The primary factors controlling dimensional changes of concrete which lead to curling are drying shrinkage, construction practices, moist or wet subgrades, and day-night temperature cycles. The following practices will help to minimize the potential for curling:
1. Use the lowest practical slump and avoid adding retempering water, particularly in hot weather.
Use the largest practical maximum size aggregate and / or the highest practical coarse aggregate content to minimize drying shrinkage.
Take precautions to avoid excessive bleeding. Use a damp, but absorptive, subgrade so that all the bleed water is not forced to the top of the slab.
Avoid using polyethylene vapor barriers unless covered with a least 2550mm of damp sand.
Avoid a higher than necessary cement content if the subgrade is wet in service. Dense, impermeable concrete will produce larger top to bottom moisture differentials and curl more. Use of fly ash is preferable to a very high cement content, and consideration should be given to specifying strength at 56 or 90 days.
Cure the concrete thoroughly, including joints and edges. If membrane curing compounds are used, apply at twice the recommended rate in two applications at right angles to each other.
For floor areas where curling tends to be a problem, cure the concrete with a heavy wax floor sealing compound of the type used on terrazzo. (Note: Tile adhesives will not stick to these materials.)
Use a joint spacing of approximately 25 to 30 times the slab thickness.
For thin toppings, clean the base slab to ensure bind and consider use of studs and wire around the edges and particularly in the slab corners.
Use a thicker slab.
The use of properly designed and places slab reinforcement may help reduce curling.
Use dowels when placing a slab adjacent to an existing slab.