Free water saturation wf

[jebjorn]

The moisture storage function is dependent on the free water saturation, w_f. However, I would like to know by what wf is determined.
I know that the maximum water content w_max is determined by the porosity of the material, but I can find nowhere by what wf is determined by. Is that also determined by porosity?

Thank you in advance.

/Johanna

[Manfred Kehrer]

Put the material in liquid water water until constant weight is reached. Theoretically this is when all pores are totally filled with water, which would then be the max. water content. Practically when you define water content uptake less than e.g. 0.1 mass percent a day as constant weight, that is what is a good approach for the free water saturation. ASTM C1699 can be used for it, though the 0.1% per day definition is not in there, but can be be taken from ASTM C1498.

[Thomas]

Hi Johanna,

the free saturation is not uniquely determined by any of the other material parameters. That is, you can not simply compute it from other material data - you need to measure it.

It is mainly determined by the details of the pore structure of the material: the pore size distribution, the interconnection structure of the pores, the amount and distribution of 'blind' pores, etc. You don't know the details of these pore characteristics, and even if you knew them, no simple method is known which would allow to compute free saturation from that knowledge.

Regards,
Thomas

[jebjorn]

Thank you for the reply!

The intention was not to calculate it, rather to understand it so this was very helpful.

/Johanna