The setting and hardening of portland cement is the main reason why cement will not dissolve again after hardening.
Cement coagulation refers to the process that cement and water are mixed to become plastic slurry, in which the minerals on the surface of cement particles begin to dissolve in water and react with water, and the oxidation in cement reacts with water to generate hydroxide, and the cement slurry gradually thickens and loses plasticity, but still has no strength.
Hardening refers to the process that the solidified cement paste begins to produce obvious strength and gradually develops into a hard cement paste with the further hydration. Coagulation and hardening are artificially divided, in fact, it is a continuous and complex physical and chemical change process.