Hello,
I've been simulating the behaviour of an in-situ concrete slab after it's been covered with a flooring material (vinyl, linoleum, etc.).
According to the norms here, a concrete floor may be covered with flooring material (plastic flooring) when the RH is lower than 85 % at 20 % of the slab's total depth. I "dryed" the concrete slab by simulating it by itself in normal environmental conditions until the RH was sufficiently low. Afterwards, I extracted the moisture distribution data and included it as an inital condition to the concrete slab in the new model, which has the flooring materials added on top of the slab. This way the moisture distribution should be somewhat realistic in the model.
However, during the "drying" process I noticed that getting from 100 % to 85 % at 20 % of the total depth in the slab takes very long time. I tested all the concrete types in the data library, but I couldn't get realistic results. Even in the quickest type it would take almost 2 years to be sufficiently dry to be coated with flooring. Other types took over 5 years to reach 90 % RH.
Environmental conditions were a constant 20 C temperature and 50 % RH on both sides of the slab. Then I improved the conditions to 30 C and 30 % RH (took 12 months to dry) and again to 40 C and 20 RH. ( took 9 months to dry). I got these results using concrete, 12/15 from Fraunhofer-catalog.
Should I change the material properties until I get realistic results? Can you give me any tips on that?
-Sami
Concrete materials in Wufi's database - drying time too long?
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Sami Roikonen
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Christian Bludau
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Re: Concrete materials in Wufi's database - drying time too long?
Hello Sami,
as the concrete is quite diffusion tight, it can take a quite long time to dry out. You only want a 20% layer to dry out. I would not check if the complete thickness of layer is bellow the value of 85%, I more would take the mean value. In reality, the moisture is measured by taken a drilling core or by resistivity. You always get a mean value. I tried that in WUFI and it needed about 5-6 month for a 4cm layer of a 20cm concrete slab to dry from 100% to 85% (concrete w/c=0.5).
Further to start with an initial moisture of 100% is to high. At the begin of the solidifying an amount of the water is bond by chemical effects. So i would start at some value at between 95-97%RH.
Last, the concrete C12/15 is a concrete with a low compressive strength and can not be used for concrete slabs. You should use the concrete w/c=0.5 (old German B25) or the C35/40.
Christian
as the concrete is quite diffusion tight, it can take a quite long time to dry out. You only want a 20% layer to dry out. I would not check if the complete thickness of layer is bellow the value of 85%, I more would take the mean value. In reality, the moisture is measured by taken a drilling core or by resistivity. You always get a mean value. I tried that in WUFI and it needed about 5-6 month for a 4cm layer of a 20cm concrete slab to dry from 100% to 85% (concrete w/c=0.5).
Further to start with an initial moisture of 100% is to high. At the begin of the solidifying an amount of the water is bond by chemical effects. So i would start at some value at between 95-97%RH.
Last, the concrete C12/15 is a concrete with a low compressive strength and can not be used for concrete slabs. You should use the concrete w/c=0.5 (old German B25) or the C35/40.
Christian