Hi,
I have trouble finding an answer to this trivial question*:
I suppose I have 24 liters of water in which I introduce 6kg of malt (crushed). What is the new volume in the kettle?
The real question is why do you need to know that? In brewing beer you are not really concerned with that measurement. You are concerned with the amount of wort after the wort is removed from the grain. That would be the strike water - the water absorbed in the grain.
The only reason to need to know is to see if your mash tun is big enough. There are estimates and calculators for mash tun capacity around, and e.g. Beersmith does this. It's probably a rough estimate - you don't want to get exactly to capacity on your mash tun anyway.
Not a trivial question in my opinion! It's important to know and others felt strongly enough on the matter to create brewing calculators so you know if you have enough room in your kettle.
My favorite: https://pricelessbrewing.github.io/BiabCalc/#Advanced
In fact, I want to know if my mash tun is big enough. But according to the chart you directed me to, and if I understand it correctly, it seem that 24 lbs of grain increase the volume of the wort by roughly 2.24 gal.
It is 100% an important question, as you don't want to attempt a mash with 23 lbs of grain and find 3 gallons of it on your floor because it didn't fit in the mashtun.