Q.: We have been paving 12- to 15-inch-thick taxiways containing welded wire fabric located 1/3 the thickness from the top and lapped 12 inches. The taxiways are from 150 to 250 feet long and have joints every 50 feet, sawcut at night. Each taxiway consists of three 25-foot-wide lanes. The construction procedure has been to place Lane 1 the first day, Lane 3 the second day and Lane 2 (the fill-in lane) four days later. We have been required to tie the lanes together with dowels. These are ungreased. We are now [in November] in the last days of the job, the weather has turned cold, and we have been covering the concrete for 3 days or longer with curing blankets. We are suddenly getting cracking in the fill-in lanes about every 10 or 12 feet. What causes the cracking and what can we do to prevent it?
A.: The problem seems to be the restraint offered by the dowels. Lanes 1 and 3 have a head start in undergoing drying shrinkage. When Lane 2 is cast the dowels tying it to Lanes 1 and 3 restrain it from shrinking freely and thus cause cracking. An unusually heavy coating of grease on the ends of the dowels that go into Lane 2 might provide just enough extra space around them to allow Lane 2 to move lengthwise (perpendicular to the dowels) without cracking.