[Porsche-O-Phile]

Thank you. It irritates the hell out of me when people use the words "concrete" and "cement" interchangeably. They're not the same thing. Cement (as Lube correctly pointed out) is a constituent ingredient of concrete and is not nearly as strong on its own as a fully-developed concrete matrix including coarse and fine aggregates and possibly one or more admixtures.

It is possible to do some pretty amazing stuff with concrete - there are compressive strengths over 20,000 psi being attained with certain admixtures (notably fly ash), there are lightweight concretes that can span much further than previously possible, etc. It's a pretty good material overall although one does have to consider whether it's appropriate for the given use/application they're considering or not. Its R value is extremely low, it is extremely weak in tension (necessitating the need for steel reinforcing, and steel is $$$ right now), it has a somewhat-high up-front cost of installation (you essentially end up building two structures, one out of wood, one out of concrete and then tearing the wood one down), etc.

If you want an absolutely indestructable countertop I'd say it IS possible to do with concrete, but there are other things that can be made similarly strong. Certain plastics now are amazingly tough/durable. I suppose you could also go with plate steel. . . Might be an interesting little design project. Also consider that the heavier the countertop, the beefier (and more expensive) the support structure required.