This study proposes separation techniques of unhydrated cement grains from waste fresh concrete: freeze-drying method and oven-drying method. These methods enable one to reuse the recovered cement as cementitious admixtures of concrete. The hydration reaction can sufficiently take place again by adding batch water to the recovered cement powders. The cement paste of recovered cement can produce the compressive strength 92-87% against the corresponding strength of reference cement paste using ordinary Portland cement for w/c of 0.3. The use of retarding admixture to the cement paste before freezing or oven-drying results in significantly higher strength compared with the cement paste without retarding admixture.
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