Recycling solid waste to produce eco-friendly ultra-high performance concrete: A review of durability, microstructure and environment characteristics.

Recycling waste materials (WMs) is a cost-effective method for saving natural resources, protecting the environment, and reducing the use of high-carbon raw materials. This review aims to illustrate the impact of solid waste on the durability and microstructure of ultra-high performance concrete (UHPC) and to provide guidance for the research of eco-friendly UHPC. The results show that the proper use of solid waste to replace part of the binder or aggregate has a positive effect on the performance development of UHPC, but further enhancement techniques should be developed. When solid waste is prepared as a binder, the durability of waste based UHPC can be effectively improved by grinding and activation. When solid waste is used as an aggregate, its rough surface, potential reactivity and internal curing effect are also beneficial to the improvement of UHPC performance. Since UHPC has a dense microstructure, it can effectively prevent the leaching of harmful elements (heavy metal ions) in solid waste. However, the effect of waste modification on the reaction products of UHPC needs to be further studied, and design methods and testing standards suitable for eco-friendly UHPCs should be developed. The use of solid waste in UHPC effectively reduces the carbon footprint of the mixture, which is beneficial to the development of cleaner production technologies.