Gas transport through concrete slabs

Odeh, Abdalla M.; Abu-El-Sha’r, Wa’il Y.; Al‐Ruzouq, Rami

doi:10.1016/j.buildenv.2005.02.004

Cited by 8 publications

(7 citation statements)

References 14 publications

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“…This effect occurs if the pore width is comparable with the free path length of the gases in the open space of the pore network. For amorphous materials, is is assumed that the transient state begins approximately when pore radii are below 30 nm to 200 nm [ 81 , 87 , 88 , 89 , 90 ]. In pores with a width of 1

m, the Knudsen effect leads to a reduction of the molecular diffusion of around 3%.…”

Section: Discussionmentioning

confidence: 99%

About the Dominance of Mesopores in Physisorption in Amorphous Materials

2021

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Amorphous, porous materials represent by far the largest proportion of natural and men-made materials. Their pore networks consists of a wide range of pore sizes, including meso- and macropores. Within such a pore network, material moisture plays a crucial role in almost all transport processes. In the hygroscopic range, the pores are partially saturated and liquid water is only located at the pore fringe due to physisorption. Therefore, material parameters such as porosity or median pore diameter are inadequate to predict material moisture and moisture transport. To quantify the spatial distribution of material moisture, Hillerborg’s adsorption theory is used to predict the water layer thickness for different pore geometries. This is done for all pore sizes, including those in the lower nanometre range. Based on this approach, it is shown that the material moisture is almost completely located in mesopores, although the pore network is highly dominated by macropores. Thus, mesopores are mainly responsible for the moisture storage capacity, while macropores determine the moisture transport capacity, of an amorphous material. Finally, an electrical analogical circuit is used as a model to predict the diffusion coefficient based on the pore-size distribution, including physisorption.

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m, the Knudsen effect leads to a reduction of the molecular diffusion of around 3%.…”

Section: Discussionmentioning

confidence: 99%

About the Dominance of Mesopores in Physisorption in Amorphous Materials

2021

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“…[26] This reduces the available free space or leads to the full saturation of small pores. [6,27,28] The Knudsen effect is then increased and reduces the effective gas diffusion significantly. [21,29] In addition, swelling of the material due to interlayer water further reduces the free space for molecular diffusion.…”

Section: Introductionmentioning

confidence: 99%

“…[16] Furthermore, a simple analytical consideration based on Fick's law generally fails because it is valid only for molecular diffusion. [6,16,23] To take this issue into account, some authors have incorporated the limited space of dry pores and calculated the Knudsen effect for the given pore system. [20,24,25] However, this does not take the influence of pore saturation on the Knudsen effect into account.…”

Section: Introductionmentioning

confidence: 99%

“…However, only the average pore radius of the concrete was used, and the pore distribution was not considered. [ 6 ] Some authors have investigated small samples of a few centimeters and incorporated the entire pore distribution and its varying water layer thickness during adsorption. They concluded that pore saturation significantly influences the predicted effective gas diffusion and that this issue should therefore receive greater attention.…”

Section: Introductionmentioning

confidence: 99%

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Quantification of the Knudsen Effect on the Effective Gas Diffusion Coefficient in Partially Saturated Pore Distributions

Strangfeld

2021

Adv Eng Mater

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The effective gas diffusion coefficient describes the process of gas diffusion in porous materials. Several materials have a significant number of micropores in the lower nanometre range leading to a reduction of gas diffusion (Knudsen effect). In the case of partial pore saturation during adsorption, the available pore space is further reduced, as is the gas diffusion. In this study, the influence of partially saturated pores on the Knudsen effect and on the gas diffusion is quantified. Three different pore geometries are investigated (slit, cylindrical and spherical pores) and three different types of pore size distribution, including a broad equal distribution, three narrow normal distributions and two measured distributions of concrete. Besides the intensive computation of the exact pore saturation, a simplified model with low computational requirements is suggested. This study shows that the influence of the water layer thickness on the effective diffusion becomes significant for pore radii below 50 nm and the assumed pore geometry is important. At the end, the overall effect is quantified for an amorphous material with most pore radii below 30 nm. At a moisture level of 50% relative humidity, the effective diffusion is reduced by 35% due to partial saturation.

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“…The issue of vapor intrusion in buildings has received great attention during the last decades (Little et al 1992; Odeh et al 2006; Abreu and Johnson 2005; Yu et al 2009; Provoost et al 2010). For example, vapor intrusion has become a potential primary risk driver for sites contaminated by chlorinated solvents.…”

Section: Introductionmentioning

confidence: 99%

Determination of Chlorinated Solvent Sorption by Porous Material—Application to Trichloroethene Vapor on Cement Mortar

Musielak¹,

Brusseau²,

Marcoux³

et al. 2014

Transp Porous Med

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Experiments have been performed to investigate the sorption of trichloroethene (TCE) vapor by concrete material or, more specifically, the cement mortar component. Gas-flow experiments were conducted using columns packed with small pieces of cement mortar obtained from the grinding of typical concrete material. Transport and retardation of TCE at high vapor concentrations (500 mg L−1) was compared to that of a non-reactive gas tracer (Sulfur Hexafluoride, SF6). The results show a large magnitude of retardation (retardation factor = 23) and sorption (sorption coefficient = 10.6 cm3 g−1) for TCE, compared to negligible sorption for SF6. This magnitude of sorption obtained with pollutant vapor is much bigger than the one obtained for aqueous-flow experiments conducted for water-saturated systems. The considerable sorption exhibited for TCE under vapor-flow conditions is attributed to some combination of accumulation at the air-water interface and vapor-phase adsorption, both of which are anticipated to be significant for this system given the large surface area associated with the cement mortar. Transport of both SF6 and TCE was simulated successfully with a two-region physical non-equilibrium model, consistent with the dual-medium structure of the crushed cement mortar. This work emphasizes the importance of taking into account sorption phenomena when modeling transport of volatile organic compounds through concrete material, especially in regard to assessing vapor intrusion.

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Gas transport through concrete slabs

Cited by 8 publications

References 14 publications

About the Dominance of Mesopores in Physisorption in Amorphous Materials

About the Dominance of Mesopores in Physisorption in Amorphous Materials

Quantification of the Knudsen Effect on the Effective Gas Diffusion Coefficient in Partially Saturated Pore Distributions

Determination of Chlorinated Solvent Sorption by Porous Material—Application to Trichloroethene Vapor on Cement Mortar

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