Abstract
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.
Highlights
Due to the large volume of construction and demolition wastes and the deficiency of natural resources, the recycling of building material wastes is urgent and of great importance
differential scanning calorimetry (DSC) detection can explain the heat change of waste concrete powders (WCPs) in the process of thermal treatment (Figure 2), where a big endothermic peak occurred at temperatures from about 700 to 900 ◦ C because of decomposition of calcium carbonate
WCP mass was lost in the thermal treatment process; with the increase in temperature, more mass losses occurred because of the water escape and chemical reaction
Summary
Due to the large volume of construction and demolition wastes and the deficiency of natural resources, the recycling of building material wastes is urgent and of great importance. The use of building material wastes in concrete can realize up-recycling for building materials. Concrete wastes can rarely be reused as recycled aggregate to prepare concrete because recycled aggregates “contaminated” with cement paste have lower mechanical properties owing to the presence of cement paste. Many experiments were carried out to enhance the quality of recycled aggregate, e.g., incorporation of thermal and mechanical treatment [4] and carbonation treatment to strengthen the recycled aggregates [5,6]. In the process to treat the recycled aggregate, some fine powders including cement paste, sand, and coarse aggregate powder are produced, and some studies focused on the quality improvement and application. Increasing the particle size of recycled cement powder with 450 ◦ C treatment and partially replacing the cement powder with ground-granulated blast-furnace slag could effectively improve the quality of recycled cement [7]. Xuan and Shui [8,9] reported that new calcium silicate hydrate (C-S-H)
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