ACI 302.1R-15, Guide for Concrete Floor and Slab Construction was recently published by the American Concrete Institute. Anyone who places concrete flatwork should get and study this document—it contains the boiled-down wisdom of the entire concrete industry on the simple (yet not) concrete floor.

One important change in this version—the first new edition since 2004—is the flow chart that indicates where to place the vapor barrier beneath a slab on ground. While there was a similar flow chart in the previous edition, this one strengthens the recommendation to place nearly all concrete slabs directly in contact with the vapor barrier.

But how do concrete slabs placed directly on plastic vapor retarders behave? Is curling increased? What is a dominant joint and is this problem more pronounced with slabs placed directly on a vapor retarder? How can these problems be avoided? Is the solution to simply eliminate joints?

To try to answer these questions, we are planning a luncheon session at the 2016 World of Concrete, as I mentioned in a June 2015 blog. A four-person panel of slab experts and members of ACI Committee 302 (Construction of Concrete Floors) led by Peter Craig (Concrete Constructives) will explore the issues and respond to audience comments. The rest of the panel is Scott Tarr (North S.Tarr Consulting), Steve Lloyd (Lloyd Concrete Services), and Rick Smith (Structural Services Inc.). The luncheon will be on Wednesday, February 3. Don’t miss it!