Do harder floors prevent tunneling?

Nope, the floor you choose is mostly cosmetic; floors do effect the movement speed of people moving over them.

Sources: Experience and It's not been mentioned in-game, or by IV Software.

Floor textures do not prevent your inmates from tunneling, but walls do. Brick walls take longer to tunnel through than open spaces. Fences have almost no slowdown effect. But by far the best way to slow down inmate tunnels is the perimeter wall which take really long to dig through. Unfortunately this wall is very expensive, so surrounding your whole prison with it might be outside of your financial possibilities. By the way: Large pipes speed up tunneling, so you should avoid placing them near the outer wall.

However, a much cheaper way to prevent inmates from tunneling is to prevent them from getting the tools in the first place. Tools used for digging are spoons from the canteen and workshop tools. Placing metal detectors at the exits of these rooms will catch most of them. However, metal detectors are not 100% reliable and there are also other sources of contraband which are hard to control. That means you should routinely search all cell blocks for hidden tools. The best time to initiate a cell block search is during meal- or yard-time when no inmates are in the block. This prevents that the inmates will be searched personally, which causes unrest (they do not care when their cells are searched, even when they are present).