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Claire E White - One of the best experts on this subject based on the ideXlab platform.
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symmetry induced stability in alkali doped Calcium Silicate Hydrate
Journal of Physical Chemistry C, 2019Co-Authors: Ongun V Ozcelik, Nishant Garg, Claire E WhiteAbstract:CO2 emissions originating from the construction industry have a significant impact on global warming where the production of ordinary Portland cement clinker is responsible for ∼8% of all human-made CO2. Alkali-doped Calcium Silicate Hydrate (C-S-H) is a critical Silicate material in industry since the use of blended cements and alkali-activated materials in construction can substantially reduce human-made CO2 emissions. However, the effect of alkali doping (Na and K) on the long-term stability and associated durability of C-S-H remains an open question. Here, using first-principles quantum chemistry calculations on the model crystalline phase clinotobermorite, we show that there is a strong interplay between the thermodynamic stability of alkali-doped C-S-H and the symmetry of the alkali atoms in the structure. Our results reveal that a symmetrical distribution of alkali atoms leads to a higher stability value such that stable structures with moderate alkali concentrations can be obtained provided that t...
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symmetry induced stability in alkali doped Calcium Silicate Hydrate
arXiv: Materials Science, 2018Co-Authors: Ongun V Ozcelik, Nishant Garg, Claire E WhiteAbstract:CO$_2$ emissions originating from the construction industry have a significant impact on global warming where the production of ordinary Portland cement clinker is responsible for approximately 8\% of all human-made CO$_2$. Alkali doped Calcium-Silicate-Hydrate (C-S-H) is a critical Silicate material since the use of blended cements and alkali-activated materials in construction industry can substantially reduce human-made CO$_2$ emissions. However, the effect of alkali doping (Na and K) on the long-term stability and associated durability of C-S-H remains an open question. Here, using first principles quantum chemistry calculations on the model crystalline phase clinotobermorite, we show that there is a strong interplay between the thermodynamic stability of alkali doped C-S-H and the symmetry of the alkali atoms in the structure. Our results reveal that a symmetrical distribution of alkali atoms leads to a higher stability value such that stable structures with moderate alkali concentrations can be obtained provided that the alkali atoms are allowed to settle into a symmetrical distribution. We investigate the associated structural mechanisms by calculating the migration barriers of alkali atoms within the material, the electronic charge distribution in the material and the variation of basal spacing by using both computational methods and X-ray diffraction analysis.
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nanoscale charge balancing mechanism in alkali substituted Calcium Silicate Hydrate gels
Journal of Physical Chemistry Letters, 2016Co-Authors: Ongun V Ozcelik, Claire E WhiteAbstract:Alkali-activated materials and related alternative cementitious systems are sustainable technologies that have the potential to substantially lower the CO2 emissions associated with the construction industry. However, these systems have augmented chemical compositions as compared to ordinary Portland cement (OPC), which may impact the evolution of the Hydrate phases. In particular, Calcium-Silicate-Hydrate (C–S–H) gel, the main Hydrate phase in OPC, is likely to be altered at the atomic scale due to changes in the bulk chemical composition, specifically via the addition of alkalis (i.e., Na or K) and aluminum. Here, via density functional theory calculations, we reveal the presence of a charge balancing mechanism at the molecular level in C–S–H gel (as modeled using crystalline 14 A tobermorite) when alkalis and aluminum atoms are introduced into the structure. Different structural representations are obtained depending on the level of substitution and the degree of charge balancing incorporated in the st...
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in situ x ray pair distribution function analysis of accelerated carbonation of a synthetic Calcium Silicate Hydrate gel
Journal of Materials Chemistry, 2015Co-Authors: Antoine E Morandeau, Claire E WhiteAbstract:Calcium–Silicate–Hydrate (C–S–H) gel is the main binder component in Hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic Calcium–Silicate–Hydrate gel exposed to pure CO2 vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as the C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline Calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual Calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous Calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.
Dongshuai Hou - One of the best experts on this subject based on the ideXlab platform.
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modified lucas washburn function of capillary transport in the Calcium Silicate Hydrate gel pore a coarse grained molecular dynamics study
Cement and Concrete Research, 2020Co-Authors: Dongshuai Hou, Pan Wang, Muhan Wang, Wei Zhang, Ming Sun, Jinrui ZhangAbstract:Abstract Water migration in the gel pore of the Calcium Silicate Hydrate (C-S-H) influences the durability of cement-based material. The water transport in nanoscale gel pore is dramatically different from transport in capillary pore that is governed by the Lucas-Washburn (L-W) function. Coarse grained molecular dynamics (CGMD) is first utilized to model the capillary transport process of water in the 8 nm channel of C-S-H gel. A new capillary transport model is proposed by modifying the classic L-W function, taking into consideration the effects of dynamic contact angle and inertia force, slip length next to interior walls of gel pore and viscosity variation for liquid ultra-confined in nanopores. Theoretical modification reaches reasonable agreement with CGMD results. The effect of pore size on capillary transport is then simulated to confirm the model's transferability. The new model is helpful to understand the transport behavior of liquid in the gel pore of cement-based material.
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Molecular dynamics simulation study on interfacial shear strength between Calcium-Silicate-Hydrate and polymer fibers
Construction and Building Materials, 2020Co-Authors: Pan Wang, Muhan Wang, Dongshuai Hou, Yue Zhang, Gang Qiao, Jinrui Zhang, Xinpeng WangAbstract:Abstract The macroscopic mechanical performance of fiber reinforced concrete (FRC) is determined by the interfacial microstructure and the interfacial bonding properties between hydration products and fibers. This research is dedicated to study the interfacial shear strength, structure and dynamics between Calcium-Silicate-Hydrate (C-S-H) and polymer fibers. To better understand the effects of fiber types on the interfacial shear strength, three kinds of fibers were investigated, including polypropylene (PP), polyvinyl alcohol (PVA) and polyacrylic acid (PAA). The calculation results indicate that the interfacial shear strength is closely related to the fiber types. The interfacial shear strength of fibers restricted in the C-S-H substrate was arranged in the following order PAA fiber > PVA fiber > PP fiber. After measuring the interfacial shear strength, the static molecular structure and dynamics properties, especially at the interface between the fiber and the C-S-H matrix, the cause for the interfacial shear strength discrepancy between different fibers was uncovered. It shown that the Ca atoms in the interface play an important role in the interfacial bonding interactions by the formation of OCSH-Ca-Opolymer connection. The H bonds can be formed between PAA/PVA fibers and C-S-H substrate, also provide some contribution for enhancing the interfacial bonding strength. The chemical bond stability revealed that the interfacial bonding strength of three fibers follows the order of PAA fiber > PVA fiber > PP fiber, which is consistent with the order of interfacial shear strength.
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atomistic insights into cesium chloride solution transport through the ultra confined Calcium Silicate Hydrate channel
Physical Chemistry Chemical Physics, 2019Co-Authors: Pan Wang, Qingen Zhang, Muhan Wang, Bing Yin, Dongshuai Hou, Yue ZhangAbstract:The transport of water and ions in the gel pores of Calcium Silicate Hydrate (C–S–H) determines the durability of cement material. In this study, molecular dynamics was employed to investigate the capillary imbibition process of CsCl solution in the C–S–H channel. The advanced frontier of CsCl solution flow inside the C–S–H capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the C–S–H substrate. Reynolds number calculations show that the transport process is laminar flow and dominated by viscous forces. The invading depth of the CsCl solution deviates from the theoretical prediction of the classic Lucas–Washburn (L–W) equation, but the modified theoretical equation, by incorporating the effect of slip length, dynamic contact angle, and effective viscosity into the L–W equation, can describe the penetration curve of the solution very well. The validity of our developed theoretical equation was confirmed by additional systems with different ion concentrations. In addition, the local structure of ions was analyzed to elucidate the effect of ion concentration on the transport process. The adsorption and accumulation of ions retard the transport process of water. With an increase in the ionic concentration, the effects of immobilization and cluster accumulation became more pronounced, further reducing the transport rate of water. This study provides fundamental insight into the transport behavior of liquid in the gel pores of cement-based material.
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insights into the interfacial strengthening mechanisms of Calcium Silicate Hydrate polymer nanocomposites
Physical Chemistry Chemical Physics, 2018Co-Authors: Guoqing Geng, Dongshuai Hou, Pan Feng, Yang Zhou, Jinyang JiangAbstract:The mechanical properties of organic/inorganic composites can be highly dependent on the interfacial interactions. In this work, with organic polymers intercalated into the interlayer of inorganic Calcium Silicate Hydrate (C-S-H), the primary binding phase of Portland cement, great ductility improvement is obtained for the nanocomposites. Employing reactive molecular dynamics, the simulation results indicate that strong interfacial interactions between the polymers and the substrate contribute greatly to strengthening the materials, when C-S-H/poly ethylene glycol (PEG), C-S-H/poly acrylic acid (PAA), and C-S-H/poly vinyl alcohol (PVA) were subject to uniaxial tension along different lattice directions. In the x and z direction tensile processes, the Si–O⋯Ca bonds of the C-S-H gel, which were elongated and broken to form Si–OH and Ca–OH, play a critical role in loading resistance, while the incorporation of polymers bridged the neighboring Silicate sheets, and activated more the hydrolytic reactions at the interfaces to avoid strain localization, thus increasing the tensile strength and postponing the fracture. On the other hand, Si–O–Si bonds of C-S-H mainly take the load when tension was applied along the y direction. During the post-yield stage, rearrangements of Silicate tetrahedra occurred to prevent rapid damage. The polymer intercalation further elongates this post-yield period by forming interfacial Si–O–C bonds, which promote rearrangements and improve the connectivity of the defective Silicate morphology, significantly improving the ductility. Among the polymers, PEG exhibits the strongest interaction with C-S-H, and thus C-S-H/PEG possesses the highest ductility. We expect that the molecular-scale mechanisms interpreted here will shed new light on the stress-activated chemical interactions at the organic/inorganic interfaces, and help eliminate the brittleness of cement-based materials on a genetic level.
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uniaxial tension study of Calcium Silicate Hydrate c s h structure dynamics and mechanical properties
Materials and Structures, 2015Co-Authors: Dongshuai Hou, Jinrui Zhang, Yu ZhuAbstract:Calcium Silicate Hydrate (C–S–H) gels, the main binding phase of cement paste, determine the mechanical properties of cementitious materials. In order to obtain the cohesive force in C–S–H gel, molecular dynamics was carried out to simulate the uniaxial tension test on C–S–H model along x, y and z direction. Due to the structure and dynamic differences of the layered structure, C–S–H model demonstrates heterogeneous mechanical behavior. The Calcium Silicate layer, constructed by Ca–O and Si–O ionic-covalent bonds, has stronger cohesive force than that of interlayer H-bond network. In addition, composition influence on mechanical performance has been investigated by variation of the Ca/Si ratio. High Calcium content, de-polymerizing the Silicate chain structure in C–S–H gel, weakens uniaxial tension strength and elastic modulus in three directions. More water molecules penetration into the defective Silicate region further reduces the mechanical properties of C–S–H gel at high Ca/Si ratio. Composition analysis at nano-scale can provide molecular insights on the cementitious materials design with different Ca/Si ratios.
Ongun V Ozcelik - One of the best experts on this subject based on the ideXlab platform.
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symmetry induced stability in alkali doped Calcium Silicate Hydrate
Journal of Physical Chemistry C, 2019Co-Authors: Ongun V Ozcelik, Nishant Garg, Claire E WhiteAbstract:CO2 emissions originating from the construction industry have a significant impact on global warming where the production of ordinary Portland cement clinker is responsible for ∼8% of all human-made CO2. Alkali-doped Calcium Silicate Hydrate (C-S-H) is a critical Silicate material in industry since the use of blended cements and alkali-activated materials in construction can substantially reduce human-made CO2 emissions. However, the effect of alkali doping (Na and K) on the long-term stability and associated durability of C-S-H remains an open question. Here, using first-principles quantum chemistry calculations on the model crystalline phase clinotobermorite, we show that there is a strong interplay between the thermodynamic stability of alkali-doped C-S-H and the symmetry of the alkali atoms in the structure. Our results reveal that a symmetrical distribution of alkali atoms leads to a higher stability value such that stable structures with moderate alkali concentrations can be obtained provided that t...
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symmetry induced stability in alkali doped Calcium Silicate Hydrate
arXiv: Materials Science, 2018Co-Authors: Ongun V Ozcelik, Nishant Garg, Claire E WhiteAbstract:CO$_2$ emissions originating from the construction industry have a significant impact on global warming where the production of ordinary Portland cement clinker is responsible for approximately 8\% of all human-made CO$_2$. Alkali doped Calcium-Silicate-Hydrate (C-S-H) is a critical Silicate material since the use of blended cements and alkali-activated materials in construction industry can substantially reduce human-made CO$_2$ emissions. However, the effect of alkali doping (Na and K) on the long-term stability and associated durability of C-S-H remains an open question. Here, using first principles quantum chemistry calculations on the model crystalline phase clinotobermorite, we show that there is a strong interplay between the thermodynamic stability of alkali doped C-S-H and the symmetry of the alkali atoms in the structure. Our results reveal that a symmetrical distribution of alkali atoms leads to a higher stability value such that stable structures with moderate alkali concentrations can be obtained provided that the alkali atoms are allowed to settle into a symmetrical distribution. We investigate the associated structural mechanisms by calculating the migration barriers of alkali atoms within the material, the electronic charge distribution in the material and the variation of basal spacing by using both computational methods and X-ray diffraction analysis.
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nanoscale charge balancing mechanism in alkali substituted Calcium Silicate Hydrate gels
Journal of Physical Chemistry Letters, 2016Co-Authors: Ongun V Ozcelik, Claire E WhiteAbstract:Alkali-activated materials and related alternative cementitious systems are sustainable technologies that have the potential to substantially lower the CO2 emissions associated with the construction industry. However, these systems have augmented chemical compositions as compared to ordinary Portland cement (OPC), which may impact the evolution of the Hydrate phases. In particular, Calcium-Silicate-Hydrate (C–S–H) gel, the main Hydrate phase in OPC, is likely to be altered at the atomic scale due to changes in the bulk chemical composition, specifically via the addition of alkalis (i.e., Na or K) and aluminum. Here, via density functional theory calculations, we reveal the presence of a charge balancing mechanism at the molecular level in C–S–H gel (as modeled using crystalline 14 A tobermorite) when alkalis and aluminum atoms are introduced into the structure. Different structural representations are obtained depending on the level of substitution and the degree of charge balancing incorporated in the st...
Sowhsin Chen - One of the best experts on this subject based on the ideXlab platform.
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microstructural changes of globules in Calcium Silicate Hydrate gels with and without additives determined by small angle neutron and x ray scattering
Journal of Colloid and Interface Science, 2013Co-Authors: Weishan Chiang, Emiliano Fratini, Piero Baglioni, Francesca Ridi, Sunghwan Lim, Yiqi Yeh, Sungmin Choi, User Jeng, Sowhsin ChenAbstract:Abstract The microstructure of Calcium–Silicate–Hydrate (C−S−H) gel, a major Hydrated phase of Ordinary Portland Cement, with and without polycarboxylic ether (PCE) additives is investigated by combined analyses of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) data. The results show that these comb-shaped polymers tend to increase the size of the disk-like globules but have little influence on the thickness of the water and Calcium Silicate layers within the globules. As a result, the fractal packing of the globules becomes more open in the range of a few hundred nanometers, in the sense that the mass fractal dimension diminishes, since the PCE adsorption on the globules increases the repulsive force between and polydispersity of the C−S−H units. Moreover, scanning electron microscope (SEM) study of the synthesized C−S−H gels in the micrometer range shows that the PCEs depress the formation of fibrils while enhancing the foil-like morphology.
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dynamic behavior of hydration water in Calcium Silicate Hydrate gel a quasielastic neutron scattering spectroscopy investigation
APS, 2012Co-Authors: Emiliano Fratini, Weishan Chiang, Piero Baglioni, Eugene Mamontov, Sowhsin ChenAbstract:The translational dynamics of hydration water confined in Calcium-Silicate-Hydrate (C-S-H) gel was studied by quasielastic neutron scattering spectroscopy in the temperature range from 280 to 230 K. The stretch exponent β, the self-diffusion constant D, the average translational relaxation time {τ}, and the temperature dependence of confinement radius α extracted from the elastic fraction of immobile water molecules p(Q) were obtained from the analyses of the low-Q spectra according to the relaxing cage model. Measurements were made using C-S-H of three different water contents, 10%, 17%, and 30%. Among the three samples of C-S-H gel with different water contents, the values of β decrease with increasing water contents, while α increases. The values of D and {τ} are insensitive to temperature for the two lower water contents, as opposed to the 30% case where a slight variation is observed. The trend for violation of the Stokes-Einstein relation is only visible in the case of 30% water content.
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microstructure determination of Calcium Silicate Hydrate globules by small angle neutron scattering
Journal of Physical Chemistry C, 2012Co-Authors: Weishan Chiang, Emiliano Fratini, Piero Baglioni, Dazhi Liu, Sowhsin ChenAbstract:The basic building block of Calcium-Silicate-Hydrate (C–S–H) gel, which is the major hydration product of a commercial Portland cement paste, is usually referred as “globule” in the Jennings’ colloidal model-II developed for C–S–H. The detailed nanostructure of the globule is so far not given quantitatively. In this paper, we determine the structural parameters of the building block with good accuracy by small-angle neutron scattering technique probing an extended interval of the scattering vector, Q, from 0.015–1.0 A–1. In this Q-range an interlamellar peak at 0.65–0.80 A–1 is present, shifting as a function of the water content present in the C–S–H gel. This additional feature enables us to confirm the presence of a lamellar structure and determine the thicknesses of both the water and the Hydrated Calcium Silicate layers respectively proper of the C–S–H globules.
Hamlin M Jennings - One of the best experts on this subject based on the ideXlab platform.
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composition and density of nanoscale Calcium Silicate Hydrate in cement
Nature Materials, 2007Co-Authors: Andrew J Allen, Jeffrey J Thomas, Hamlin M JenningsAbstract:Although Portland cement concrete is the world’s most widely used manufactured material, basic questions persist regarding its internal structure and water content, and their effect on concrete behaviour. Here, for the first time without recourse to drying methods, we measure the composition and solid density of the principal binding reaction product of cement hydration, Calcium–Silicate–Hydrate (C–S–H) gel, one of the most complex of all gels. We also quantify a nanoscale Calcium hydroxide phase that coexists with C–S–H gel. By combining small-angle neutron and X-ray scattering data, and by exploiting the hydrogen/deuterium neutron isotope effect both in water and methanol, we determine the mean formula and mass density of the nanoscale C–S–H gel particles in hydrating cement. We show that the formula, (CaO)1.7(SiO2)(H2O)1.80, and density, 2.604 Mg m−3, differ from previous values for C–S–H gel, associated with specific drying conditions. Whereas previous studies have classified water within C–S–H gel by how tightly it is bound, in this study we classify water by its location—with implications for defining the chemically active (C–S–H) surface area within cement, and for predicting concrete properties.
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solubility and structure of Calcium Silicate Hydrate
Cement and Concrete Research, 2004Co-Authors: Jeffrey Chen, Jeffrey J Thomas, Hal Taylor, Hamlin M JenningsAbstract:Abstract The poorly crystalline Calcium Silicate Hydrate (C-S-H) phases that form near room temperature, which include the technically important C-S-H gel phase formed during the hydration of Portland cement, have a broad similarity to the crystalline minerals tobermorite and jennite, but are characterized by extensive atomic imperfections and structural variations at the nanometer scale. Relationships between the aqueous solubility and chemical structure are reported for specimens formed by different preparation methods and with a broad range of compositions. Both new and previously published data show that these phases generate a family of solubility curves in the CaO–SiO2–H2O system at room temperature. As demonstrated by 29Si magic-angle spinning (MAS) NMR data and by charge balance calculations, the observed solubility differences arise from systematic variations in Ca/Si ratio, Silicate structure, and Ca–OH content. Based on this evidence, the solubility curves are interpreted as representing a spectrum of metastable phases whose structures range from purely tobermorite-like to largely jennite-like. These findings give an improved understanding of the structure of these phases and reconcile some of the discrepancies in the literature regarding the structure of C-S-H at high Ca/Si ratios.
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a model for two types of Calcium Silicate Hydrate in the microstructure of portland cement pastes
Cement and Concrete Research, 2000Co-Authors: Paul D Tennis, Hamlin M JenningsAbstract:A new physical basis for a previously published model for the structure of Calcium Silicate Hydrate (C-S-H) as measured by nitrogen sorption is described. This refined model provides a method of predicting the density, the nitrogen accessible gel porosity, and associated surface area of C-S-H in Portland cement pastes. The basis for the model is that C-S-H forms as one of two types, high- or low-density C-S-H. This provides a promising tool for characterizing the microstructure in a way that can be applied to understanding properties of engineering significance.
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a model for the microstructure of Calcium Silicate Hydrate in cement paste
Cement and Concrete Research, 2000Co-Authors: Hamlin M JenningsAbstract:A model is proposed for the structure of Calcium Silicate Hydrate (C-S-H) as it is formed during the hydration of Portland cement. One purpose of the model is to move toward an ability to evaluate the microstructure quantitatively, so that it can be related to properties on the one hand and processing on the other hand. It is a hypothesis intended to promote discussion and motivate experiments. Furthermore, the model is an attempt to rationalize disparate measurements of specific surface area reported in the literature by describing an underlying structure, which, when observed by different instruments, gives different results. It is a simplified representation of the microstructure within the size range of about 1 to 100 nm. The basic building block is a unit of C-S-H that is roughly spherical and approximately 2 nm across with a specific surface area of about 1,000 m2/g. These building blocks flocculate to form larger units. This paper describes the structure of the basic units and how they pack to form larger structures and microstructures. The model also explains a number of variant observations for such measured attributes as specific surface area, pore size, and density as determined by different techniques, as well as water content at different relative humidities.
