Portland cement (and the concrete, mortar, thin set, or other masonry product made from it) doesn't dry. Rather, it cures by a chemical reaction initiated by putting water in it. The reaction is irreversible; hence, adding water to cement is an irreversible change.
No, once water is mixed with cement, an irreversible reaction occurs
Irreversible
mixing cement with water is a irreversible change
reversible
It isn't easily reversible but, it is reversible. You can use a molecular sieve or a distillation column to separate them.
Yes it is. Once mixed it can never be altered or undone
Actually both physical and chemical changes are happening during cement mixing.
mixing cement with water is a irreversible change
It is reversible. You can allow the water to evaporate, leaving the salt behind.
Sugar and Salt
no
Irreversible
reversible
A. Cement
cement
the strength of concrete is effected by water /cement ratio as the water/cement ratio increases the strength of the concrete decreases
That depends on what is being mixed together. Two examples of this are: If you mix sand, gravel, and water it is reversible and you can separate the mixture back to its original three parts. If you mix sand, gravel, water, and cement powder it is not reversible as the water will react with the cement powder creating liquid cement and the sand and gravel will form concrete with the liquid cement. After a few hours the liquid cement in the concrete will set and the concrete mixture will become as hard as rock. It is now no longer possible to separate the mixture back to its original four parts.
Because - you can simply evaporate the water by heating it, and collect the water in a separate vessel - leaving the dry sand intact.
It isn't easily reversible but, it is reversible. You can use a molecular sieve or a distillation column to separate them.