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See detailPOROSIMETRY BY DOUBLE-RANDOM MULTIPLE TREE STRUCTURING IN VIRTUAL CONCRETE
Stroeven, Piet; L.B.Le, Nghi; Sluys, L.J. et al

in Image Analysis and Stereology (2012), 31(1), 55-63

Two different porosimetry methods are presented in two successive papers. Inspiration for the development came from the rapidly-exploring random tree (RRT) approach used in robotics. The novel methods are ... [more ▼]

Two different porosimetry methods are presented in two successive papers. Inspiration for the development came from the rapidly-exploring random tree (RRT) approach used in robotics. The novel methods are applied to virtual cementitious materials produced by a modern concurrent algorithm-based discrete element modeling system, HADES. This would render possible realistically simulating all aspects of particulate matter that influence structure-sensitive features of the pore network structure in maturing concrete, namely size, shape and dispersion of aggregate and cement particles. Pore space is a complex tortuous entity. Practical methods conventionally applied for assessment of pore size distribution may fail or present biased information. Among them, mercury intrusion porosimetry and 2D quantitative image analysis are popular. The mathematical morphology operator “opening” can be applied to sections and even provide 3D information on pore size distribution, provided isotropy is guaranteed. Unfortunately, aggregate grain surfaces lead to pore anisotropy. The presented methods allow exploration of pore space in the virtual material, after which pore size distribution is derived from star volume measurements. In addition to size of pores their continuity is of crucial importance for durability estimation. Double-random multiple tree structuring (DRaMuTS), presented herein, and random node structuring (RaNoS) provide such information. The latter method will be introduced in a next issue of Image Anal Stereol. [less ▲]

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See detailInfluence of Particle Packing on Elastic Properties of Concrete
He, Huan ULg; Stroeven, Piet; Stroeven, Martijn et al

in Magzine of Concrete Research (2012), 64(2), 163-175

Concrete is a complex composite material. Hence, the main components of concrete on meso-scale should be considered when studying its global elastic properties. As a main ingredient of concrete, aggregate ... [more ▼]

Concrete is a complex composite material. Hence, the main components of concrete on meso-scale should be considered when studying its global elastic properties. As a main ingredient of concrete, aggregate will exert influences on the elastic properties of concrete. In the present study, particularly particle shape and particle packing are considered of relevance. The densely packed structure of arbitrary shaped aggregate is simulated by a concurrent algorithm-based discrete element modelling (DEM) system. A comparison is pursued of data, produced by numerical models, either based on arbitrary angular-shaped particles or on spherical ones. This will be accomplished by means of the finite element method (FEM). The results can be used to evaluate the adequacy for this purpose of conventional numerical or analytical models based on spherical aggregates. The influences exerted on the elastic properties of concrete by other factors, such as the mechanical and physical properties of the aggregate, the ITZ and the matrix will also be addressed in this study. [less ▲]

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See detailOptimization of particle packing by analytical and computer simulation approaches
He, Huan ULg; Stroeven, Piet; Stroeven, Martijn et al

in Computers and Concrete (2012), 9(2), 119-131

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 ... [more ▼]

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. [less ▲]

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See detailParticle packing density and limestone fillers for more sustainable cement
He, Huan ULg; Courard, Luc ULg; Pirard, Eric ULg

in Key Engineering Materials [=KEM] (2012), 517

Cement blending with mineral admixtures, especially with byproduct or waste product powder, can effectively reduce consumption of cement and promote the ecology. Recently, an innovative concept was ... [more ▼]

Cement blending with mineral admixtures, especially with byproduct or waste product powder, can effectively reduce consumption of cement and promote the ecology. Recently, an innovative concept was proposed to replace of “coarse” cement grains by the inert fillers for sustainable cement in the low w/c concrete cement. As a basic mechanism, particle packing plays an important role in such replacement or blending. In the first part of study, the paper discusses the particle packing aspect of cement grains, limestone filler (LF) and LF blended cement. The new developed wet packing method and a dry packing method are proposed for the evaluation purpose. The paper presents results of packing tests with the influences of PSD, cement type, vibration, mixing, blending proportions, etc. The advantages and limitations of two packing methods are also discussed in this paper. [less ▲]

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See detailMethodological approaches to 3D pore structure exploration
Stroeven, Piet; Le, L.B. Nghi; He, Huan ULg

in Key Engineering Materials [=KEM] (2012), 517

About 6% of global CO2 emissions are due to cement production. Blending of Portland cement with a significant fraction of mineral admixture could therefore be instrumental in reducing such emissions. Use ... [more ▼]

About 6% of global CO2 emissions are due to cement production. Blending of Portland cement with a significant fraction of mineral admixture could therefore be instrumental in reducing such emissions. Use of an admixture of vegetable origin such as rice husk as will additionally contribute to waste management and its incineration produces energy. This paper will stress the importance of properly designing such blends. Preferably gap-graded concepts should be employed, since blending efficiency in terms of strength development is promoted as shown in earlier publications. The paper therefore only briefly covers these aspects. Assessment of this blending concept on durability of cementitious materials constitutes a far more complicated problem. This requires careful porosimetry. Mostly, this problem is approached by MIP or by quantitative image analysis. Both can provide 3D information, although that of MIP is generally significantly biased. Quantitative image analysis is however time-consuming and laborious, and thus expensive. Moreover, it does not provide information on continuity of pores. Present day computer facilities offer therefore a better alternative. When using a proper DEM system, the concrete can be simulated in a realistic way. The paper describes new methods for investigating the pore structure in virtual concrete and presents some data on pure cement and blended cement. Differences will have impact on durability risks. [less ▲]

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See detailAsphalt concrete with fly ashes of different sources as filler replacement
Stroeven, Piet; He, Huan ULg; Huu Hanh, Pham

in Key Engineering Materials [=KEM] (2012), 517

Paper presents and discusses data obtained in a testing program on the replacement of limestone powder in asphalt concretes by fly ashes. This would combine economic, environmental and technical benefits ... [more ▼]

Paper presents and discusses data obtained in a testing program on the replacement of limestone powder in asphalt concretes by fly ashes. This would combine economic, environmental and technical benefits. The finest fly ash of Vietnamese origin scored best. This is proposed due to the gap-graded design of the particulate mixture of coarse crushed rock fractions, fine fluvial sand and the mineral admixture. The test program encompassed Marshall tests, creep tests and splitting tensile tests. [less ▲]

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See detailInfluence of Particle Packing on Fracture Properties of Concrete
He, Huan ULg; Stroeven, Piet; Stroeven, Martijn et al

in Computers and Concrete (2011), 8(6), 677-692

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 ... [more ▼]

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. [less ▲]

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See detailCharacterization of fine aggregates in concrete by different experimental approaches
He, Huan ULg; Courard, Luc ULg; Pirard, Eric ULg et al

in Proceedings 13 Int. Congress for Stereology (2011, October)

Being its major component, aggregate can occupy up to three-quarter of the volume of concrete. The structure of aggregate formed in hardened state impacts largely on mechanical and durability properties ... [more ▼]

Being its major component, aggregate can occupy up to three-quarter of the volume of concrete. The structure of aggregate formed in hardened state impacts largely on mechanical and durability properties of concrete. On another hand, physical characteristics of aggregate are primarily assumed to be relevant to granular behavior of aggregate. Therefore, characterization of aggregate is of high relevance to concrete studies. In this study, different types of fine aggregate used in concrete, namely river sand and crushed limestone, are selected for morphological characterization. Traditional sieve analysis and laser diffraction method are employed for separation and size analysis of specimens. Different types of fine aggregate samples with comparable size ranges are then analyzed by two advanced dry (static) and wet (dynamic) image analysers. These new analysers are especially suitable for characterization of fine particles, which is difficult by traditional image analysis equipments. Size and shape characteristics of different fine aggregates will be revealed by different experimental methods. The results on different parameters for shape characterization will be compared and discussed. [less ▲]

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See detail3D EXPLORATION OF PERCOLATED POROSITY IN VIRTUAL CONCRETE
Stroeven, Piet; Le, L. B. N.; He, Huan ULg

(2011, October)

The paper introduces two novel methods developed for porosimetry in DEM-produced virtual concrete. Inspiration came from robotics. Some available methods like quantitative image analysis render possible ... [more ▼]

The paper introduces two novel methods developed for porosimetry in DEM-produced virtual concrete. Inspiration came from robotics. Some available methods like quantitative image analysis render possible assessment of porosity and 3D pore size distribution. For durability applications it is necessary also to know the fraction of porosity that is continuous (percolated). This can be easily obtained from the methods introduced herein. [less ▲]

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See detail2D AND 3D ROUTES TO INVESTIGATING PORES IN CONCRETE
Stroeven, Piet; He, Huan ULg; Le, L. B. N.

(2011, October)

Pores are of crucial engineering significance because they allow water and other harmful substances to enter the material. This paper reviews various methods for porosimetry that are applicable to ... [more ▼]

Pores are of crucial engineering significance because they allow water and other harmful substances to enter the material. This paper reviews various methods for porosimetry that are applicable to cementitious materials. Methods generally provide information on porosity and pore size distribution, yet pore continuity is required for transport, so should be investigated as well. Modern ways to approach such problems make use of computer facilities. Hence, the cementitious materials are produced in our case by a concurrent algorithm-based dynamic DEM system. Two novel methods that additionally render possible investigation of pore continuity are described in a separate paper on this conference [1] [less ▲]

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See detailNumerical assessment of concrete damage: procedures and pitfalls
Stroeven, Piet; He, Huan ULg

in Heron (2011), 56(3), 123-140

The paper focuses on the quality of predicting the damage characteristics of the loaded engineering structure by subjecting section images of cores supposedly drawn from the concrete of the structure to ... [more ▼]

The paper focuses on the quality of predicting the damage characteristics of the loaded engineering structure by subjecting section images of cores supposedly drawn from the concrete of the structure to quantitative image analysis by sweeping test lines. Automation of this data acquisition stage is shown, generally leading to information that is biased to an unknown degree. This is accomplished mathematically and graphically according to Underwood. When the Stroeven/Saltikov (S/S)-concept of a partially linear-planar model for damage is accepted and (four-connexity) digitization is accomplished in a direction adjusted to the prevailing orientation direction of the cracks, the paper shows that orthogonal observations in vertical sections are sufficient for the unbiased assessment of total crack length per unit of area (2D), or specific crack surface area (3D), also when digitized images are employed. This is possible in situations where (uniaxial) compressive or tensile stresses dominate. The crack orientation distribution is however always biased when determined on digitized images in an automated set up when pixel directions are not compensated for, such as by the quantified S/S-concept of damage. [less ▲]

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See detailRobots wijzen de weg
Stroeven, Piet; Sluys, Bert; Le, Nghi et al

in Cement (2011), 122(4), 1-4

Beton is een prachtig materiaal voor constructiedoeleinden. Maar het bezit ook tekortkomingen. Eén daarvan is dat het van nature niet volledig dicht is. Zo kunnen water en de daarin eventueel aanwezige ... [more ▼]

Beton is een prachtig materiaal voor constructiedoeleinden. Maar het bezit ook tekortkomingen. Eén daarvan is dat het van nature niet volledig dicht is. Zo kunnen water en de daarin eventueel aanwezige schadelijke stoffen via het poriesysteem het beton binnendringen en daarmee de duurzaamheid van de wapening of het beton zelf bedreigen. De aandacht van onderzoekers is daarom al geruime tijd op dit fenomeen gericht in de hoop ontwerpparameters van het beton te kunnen relateren aan duurzaamheidrisico’s. Dit vraagt om onderzoek naar het poriesysteem in beton. [less ▲]

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See detailChapter 7 - Impact of Brazil Nut Effect on Concrete’s Structure and its Engineering Properties
Stroeven, Piet; He, Huan ULg

in Doyle, Sophie G. (Ed.) Construction and Building: Design, Materials, and Techniques (2011)

This chapter presents evidence of the impact of the Brazil Nut Effect on concrete’s particulate structure on meso-level (aggregate) as well as on micro-level (cement paste). Brazil nut effect is compared ... [more ▼]

This chapter presents evidence of the impact of the Brazil Nut Effect on concrete’s particulate structure on meso-level (aggregate) as well as on micro-level (cement paste). Brazil nut effect is compared to more commonly recognized features like the wall effect. The information is mostly obtained on virtual concrete produced by discrete element modelling systems. The requirements imposed on such systems are indicated and compared to sequential random addition systems that are still common in concrete technology. In the present case use is therefore made of so called dynamic solutions of physical concurrent algorithm-based modeling systems. Some consequences of BNE for structure and properties are discussed. [less ▲]

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See detailIMAGE ANALYSIS OF CRACKS IN CONCRETE: METHODOLOGY, OPPORTUNITIES AND PITFALLS
Stroeven, Piet; He, Huan ULg

in International Journal of Design and Nature and Ecodynamics (2011), 6(2), 145-161

Damage in concrete is mostly visualized 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 ... [more ▼]

Damage in concrete is mostly visualized 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 finger-print of the material reflecting its history of loadings under given environmental conditions. The methodology of contrast improvement as an essential link in visualizing 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 “Stroeven-concept”). 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 simplifies the image analysis stage as well, of course. Only two orthogonal intersection counting operations are required for the assessment of specific 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. [less ▲]

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See detailDiscrete element modelling approach to assessment of granular properties in concrete
Stroeven, Piet; He, Huan ULg; Stroeven, Martijn

in Journal of Zhejiang University. Science A (2011), 12(5), 335-344

This paper presents the technological relevance of a concurrent algorithm-based discrete element modelling (DEM) system, HADES. This new system is the successor of SPACE that is limited to spherical ... [more ▼]

This paper presents the technological relevance of a concurrent algorithm-based discrete element modelling (DEM) system, HADES. This new system is the successor of SPACE that is limited to spherical grains only. It can realistically simulate the packing of arbitrary-shaped particles up to the fully compacted state. Generation of families of such particles, i.e., generally representing aggregate of fluvial origin and crushed rock, respectively, and the forming way of particulate structure are described. Similarly shaped particles are proposed for simulation of cement paste because of conformity with experimental results obtained by the X-ray tomography method. Technologically relevant territories inside and outside concrete technology are presently explored in this efficient, reliable, and economic way. Some results obtained by this DEM approach are presented. [less ▲]

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See detailParticle packing of concrete containing blended cement
He, Huan ULg; Courard, Luc ULg; Pirard, Eric ULg

Conference (2010, September 20)

Physical particle packing is becoming a hot topic in concrete technology as more and more types of granular materials are used in concrete either for ecological or for engineering purposes. Aggregate is ... [more ▼]

Physical particle packing is becoming a hot topic in concrete technology as more and more types of granular materials are used in concrete either for ecological or for engineering purposes. Aggregate is used as concrete’s skeleton, whereby the particles are stabilized by the cementitious matrix. Packing efficiency governs the spatial characteristics of this structure and thereby influences concrete’s properties. Fine-grained sand can be used to further improve density of the aggregate structure. The particulate cement is also frequently blended by fine mineral admixtures to influence performance of the paste and the properties of the matured concrete. The so-called filler effects increase packing density of the blended cement and possibly reduce water demand. High performance characteristics require suitable blending materials of proper properties (fineness, shape, chemical components, etc.). A number of theoretical packing models have been proposed for prediction of packing characteristics and the resulting concrete properties. A minimum voids ratio has been mathematically derived for certain particle size distributions. This allowed establishment of some optimum graded mixtures for concrete production. On the other hand, the computer simulation approach provides a powerful tool for simulating particle packing. Computational concrete (compucrete) has been developed for a wide range of research purposes. Application of computer simulation to particle packing offers a promising perspective in concrete technology; it provides a proper representation of the heterogeneous concrete material, and renders the possibility of studying the effects of a wide range of technological parameters. In this study, an advanced DEM will be utilized for investigate the packing properties of admixtures blended cement. This new-developed system is capable of packing simulations of arbitrary-shaped particles. Experimental shape analysis of each identical group of particles provides fundamental references of shape simulation strategy. Finally, computer simulation structures of blended cement paste both in fresh and hardened states will be compared with the experimental approach. Correlation of particle packing characteristics and properties of blended cement paste will be analyzed and discussed. Optimization of blending efficiency and improvement of concrete properties are pursued using packing modeling. [less ▲]

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See detailStrategy on simulation of arbitrary-shaped cement grains in concrete
He, Huan ULg; Guo, Zhanqi; Stroeven, Piet et al

in Image Analysis and Stereology (2010), 29

The shape of cement particles plays an important role in the hydration process due to surface dissolution and hardening process. Nevertheless, a spherical particle shape is normally assumed in ... [more ▼]

The shape of cement particles plays an important role in the hydration process due to surface dissolution and hardening process. Nevertheless, a spherical particle shape is normally assumed in conventional simulation systems, because of the inherent simplification in algorithm formulations and corresponding reduced computer time, however, at the cost of possibly biased simulation results. Recently, some reference cement was analyzed by X-ray micro-tomography. The results provide a real experimental database of this cement that yields valuable parameters for simulation of cement hydration. A shape analysis study was conducted with some simpler shape solutions, whereby the X-ray micro-tomography results served as a reference. Based on this analysis, a simulation strategy is proposed as a preferred approach to cement particle simulation. The generation of the densely packed microstructure of fresh cement paste in this study was conducted by using an advanced discrete element method (DEM). [less ▲]

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