Simulating concrete - 1) initial drying then 2) ongoing behaviour

[james bertram]

Guten morgen Fraunhofer

I have read all the concrete posting I can find, but have a question about the transition from 1) to 2) below.

1) Initial drying - for site poured concrete, in one posting using RH=97% approx as the Initial Conditions and "Concrete w/c 0.5" was suggested.

2) Ongoing behavior - in another posting, reference is made to "Hygrothermal Properties and Behaviour of Concrete" and splitting the concrete into two layers: weather side with with "Liquid Transport" settings untouched and the non-weather side without "Liquid Transport=0".

My questions are:

Do I transition from 1) to 2) by running 1) for say 3 month, then using the end of simulation Temp/RH profile=Initial Conditions for 2) which runs for 3 or 5 year etc?

When modelling a suspended concrete floor that is not exposed to sun or rain after the first 3 months, can I just use Temp and RH data, or do I also need to use the Liquid Transport=0?

Thank you for your continued support.

[Christian Bludau]

Hallo James,

yes, that would be the way. First simulate from maybe about rh=97% as long as there are no indoor conditions. After the building goes on, you will get a indoor climate. do a new calculation for that using the end conditions of your first calcualtion as inital conditions. Here AT and RH is enough.

The liquid trtansport coefficients are used to calcualte the rain uptake and the liquid transport in the concrete. You either can use the concrete wc=0,5 with liquid transport coefficients or you use the concretes from the swedish database, which do not contain liquid transport coefficients, here all transport is expressed by diffusion (but this will not take up rain from the boundary condition).

Greetings,
Christian

[james bertram]

G'day Christian- thanks for your reply...

To check that I understand...if there is no sun or rain exposure (building above) can I just use Temp and RH data for the Boundary Conditions and leave the Liquid Transport Coeff as they are for Concrete wc=0.5.

That is, if I don't provide data, does WUFI ignore the affect?

Outcomes for Liquid Transport Coeff=0 + Temp/RH data and Liquid Transport Coeff=Concrete wc=0.5 + Temp/RH data are very different

Thank you, James

[Manfred Kehrer]

James, I think the boundary condition decisions are not coupled to the decision how to model the concrete.

Depending on other parameters, yes there are differences in the drying behavior when setting Liquid Coeff. to zero.
Hope this help

[james bertram]

Hello Manfred - Thank you for your response, I hope you are enjoying America.

I am trying to make sure I understand "how wufi thinks

For example (for concrete), if I only use Temp/RH data because the slab is covered above, can I leave Liquid Trans Coeff settings as they are because there is no rain data?

Apologies for the persistence...its lonely down under

[Christian Bludau]

Hello James,

the liquid transport coefficients are used the following:
At the hours with is rain in the climate file and the rainwater adsorption of the outer surface not switched off, the liquid transport is set to suction for the whole construction. For the hours there is no rain or if the adsorption is switched off, the coefficients for redistribution (much slower) are used in the hole construction.
So if you have a slab over a parking deck and you maybe have rain on the top, during the rain the suction coefficients are used, no matter what climate is used for the park deck. At the interior side you can not set rain or radiation in WUFI Pro. For expressing an interior climate the values of T and RH are enough.
Thats for the climate.

About the idea you read to set the liquid transport in the inner layer to zero. I think that idea is far from reality. The original idea was the fear, that during rain the suction in thick elements is much to high and so is the speed of water transport. But in this case I would not set the coefficient to zero but to the redistribution coefficient, because then also during rain the transport of liquid water stays at the same speed as during rain. Further there can be the case, that liquid transport is blocked in certain depths of the concrete because a chemical tightening. In this case it might be the better way to use a concrete from the Swedish (Lund) Source, which do not contain liquid transport coefficients but express the moisture transport only by diffusion. But take care, this concrete will NOT take up any rain from the climate.

Hope thats understandable,
Christian

[james bertram]

Danke Christrian - for the detailed response...much appreciated, was , now

Best wishes to everyone from the far side of the world, James