Geotechnical properties of sludge blended with crushed concrete and incineration ash

Abstract

Generation of large amounts of waste material reduces the capacity of landfill disposal sites. To make effective use of drinking water sludge (DWS) and DWS blended with crushed concrete (CC) and incineration ash (IA) as geotechnical materials, the geotechnical properties of DWS for suitability of a road subgrade were examined. A series of laboratory tests measuring compaction, California bearing ratio (CBR), undrained triaxial compression, and consolidation was conducted by changing the mixing proportions of tested materials. The compaction test showed that maximum dry density and optimum water content have a unique linear relationship with the proportion of CC/IAs mixed with DWS. Measured CBR values of mixtures of CC/IA blended with DWS at both low energy (600 kJ/m3) and high energy (1800 kJ/m3) showed linear relationships, and an empirical equation was newly proposed in terms of mixing fraction and maximum dry density at low energy compaction. The result of the consolidated undrained triaxial compression test showed that the blend of CC/IA with DWS increased friction angles but did not contribute to an increase in the undrained shear strength. The results of consolidation tests showed that the blend of CC reduced the compressibility of DWS highly, especially samples that contained a proportion of CC and CC/IA greater than 50%. Overall, the blend of CC raised the compaction property of DWS accompanying an increase in bearing capacity, compressibility and can be effective to improve geotechnical properties of DWS for application as a road subgrade.