Q.: Is it permissible to put concrete test cylinders in a tub of water to cure them?
A.: For initial curing, test cylinders can be immersed in saturated limewater at 60 degrees F to 80 degrees F immediately after molding if they're not cast in cardboard molds or molds that expand when immersed in water. After 24 ± 8 hours they should be immersed in water at 73.4 ± 3 degrees F until they're tested.
If the cylinders are in cardboard molds, prevent loss of moisture by covering them and keep the temperature at 60 degrees F to 80 degrees F. Then they can be removed from the molds and immersed in saturated limewater at 73.4 ± 3 degrees F.
Immersion in water provides the best possible curing environment. This is particularly important when the concrete has a low water-cement ratio. Immersion is also a nearly foolproof way of curing. If moist room fogging nozzles clog or there's a temporary loss of water pressure, cylinders in the moist room could dry, reducing strength. Immersion eliminates that concern.