Q.: We are placing 4-inch-thick slabs. Can we use dowels or keyways for load transfer?
A.: In ACI 302.1R-89, "Guide for Concrete Floor and Slab Construction," ACI Committee 302 does not recommend keyed joints for slabs thinner than 6 inches, and also doesn't provide guidance for dowels in slabs thinner than 5 inches. We've seen metal key forming systems with knockouts for dowels advertised for 3- and 4-inch slabs, but we don't have information on field performance of these joints. You might consider thickening your slab edges, beginning 2 or 3 feet from the joint, and detailing a doweled joint in a 5-inch slab.
We'd like to hear from readers who have tried dowels or keyways in thin slabs.