Transforming ceramic residues into circular economy solutions in geotechnical engineering

The escalating ecological concerns related to ceramic residue disposal have encouraged their valorization in geotechnical engineering as a sustainable alternative. This study evaluates the effectiveness of ceramic waste calcined at 900 °C (CW), used alone or with 2% ordinary Portland cement (OPC), for improving low-bearing-capacity clay soils. CW was incorporated from 3 to 18%, and its effects were assessed using methylene blue value (MBV), Atterberg limits (LL, PL, PI), compaction (MDD), unconfined compressive strength (UCS), California Bearing Ratio (CBR), and compressibility (Cc, Cs). Response surface methodology (RSM), supported by ANOVA and regression modeling, was used for optimization and prediction. Results showed significant improvements: MBV decreased by 59.19% at 18% CW; MDD increased by 5.57% and up to 7.55% with OPC. The liquid limit decreased by 23.83% at 9% CW, while the plastic limit dropped to 21.9% at 15% CW and to 20.45% with 12% CW + 2% OPC (- 37.71%). The lowest PI was obtained at 9% CW, reaching 24.06%, corresponding to a reduction of approximately 28.44% compared with the untreated clay. The CBR increased by 351.67% with OPC. UCS improved by 321.71% at 9% CW and reached 698.76% with 9% CW + 2% OPC after 56 days. Compressibility parameters were reduced, with Cs and Cc decreasing by 73.56 and 59.49% at 9% CW, and by 79.58 and 72.46% with OPC. The developed models showed high predictive accuracy (R² ranging from 0.77 to 0.98, p < 0.0001). These findings confirm that calcined ceramic waste, particularly combined with OPC, is an effective and sustainable solution for soil stabilization, supporting circular economy practices.