Our kitchen 'island' has a single slab measuring 73" X 39" with a 12" overhang to accommodate a couple of high bar chairs. Instead of using 'L' braces to support the overhang, they installed 3 heavy steel plates into 3 slots that were routered into the top of the cabinet work. Completely invisible & strong.

We have friends that had concrete counter tops in their 'mansion' because they were all the rage about a decade ago.

We didn't like the looks of it at all - looked to me like a DIY job to me. It didn't prove to be durable either. Unless concrete installations are better today, I would never go that way...

TAM