Field trial of all-solid-waste stabilized soda residue for roadway subgrades: mechanical performance and...

Soda residue (SR), a highly alkaline and saline by-product of the ammonia-soda process, remains difficult to reuse at high dosage because of its high water content and soluble-salt release. Here, an all-solid-waste stabilized soda residue (S-SR) containing 70 wt.% SR was validated in a full-scale roadway subgrade to assess field constructability, engineering performance, and environmental behavior under natural exposure. Under low-temperature natural curing, mean California bearing ratio (CBR) increased from 38.6% at 1 d to 164.6% at 28 d, resilient modulus from 260.8 to 388.6 MPa, and dynamic deformation modulus from 65.6 to 199.9 MPa, while rebound deflection decreased from 0.374 to 0.190 mm. Degree of compaction and initial water content jointly controlled spatial variability. Leached Cl^- decreased from 3028 mg/L at 1 d to 268 mg/L at 60 d and SO₄^2- from 286 to 15 mg/L. Over five months, lysimeter leachate pH decreased from 10.87 to 8.32 and electrical conductivity from 15,469 to 4,236 μS/cm (a 72.6% reduction), indicating gradual decreases in leachate alkalinity and overall dissolved-ion level during the middle-to-late monitoring period. The dynamic cone penetration index (DCPI) showed strong power-law relationships with field mechanical indices (R² = 0.94-0.99) and evolved consistently with anion leaching. Compared with reported SR-based systems, S-SR achieved higher SR utilization and 7-d CBR, together with lower material-related cost and production-stage carbon emissions. The study provides field-scale evidence for high-content SR reuse while documenting age-dependent leaching attenuation and field environmental responses under natural exposure.