Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash (ISSA) and dredged contaminated marine sediments (CMSs) is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity. The present study investigates the use of high content (20% of sediment by mass) of ISSA in combination with cement/lime for solidification/stabilization (S/S) treatment of CMSs to provide a way to reuse the wastes as construction materials. The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content (∼80%). The S/S treatment improved the engineering properties of the sediment, but reduced the workability, especially for the lime-treated samples. Lime can be used to replace ordinary Portland cement (OPC) for better heavy metal immobilization and carbon emission reduction. The hardened sediment samples prepared with 10% of lime and 20% of ISSA could attain a strength of 1.6 MPa after 28 d of curing. In addition, leaching tests confirmed that there was no environmental risk induced by these stabilized materials. The formation of hydrated cementitious compounds including calcium silicate hydrate (C–S–H)/calcium aluminate silicate hydrate (C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.