Concrete Mix Design Reducing Water Absorbtion

Have you considered waterproofing the concrete after it is placed and before the absorption test? All concretes are porous and will absorb water unless you render it hydrophobic. www.StableCrete.com/projects will give you an idea of how different concrete structures are waterproofed after placement.

Waterproofing also creates a No-Low Moisture/ Oxygen environment to prevent corrosion of embedded steel reinforcing members. May be easier than a new mix design?

I'm assuming that your concrete mixture is intended for a water retaining structure perhaps? Then if so, you may want to look into the concrete admixture product called "Xypex". There are several similar products by other chemical manufacturers out there in the market. Also, check/search the CR4 forum blogs as I believe that this very question was discussed sometime in the Winter or Spring of 2010.