ECO-FRIENDLY STABILIZATION OF SOFT CLAYS: UTILIZING SEWAGE SLUDGE AS A SUSTAINABLE ALTERNATIVE TO CEMENT

Date

2026-1-19

Author

Haroon, Muhammad Usama

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

206
views

0
downloads

Cite This

Rapid growth in wastewater treatment has intensified the challenge of managing sewage sludge (SS), while the energy- and carbon-intensive nature of Portland cement underscores the need for lower-impact soil stabilisation methods. This thesis investigates the technical and environmental feasibility of partially replacing cement with SS and thermally treated sewage sludge ash (SSA) in cement-stabilised clay. The program spans five SS/SSA conditions (fresh SS; SS at 105°C; SSA at 300, 600, and 1100°C), three cement contents (5, 7, 10 %), four replacement levels (3, 5, 7, 10% by cement mass), two target dry densities (1.5 and 1.7 g cm-3), and three curing ages (7, 28, 60 days). Unconfined compressive strength (UCS), freeze–thaw durability (accumulated loss of mass, ALM), and microstructure (SEM/XRD) were evaluated, and a cradle-to-gate life-cycle assessment (LCA) was performed for representative mixes. Across the matrix, strength increased systematically with cement content, density, and curing time; higher dry density (1.7 g cm-3) and longer curing (7→28→60 days) produced the greatest UCS gains. SSA incinerated at 600°C and fresh SS delivered the most effective low-dosage replacements, with optima typically at 3–5 % SS and ~3–7 % SSA depending on cement level and density; SSA at 1100°C behaved essentially inert, and 300°C/105°C treatments yielded limited benefits. Freeze–thaw testing showed that moderate SS/SSA contents ≈3–7 %) at higher density and longer curing commonly achieved 11–12 cycles with delayed damage accumulation, confirming strong durability at those formulations. SEM/XRD revealed denser matrices with increased C–(A)–S–H formation, especially with 600°C SSA, supporting the observed mechanical trends. LCA results indicated consistent impact reductions relative to cement-only controls across six ReCiPe midpoint categories, with ~8% decreases typical as SS content increased at fixed cement levels; the most efficient environment–durability balance occurred at low-to-moderate SS (≈3–7%). A dimensionally consistent, empirical power-law model quantified the influence of key variables and achieved strong predictive performance (R²≈0.85, low RMSE), providing a practical tool for mix optimisation. Overall, partial cement replacement with fresh SS or 600°C SSA at modest dosages offers a technically robust and environmentally advantageous pathway for stabilising clayey soils.

Subject Keywords

Cement Replacement, Life Cycle Assessment, Sewage Sludge, Soil Stabilisation, Waste Reuse

URI

https://hdl.handle.net/11511/118402

Collections

Northern Cyprus Campus, Thesis