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Reduce Plastic Shrinkage Cracks

28th October 2014

Reduce Plastic Shrinkage Cracks

Plastic shrinkage cracks appear in the surface of fresh concrete soon after it is placed and while it is still plastic. These cracks appear mostly on horizontal surfaces, relatively shallow, and generally do not intersect the perimeter of the slab.

Why do Plastic Shrinkage Cracks occur?

Plastic shrinkage cracks are caused by a rapid loss of water from the surface of concrete before it has set. Conditions that cause high evaporation rates from the concrete surface and can increase the possibility of plastic shrinkage cracking include:

  • Wind
  • Low relative humidity
  • High ambient / concrete temperatures

Small changes in any one of these factors can significantly change the rate of evaporation. Factors that delay concrete setting can also increase the possibility of plastic shrinkage cracking. Delayed setting can result from a combination of one of more of the following: cool weather, cool subgrades, high water contents, lower cement contents, retarders, some water reducers and supplementary cementing materials.

How to minimise Plastic Shrinkage Cracking?

The most effective way to prevent plastic shrinkage cracking is to prevent rapid loss of moisture from the surface of the concrete. Curing compounds are generally used once the concrete is trafficable to reduce plastic shrinkage cracks, however cracks can form while the concrete is still in its plastic state. A method widely used is the application of an evaporation retardant sprayed on the surface of concrete immediately after initial screeding has been completed.

The use of an evaporation retarder such as Concure AV is used as a precaution to greatly reduce cracking caused by unfavourable weather conditions. Concure AV, a water based evaporation retarder is recommended for spray applications locking in moisture until concrete has set and before a curing compound can be applied.

Concure AV completely evaporates making it compatible with any curing compound on the market. Concure AV is useful in all types of flat concrete applications, whether plain or coloured, machine or hand finished, including stamped concrete.

Advantages of Concure AV

  • Reduces and often eliminates the formation of shrinkage cracks in plastic concrete
  • Gives superior finishing properties during unfavourable weather conditions.
  • Maintains a plastic and workable surface.
  • Prevents surface crusting
  • Full evaporation ensures compatibility with all curing compounds.
  • Violet in colour for ease of application, Concure AV will not discolour the finished concrete or leave any residue.

For more information contact Concrete Plus

Concure AV Technical Data