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Calcium oxychloride formed in concrete exposed to a calcium chloride (CaCl 2) solution may reduce the durability of cementitious materials. A thermodynamic modeling technique is employed to predict the phase assemblage of the hardened cement paste (HCP) at various temperatures, CaCl 2 concentrations, and types and dosages of supplementary cementitious materials (SCMs) and to explore the degradation mechanism of HCP subjected to the CaCl 2 attack. The results indicate that monocarbonate decomposes under CaCl 2 attack to generate Kuzel's salt, and Kuzel's salt is then replaced by Friedel's salt at an even higher CaCl 2 concentration, while calcium hydroxide (CH) transforms into 3-1-12. The strength loss in HCP is directly proportional to the volume ratio of the solid phases in the HCP before and after chloride attack. Increasing the replacement level of silica fume (SF), fly ash (FA), slag (SL), or metakaolin (MK) reduces the amounts of CH and 3-1-12 formed in HCP. [Display omitted] • Reliable thermodynamic phase diagrams of the Ca(OH) 2 -CaCl 2 -H 2 O system at 5 °C and 25 °C are constructed. • The relationship between the amount of calcium oxychloride formed and CaCl 2 concentration and temperature is established. • 3Ca(OH) 2 ·CaCl 2 ·12H 2 O forms more readily as temperature lowers, whereas higher temperature promotes the formation of CaClOH. • The volume ratio of all solid phases in the HCP after and before chloride attack and strength loss are directly proportional. [ABSTRACT FROM AUTHOR]

Magnesium ammonium phosphate cement (MAPC) is commonly used in the rehabilitation of infrastructure and waste stabilization/solidification. Few studies have investigated the influence of temperature on the phase assemblages of MAPC. A thermodynamic modeling approach is employed to investigate the phase evolution of MAPC at slightly elevated temperatures. The results reveal that when n (MgO)/ n (NH 4 H 2 PO 4) (M/P) is less than 1, MgNH 4 PO 4 ·6H 2 O is predicted to form in the temperature range of 0–6.6 °C. The increase in temperature improves the formation of (NH 4) 2 Mg(HPO 4) 2 ·4H 2 O and MgHPO 4 ·3H 2 O. When the temperature reaches 37.2 °C, MgNH 4 PO 4 ·6H 2 O cannot form in the system. The volume of the solid phase expands as the temperature increases. MgNH 4 PO 4 ·6H 2 O is the stable phase within the temperature range from 0 to 41.2 °C when the M/P is higher than 1. MgNH 4 PO 4 ·H 2 O and traces of MgHPO 4 ·3H 2 O precipitate when the temperature is within a range of 41.2 – 70 °C. The unreacted MgO is thermodynamically stable and not involved in the reaction when the temperature changes. The volume of the solid phases of MAPC with mix proportions of M/P higher than 1 decreases with increasing temperature. • The phase assemblages of MAPC are closely related to M/P and temperature. • The volume of the solid phase expands as the temperature increases when M/P is less than 1. • The volume of the solid phases of MAPC with M/P higher than 1 decreases with increasing temperature. [ABSTRACT FROM AUTHOR]

On the mesoscopic scale, concrete can be treated as a two-phase composite consisting of aggregates and mortar matrix. The geometrical feature of aggregate particles usually has significant impact on the structural evolution of concrete and then affects the macro-mechanical properties. To explore the relation between the aggregate characteristics and the macroscopic properties of material, a variety of packing models of particles such as spheres and ellipsoids have been widely applied in previous studies. In the paper, a family of polyhedron-like particles which are defined as the superball is applied to represent the aggregate particles. Based on the Monte Carlo simulation, the models of concrete mesostructure are generated in a random manner. By combining the semi-periodic models of these particles with the section analysis technique, three parameters (i.e., the volume fraction of aggregates V V , the specific surface area of aggregates S V and the mean free spacing between aggregates λ at the cross-section of the models) can be obtained. On the basis of different particle packing systems, we further study the effect of the aggregate characteristics (e.g., particle size distribution, particle shape, particle packing volume fraction, etc.) on the variation of the interfacial layers (which are caused by the wall effect) near the boundaries of formwork and a series of meaningful results are successively obtained. Based on the simulated results in the work, a more comprehensive insight into the phenomenon of the wall effect in concrete can be gained. It is hoped that the conclusions may provide a helpful guidance for the design of the composite materials. Unlabelled Image • The aggregates in concrete are treated as a series of 3D superball-shaped particles. • Effect of particle characteristics on interfacial layers in concrete is studied. • The characteristic of interfacial layer is quantified by the stereological parameters. [ABSTRACT FROM AUTHOR]

Abstract Continuum percolation in particle systems underlies a wide spectrum of material properties. Previous studies on the percolation phenomena of 2D particle systems focused on the random packing of some simple particles including circles, ellipses, rectangles, etc. In this work, the geometrical model of superellipses which can capture more of essential features of particle shapes from rhombuses via ellipses to rectangles is introduced and an efficient algorithm for detecting the collision of these particles is proposed then. By using finite-size scaling technique, the global percolation thresholds ϕ c for homogeneous systems comprising congruent superellipses with aspect ratio a / b in [0.1, 10.0] and shape parameter m in [0.5, +∞) are explored and the effect of particle characteristic on the values of ϕ c is quantified by an approximately numerical formula. Afterwards, the algorithm of particle percolation is extended to the heterogeneous systems consisting of the binary superellipses with different a / b or m. The dependence of percolation threshold ϕ c for these particulate systems on the number fraction λ of the particles is further studied briefly. The results reveal that ϕ c is closely related to the aspect ratio a / b and parameter m for all the superellipse systems. Besides, for the heterogeneous systems comprising the binary superellipses, the value of ϕ c is not only dependent on the number fraction of these adopted particles but also the specific thresholds of the homogeneous systems comprising the corresponding particles. Graphical ABSTRACT Unlabelled Image Highlights • An efficient algorithm for detecting the collision of superellipses is proposed. • The percolation behavior of particulate system comprising superellipses is studied. • The relation between particle shape and global percolation threshold is quantified. • Percolation threshold is a heavily shape-dependent quantity for soft particle system. [ABSTRACT FROM AUTHOR]

Abstract Concrete canvas (CC) has the potential to become a widely used slope protection material owing to advantages such as flexibility, fast construction with low labor costs, and quick strength development. This article studies the mechanical properties and stability of CC slope protection by comparing it with conventional material (shotcrete). The compressive strength development and tensile strength of CC are first tested. To further improve the tensile strength of CC, an Aramid fiber reinforced sheet (called AFRP) is glued to the surface of CC. The tensile and shear behaviors of FRP-reinforced CC are investigated as well. Then, a finite element model is used to simulate the stability of the slope of CC (FRP-reinforced CC) and shotcrete with different curing times and the stability of CC slope protection under heavy rainfall. The results indicate that FRP-reinforced CC can satisfy the design requirements of slope protection when the height of the slope is below 10 m. Compare with traditional cementitious material (e.g., shotcrete), CC provides a more suitable solution for the rapid and abominable (e.g., heavy rainfall) construction of slope protection. Graphical abstract Unlabelled Image Highlights • SSRFEM is used to evaluate the performance of CC slope protection. • The stability of CC slope protection at early curing age is analyzed. • The stability of CC slope protection for rainfall condition is analyzed. • FRP reinforced CC is used to extend the application of CC in slope engineering. [ABSTRACT FROM AUTHOR]

The influences of modifier and carbonation on the phase assemblage of magnesium oxychloride cement (MOC) are little concerned in the literature. A thermodynamic modeling approach is employed to explore the influencing mechanisms of two commonly used modifiers (i.e. FeSO 4 and KH 2 PO 4) and phase assemblage of MOC under natural and accelerated carbonation. And quantitatively XRD test of the modified or carbonated MOC samples is used to verify the reliability of thermodynamic modeling results. The results indicate that the addition of FeSO 4 ·7H 2 O has no effect on the phase assemblage of MOC, but can improve the formation of 5 Mg(OH) 2 ·MgCl 2 ·8H 2 O (phase 5), whereas KH 2 PO 4 inhibits the formation of phase 5. FeSO 4 ·7H 2 O and KH 2 PO 4 raise the concentration of Mg2+ in pore solution, hence enhancing the stability of phases in the matrix. The carbonate product (i.e. chlorartinite) typically identified in MOC is metastable. The carbonation of MOC may result in the following evolution of Mg-carbonates: chlorartinite → MgCO 3 ·MgCl 2 ·7H 2 O → nesquehonite → hydromagnesite. [ABSTRACT FROM AUTHOR]

Particle morphology is a crucial factor of influencing the prediction of percolation threshold in the study of continuum percolation of particle systems. Previous works on the percolation of particle synthesis mainly focused on spheres, ellipsoids and spherocylinders. In this paper, the newly synthesized superballs which smoothly interpolate between octahedrons, spheres and cubes are introduced, and a simple contact detection algorithm for superballs is proposed. By combing Monte Carlo method and percolation theory, the continuum percolation of randomly orientated congruent overlapping superballs is investigated in detail. The global percolation threshold ψ c for superballs with shape parameter m in [0.5, +∞) are obtained in terms of a finite-size scaling technique. Finally, an analytical approximation for percolation threshold ψ c of superballs is derived and verified by existing data from literature. It is found from the study that when the parameter m varies between 0.5 and 1.0, the percolation threshold ψ c significantly increases with the increasing m , whereas the value of m continues to increase from 1.0 to +∞, ψ c will gradually decrease. We hope this study can provide good guidance for the development of percolation theory about non-spherical particle packing systems. [ABSTRACT FROM AUTHOR]

Concrete canvas (CC) is a promising material in civil and military engineering due to its flexibility, fast construction with low labor cost, and rapid strength development. However, relatively lower tensile and flexural strength limit the application of CC products. This paper presents an experimental study of the improvement of the tensile and flexural strength of CC panels through the employment of external reinforcement by a fiber-reinforced polymer (FRP) sheet. The tensile and flexural behaviors of CC and FRP reinforced CC panels are investigated through uniaxial tensile and four-point bending tests in both warp and weft directions. The bond behavior between FRP sheets and CC is investigated through a single-shear pull-off test, by which both strain distribution and local bond stress-slip relationships are experimentally measured. Experimental results reveal that the tensile and flexural properties, especially the reinforcing efficiency of flexural strength, are significantly improved in the FRP reinforced CC samples. [ABSTRACT FROM AUTHOR]

Magnesium potassium phosphate cement (MKPC) is normally applied in civil engineering because of its short setting time and superior mechanical properties. This study investigates the hydration behavior and hydration products of MKPC influenced by molar ratio between magnesia and phosphate (M/P ratio) through thermodynamic method. Results show that the composition of ultimate hydration products are controlled by concentration of KH 2 PO 4 and MgO, activity of water and pH value of solution. When M/P ratio is lower than 0.64, the hydration product is MgHPO 4 ·3H 2 O; When M/P ratio is between 0.64 and 0.67, the hydration products are MgHPO 4 ·3H 2 O and Mg 2 KH(PO 4 ) 2 ·15H 2 O. When M/P ratio is between 0.67 and 1.00, hydration products are Mg 2 KH(PO 4 ) 2 ·15H 2 O and KMgPO 4 ·6H 2 O; When M/P ratio is higher than 1.00, the hydration product is KMgPO 4 ·6H 2 O together with unreacted MgO. This study also investigated the effect of additives, namely B(OH) 3 , H 3 PO 4 , K 2 HPO 4 and KH 2 PO 4 . [ABSTRACT FROM AUTHOR]

Interfacial transition zone (ITZ) between matrix and aggregate often plays a major role in transport and mechanical behaviors of cementitious composites as its physical nature of relatively high porosity and low rigidity. However, the ITZ thickness may be overestimated via sectional plane analysis technologies, this is attributed to a random sampling plane rarely passing through the normal to the surface of aggregates. So, it is necessary to quantify the overestimation degree of the ITZ thickness. In this study, a methodology to construct the ITZ layer around ellipsoidal aggregate particles is proposed. Then, a systematic line sampling algorithm is employed to obtain the statistical mean value of the ratio of the apparent to the actual ITZ thickness. The influence of aggregate shape and particle size distribution is discussed on the overestimations of the thickness and volume fraction of the ITZ, and the effective diffusivity of three-phase composites using the differential effective medium approximation. Results show that the aggregate shape has a significant impact on the apparent ITZ thickness, which mainly reflects in the sphericity of the aggregate shape. And the ranking of the overestimation of ITZ thickness, ITZ volume fraction and diffusivity for two types of spheroidal aggregate which have the same sphericity with the specified Platonic particle follow: Platonic particle > Oblate ellipsoid > Prolate ellipsoid. Sphericity is not a unique parameter characterizing the influence of particle shape on the overestimation degree of ITZ thickness. For quantification, other shape parameter needs to be developed in the future. We hope this article will be helpful to guide the practice of evaluating the contribution of aggregate particle shape to the ITZ microstructure and the influence of the ITZ on macroscopic performance of composite materials. [ABSTRACT FROM AUTHOR]

The interfacial transition zone (ITZ) between cement paste and aggregate is the weakest part of composites. To quantify the influence of the ITZ on macro-properties of composites, the ITZ area fraction should be considered. In this paper, apparent ITZ thickness around regular polygon and ellipse is determined by using a systematic line sampling algorithm. A generalized formula is proposed to obtain ITZ area fraction of concrete with 2D convex aggregates. Overestimation of ITZ area fraction and concrete diffusivity are calculated. Our study demonstrates that aggregate shape exerts an unneglectable impact on the ITZ thickness, and further on macro-properties of composites. [ABSTRACT FROM AUTHOR]

The interfacial transition zone (ITZ) between matrix and aggregate is a weak region because of its physical nature of relatively high porosity and low rigidity. ITZ microstructural configurations such as its thickness and volume fraction play an important role in transport and mechanical behaviours of cementitious composites. However, such ITZ characteristics are usually overestimated since random sampling planes from conventional sectional plane analysis technologies rarely pass through the normal to the surface of anisotropic aggregates. In this study, we first propose a normal line sampling (NLS) algorithm to evaluate the overestimation degrees of these microstructures for complex geometrical shaped aggregates like Platonic particles. The NLS algorithm applies the sampling lines along the normal of aggregate boundary at the given section plane that is significantly different from the previous methods in the literature. Then, the ITZ volume fraction can be determined by the ITZ thickness according to a generalized formula. We also extend these practical ITZ characteristics to estimate the effective diffusivity of cementitious composites by the classical effective medium approximation. The derived results show that the ratio of the apparent ITZ thickness to the actual ITZ thickness is dependent on the sphericity which is a shape descriptor of particles. Moreover, the overestimation degree of ITZ volume fraction and diffusivity of three-phase composites are governed by aggregate volume fraction, particle size distribution and particle shape. Finally, the results reflect that the aggregate shape has a significant effect on the apparent ITZ thickness, and the sampling process of ITZ thickness by using NLS algorithm is similar to the sampling techniques in experiment. [ABSTRACT FROM AUTHOR]

• A generalized implicit solution is developed to capture the ITZ percolation threshold. • ITZ percolation threshold of concretes including poly-shaped aggregates are obtained. • Coupling effect of aggregate shape- and size-polydispersities on ITZ percolation is suited. • Influence of aggregate shape- and size-polydispersities on diffusivity is investigated. Concrete is usually assumed to be a three-phase particulate composite composed of aggregate, cement paste and interfacial transition zone (ITZ) around the aggregate. Due to the high porosity of the ITZ, the transport of aggressive media in the ITZ is more rapid than that in the cement paste. However, it is still unclear how concrete components, like ITZ thickness and aggregate shape- and size-polydispersities affect the ITZ percolation threshold. This paper develops a generalized implicit solution to establish the quantitative relationship between the ITZ percolation threshold and concrete components using an analogy between lattice and continuum percolation. The reliability of the generalized implicit solution is confirmed by comparing the theoretically calculated ITZ percolation thresholds with the numerical results in this work and other literature. The concrete diffusivity is also predicted by combining the obtained ITZ percolation threshold with the differential effective medium approximation and the multi-component percolation-based effective medium model. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, granular phase change material (PCM) composites were developed by absorbing paraffin into the pores of expanded perlite particles with two grades of particle size. Because of the different particle sizes and pore structures, the absorption mechanisms of the expanded perlite particles were found to differ. A significant amount of paraffin leakage was found when the PCM composites were applied directly into the cement mixture. To prevent such leakage, a new method by using hydrophobic silane was investigated as surface modification for the PCM composites. The method was then compared with nanosilica deposition method. Although both methods prevented leakage effectively, cement composites incorporating silane-modified PCM composites had lower compressive strength than those incorporating nanosilica modified PCM composites. Thermal performances of expanded perlite/paraffin composites were compared with that of microencapsulated PCM and the results showed expanded perlite/paraffin composites were superior under certain conditions. [ABSTRACT FROM AUTHOR]

Concrete canvas (CC for short), which is a flexible cement powder impregnated fabric that hardens on hydration to form a thin, durable water proof and fire-resistant concrete layer, has been used in slope protection, and CC may also have widely potential application in retaining wall structure. This article presents the design methodology for the CC-faced reinforced soil retaining wall structure according to the mechanical properties of CC. The result demonstrates that carbon nanotube (CNT) modified ultra-high molecular weight polyethylene (UHMWPE) unidirectional fabric reinforced CC can be applied to the reinforced soil retaining wall with a height of between 3 m and 10 m, and reasonable spacing of reinforcements is 0.5 ∼ 1 m. In addition, the connection between the reinforcement and CC wall can be safely against bearing capacity failure. Finally, the results of a FEM parametric study indicate that the horizontal displacement of CC is a little large (about 20 mm @ 6 m height retaining wall). Relative large maximum displacement of the CC wall indicates that the high stiffness reinforcement should be used to reduce the overall horizontal displacement of the wall. [ABSTRACT FROM AUTHOR]

We investigated the integration of form-stable paraffin/nanosilica composites into vacuum insulation panels (VIPs) to improve the thermal mass. In total, six form-stable paraffin/nanosilica composites were produced by absorbing paraffin in different types of nanosilica with different surface characters, hydrophobic and hydrophilic. In view of cost, a phase change material (PCM) composite prepared by hydrophilic precipitated silica was chosen to produce the PCM-integrated VIPs. The microstructure and phase change behaviour of the PCM composites were investigated. The thermal mass of the PCM-integrated VIPs was found to be improved. With integration of PCM the thermal conductivity of the VIPs was increased, although it was still very low compared to normal foam insulations. [ABSTRACT FROM AUTHOR]

Determining the overlapping degree of interfaces around solids is an open problem with great significance in a variety of materials. So far, this search has been performed only on a case-by-case basis, particularly for hard spherical particles. Here, we present a generalized scheme to evaluate analytically the interfacial overlapping degree with complex convex particles. It is essentially an extension of spheres to complex convex particles like convex polyhedrons and ellipsoids for the interfacial overlapping degree. Additionally, a numerical model is also proposed to numerically derive the interfacial overlapping degree on the basis of the Minkowsky addition manner. Comparing with the theoretical data reported in the literature and numerical results from the present numerical model, the proposed theoretical scheme is confirmed with a favorable reliability. Furthermore, we find a quantitative mechanism between the interfacial overlapping degree and the surface configurations of convex particles. Such a mechanism can be used as a theoretical criterion to provide guidance for practical industries of composite media. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) has been investigated by many researchers who have studied its hydration products and properties. Previous works mainly concentrated on experimental studies. This study uses a thermodynamic approach to understand the formation conditions of two major hydration products of MOC, Mg 3 (OH) 5 Cl · 4H 2 O (phase 5) and Mg 2 (OH) 3 Cl · 4H 2 O (phase 3) at room temperature. The hydration reaction equilibrium of MOC phases has been predicted by using the geochemistry speciation code PHREEQC together with the extended ‘Pitzer.dat’ database. The results show that the formation of the hydration products are controlled by MgCl 2 concentration, activity of H 2 O and pH values of the system. The equilibrium of solid phase diagram, the solubility of different hydration phases are consistent with those results obtained from experimental studies, which validates the thermodynamic model. The phase diagram provides qualitative insights on the synthesis of pure phase 3 and phase 5. For MgO-MgCl 2 -H 2 O system, the minimum MgCl 2 concentration for phase 5 and phase 3 to form are 1.47 mol · kg − 1 and 2.25 mol · kg − 1 , respectively. Increasing water volume can result in the transformation from phase 5 and phase 3 to brucite. Additionally, the stability analysis suggests that phase 5 prefers to formation at a higher condition of the a Mg 2 +, pH and a H2O as compared to the phase 3. Phosphate can significantly influence the hydration products composition of MOC during hydration but no new phosphate appears. [ABSTRACT FROM AUTHOR]

Thermal energy storage composites were developed by incorporating granular phase change materials (PX25 from Rubitherm®) into cement paste. Without prevention, however, a significant amount of phase change material (paraffin) leaked from the PX25 during the fabrication process. To prevent paraffin leakage during fabrication, three types of nano-SiO 2 powder (hydrophilic fumed silica (fs1), hydrophobic fumed silica (fs2), and precipitated silica (ps2)) were chosen to modify PX25. The influence of dosage of these modifiers was investigated with reference to PCM leakage during fabrication. Paraffin leakage was eliminated when hydrophobic fs2 or ps2 was used in a 2.3% and 9.0% mass fraction (relative to PX25), respectively. However, hydrophilic fs1 did not prevent leakage of paraffin. Microstructural and mechanical analyses of the thermal energy storage composites were used to analyze the prevention mechanism of hydrophobic nano-powder against paraffin leakage. [ABSTRACT FROM AUTHOR]

• Temperature in a lower range has little effect on the phase assemblage of MOC. • Phase 5 is not predicted to form at higher temperatures. • phase 3 and brucite become stable at higher temperatures. • MOC samples with the optimal proportion cured at higher temperatures experience volume shrinkage. • The volume of MOC with a high content of H 2 O or MgCl 2 expands with increasing curing temperature. Magnesium oxychloride cement (MOC) is usually applied in industrial flooring, thermal insulation wall panels, flue pipes and grinding wheels. However, studies on the influence of temperature on the phase assemblage in MOC are limited and inconsistent. A thermodynamic modeling approach is employed to explore the influence of temperature on the stable hydrate assemblage in MOC. The results reveal that at lower temperatures, a variation in temperature has little effect on the hydrate phase assemblage in MOC, and the volume deformation of the samples prepared with the optimal proportion is very small. Phase 3 and brucite become stable phases at relatively higher temperatures. MOC samples prepared with the optimal proportion cured at higher temperatures experience volume shrinkage. [ABSTRACT FROM AUTHOR]

Abstract: This contribution first presents a fatigue model to elaborate fatigue behavior of materials subjected to thermal mechanical effect. To calibrate the presented model, a valid experiment is then conducted on cement asphalt mortar. The model can be further extended to other materials and valid experimental data from literature is utilized for verification. Results suggested the model is sufficient to describe thermo-mechanical fatigue behavior of cement-based materials, under the condition that no phase or morphological change occurred in the fatigue temperature range. Finally, the developed model is applied to predict fatigue life of one current track. [Copyright &y& Elsevier]

Abstract: Crack-repairing technology via embedded capsules containing repair-agent is becoming a promising approach to sustain the performance of structure materials. From the viewpoint of geometric probability and the application of concept of integral geometry, this contribution aims to develop and determine the theoretical solution on dosage of capsules required to repair the cracks. Based on a general fact that the capsules are randomly dispersed in the matrix and the discrete cracks occur independently in matrix, we present the probability of capsules hit by the cracks to develop the theoretical solution on dosage of capsules for self-healing technology via embedded capsules in two- and three-dimensional self-healing system. Then, according to the targeted healing level, a philosophy proposed to fulfill the healing expectations from the probabilistic (risk-based) healing approach, the volume fraction of capsules required in the matrix is determined. At the same time, under the assumption that the healing capacity of a capsule is sufficient to repair the crack meeting the capsule, it shows that the volume fraction of capsules required is opposite to the size of cracks as the cracks grow. Also the influence of the elongated capsules fabricated with different aspect ratios on the hitting probability is discussed and it shows that for discrete cracks mode the hitting probability of elongated capsules with aspect ratio is not always larger than that of spherical capsules. The hitting probability referred the size, shape and amount of capsules and the geometric characterizations of cracks would be helpful for designing self-healing materials with pre-embedded capsules. Finally, computer simulation is employed to verify the reliability of these theoretical models. [Copyright &y& Elsevier]

Abstract: Particulate composites are composed of random packing of polydispersed particles, such as cementitious composites. The packing behavior of particles plays an important role in the mesostructural evolution of particulate composites. The preponderance of previous works has focused on the random packing of spherical, cylindrical or elliptical particles, and little is known about ellipsoidal particles. In the present work, a contact detection algorithm of ellipsoids is presented in detail, which can quantitatively describe relative positions of ellipsoids in a three-dimensional space. The accuracy and efficiency of the algorithm are tested and compared with algorithms developed in previous literature, and its reliability is verified by a random sequential packing model of polydispersed ellipsoids with semi-periodic boundary conditions. Moreover, the algorithm is applied to simulate a mesostructure model of cementitious composites. By means of stereological tools and section analysis technologies, the mesostructure of cementitious composites is quantitatively characterized. Finally, the reliability of the statistical results from the present methodology is verified by valid experimental and theoretical results. [Copyright &y& Elsevier]

Abstract: Random packing of particles in cement-based materials plays an important role in microstructural evolution. The preponderance of preview work has focused on the microstructural model by the random packing of spherical or two-dimensional elliptical particles, and little is known about three-dimensional ellipsoidal particles. In the present work, a new random packing model of three-dimensional ellipsoidal particles was developed to simulate microstructure of cement-based materials. It was based on a novel numerical algorithm for detecting the contact of ellipsoidal particles. The accuracy and reliability of the algorithm were verified by a visualization of the random packing of monodispersed ellipsoidal particles with rigid boundary conditions. According to these numerical algorithms, microstructural model of cement-based materials was constructed by the random packing of polydispersed ellipsoidal particles, of which sizes satisfy a specific distribution. Finally, applied stereological tools and serial sectioning analysis technique, microstructure of cement pastes, composed of ellipsoidal cement particles, was characterized and compared with that of spherical cement particles. [Copyright &y& Elsevier]

Abstract: Nuclei of unhydrated cement particles left in hardened cement paste after maturation can provide self-healing capability to micro-cracked matrix under favorable conditions. In this present study, a model study is conducted to characterize the influence of hydration reaction of the unhydrated cement nuclei on self-healing efficiency of cracks in hardened cement paste. Based on two different cracking modes of unhydrated cement nuclei, i.e., the splitting crack mode and the dome-like crack mode, the mathematical expressions on the self-healing efficiency are presented from the viewpoint of geometrical probability. Recurring to a generalized hydration reaction model of cement particles, the self-healing efficiency model quantitatively consider the influence of the volume fraction, particle size distribution and cracking modes of unhydrated cement nuclei randomly distributed in hardened cement paste. [Copyright &y& Elsevier]

[Display omitted] • A new algorithm is proposed to detect whether the inter-oval crack contact or not. • Percolation behaviors of polydispersed oval crack are investigated. • Coupling effect of shape- and size-polydispersity on percolation is suited. • Influence of crack's polydispersity on permeability of fractured concrete is present. Crack's shape- and size-polydispersities affect the macro-property of concrete attributed to the changes of microstructure. In particular, the percolation of crack networks causes dramatic changes of concrete's macro-property, such as diffusivity, thermal conductivity and permeability. This work quantitatively captures the percolation thresholds of complex crack networks comprising shape- and size-polydispersed oval cracks, and their effects on the permeability of concrete. Comparing of experimental and numerical data from literature with our results, the reliability of the proposed theoretical framework in this work is verified. The results reveal that the synergistic effect of shape- and size-polydispersities on the percolation threshold can be quantified by introducing an increment to correct the thresholds of polyshaped-monosized crack network. And the influence of the cracks' shape, size-polydispersity on concrete's permeability can be attributed to the effects of the above factors on the percolation threshold as well as surface area of cracks per unit volume of concrete. [ABSTRACT FROM AUTHOR]

Abstract: Sectional analysis is commonly used to characterize qualitatively and quantitatively the interfacial transition zone (ITZ) of concrete, especially its thickness. However, the normal of the sectioning plane is in general not perpendicular to the normal of the aggregate surface due to the irregularity of the shape of the aggregates. Therefore, the sectional approach overestimates ITZ thickness. Calculating the degree of overestimation is key to obtain a precise measure of ITZ thickness and therefore the influence of the ITZ on the macro-properties of composites. However, the irregularity of the aggregates makes this a difficult task. In this contribution, some related theorems and results from geometrical probability were used to study the relationship between the statistical value of the apparent ITZ thickness and actual ITZ thickness. General solutions are derived for an arbitrary convex-shaped aggregate grain for both two- and three-dimensional cases. [Copyright &y& Elsevier]