Loess soil stabilisation by addition of non-conventional binder materials

Conventional stabilisation with lime or cement enhances soil performance but entails significant environmental costs. This study explored three widely available waste materials, steel slag (SS), construction and demolition waste (CDW) and eggshells (ES) as non-conventional binders. These materials were selected for their comparable chemical or physical properties to those of conventional binders and for their abundance, low cost and their capacity to reduce the environmental impact of landfilling through effective reuse. Experimental results demonstrate that a 3% addition of ES increased unconfined compressive strength (UCS) to values exceeding 4000 kPa after 56 days of curing, outperforming the reference lime-stabilised sample (2000 kPa). Likewise, the corresponding secant modulus (Es) reached 254.9 MPa with ES, compared with 187.7 MPa for lime. For granular additions, 30% SS yielded UCS values above 1500 kPa, while 24% CDW achieved over 500 kPa. Microstructural analyses confirmed that hydration and pozzolanic reactions are responsible for the improvement. Overall, the stabilised samples exhibited a mechanical performance comparable to that of conventional binders, which would promote the reuse of substantial waste streams and contribute to reductions in greenhouse gas emissions. These findings indicate a viable pathway towards more sustainable ground improvement practices within the framework of a circular economy.