Abstract
Foundation of buildings in soft soil such as quaternary clay is often associated with difficult compaction, settlement, non-uniform and/or excessive deformation, and unsatisfactory shear resistance. The present study aims to assess the possibility of using recycled fines from construction and demolition waste, such as mechanically treated gypsum and waste concrete powder (WCP), instead of ordinary binders or industrial waste, in the stabilization of quaternary clay. A detailed characterization of soil components is presented. Seven mixes with various proportions of gypsum and WCP are prepared. Main geotechnical parameters of the modified soil are studied by applying standardized methods with a few deviations. XRD analysis and pH measurements are performed. It was found that the effect of 5% to 20% recycled di-hydrate gypsum is limited to improvement in moist soil compatibility. A gypsum content of 10% positively impacts soil cohesion and the oedometer modulus. WCP is an active component, containing non-hydrated cement, portlandite, calcite and calcium silicates hydrate. As a result, by adding 5% of WCP only, significant improvement can be achieved: greater soil cohesion, reduced deformability and higher UCS. When 5% of recycled gypsum is also added, soil cohesion is further improved because of ettringite formation.