Eco-efficient mortars from tunnel excavated soils for wall panels: Performance enhancement and life cycle evaluation

Valorizing the millions of tonnes of tunnel excavated soil (ExS) from urban mega-projects like the Grand Paris Express is a critical challenge for the circular economy, while the construction sector simultaneously seeks low-carbon alternatives to conventional finishing materials. This study pioneers a holistic approach to upcycling ExS into mortars for sustainable products (non-structural interior wall panels), by systematically comparing conventional (CEM I, slag) and novel biopolymer (tannin) stabilizers combined with hemp fibers across fourteen formulations. The tannin-stabilized formulation (Mix10: 5 % CEM I, 2 % tannin, 0.8 % hemp) achieved an optimal balance of properties, with a 28-day compressive strength of 0.85 MPa and a low thermal conductivity of 0.459 W/m·K. A cradle-to-gate Life Cycle Assessment (LCA) revealed that slag-based mortars (M4) reduced Global Warming Potential (GWP) by 96 % and 44 % compared to conventional gypsum mortars and a reference ExS mortars, respectively. By introducing and validating a CO₂ intensity index for earthen mortars, this work provides a new benchmark for evaluating eco-efficiency. The findings demonstrate that ExS mortars can be upcycled into panels that are both technically proficient and environmentally superior to market alternatives, offering a scalable solution for sustainable urban construction. • Tunnel excavated soil upcycled into eco-efficient wall mortars. • Fourteen mixes with CEM I, slag, lime, tannin, and hemp fibers assessed. • Multi-criteria analysis identified optimal ExS mortars for wall panel use. • Slag-based mortar cut global warming potential by up to 96 % • LCA and CO 2 -intensity index demonstrated strong eco-efficiency.