Effect of moisture on fractal dimension and specific surface of hardened cement paste by small-angle X-ray scattering

Small-angle x-ray and neutrons scattering is a widespread experimental tool for the investigation of the microstructure of random heterogeneous materials. Validation of (computer-generated) model microstructures often requires the numerical computation of the scattering intensity, which must be carried out with great care due to finite size effects. In this paper, a new method for this computation is presented. It is superior to previously existing methods for three reasons: First, it applies to any type of microstructure (not necessarily granular). Second, closed-form expressions of the size effects inherent to the proposed method can be rigorously derived and removed (in this sense, our method is free of size effects). Third, the complexity of the new algorithm is linear and the computation can easily be updated to account for local changes of the microstructure, while most existing algorithms are quadratic and any change of the microstructure requires a full recomputation. The present paper provides full derivation and validation of this method. Application to the computation of the scattering intensity of dense, polydisperse assemblies of spheres is then presented. A new, simple algorithm for the generation of these dense configurations is introduced. Finally, the results are critically reviewed in the perspective of hardened cement pastes.

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“…with s 0.2 and v 0.5, which is in good agreement with many other published results [14,53,55,58,59,67,68]. As stated in Sec.…”

Section: Perspectives: Application To Cement Pastessupporting

confidence: 93%

Small-angle scattering of dense, polydisperse granular porous media: Computation free of size effects

Brisard

Levitz

2013

Phys. Rev. E

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“…Drying reduced the surface area, with the maximum reduction occurring at 33% RH. Qualitatively similar results for drying of cement paste have been obtained from small‐angle X‐ray‐scattering measurements, 28,33,34 using a different method to calculate the surface area. On resaturating from the higher RH levels the surface area is largely recovered, but at lower RH levels there is a permanent surface area loss.…”

Section: Resultssupporting

confidence: 66%

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Thomas

Allen

Jennings

2008

Journal of the American Ceramic Society

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The effects of drying to various relative humidity (RH) levels on the internal structure of hydrated cement paste were investigated using small‐angle neutron scattering (SANS). Specimens of young and mature portland cement paste were analyzed in the initial saturated state, in the dried state, and then again after resaturation, allowing reversible and irreversible effects to be separated. While the observed changes on drying are mainly physical in nature, the ability of the microstructure to resist permanent structural rearrangement increased over time as the hydration and aging reactions progressed. Permanent changes to the nanometer‐to‐micrometer scale microstructure induced by drying were quantified by applying a fractal model to the SANS data for resaturated pastes. At RH levels above ≈54%, capillary stresses compact the nanometer‐level pore structure of the calcium–silicate–hydrate (C–S–H) gel phase, increasing the gel density by a mechanism related to that governing the classical “constant rate period” for pure gels. Owing to the restraining effects of the other solid phases in cement paste, this decrease in the volume of the C–S–H gel also increases the intensity of surface fractal scattering that arises from the deposition of hydration product onto the surface of the reacting cement particles. At all RH levels, but particularly below 54%, drying decreases the measured total internal surface area of the specimens. This is attributed to a loss of surface area at particle contacts as the average separation distance between adjacent C–S–H gel nanoparticles decreases on drying.

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“…There is good correlation between the two sets of data, with an overlap in a limited q ‐range from 10 −2 A −1 to 4 10 −2 A −1 . The computed I ( q ) exhibits some interesting features which can be compared to the numerous investigation of cement pastes by SAXS or SANS started in the mid‐eighties . Regardless of the precise composition or the age of the hardened cement paste, the scattering intensity I ( q ) invariably behaves as a fractional power of q in a low and very low q range.…”

Section: Resultsmentioning

confidence: 86%

Developments in TEM Nanotomography of Calcium Silicate Hydrate

et al. 2015

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This investigation was designed to explore the possibility of using transmission electron microscope (TEM) tomography on cement-based systems gain a greater understanding of their nanostructure and pore network. The preliminary results show a clearly a well-defined pore network at the nanoscale, with pore size approximately 1.7-2.4 nm in diameter and spaced around 5-8 nm apart. A comparison of small angle X-ray scattering data with 2-D TEM images analyzed with the Fourier slice theorem documents an excellent structural correlation.

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Effect of moisture on fractal dimension and specific surface of hardened cement paste by small-angle X-ray scattering

Cited by 35 publications

References 5 publications

Small-angle scattering of dense, polydisperse granular porous media: Computation free of size effects

Small-angle scattering of dense, polydisperse granular porous media: Computation free of size effects

Structural Changes to the Calcium–Silicate–Hydrate Gel Phase of Hydrated Cement with Age, Drying, and Resaturation

Developments in TEM Nanotomography of Calcium Silicate Hydrate

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