the aggregates, ASR imposes internal pressure on the surrounding material. In the current paper, we study the possibility of crack growth due to such internal loading. This study is done by employing a semi-analytical mechanical model comprising an elastic solution to a well-known Eshelby problem and a linear elastic fracture mechanics solution to a ring-shaped crack encircling a spheroidal inclusion. The proposed method implies the availability of pre-existing micro-fissures within the aggregate. The study reveals dependence of the crack growing potential on the spheroid's shape: the larger is the ASR pocket - the longer crack it can open. Two most critical shapes, causing a highest stress intensity factor and developing the longest crack, are a sphere and a spheroid with 1/4 aspect ratio respectively. The size analysis of the problem suggests a critical spheroid's radius below which no crack growth is expected. For a chosen material properties and expansion value, such radius lays in the range between 0.1 and 1 micrometer. Independently of the expansion value and the shape of the pocket of ASR product, the maximum crack length has a power-law dependence on the size of a spheroid. All the theoretical predictions are confirmed by a numerical model based on the combination of the finite element method and cohesive element approach.

2021

Meso-scale modelling of ASR in concrete: effect of viscoelasticity

Mauro Corrado, Emil Gallyamov, Jean-François Molinari, Roozbeh Rezakhani

A meso-scale numerical model for simulating damage in concrete due to ASR is presented. It accounts for the internal structure of concrete including aggregates and mortar. ASR sites are explicitly represented. This model is extended to account for viscoelastic effects in the mortar. An ASR product expansion law is based on the phenomenological reaction extent equation. The model is calibrated on free ASR expansion experiments. Mortar is modelled both as elastic- and viscoelastic-brittle material. In case of the viscoelastic-brittle mortar, simulations result in a lower level of damage and lower stiffness reduction than in the elastic-brittle case. However, the macroscopic expansion becomes lower than the experimental values. This suggests that to reach sufficient macroscopic strain, a larger damage extent within aggregates is necessary.

2020

Micro-scale Cracking of Concrete due to the Alkali-Silica Reaction

Emil Gallyamov, Barbara Lothenbach, Jean-François Molinari

Alkali-silica reaction (ASR) is a concrete disease that leads to its degradation. ASR is the reaction between the amorphous silica (SiO2 ) and the alkali ions (Na + , K + ), leading to expansion of concrete in presence of Ca 2+ . In this study, it is assumed that the internal pressure exerted on a concrete matrix by the expanding products leads to its cracking and loss of its bearing capacity.

2020