This afternoon the slab was poured inside the house. Last week, back fill and gravel were placed inside the foundation walls and compacted. The interior footings were located, formed, and reinforced with steel. Speaking of forms, you can see the tall wood blocks sticking up out of the wall. They were placed there before the foundation wall pour to create a space for a structural floor beam to rest. That's called a beam pocket. Perfect example of how things that need to happen in a later stage of construction need to be coordinated earlier, as well as how the different trades need to coordinate.
A thick poly vapor barrier is laid down under the entire slab to prevent moisture from the ground entering the slab. If reinforcing is being used, it would be placed. This slab does not have any steel reinforcing in it. The concrete trucks delivered concrete that had fiber reinforcing in the mix, and this will replace the steel mesh that usually helps strengthen concrete. Because this is only a short crawlspace and the space won't be used for mechanical systems or storage, the slab is what is called a "rat slab". I don't know how it got that unbecoming name, but it just means it's 3" thick instead of 4" and possibly made to less stringent standards than a slab that needs to withstand a lot - like in a garage. Remember this slab is essentially on grade, so no drainage was necessary, either.