Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste

Abstract Hybrid Recycled Powder (HRP), which was collected from construction and demolition waste (C&DW), normally possessed potential activity due to it contained unhydrated cement and clay particles. In order to realize high-valuable utilization of HRP, it is necessary to find a suitable activation method that can stimulate the potential activity of HRP. Therefore, the effect of HRP subjected to mechanical, chemical, or nano activation, on the compressive strength and microstructure of cement pastes, was analysed in this study. Results showed that the original HRP presented low activity and uneven size distribution. Activation for HRP was helpful to increase the compressive strength of cement pastes, owing to the modification for particle sizes and distribution, and the optimisation for shape and surface cracks. The compressive strengths of the cement paste with chemically activated 20% HRP were 23.25 MPa and 73.46 MPa, at 3 days and 28 days, which were 35.94% and 34.75% higher, respectively, than for the cement paste with non-activated 20% HRP. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the changes in the mineral composition and micromorphology of cement pastes with HRP, and thermogravimetric differential thermal analysis (TG-DTA) was used to quantitatively analyse the hydration processes in cements with and without HRP. Results indicated that chemical activation had the best effect on the hydration degree of cements, compared with the mechanical and nano activation methods. This paper implies a useful combined activation method for HRP, which is contributed to the potential application of HRP.