The carbon dioxide fixing sludge fine powder, its production method and hydraulically hardened body

A production method of carbon dioxide fixing sludge fine powder comprising:

• a slurrying step of adding water to residual concrete or returned concrete to form a slurry;
• a separation step of separating-removing gravel and sand from the slurry to obtain sludge water;
• a fine sand removal step of separating-removing fine sand from the sludge water by a wet cyclone to obtain concentrated sludge water;
• a dehydration step of dehydrating the concentrated sludge water to obtain a sludge cake;
• and
• a crushing-drying-carbonation step of putting the sludge cake into a rotary drum to supply hot air and highly concentrated carbon dioxide into the rotary drum, and of crushing-drying the sludge cake while fixing the carbon dioxide to obtain the carbon dioxide fixing sludge fine powder;
• wherein
• if only the hot air is supplied into the rotary drum to crush and dry the sludge cake to obtain the sludge fine powder, the sludge fine powder has such quality that area fraction of unhydrated cement to the entire sludge fine powder is 0.5 or more.