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Curing and Placing
Placing Concrete
Curing Concrete

Curing and Placing

Steps to Curing Concrete

Basics

Curing enables concrete to become stronger and more durable.  Proper curing requires:

• Sufficient moisture content – use curing method to supply or retain moisture.
• Favourable temperature – 50F to 90F.
• Time – minimum of seven days or until concrete reaches 70% of its specified strength.

Cure concrete by immediately after finishing by:

Ponding

• Build dike, then fill with water to cover the entire concrete slab.
  Avoid water or dike material that can stain the concrete.
• Use curing water at a temperature within 20F of the concrete temperature.
• Avoid premature or sudden release of ponded water, which can damage the surrounding environment.

Sprinkling or Fog Spraying

• Keep surface continuously wet; alternate wetting and drying causes craze cracking.
• Use a water temperature within 20F of the concrete temperature.
• Avoid if water runoff can damage the surrounding environment.

Using Wet Materials

• Cover the concrete with wet burlap, straw, sawdust, or sand.
• Wet continuously or cover plastic sheets and wet frequently.
• Avoid materials that discolour concrete.
• Prevent materials from blowing away.

Using Plastic Sheets or Waterproof Paper

• Use flat, lap edges 6 inches, and cover exposed concrete edges.
• Use minimum 4-mil-thick plastic sheet: white in hot weather and black in cold weather.
• Don’t use on architectural concrete
• Secure covering to prevent concrete exposure.

Using Curing Compounds

• Apply after finishing when bleedwater disappears.
• Apply in two applications, at right angles, to form a continuous film.
• Typical coverage rates are 150 – 200 square feet per gallon.
• Avoid using on surfaces to be covered with paint or toppings, unless approved by the manufacturer.

Settlement Cracks

These are cracks which occur directly over deep sections of concrete.  They usually adopt a pattern similar to that of the reinforcement directly under it.  Since all concrete settles within a few hours after being placed, and the deeper the section the greater the settlement will be, settlement cracks occur over beams mainly.

Both types of cracking are influenced by additional water in the concrete, improper curing, improper placing, insufficient compaction.  Shrinkage cracks are also influenced by high winds, direct sunlight, hot and humid weather which all speed up the drying of the surface of freshly placed concrete.