Question

Cement hardening is chemical change or physical change .

Answer 1

Hydration is chemical rxn in which major compounds in cement from chemical bonds with water molecules and become hydrates or hydration products.

Answer 2

Chemical. Water evaporates as bonds form, heat is evolved, and cement crystals form to harden the concrete, thus both new physical and chemical properties form.                                                                

The changes which can not be undone are called permanent changes.

Cement, when it comes in contact with moisture, it gets hardened. It cannot be converted back to powdered cement again. Hence, it is a permanent change.                                                                    

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