Q.: We have had more than one complaint about vertical movements in keyed joints when heavy lift trucks run over them. In some cases this has been enough to cause spalling. We have used premolded tongue and groove strips to form these joints. Would dowels solve this problem?
A.: Dowels are a recommended method of solving the problem. They should be coated to prevent bond with the concrete. For 5-inch slabs the dowels should be 12 inches long and 5/8 inch in diameter. For 6-inch, 7-inch and 8-inch slabs dowels should be 14 inches long and 3/4, 7/8 and 1 inch in diameter respectively. For 9-inch and 10-inch slabs dowels should be 16 inches long and 1 1/8 inch and 1 1/4 inch in diameter respectively. All dowels should be spaced 12 inches center to center.