Jithender J. Timothy

• Doctor of Engineering (Dr.-Ing.)
• Head of Research - Modeling and Simulation at Technical University of Munich

The effective permeability of microcracked heterogeneous materials such as rocks, ceramics and concrete can be determined using analytical and computational homogenization methods. While in the companion paper (Timothy and Meschke, 2017) a semi-analytical Cascade Continuum Micromechanics (CCM) model is proposed to predict the effective permeability...

Within the framework of mean-field homogenization methods, we propose a lattice version of the cascade micromechanics model for the estimation of the effective permeability of microcracked materials with a physically consistent percolation threshold. We also investigate a link between the cascade scheme, self-similarity and critical phenomena. The...

The paper presents a synthesis of analytical modeling and computational simulations of the intrinsic permeability of microcracks, embedded in porous materials taking into account the interaction of the fluid flow in the microcrack with the surrounding porous material. In the first part of the paper, using the DARCY, STOKES, BRINKMAN and the BEAVERS...

The transport and fluid flow in heterogeneous materials such as rocks, ceramics and concrete with a distributed random microcrack network is strongly influenced by the density and the topology (distribution and connectivity) of microcracks. The overall fluid flow characteristics of such microcracked solids can be quantified in terms of an effective...

The elastic properties of porous materials with a disordered pore structure are estimated using the mean-field Eshelby homogenization scheme together with the principle of recurrence to generate a cascade of effective microstructures as a function of the porosity and the cascade level n. Starting with the Hashin-Shtrikman upper bound for porous mat...

Monitoring and assessing infrastructure health are prerequisites for efficient maintenance. New technologies and methods enable deeper insights and thus offer improved information for decision makers. The development of such new methods for application requires holistic understanding not only of the method itself, but also of the specific challenge...

The microstructure of concrete can be affected by many factors, from non-destructive environmental factors through to destructive damage induced by transient stresses. Coda wave interferometry is a technique that is sensitive enough to detect weak changes within concrete by evaluating the ultrasonic signal perturbation compared to a reference state...

Changing stress regimes control fracture network geometry and influence porosity and permeability in carbonate reservoirs. Using outcrop data analysis and a displacement-based linear elastic finite-element method, we investigate the impact of stress regime change on fracture network permeability. The model is based on fracture networks, specificall...

The datasets (original field photographs, drone images and finite-element modelling algorithms and results) presented here are drawn from the extensive fieldwork, and finite-element modelling of the impact of stress regime change on the permeability of a naturally fractured carbonate buildup (Latemar, the Dolomites, northern Italy) by the author(s)...

Precisely estimating material parameters for cement-based materials is crucial for assessing the structural integrity of buildings. Both destructive (e.g., compression test) and non-destructive methods (e.g., ultrasound, computed tomography) are used to estimate Young’s modulus. Since ultrasound estimates the dynamic Young’s modulus, a formula is r...

Understanding the transient properties of cementitious pastes is crucial for construction materials engineering. Computational modeling, particularly through Computational Fluid Dynamics (CFD), offers a promising avenue to enhance our understanding of these properties. However, there are several numerical uncertainties that affect the accuracy of t...

To develop new cementitious materials with the goal of reducing the carbon footprint a rapid assessment of information about their resistance against damaging processes is of utmost importance to ensure long‐term durability. The Oxygen diffusion test is an efficient method to evaluate the ingress of gas in concretes and mortars without changing the...

Kurzfassung Eine Herausforderung performancebasierter Prüfverfahren zur Bewertung der Dauerhaftigkeit ist die Beschleunigung natürlicher Mechanismen. Dies ist notwendig, um innerhalb kurzer Zeit die Langzeit‐Leistungsfähigkeit ermitteln zu können. Die Bestimmung der Frost‐Tausalzbeständigkeit von Beton kann durch den CDF‐Test erfolgen, welcher für...

The expected lifespan of cement-based materials, particularly concrete, is at least 50 years. Changes in the pore structure of the material need to be considered due to external influences and associated transport processes. The expansion behaviour of concrete and mortar during freeze–thaw attacks, combined with de-icing salt agents, is crucial for...

Changes in stress regimes impact the geometry of fracture networks and affect the porosity and permeability of carbonate reservoirs. This is, predominantly, because of the complexity of the deformation phases, the poor understanding of the mechanical and diagenetic mechanisms that affect apertures, and the difficulty in precisely characterizing ape...

Surface deterioration of concrete subjected to freezing and thawing in combination with deicing salts is one of the most important factors determining the durability of concrete infrastructure in cold climates. The freeze–thaw deicing salt (FTDS) resistance of cementitious materials can be determined by the capillary suction of de‐icing chemicals a...

Identifying and preventing damage in concrete structures at an early stage ofmaterial degradation can significantly reduce costs associated with the maintenance andrepair of concrete infrastructure. Weak material degradation, such as load-induced initiationand propagation of microcracks, is a precursor of localized damage (macrocracking) in concret...

Performance test methods intend to provide a fast, accurate and precise determination of a particular building material property and thus determine the associated material performance. In concrete, various performance tests are used to classify existing or to approve new materials, to compare concrete compositions or to determine causes of damage i...

In this chapter, important research results for the development of a robust and damage-tolerant multimaterial tunnel lining are presented. This includes the production, design and optimization of fiber-reinforced hybrid segmental lining systems based on numerical models and experimental investigations under tunneling loads. In addition, novel tail...

Deterioration of concrete subjected to freezing and thawing climatic conditions is one of most important factors affecting the durability of concrete infrastructure in cold climates. The freeze-thaw resistance of cementitious materials like concrete and mortar can be determined by the CDF test (Capillary Suction of De-icing chemicals and Freeze-Tha...

Damage induced by repetitive freezing and thawing processes is one of the critical factors that affect concrete durability in cold climates. This deterioration process manifests as surface scaling and internal damage. The damage processes are governed by physicochemical mechanisms that are active across multiple scales. In this contribution, we pre...

Das Porensystem im Beton, bestehend aus Gel‐ und Kapillarporen, beeinflusst dessen Wasseraufnahmefähigkeit und so direkt auch den Frost‐Tausalz‐Widerstand. Unterschiedliche Expositionsbedingungen im jungen Alter des Betons haben dabei einen ausgeprägten Einfluss auf die Ausbildung des Porensystems. Um die Rolle der Vorkonditionierung auf das sich a...

Changing stress regimes control fracture network geometry and influence porosity and permeability in carbonate reservoirs. We investigate the impact of stress-regime change on fracture network permeability utilizing outcrop data analysis and a displacement-based linear elastic finite element method. The model is based on fracture networks, specific...

In this paper, the flow of concrete in a reinforced bored pile is analysed using computational simulations. In order to reduce the computational time, a porous medium that equally mimics the presence of the reinforcement is used. Experimental measurements are used as bounds on the material parameters describing the flow of fresh concrete. The influ...

Introduction Coracoid fractures after arthroscopic treatment of acromioclavicular (AC) joint separations lead to poor clinical outcomes. In this study, different configurations of bone tunnels in the lateral clavicle and coracoid were examined concerning the amount of stress induced in the coracoid. Methods An authentic 3D finite element model of...

High costs for repair of concrete and reinforced structures can be prevented if damage at an early stage of degradation is detected and precautionary measures are applied. The multiple-scattered late arriving signals (so-called coda waves) contain rich information that can be used to detect weak changes in complex heterogeneous materials such as co...

Age-related macular degeneration (AMD) is the leading cause of vision loss in older adults above the age of 50. AMD is attributed to the degeneration and loss of normal function of the outer retina in the macular region. Presence of extracellular material called drusen between the Bruch's membrane (BrM) and the retinal pigment epithelium (RPE) is t...

Concrete is a composite material with heterogeneities across multiple length scales. Degradation of concrete due to external loadings starts with diffuse microcracking, followed by damage localization that eventually leads to structural failure. Identification of damage at an early stage of degradation reduces the costs associated with maintenance...

The integrity of tunnel structures deployed in difficult geological conditions such as expansive soils can be improved by incorporating compressible layers in the tunnel lining. Such compressible lining materials can be obtained by embedding weak inclusions (Expanded polystyrene, Expanded glass beads, Air voids) into a cement paste material. The ma...

The process of ASR (Alkali-Silica Reaction) induced expansion and damage in pavement concrete specimens is investigated using laboratory experiments and computational modeling. In the experimental program, the concrete specimens are subject to CS-CPT (climate simulation concrete prism test) to obtain ASR induced expansion with and without external...

High costs for the repair of concrete structures can be prevented if damage at an early stage of degradation is detected and precautionary maintenance measures are applied. To this end, we use numerical wave propagation simulations to identify simulated damage in concrete using convolutional neural networks. Damage in concrete subjected to compress...

Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in inta...

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early stage of concrete degradation and ap...

Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in inta...

Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behaviour of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and multiscale computational modelli...

High costs for the repair of concrete structures can be prevented if damage at an early stage of degradation is detected and precautionary maintenance measures are applied. To this end, we use numerical wave propagation simulations to identify simulated damage in concrete using convolutional neural networks (CNN). Damage in concrete subjected to co...

Concrete is a heterogeneous material with a disordered material morphology that strongly governs the behavior of the material. In this contribution, we present a computational tool called the Concrete Mesostructure Generator (CMG) for the generation of ultra-realistic virtual concrete morphologies for mesoscale and multiscale computational modeling...

Damage in concrete structures initiates as the growth of diffuse microcracks that is followed by damage localisation and eventually leads to structural failure. Weak changes such as diffuse microcracking processes are failure precursors. Identification and characterisation of these failure precursors at an early stage of concrete degradation and ap...

Mechanized tunneling in difficult geological conditions, such as soils with significant swelling potential due to water uptake by the clay minerals, depends not only on the calibration of the tunnel boring machine to the ground characteristics, but also on the ability of the tunnel lining to tolerate localized swelling pressures. In order to avoid...

Concrete is a quasi‐brittle material with a heterogeneous morphology across multiple scales, which also influences the evolution of damage in case of loading. Damage in concrete structures is initiated by growth of diffuse microcracks that is followed by damage localization eventually leading to structural failure. Thus, diffuse microcracking proce...

Age‐related macular degeneration (AMD) is the leading cause of vision loss in older adults above the age of 50. AMD is attributed to the degeneration and loss of normal function of the outer retina in the macular region. Presence of extracellular material called drusen between the Bruch's membrane (BrM) and the retinal pigment epithelium (RPE) is t...

Age‐related macular degeneration (AMD) is a disease that affects the macular region of the outer retina. AMD is characterized by the presence of large extracellular debris called drusen between the Bruch's Membrane (BrM) in the choroid and the retinal pigment epithelium (RPE) in the outer retina. An important feature of AMD is the degenerative chan...

Compressible cementitious materials are used in tunnel lining systems deployed in ground conditions characterised by expansive soils. The deformation capacity of a cementitious material can be enhanced by the introduction of weak inclusions (EPS) and/or pores. The overall behaviour of such porous cementitious composite materials is strongly influen...

There is an increasing need for the development of novel technologies for tunnel construction in difficult geological conditions to protect segmental linings from unexpected large deformations. In the context of mechanized tunneling, one method to increase the damage tolerance of tunnel linings in such conditions is the integration of a compressibl...

We analyse the dynamics of COVID-19 using computational modelling at multiple scales. For large scale analysis, we propose a 2-scale lattice extension of the classical SIR-type compartmental model with spatial interactions called the Lattice-SIRQL model. Computational simulations show that global quantifiers are not completely representative of the...

Systematic investigations of hardened cement paste, high‐performance concrete and mortar with and without microfibers, subjected to static and cyclic tensile loadings, were conducted. The material degradation was investigated by means of microscopic analyses of the microcrack development. Notched specimens were subjected to a predefined number of l...

We investigate the influence of distributed microcracks on the overall diffusion properties of a porous material using the self-similar cascade continuum micromechanics model within the framework of mean-field homogenization and computational homogenization of diffusion simulations using a high-resolution pixel finite element method. In addition to...

Concrete is a material with a random disordered microstructure across multiple scales. The effective macroscopic material behavior of concrete is strongly dependent on the material properties and the interactions of the individual constituents at the micro‐scale. Failure of concrete as a quasi‐brittle material is generally characterized by fracture...

ASR is a microscopic process in concrete characterized by the formation of a hydrophilic alkali‐silica gel due to the reaction of the alkali in the pore‐fluid with silica in the aggregates. In the presence of moisture, the gel swells and induces an internal pressure that leads to microcracking, expansion and overall deterioration of the material. W...

A multi-scale micromechanics model is proposed to describe the expansion and deterioration of concrete due to Alkali-Silica Reaction (ASR). The mechanics of ASR induced deterioration of a Representative Elementary Volume (REV) of concrete is modeled through a synthesis of distributed microcracking and mean-field homogenization. At the microscale, A...

The effective thermal conductivity of Carbon Nanotube (CNT)-polymer composites has been estimated using analytical and computational models. The analytical approach is based on the Cascade Continuum Micromechanics (CCM) model formulated within the framework of mean-field homogenization and the computational approach is based on numerical homogeniza...

Peridynamics is a nonlocal continuum model which offers benefits over classical continuum models in cases, where discontinuities, such as cracks, are present in the deformation field. However, the nonlocal characteristics of peridynamics leads to a dispersive dynamic response of the medium. In this study we focus on the dispersion properties of a s...

The behavior of high performance fiber reinforced cementitious composites is simulated using semi-analytical and computational sub-models specified at multiple scales. At the scale of a single fiber, a semi-analytical model is developed to characterize the microslip behavior at the interface between the matrix and the fiber. The microcrack bridging...

The paper presents a synthesis of analytical modeling and computational simulations of the intrinsic permeability of microcracks, embedded in porous materials taking into account the interaction of the fluid flow in the microcrack with the surrounding porous material. In the first part of the paper, using the DARCY, STOKES, BRINKMAN, and the BEAVER...

According to the objectives of the research group 1498, this paper deals with degradation effects in concrete structures that are caused by cyclic flexural loading. The goal is to determine their influence on the fluid transport processes within the material on the basis of experimental results and numerical simulations. The overall question was, t...

The effective mechanical and transport properties of microcracked porous materials such as cementitious materials, rocks and ceramics strongly depend on the complexity of the microstructure of the material. The influence of the porosity, the geometry of the pore-space, the microcrack density and the microcrack shape on the effective elastic propert...

A multiscale model for FRC composite structures taking into consideration the complex interactions at the scales of the fiber and microcracks is proposed. At the scale of the single fiber, a semi-analytical model characterizes the microslip behavior at the interface between the matrix and the fiber in terms of the overall composite stresses. The in...

Using the framework of the mean-field homogenization method, we propose a continuum and a lattice version of the cascade micromechanics model for the estimation of the effective permeability of microcracked materials. Estimates for the critical microcrack density below which the REV becomes effectively impermeable are derived for both the continuum...

The effective molecular diffusivity of porous materials such as cementitious, geological or synthetic materials is strongly affected by the complexity of the pore-space which may span across multiple scales from the nanometer to the sub-millimeter range. Recently, a semi-analytical Cascade Continuum Micromechanics (CCM) Model [1, 2] was proposed, w...

This paper presents a computational multi-level model for the description of alkali and moisture transport in concrete structures coupled to a macroscopic ASR induced phase-field damage model. Concrete is modeled as a heterogeneous material consisting of a partially saturated pore space with diffusively distributed microcracks and the solid skeleto...

Molecular diffusion in fully saturated porous materials is strongly influenced by the pore space, which, in general, is characterized by a complex topological structure. Hence, information on macroscopic diffusion properties requires up-scaling of transport processes within nano-pores and micro-pores over several spatial scales. A new model in the...

Auf Grundlage der Zielsetzung der Forschergruppe 1498 beschäftigt sich dieser Beitrag mit den Auswirkungen einer zyklischen mechanischen Belastung im Vierpunktbiegeversuch auf das Transportverhalten in Betongefüge. Hierzu wurde zunächst die Degradation des Mikrogefüges mittels Ultraschallmessungen sowie rissmikroskopischen Untersuchungen an Dünnsch...

This paper presents a multi-level model for the description of hydraulic effects of fracture within the context of Enhanced Geothermal Systems. The standard Biot's poroelastic formulation is used to model the physical processes in a geomechanical reservoir in terms of the material deformation and the fluid pressure. Crack propagation is modeled usi...

This paper presents a macroscopic model for the prognosis of the initiation phase and the swelling process leading to ASR induced damage in concrete. Concrete is assumed to be a fully saturated deformable porous media with interacting constituents such as the solid skeleton and ions in the pore fluid. Ion transport is assumed to be governed by the...

A multiscale modeling approach for Fiber Reinforced Concrete (FRC) is proposed, which is based on the upscaling of micro cracks and the crack bridging effect of fibers from the scale of the individual micro-crack to the macro scale. Assuming the validity of Linear Fracture Mechanics at the scale of micro-cracks, a LEFM crack growth criterion for Mo...

The diffusion properties of fracturing porous materials, such as concrete or geological materials, are strongly influenced by the complex and random topological structure of the pore space, the state of distributed micro-cracks inevitably caused by processes such as autogenous and drying shrinkage of concrete, and finally by propagating cracks caus...

The paper addresses various scale-bridging modeling and discretization strategies for multiphase materials, starting with a novel cascade micromechanics model for ion transport in porous materials, covering multiple scales involved in the pore structure of cementitious materials, to generate homogenized diffusion coefficients. Using homogenized mac...

Electrolyte transport in fracturing porous materials such as concrete is strongly influenced by the complex and random topological structure of the pore space, the state of distributed micro-cracks inevitably caused by autogenous and drying shrinkage of concrete and finally by propagating cracks caused by various loading conditions. Information on...

Electrolyte transport in fracturing porous materials such as concrete is strongly influenced by the complex and random topological structure of the pore space, the state of distributed micro-cracks inevitably caused by autogenous and drying shrinkage of concrete and finally by propagating cracks caused by various loading conditions. Information on...

Electrolyte transport in fracturing porous materials such as concrete is strongly influenced by the complex and random topological structure of the pore space, the state of distributed micro-cracks inevitably caused by autogenous and drying shrinkage of concrete and finally by propagating cracks caused by various loading conditions. Information on...

Electrolyte transport in fracturing porous materials such as concrete is strongly influenced by the complex and random topological structure of the pore space, the state of distributed micro-cracks inevitably caused by autogenous and drying shrinkage of concrete and finally by propagating cracks caused by various loading conditions. Information on...

Continuum micromechanics [2,3] is used to model tortuosity within the context of ion transport to obtain the homogenized diffusivity of intact and micro-cracked porous materials. A novel cascade homogenization technique to model ion diffusion in porous materials is proposed. A REVuc that represents the porous material is modelled as a spherical por...

The paper addresses various scale-bridging modeling and discretization strategies for multiphase porous materials, starting with a micromechanics model for ion transport within the pore space to generate homogenized diffusion coefficients. Using homogenized macroscopic properties, the theory of poromechanics provides the modeling framework for the...

The paper addresses various scale-bridging modeling and discretization strategies for multiphase porous materials, starting with a micromechanics model for ion transport within the pore space to generate homogenized diffusion coefficients. Using homogenized macroscopic properties, the theory of poromechanics provides the modeling framework for the...

Methods of micromechanics [2, 3] are used to obtain homogenized diffusion properties for intact and micro-cracked porous materials. A two scale homogenization technique is proposed. A REVuc that represents the porous microstructure is modelled as a spherical pore-space inclusion in a matrix, whose diffusion coefficient does not depend on the micros...