What's in a Concrete Slab?

What’s in a concrete slab? A lot!

A project I’m working on is under construction with an elevated post-tensioned concrete slab pour imminent. There is an amazing amount of infrastructure within a slab of this type so I took my camera last time I went on site and took a few pictures.

There obviously is a lot going on within this slab. We have our standard rebar for reinforcing, with bars up to #9 size (those are over an inch thick!). We have post-tensioning tendons — essentially cables within lubricated sleaves. These cables will be tensioned after the concrete has started curing to improve the structural performance of the slab. There are also stud rails, metal fabrications that help distribute structural loads at columns. As there will be a wood framed structure sitting on this slab, there are also anchor bolts and tie-downs throughout. Then we have all of the plumbing and electrical penetrations. In areas where we have bands of tendons and multiple levels of rebar it gets so you almost can’t see the formwork below:

Looking at all of this infrastructure, I can’t help but marvel at the amount of engineering, coordination, and meticulous placement all of this requires. We often walk on a concrete slab unaware of what goes in it — all of the human ingenuity and craftsmanship that gets covered up when the pump trucks arrive on site.