Abstract: Aggregate is separated from sludge consisting of, what is called, "the residual raw concrete" remaining in a raw concrete mixing truck from which raw concrete has been discharged, and waste water resulting from washing the mixing truck. Then, the air is forced into the sludge to form bubbles. A chemical admixture in the sludge is allowed to adhere to the bubbles, and an admixture coating within the sludge is destroyed, thereby promoting the hydration of the cement. Subsequently, the resultant sludge is dehydrated to obtain a dehydrated cake of high hardness. Powder formed of the same quality of the cake is spread over the cake, which is then cured for a few hours. The resultant cake is then crushed so that granular aggregate can be formed.

Abstract: Aggregate is separated from sludge consisting of, what is called, "the residual raw concrete" remaining in a raw concrete mixing truck from which raw (uncured) concrete has been discharged, and waste water resulting from washing the mixing truck. The sludge is stored in a pretreatment vessel. Then, air is forced into the sludge to form bubbles. A chemical admixture in the sludge is allowed to adhere to the bubbles, and an admixture coating within the sludge is removed, thereby promoting the hydration of the cement. Subsequently, the resultant sludge is dehydrated to obtain a dehydrated cake of high hardness. Powder formed of the same quality of the cake is spread over the cake, which is then cured for a few hours. The resultant cake is then crushed so that granular aggregate can be formed.