Investigation on the mechanical properties and microscopic mechanism of solidified engineering waste soil with CSG

Improper disposal of engineering waste soils (EWS) in China’s coastal urban areas via landfill and marine dumping poses environmental and geotechnical risks, highlighting the need for sustainable recycling methods. This study investigates the mechanism of EWS specimens from Ningbo, Zhejiang Province, dealing with an optimized cement-slag-gypsum (CSG) stabilizing agent. Comprehensive analyses, including unconfined compressive strength (UCS), water stability tests, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy, were conducted to elucidate stabilization mechanisms. Life-cycle assessments quantified the economic and ecological advantages of CSG implementation. Results indicated superior long-term stabilization performance with UCS reaching 3885 kPa at 28-day curing (10% additive). The formulation exhibited robust organic tolerance, maintaining UCS above 1.0 MPa in waste soils containing 10% organic matter at an 8% dosage. The specimens also demonstrated water stability coefficients up to 0.969, exceeding standard requirements by 21.3%. Microstructural analyses confirmed pozzolanic reactions forming C-S-H/C-A-H gels, portlandite, ettringite, and calcite, enhancing soil integrity through pore-filling and inter-particle bridging. Techno-economic evaluation showed that CSG reduced material costs by 38-45% and CO2-equivalent emissions by 62-70%. These synergistic benefits substantiate CSG’s viability as an eco-efficient solution for coastal geotechnical applications.