The sorptivity is the ratio between the mass gain (W) to the cross section area multiply by the water density ( W/ A* water density).

This is equal to the initial sorption plus the sorption as a function of time described by the square root relationship. ( Sorptivity = initial sorption + S * SQRT (t).

If the cross section increases, the mass gain of the specimen will increase as well (vice versa). Therefore, it seems that the cross section have no effect on the obtained results. The attached URL contains a paper discuss the effect of coating and the specimen size on the sorptivity.

The author revealed that a little effect of the specimen size has been observed  on the sorptivity results and this might confirm the  above discussion based on the theoretical background of this phenomenon. .

Regards

http://www.icevirtuallibrary.com/content/article/10.1680/macr.2004.56.9.537

Thanks for your answer. I have already studied this paper. I look for other papers in which this question is discussed  and concluded or even mentioned.

From a quick search in google, I found this:

http://books.google.gr/books?id=su_hmD6PrwEC&pg=PA138&lpg=PA138&dq=effect+of+size+on+sorptivity&source=bl&ots=KchAJH250U&sig=WxuysxqQUVqN7nspgEC-omCc7ws&hl=el&sa=X&ei=LXFmVPXjFIbiapXygJAH&ved=0CFYQ6AEwBQ#v=onepage&q=effect%20of%20size%20on%20sorptivity&f=false

where a "small but distinct effect" is reported. Having conducted several laboratory tests for sorptivity myself, I have the same -though not experimentally justified- impression (I know I am not helping much, but thought I should share my own experience)

Theoretically no, as suggested by Mahmoud, but practically yes, especially with cast specimens where granular content is lower close to the wall. Even, with cored specimen, some wall effects are able to take place if the lateral sealing is not perfect.

Thank you very much for your answer. Do you know any publications in which it is clearly stated that it does not depend (cause you have written "theoretically no"). :)

Theory refers to constitutive equations of permeability and diffusivity within porous media. You can find it in many books. If you consider uniaxial water transfers inside homogeneous material, no size effect should occur if the representative volume or section is large enough compare to the size of the heterogeneities of the material.

valuable answer Mahmoud

I agree with Vincent Picandet .