What are the probable causes and possible remedies for curling of five-inch-thick interior slabs on grade 20,000 to 50,000 square feet in area and containing welded wire mesh? These have sometimes been placed in heated areas, sometimes in covered areas, but sometimes in neither. Soil compaction is good and construction joints are provided at columns and every 20 feet. In less than 30 days all edges of all slabs curled upward about 1/2 inch at all construction joints but not where dowelled to perimeter walls.
Warping and curling is usually caused by more rapid shrinkage of the top surface than the bottom. Slabs on grade usually cannot dry or carbonate at the bottom surface but only at the top. If the top dries rapidly there will be a greater difference in moisture content between the top and bottom than if it d ries slowly. Hence, rapid-drying slabs will curl more. One method of minimizing curling should be to cure the concrete a long time and to take any measures possible to slow the drying process. Application of liquid curing membranes perhaps even frequent periodic reapplication in trafficked areas during the early life of the floor should help. Curled slabs can be uncurled as described on page 319 of the June 1972 issue.