Recycling stone powder as a partial substitute for cementitious materials into eco-friendly manufactured sand ultra-high performance concretes: Towards cleaner and more cost-effective construction production

The increasing scarcity of natural sands has led to a growing preference for manufactured sand in the production of construction materials in response to sustainable development. However, existing research typically applies it to ordinary concrete, its application in advanced concrete still remains relatively limited to date. In this study, manufactured sand was used as aggregate to prepare the eco-friendly ultra-high performance concrete (UHPC). To further improve the effectiveness of solid waste management and alleviate its impact on the environment, the feasibility of ecological utilization of recycling stone powder (SP), a by-product from manufactured sand industry, as partial substitutes for cementitious materials was explored. The fresh and hardened properties, microstructural characteristics, environmental and economic implications were evaluated. Results indicated that the introduction of SP considerably enhanced the rheological properties and reduced the exothermic peak temperature of UHPC paste. With the increase of SP, a first increasing and then decreasing trend was seen in flowability. An equivalent or slightly improved level of mechanical strength was revealed at low SP content (i.e., 10%). Different lithological SP was found to enhance the toughness and suppress the early shrinkage of UHPC. Incorporating SP increased the total pore volume and refined the distribution of pore sizes, and could also change the morphology of hydration products and Si/Ca ratio of interfacial transition zone. Additionally, the lowest unit compressive strength costs were achieved at the substitution of 20%, 10% and 20% for granite, tuff and limestone mixtures, and the carbon emissions could be lowered by 26.9% compared with traditional UHPC when 30% of SP was involved, showing excellent economic and environmental benefits.