Abstract: Carbonation reaction and carbonation process of portland cement concrete were introduced,and carbonation of Ca(OH)_2 and calcium silicate hydrated(C-S-H)was analyzed. The analysis showed: C-S-H also reacted with CO_2 while Ca(OH)_2 reacted with CO_2. The main carbonated product of Ca(OH)_2 was calcite and that of C-S-H was amorphous silica gel, and maybe unstable, poorly crystallized aragonite and vaterite were formed. Decomposition temperature of aragonite and vaterite was lower than calcite. C-S-H with low C/S and poor crystallinity was prone to carbonation; the rate of carbonation became higher with higher alkali content.

Key words: concrete%carbonation%Ca(OH)_2%calcium silicate hydrated(C-S-H)