Concrete and timber

I built a suspended slab 100mm thick and spanning 8 feet  and 25 mpa with 60 steel mesh and the concrete was on six piers of bricks and a wall of bricks on the opposite side and put a 3,500 gallon water tank on this structure without any problems, "that's about three tons of water." So the previous posts cement thicknesses are probably an over kill. Cement likes to be in compression and if you design with this in mind you can use less of the stuff.

Timber is used in conjunction with concrete, I have seen where they drove the timbers into the ground and then built a concrete building on the wooden posts.This was a massive three story building...!