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Freeze-thaw weathering

You will need:

  • Cheap pavement chalk
  • Cold water in a bowl
  • Hot water in a bowl and tongs
  • Freezer and a plastic bag
  • Patience!

Instructions


1. Snap a chalk piece in half

2. Soak the chalk piece in water until no more air bubbles rise from the chalk - as a precaution, move the chalk around to shake loose any surface air bubbles clinging to the chalk sides.

2. Remove the chalk from the water and place the chalk into the plastic bag.

3. Place the plastic bag in the freezer and wait 6 hours.

4. Pour hot water into a bowl and place the now frozen chalk into it. Ideally a hot dry oven dry would be better as the thermal change would be greater. If you do use an oven, you will need to re-soak the chalk again.

5. Repeat steps 2 to 4 until the chalk breaks
frost-shatter

Why Does This Happen?

Freeze-thaw weathering is common in mountainous areas where the temperature is around freezing point. This type of weathering is caused by the expansion and contraction of water within porous rocks. As ice crystals form, they grow larger, attracting liquid water from the surrounding pores. The ice crystal growth weakens the rocks which can then crack, exfoliate or shatter with the stresses imposed.

Chalk is a quite porous material, containing numerous air pockets. Soaking the chalk replaced the air with water, setting up a situation where the chalk could be broken by rapidly changing the temperature of the materials.

Check out this link on concrete damage from freeze thaw weathering.
 
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Reference: Brady, J. E. & Holum, J. R. (1993). Chemistry. The Study of Matter and Its Changes.
John Wiley & Sons, New York

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