We've been asked to repair deteriorated joints in a 2-year-old concrete floor. The floor is 8 inches thick and is placed on a 4-inch-thick crushed stone base. The 3000-psi concrete was treated with 2 pounds per square foot of a dry shake hardener. Keyed joints are spaced 50 feet apart and there are two layers of wire mesh in the floor. Here's the problem. The keyed joints have opened up as much as 3/8 to 7/16 inch. Then under hard-wheel dolly traffic, the top edge of the female side of the keyed joint has broken off. There's also spalling on both sides of the joint. To repair it, I'm proposing that we saw out a 3-foot strip of concrete centered on the joint. Then at each sawed face we'll drill holes to accept smooth dowel bars and epoxy one end of the dowel while leaving the other end free to move within the concrete. We'll place a low-slump repair concrete and saw a joint above both rows of dowels. The joint will be filled with a semirigid epoxy. Does this sound like a good approach?
We asked Steve Metzger of Metzger-McGuire for a critique of the proposed repair. He thought the basic approach was sound but suggested cutting only one joint at the center of the repair section. Damage from hard-wheeled traffic is most likely at the joint. The more joints, the more damage is likely to occur. Since most of the floor shrinkage has probably occurred, the sawed joint isn't likely to open very wide and aggregate interlock should provide the needed load transfer. Metzger suggests a narrow-width sawed joint that can be achieved by using the new saws that make a cut immediately after finishing. The narrower the joint, the less likely that you'll get further joint distress.