A core-drilled post is set into a hole drilled through the concrete slab using a diamond core drill, then grouted in place with high-strength epoxy or polymer-modified grout. The drill and grout method is the strongest retrofit fixing into existing concrete, comparable to a cast-in anchor.
Typical core diameters are 75 to 125 mm, drilled 100 to 200 mm deep depending on slab thickness. The post drops into the hole, gets plumbed up, then grout fills the annular gap and locks it in.
Core-drilled posts are common for retrofit balustrades on existing concrete slabs and for high-load posts where a footplate or chemical anchor wouldn't satisfy the structural calculation. The cost is the core-drilling labour, which can be more than the post itself.