Enhancement of geotechnical properties of municipal sewage sludge for sustainable utilization as engineering construction material

The present study demonstrates potential utilization of lime-stabilized sewage sludge (SS) for construction purposes. SS samples were constituted using 0, 2, 4, 6 and 8% of lime by weight of the SS and cured for 7, 14 and 28 d. Stability of the lime-modified SS was evaluated through determination of geotechnical, microstructural and mineralogical properties. A large improvement in unconfined compressive strength (UCS) from 207 kPa to 1102 kPa was achieved after 28 d of curing SS with 6% lime. The improvement in UCS is attributed to formation of cementing compounds as a result of pozzolanic reactions. Marked reductions in swell pressure of 47, 51, 54 and 58% were obtained with the 2, 4, 6 and 8% lime treatments. Also, the plasticity index decreased with increasing lime content for different curing periods, indicating the SS becomes much more workable and less expansive. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) after lime treatment confirmed formation of the new compounds responsible for the improved engineering properties of SS. The study concludes that lime treatment can be an alternative to stabilize SS for potential use as a construction material for subbase of flexible pavement as per IRC (Indian Road Congress) 37–2012 guidelines.