Final answer:
Air entrainment should be applied to hardened concrete to protect it from deicing chemicals. This method incorporates microscopic air bubbles to alleviate the stress caused by freezing water and reduce scaling.
Step-by-step explanation:
To protect hardened concrete from deicing chemicals, air entrainment should be applied. Air entrainment adds microscopic air bubbles to the concrete, which act as relief points for the stress caused by the expansion of freezing water and can also reduce the scaling caused by deicing salts and freeze-thaw cycles.
On the contrary, sodium chloride and other salts can actually create the need for such a protective measure since they lower the freezing point of water and can increase the risk of damage to the concrete surface when used as deicing agents. Plasticizers are used to increase the workability of concrete but do not necessarily protect it from deicing agents. Inhibitors can be added to slow down corrosive processes, but they are not specifically designed to protect concrete from deicing chemicals.