How to Aid the Hydration Process of Curing Concrete

During the curing period concrete gains strength.

Concrete gains strength during the hydration process, a chemical reaction between Portland cement and water. If the water content of the mix evaporates or freezes before hydration is completed, the concrete will be weak and defective. Concrete achieves 50 percent of full strength within the first few days. Curing within this period aids the hydration process by controlling the temperature and environment to retain moisture. Protective curing measures are required to slow evaporation if the temperature is warmer than 85 degrees Fahrenheit and to keep water in the concrete from freezing when the temperature falls below 50 degrees Fahrenheit.

Things You'll Need

• Plastic sheeting, at least 4 mils thick, white, reflective
• Waterproof tape
• Sand, timber and bricks, or tape
• Hose
• Spray attachment with mist setting

Instructions

1. Keep concrete forms in place after pouring wet concrete. Lay plastic sheeting on the concrete as soon as possible but when it won't mark the finish. Smooth out all wrinkles.

2. On flat surfaces and extend the sheeting from the edges for at least twice the thickness of the slab, and hold them down with sand, timber or bricks. Alternatively, turn down the sheeting at the edges and seal with the tape. On vertical surfaces, wrap the member in sheeting and seal the edges.

3. Keep the plastic sheeting from being torn or damaged. Check under the sheets periodically that the concrete remains moist. Spray with a fine mist if the concrete is drying out, and reapply the sheeting.

4. Cure for at least three days. Remove sheets and forms.

Tips & Warnings

• Use dark plastic sheeting for temperatures below 50 degrees Fahrenheit, following the same process as warm-weather curing. Insulated materials might be necessary as well.

• Uneven application of the plastic sheeting can result in mottled concrete, or hydration stains, from uneven curing. Use waterproof paper, applied in the same way as plastic sheeting, where the appearance of the finish is critical.

• Keeping forms in place helps moderate the temperature around concrete.

• Check for specific curing times according to the type of concrete. Three days is a general recommendation for standard concrete.

References

• Cement Concrete & Aggregates Australia: Curing of Concrete
• National Ready Mixed Concrete Association; CIP 7; Curing In-Place Concrete

Resources

• Cement Concrete & Aggregates Australia: Concrete Basics