PURPOSE: To improve carbonization resistance and durability by impregnating an aq. soln. of a specific metal salt into the concrete.

CONSTITUTION: The metal salt of carboxylic acid is obtd. by compounding 3 to 8C carboxylic acid, such as propionic acid and latic acid, and metals (e.g.: Mg, Zn) having ≥Ca ionization potential and adjusting the solubility of the mixture in water to ≥3g/100ml. The lightweight foamed concrete previously subjected to a drying treatment is immersed into the aq. soln. of such metal salt of the carboxylic acid and is then dried, by which the lightweight foamed concrete having the excellent oxidation resistance is produced.