Piet Stroeven - Academia.edu (original) (raw)

Papers by Piet Stroeven

The establishment of an experimental basis for the dependence of a mechanical property on certain... more The establishment of an experimental basis for the dependence of a mechanical property on certain structural features (and the associated micro-mechanical properties) would require extensive, cumbersome and complicated testing: mechanical testing for defining the very property, quantitative (section) image analysis and stereological three-dimensional assessment of the relevant structural features. `Realistic' simulation of material structure by computer would therefore offer an interesting alternative. This paper introduces the SPACE system (Software Package for the Assessment of Compositional Evolution) as the most recent development in this field. It has been developed to assess the composition as well as configuration characteristics of dense random packing situations in opaque materials. This paper presents an introduction to the system and will thereupon highlight by means of illustrative examples of typical applications on different levels of the microstructure the system...

Transition metal silicides have attracted great attention due to their potential applications in ... more Transition metal silicides have attracted great attention due to their potential applications in microelectronics, ceramics, and the aerospace industry. In this study, experimental and theoretical investigations of tungsten based silicides were performed. Tungsten disilicide (WSi 2) was synthesized by simple thermal treatment at 1350°C for 4 h in an argon atmosphere. These optimal synthesis conditions were obtained by variation of temperatures and times of heating, and the

Journal of the Chinese Ceramic Society, 2003

Thickness of interface transition zone(ITZ) of aggregates in concrete was investigated by a secti... more Thickness of interface transition zone(ITZ) of aggregates in concrete was investigated by a sectional analysis method. The apparent thickness of the ITZ due to non-perpendicular of the section plane to the surface of irregular aggregate particles in sectional analysis, three kinds of aggregate with regular shape (spheroid, elliptical section and rectangular section) were dis-cussed. The relationship between the thickness of apparent ITZ and actually one was also analyzed by a geometrical statistical approach. The results show that the apparent thickness is larger than that of the ITZ actually, and the amplification factor is related to the shape of the aggregate. For square and spherical particle, the ratio between average thickness of the apparent ITZ and actual one is 1.12 and π/2 respectively.

Budownictwo i Architektura, 2020

The paper discusses a fictitious crack model of concrete in tension proposed by Hillerborg. This ... more The paper discusses a fictitious crack model of concrete in tension proposed by Hillerborg. This model presents a concept that illustrates the mechanism of crack initiation and its propagation in concrete on meso-level. It has proven to be a very useful tool for practical use, for both numerical and experimental research. The model was derived from findings on crack mechanisms on more advanced micro- and macro-scale, as presented in this paper. One of the paramount issues regarding crack analysis is the influence of aggregate size on mechanical and fracture parameters of concrete, and also on micro-crack development and associated macro-crack formation. Although significant progress in recognizing crack mechanisms in concrete has been achieved, there are still some aspects that should be studied in depth, for example the role of aggregate particles on crack development. This problem is analysed in the paper as well.

Materials Today Communications, 2020

Research on cementitious materials can provide geometric data on structural topics of interest. S... more Research on cementitious materials can provide geometric data on structural topics of interest. Such structural data should be subjected to a process called "geometric averaging" to be coupled on the engineering level with properties like strength, stiffness or permeability. The prime purpose of this work is to demonstrate that the mathematics underlying the process of going from the materials structure to engineering properties is governed by simple stereology-based constants. Particularly, Cauchy concepts are referred to for expressions relating the length of a curved line in a plane or in space, alternatively of a curved surface in space, to extensions of total projections on lines, respectively planes, in random directions. The two parameters due to Cauchy, i.e., 2/π and 1/2 will be demonstrated dominantly governing the geometric averaging process. The stereological methodology to assess the geometric material parameters and the engineering application of the outcomes are also briefly touched upon in the paper.

Image Analysis & Stereology, 2019

Old theorems by Cavalieri, Buffon and Cauchy that have been mentioned earlier for their relevance... more Old theorems by Cavalieri, Buffon and Cauchy that have been mentioned earlier for their relevance to materials engineering are discussed herein, whereby it is indicated how we applied them on cementbased materials. Specifically, relevant problems treated by the present author are surveyed. Particularly in the presently explored field of porosimetry and permeability estimation of virtual representations of the cement-based materials, it is demonstrated how the stereological framework - in which the theorems are embedded to day - develops with respect to the discussed problems.

MRS Proceedings, 1987

ABSTRACTThe various “building blocks” of a computational mechanics approach to plain and steel fi... more ABSTRACTThe various “building blocks” of a computational mechanics approach to plain and steel fibre reinforced concrete (SFRC) are briefly discussed. Experimental data are incorporated, as well. Theory and experiments deal with debonding as the leading mechanism of structural loosening.

Magazine of Concrete Research, 2017

To assess the pore size of virtual cementitious materials, the star volume method (SVM) can be co... more To assess the pore size of virtual cementitious materials, the star volume method (SVM) can be considered an effective tool. Unfortunately, the SVM requires a large number of plane sections in each of the very large number of random points, resulting in a time-consuming and expensive operation. As a more economical alternative, this paper presents a stereology-based contracted method, which uses a well-known theoretical concept proposed by Cauchy. This method completed pore size measurements in a shorter period of time (reductions as high as 85%) while demonstrating reliability to be maintained at the same level.

International Journal of Design & Nature and Ecodynamics, 2011

Damage in concrete is mostly visualised in sections or at the surface of specimens subjected to i... more Damage in concrete is mostly visualised in sections or at the surface of specimens subjected to internal and/or external loading. It continuously develops by growth and coalescence of tiny cracks into a spatial network structure. This structure can be seen as the fi nger-print of the material refl ecting its history of loadings under given environmental conditions. The methodology of contrast improvement as an essential link in visualising damage is touched upon. However, a major focus of the paper is on describing damage by submitting images of crack patterns consisting of lineal features in the plane to a sweeping test line system and counting intersections. To obtain three-dimensional damage information in an economic way, the damage structure is assumed in the most general case revealing a partial orientation of mixed lineal and planar nature (the so-called 'Stroevenconcept'). The practical cases are elaborated of prevailing compressive and tensile stresses. This reduces the number of unknown crack portions to two. As a consequence, quantitatively analyzing the image patterns can be restricted to vertical sections only. This involves a dramatic reduction of sawing efforts and simplifi es the image analysis stage as well, of course. Only two orthogonal intersection counting operations are required for the assessment of specifi c crack surface area and of the degree and direction of preferred crack orientation. When observations would have been obtained in more directions, so-called roses of intersections (or intersection densities) can be determined. For very large images this would be circles. For random cracks in the image plane a circle around the origin, for oriented cracks, a circle through the origin is found. This concept, in addition to mathematical formulations is employed to demonstrate that automation of quantitative image analysis generally yields biased information, unless the analysis is executed under conditions discussed herein.

Cement and Concrete Research, 2017

A numerical investigation into the influence of the interfacial transition zone on the permeabili... more A numerical investigation into the influence of the interfacial transition zone on the permeability of partially saturated cement paste between aggregate surfaces

Computers and Concrete, 2006

ABSTRACT

Computers & concrete, 2012

ABSTRACT Optimum packing of aggregate is an important aspect of mixture design, since porosity ma... more ABSTRACT Optimum packing of aggregate is an important aspect of mixture design, since porosity may be reduced and strength improved. It may also cause a reduction in paste content and is thus of economic relevance too. Several mathematic packing models have been developed in the literature for optimization of mixture design. However in this study, numerical simulation will be used as the main tool for this purpose. A basic, simple theoretical model is used for approximate assessment of mixture optimization. Calculation and simulation will start from a bimodal mixture that is based on the mono-sized packing experiences. Tri-modal and multi-sized particle packing will then be discussed to find the optimum mixture. This study will demonstrate that computer simulation is a good alternative for mixture design and optimization when appropriate particle shapes are selected. Although primarily focusing on aggregate, optimization of blends of Portland cement and mineral admixtures could basically be approached in a similar way.

Computers & concrete, 2009

ABSTRACT

Computers & concrete, 2011

ABSTRACT Particle packing on meso-level has a significant influence on workability of fresh concr... more ABSTRACT Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physical-mechanical properties of the phases, whereby the ITZ takes up a major position.

A feasibility study was performed of a method for the assessment of the uniformity of carbon fibr... more A feasibility study was performed of a method for the assessment of the uniformity of carbon fibres in cement paste. This proposed method is based on ignition losses of carbon fibres in cement paste Samples were randomly taken from a body of fresh reinforced cement paste. The sample was dried at 110°C to release the free water, weighed (G 1 ) and then put for three hours into a muffle furnace at 850°C to completely incinerate the carbon fibres. Finally, the sample was cooled down to room temperature in dry air and thereupon weighed again (G 2 ). The difference ΔG f between G 2 and G 1 is the ignition loss of a sample and can be considered as the weight of the carbon fibres in the cement paste The Ratio Test of Maximum Likelihood and the F test were used to test the distribution of the samples and the uniformity of the carbon fibre dispersion in the cement paste, respectively The results show that the method of ignition losses offers a simple and efficient tool for selecting and optimizing a dispersion agent for carbon fibres in cementitious materials. The test results show liquid CMC to be an efficient dispersion agent provided applied in sufficient quantity. In the present experiments this amounted to 1.04% of the weight of the cement. For application in practice, the concentration of CMC should be experimentally assessed.

Image Analysis and Stereology Year 2006 Vol 25 Issue 2 75 86, 2006

Structural properties of particulate materials can be described in densities of the particle pack... more Structural properties of particulate materials can be described in densities of the particle packing, more generally denoted as particle composition. Obviously, this global measure does not offer information on the way particles are mutually arranged in space. This is associated with particle configuration. This terminology and the associated categories of material behaviour that rely on either one of these extremes of structural properties are elaborated in this paper. The range of such properties will be between structure-insensitive ones, like mass or stiffness (Young's modulus), and structure-sensitive properties like crack initiation and tensile strength. The establishment of an experimental basis for the dependence of a mechanical property on certain structural features (and the associated micro-mechanical properties) would require extensive, cumbersome and complicated testing: mechanical testing for defining the very property, quantitative (section) image analysis and stereological three-dimensional assessment of the relevant structural features. 'Realistic' simulation of material structure by computer would therefore offer an interesting alternative. This paper introduces the SPACE system (Software Package for the Assessment of Compositional Evolution) as the most recent development in this field. It has been developed to assess the composition as well as configuration characteristics of dense random packing situations in opaque materials. This paper presents an introduction to the system and will thereupon highlight by means of illustrative examples of typical applications on different levels of the microstructure the system's capabilities. Although only a single application can be presented in this framework, they all concern areas of major engineering interest.

Heron 57 2, Jul 30, 2012

Experimental approaches in concrete technology are time-consuming, laborious and thus expensive. ... more Experimental approaches in concrete technology are time-consuming, laborious and thus expensive. Developments in computer facilities render possible nowadays realistically simulating the particulate structure and microstructure of cementitious materials. For that purpose, discrete element methods (DEM) are required because of more correctly simulating particle dispersion. Dynamic DEMs like Delft-produced SPACE and HADES were developed and applied. The approaches are outlined and usage is illustrated by means of assessing particle size effects on packing density of aggregate. Shape simulation is accomplished for simple shape families like ellipsoids and polyhedra. This type of particles is used so far for the simulation of structures consisting of gravel, crushed rock or cement particles.

The establishment of an experimental basis for the dependence of a mechanical property on certain... more The establishment of an experimental basis for the dependence of a mechanical property on certain structural features (and the associated micro-mechanical properties) would require extensive, cumbersome and complicated testing: mechanical testing for defining the very property, quantitative (section) image analysis and stereological three-dimensional assessment of the relevant structural features. `Realistic' simulation of material structure by computer would therefore offer an interesting alternative. This paper introduces the SPACE system (Software Package for the Assessment of Compositional Evolution) as the most recent development in this field. It has been developed to assess the composition as well as configuration characteristics of dense random packing situations in opaque materials. This paper presents an introduction to the system and will thereupon highlight by means of illustrative examples of typical applications on different levels of the microstructure the system...

Transition metal silicides have attracted great attention due to their potential applications in ... more Transition metal silicides have attracted great attention due to their potential applications in microelectronics, ceramics, and the aerospace industry. In this study, experimental and theoretical investigations of tungsten based silicides were performed. Tungsten disilicide (WSi 2) was synthesized by simple thermal treatment at 1350°C for 4 h in an argon atmosphere. These optimal synthesis conditions were obtained by variation of temperatures and times of heating, and the

Journal of the Chinese Ceramic Society, 2003

Thickness of interface transition zone(ITZ) of aggregates in concrete was investigated by a secti... more Thickness of interface transition zone(ITZ) of aggregates in concrete was investigated by a sectional analysis method. The apparent thickness of the ITZ due to non-perpendicular of the section plane to the surface of irregular aggregate particles in sectional analysis, three kinds of aggregate with regular shape (spheroid, elliptical section and rectangular section) were dis-cussed. The relationship between the thickness of apparent ITZ and actually one was also analyzed by a geometrical statistical approach. The results show that the apparent thickness is larger than that of the ITZ actually, and the amplification factor is related to the shape of the aggregate. For square and spherical particle, the ratio between average thickness of the apparent ITZ and actual one is 1.12 and π/2 respectively.

Budownictwo i Architektura, 2020

The paper discusses a fictitious crack model of concrete in tension proposed by Hillerborg. This ... more The paper discusses a fictitious crack model of concrete in tension proposed by Hillerborg. This model presents a concept that illustrates the mechanism of crack initiation and its propagation in concrete on meso-level. It has proven to be a very useful tool for practical use, for both numerical and experimental research. The model was derived from findings on crack mechanisms on more advanced micro- and macro-scale, as presented in this paper. One of the paramount issues regarding crack analysis is the influence of aggregate size on mechanical and fracture parameters of concrete, and also on micro-crack development and associated macro-crack formation. Although significant progress in recognizing crack mechanisms in concrete has been achieved, there are still some aspects that should be studied in depth, for example the role of aggregate particles on crack development. This problem is analysed in the paper as well.

Materials Today Communications, 2020

Research on cementitious materials can provide geometric data on structural topics of interest. S... more Research on cementitious materials can provide geometric data on structural topics of interest. Such structural data should be subjected to a process called "geometric averaging" to be coupled on the engineering level with properties like strength, stiffness or permeability. The prime purpose of this work is to demonstrate that the mathematics underlying the process of going from the materials structure to engineering properties is governed by simple stereology-based constants. Particularly, Cauchy concepts are referred to for expressions relating the length of a curved line in a plane or in space, alternatively of a curved surface in space, to extensions of total projections on lines, respectively planes, in random directions. The two parameters due to Cauchy, i.e., 2/π and 1/2 will be demonstrated dominantly governing the geometric averaging process. The stereological methodology to assess the geometric material parameters and the engineering application of the outcomes are also briefly touched upon in the paper.

Image Analysis & Stereology, 2019

Old theorems by Cavalieri, Buffon and Cauchy that have been mentioned earlier for their relevance... more Old theorems by Cavalieri, Buffon and Cauchy that have been mentioned earlier for their relevance to materials engineering are discussed herein, whereby it is indicated how we applied them on cementbased materials. Specifically, relevant problems treated by the present author are surveyed. Particularly in the presently explored field of porosimetry and permeability estimation of virtual representations of the cement-based materials, it is demonstrated how the stereological framework - in which the theorems are embedded to day - develops with respect to the discussed problems.

MRS Proceedings, 1987

ABSTRACTThe various “building blocks” of a computational mechanics approach to plain and steel fi... more ABSTRACTThe various “building blocks” of a computational mechanics approach to plain and steel fibre reinforced concrete (SFRC) are briefly discussed. Experimental data are incorporated, as well. Theory and experiments deal with debonding as the leading mechanism of structural loosening.

Magazine of Concrete Research, 2017

To assess the pore size of virtual cementitious materials, the star volume method (SVM) can be co... more To assess the pore size of virtual cementitious materials, the star volume method (SVM) can be considered an effective tool. Unfortunately, the SVM requires a large number of plane sections in each of the very large number of random points, resulting in a time-consuming and expensive operation. As a more economical alternative, this paper presents a stereology-based contracted method, which uses a well-known theoretical concept proposed by Cauchy. This method completed pore size measurements in a shorter period of time (reductions as high as 85%) while demonstrating reliability to be maintained at the same level.

International Journal of Design & Nature and Ecodynamics, 2011

Damage in concrete is mostly visualised in sections or at the surface of specimens subjected to i... more Damage in concrete is mostly visualised in sections or at the surface of specimens subjected to internal and/or external loading. It continuously develops by growth and coalescence of tiny cracks into a spatial network structure. This structure can be seen as the fi nger-print of the material refl ecting its history of loadings under given environmental conditions. The methodology of contrast improvement as an essential link in visualising damage is touched upon. However, a major focus of the paper is on describing damage by submitting images of crack patterns consisting of lineal features in the plane to a sweeping test line system and counting intersections. To obtain three-dimensional damage information in an economic way, the damage structure is assumed in the most general case revealing a partial orientation of mixed lineal and planar nature (the so-called 'Stroevenconcept'). The practical cases are elaborated of prevailing compressive and tensile stresses. This reduces the number of unknown crack portions to two. As a consequence, quantitatively analyzing the image patterns can be restricted to vertical sections only. This involves a dramatic reduction of sawing efforts and simplifi es the image analysis stage as well, of course. Only two orthogonal intersection counting operations are required for the assessment of specifi c crack surface area and of the degree and direction of preferred crack orientation. When observations would have been obtained in more directions, so-called roses of intersections (or intersection densities) can be determined. For very large images this would be circles. For random cracks in the image plane a circle around the origin, for oriented cracks, a circle through the origin is found. This concept, in addition to mathematical formulations is employed to demonstrate that automation of quantitative image analysis generally yields biased information, unless the analysis is executed under conditions discussed herein.

Cement and Concrete Research, 2017

A numerical investigation into the influence of the interfacial transition zone on the permeabili... more A numerical investigation into the influence of the interfacial transition zone on the permeability of partially saturated cement paste between aggregate surfaces

Computers and Concrete, 2006

ABSTRACT

Computers & concrete, 2012

ABSTRACT Optimum packing of aggregate is an important aspect of mixture design, since porosity ma... more ABSTRACT Optimum packing of aggregate is an important aspect of mixture design, since porosity may be reduced and strength improved. It may also cause a reduction in paste content and is thus of economic relevance too. Several mathematic packing models have been developed in the literature for optimization of mixture design. However in this study, numerical simulation will be used as the main tool for this purpose. A basic, simple theoretical model is used for approximate assessment of mixture optimization. Calculation and simulation will start from a bimodal mixture that is based on the mono-sized packing experiences. Tri-modal and multi-sized particle packing will then be discussed to find the optimum mixture. This study will demonstrate that computer simulation is a good alternative for mixture design and optimization when appropriate particle shapes are selected. Although primarily focusing on aggregate, optimization of blends of Portland cement and mineral admixtures could basically be approached in a similar way.

Computers & concrete, 2009

ABSTRACT

Computers & concrete, 2011

ABSTRACT Particle packing on meso-level has a significant influence on workability of fresh concr... more ABSTRACT Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physical-mechanical properties of the phases, whereby the ITZ takes up a major position.

A feasibility study was performed of a method for the assessment of the uniformity of carbon fibr... more A feasibility study was performed of a method for the assessment of the uniformity of carbon fibres in cement paste. This proposed method is based on ignition losses of carbon fibres in cement paste Samples were randomly taken from a body of fresh reinforced cement paste. The sample was dried at 110°C to release the free water, weighed (G 1 ) and then put for three hours into a muffle furnace at 850°C to completely incinerate the carbon fibres. Finally, the sample was cooled down to room temperature in dry air and thereupon weighed again (G 2 ). The difference ΔG f between G 2 and G 1 is the ignition loss of a sample and can be considered as the weight of the carbon fibres in the cement paste The Ratio Test of Maximum Likelihood and the F test were used to test the distribution of the samples and the uniformity of the carbon fibre dispersion in the cement paste, respectively The results show that the method of ignition losses offers a simple and efficient tool for selecting and optimizing a dispersion agent for carbon fibres in cementitious materials. The test results show liquid CMC to be an efficient dispersion agent provided applied in sufficient quantity. In the present experiments this amounted to 1.04% of the weight of the cement. For application in practice, the concentration of CMC should be experimentally assessed.

Image Analysis and Stereology Year 2006 Vol 25 Issue 2 75 86, 2006

Structural properties of particulate materials can be described in densities of the particle pack... more Structural properties of particulate materials can be described in densities of the particle packing, more generally denoted as particle composition. Obviously, this global measure does not offer information on the way particles are mutually arranged in space. This is associated with particle configuration. This terminology and the associated categories of material behaviour that rely on either one of these extremes of structural properties are elaborated in this paper. The range of such properties will be between structure-insensitive ones, like mass or stiffness (Young's modulus), and structure-sensitive properties like crack initiation and tensile strength. The establishment of an experimental basis for the dependence of a mechanical property on certain structural features (and the associated micro-mechanical properties) would require extensive, cumbersome and complicated testing: mechanical testing for defining the very property, quantitative (section) image analysis and stereological three-dimensional assessment of the relevant structural features. 'Realistic' simulation of material structure by computer would therefore offer an interesting alternative. This paper introduces the SPACE system (Software Package for the Assessment of Compositional Evolution) as the most recent development in this field. It has been developed to assess the composition as well as configuration characteristics of dense random packing situations in opaque materials. This paper presents an introduction to the system and will thereupon highlight by means of illustrative examples of typical applications on different levels of the microstructure the system's capabilities. Although only a single application can be presented in this framework, they all concern areas of major engineering interest.

Heron 57 2, Jul 30, 2012

Experimental approaches in concrete technology are time-consuming, laborious and thus expensive. ... more Experimental approaches in concrete technology are time-consuming, laborious and thus expensive. Developments in computer facilities render possible nowadays realistically simulating the particulate structure and microstructure of cementitious materials. For that purpose, discrete element methods (DEM) are required because of more correctly simulating particle dispersion. Dynamic DEMs like Delft-produced SPACE and HADES were developed and applied. The approaches are outlined and usage is illustrated by means of assessing particle size effects on packing density of aggregate. Shape simulation is accomplished for simple shape families like ellipsoids and polyhedra. This type of particles is used so far for the simulation of structures consisting of gravel, crushed rock or cement particles.