Re-using excavated rock from underground tunneling activities to develop eco-friendly ultrahigh performance concrete

Excavated rock from underground tunneling activities constitutes a significant portion of the overall construction and demolition (C&D) waste, yet its efficient reuse is challenging. Here we propose an integrated approach combining the utilization of the excavated rock and the production of an eco-friendly ultra-high performance concrete (UHPC). As the first steps to assess the feasibility of the approach, the workability, mechanical properties, fracture toughness test, phase stability and shrinkage of the UHPC were comprehensively studied. The results show that increasing excavated rock content in UHPC leads to a reduction in flowability but improves flexural performance with the enhancement of phase stability. However, this enhancement effect diminishes with larger excavated rock sizes. The compressive strength of the mixture with 400 kg/m³ dosage and 5–10 mm size range achieve 104.1 MPa, which is better than the reference UHPC. Meanwhile, elevated excavated rock content obviously reduces UHPC shrinkage, notably within size 5–10 mm. In addition, an overall assessment was performed to evaluate the UHPC from both environmental and economic perspectives. The results indicate that incorporating excavated rock as aggregates into UHPC can result in cost savings of up to 9.5%, an 11% reduction in embodied energy, and a 15.5% decrease in embodied carbon. Additionally, this integration can yield superior properties compared to reference UHPC. This approach also reduces dependence on natural aggregates, promoting sustainability.