Sorption behavior clay materials

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Dustin
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Sorption behavior clay materials

Post by Dustin » Mon May 16, 2022 3:01 am -1100

Hey Wufi-Experts,
I have a question about the sorption behavior of clay materials.

For clay building boards, DIN 18948:2018-12 describes a method for measuring watervaporsorption after a moisture jump. (Water absorption [g/m²] after a moisture jump from 50 to 80% RH at constant temperature) An indicator of how quickly and how much watervapor an clayboard absorbs.

How is this influence reflected in the Wufi material parameters?

At 80% RH, moisture transport into the material takes place through a combination of vapor diffusion and surface diffusion. Thus, it is defined by the watervaporsorption coefficient and the moisturetransport coefficient of the material. Right?

The results of the water vapor sorption test are available from many manufacturers. Can the results of the watervaporsorptiontest be used to draw conclusions about the corresponding materialproperties for the Wufi simulation?

Thank you :)

Thomas
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Re: Sorption behavior clay materials

Post by Thomas » Mon May 16, 2022 5:38 am -1100

Dustin wrote:
Mon May 16, 2022 3:01 am -1100
For clay building boards, DIN 18948:2018-12 describes a method for measuring watervaporsorption after a moisture jump. (Water absorption [g/m²] after a moisture jump from 50 to 80% RH at constant temperature) An indicator of how quickly and how much watervapor an clayboard absorbs.

How is this influence reflected in the Wufi material parameters?
Hi Dustin,

the total amount of moisture absorbed after long-term exposure to the higher relative humidity is simply the difference of the values of the moisture storage function at the higher and at the lower humidity.

The speed with which the moisture is taken up will be determined both by the moisture storage function (higher moisture capacity -> will take longer to fill up) and the vapour diffusion properties (mu-value) of the material (more vapour-permeable -> stronger diffusion flow into the material).
At 80% RH, moisture transport into the material takes place through a combination of vapor diffusion and surface diffusion. Thus, it is defined by the watervaporsorption coefficient and the moisturetransport coefficient of the material. Right?
Strictly speaking, yes. On the other hand, the relatively small contribution of the surface diffusion (a kind of liquid transport, as opposed to vapour diffusion) is often taken into account as a more or less slight modification of the mu-value.
The results of the water vapor sorption test are available from many manufacturers. Can the results of the watervaporsorptiontest be used to draw conclusions about the corresponding materialproperties for the Wufi simulation?
In principle, yes. The result from a long-term sorption experiment should give you information about the moisture storage function, and the absorbed amount over time should give you information about the mu-value. But a test made strictly according to the DIN standard may not provide sufficient data (I don't know the details of the standard procedure).

Kind regards,
Thomas

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