Autogenous shrinkage and nano-mechanical properties of UHPC containing waste brick powder derived from construction and demolition waste

[Display omitted] •Using recycled brick powder (RBP) derived from C&D waste as SCM to prepare UHPC.•Using 15% RBP instead of silica fume improves the solid packing state and mechanical properties of the UHPC mixture.•The 15% RBP reduces the content of unhydrated and pore phase in the UHPC matrix, but increases the content of UHD C-S-H.•It is feasible to use 15% RBP to replace silica fume to produce eco-friendly UHPC mixture. Using recycled brick powder (RBP) as an alternative material in cement-based materials is an effective way to make high-value utilization of construction and demolition (C&D) waste. In this study, RBP was used to replace part of silica fume (SF) to improve the volume stability and environmental benefits of ultra-high performance concrete (UHPC), and the influence of different RBP contents on the mechanical strength, autogenous shrinkage, and microstructure of UHPC mixture was explored. The results show that although using 30–45% of RBP to replace SF reduces the strengths, an appropriate amount of RBP (15%) can significantly improve the mechanical strength of UHPC. Meanwhile, as the replacement rate of RBP increases, the autogenous shrinkage of UHPC decreases significantly. In addition, the incorporation of 15% RBP improves the solid packing state, and the internal curing effect of RBP improves the performance of the interface transition zone. From the perspective of nano-scale characteristics, the appropriate amount of RBP (15%) reduces the content of unhydrated phase, pore phase and high-density C-S-H in the matrix, while makes the ultra high-density C-S-H content increase significantly. Furthermore, UHPC mixed with 15% RBP shows lower cost and CO2-e emission. Therefore, it is feasible to use 15% RBP to replace SF to produce eco-friendly UHPC mixture.