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Waste concrete must be crushed, screened, and ground in order to produce high-quality recycled aggregate. In this treatment process, 15–30% waste concrete powder (<0.125 mm) can be generated. Hydration activity and the reuse of waste concrete powders (WCPs) were studied in this work, and the results illustrated that the particle size changed after a series of thermal treatments at temperatures from 400 ℃ to 800 ℃. The particle size of waste concrete powder decreased by 700 ℃ thermal treatment, and by 600 ℃ thermal treatment, it increased. More active elements appeared in WCP heated by 800 ℃. Nevertheless, the activity index (AI) of WCP, measured by the ratio of mechanical strengths between mortar with a 30% replacement of the cement with WCP and normal mortar without WCP, indicated that the WCP by 700 ℃ thermal treatment had an optimal AI value, which meant WCP treated at 700 ℃ could be used in mortar or concrete as an admixture.

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Abstract. Calcium carbonate concrete is a normally concrete in the area with rich limestone. With the heavy use, a large of Calcium carbonate concrete waste is generated, how to reuse the waste is an important problem. The generation of reactive powder concrete (RPC) with silica fume is relative more expensive than normal concrete. Using the calcium carbonate concrete waste instead of silica fume in RPC can realize the recycling of construction and demolition waste, moreover, the high price of RPC manufacture can be decreased. The study mainly focused on the mechanical properties and durability as well as the microstructure of RPC with calcium carbonate concrete waste powder (CCWP) instead of silica fume, the results confirmed that the mechanical strengths of 3, 7, 28 days of RPC with CCWP did not obviously decrease, freezing and thawing test could attain to 500 recycles without obvious destruction and carbonation did not happen after 28 days. RPC with CCWP had no more amorphous material and good crystallinity, its microstructure was dense as that of RPC without CCWP.