Recycled cement

Cement recycling can reduce the environmental impact caused by the landfills of demolished concrete and the demand of raw materials for producing cement because the waste cement paste in demolished concrete could be used to produce recycled cement. Recycled cement was produced through burning a 2-year-old waste cement paste at 4 different temperatures (120 degrees C, 450 degrees C, 750 degrees C and 1150 degrees C) and then grinding into powder. The selected temperatures were the temperatures where there was a significant weight loss based on the thermogravimetric analysis (TGA) result of the old cement paste. The results show that the highest compressive strength happened at 450 degrees C and the recycled cement paste had a similar strength as OPC paste but with a poor workability which was even beyond the measurement range of a rheometer. Increasing the particle size of recycled cement powder and partially replacing the cement powder with ground-granulated blast-furnace slag (GGBS) were found to be able to improve the workability of recycled cement paste effectively and at same time without reducing the compressive strength. (C) 2018 Elsevier Ltd. All rights reserved.