Strength, durability and microstructure of geopolymers based on municipal solid waste incineration fly ash and metakaolin for dredged sediment stabilization

This study employs municipal solid waste incineration fly ash (MSWIFA) and metakaolin (MK) as precursors to stabilize dredged sediment (DS) through alkali-activated technology. The effects of MK/MSWIFA mass ratio and alkali-activator (AA) content on the unconfined compressive strength (UCS) of MSWIFA-MK-stabilized DS (MMDS) and its durability subjected to wetting–drying cycle and immersion tests were investigated. Then the heavy metals leaching, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) tests were conducted on MMDS after 9 wetting–drying cycles and 28 days of water immersion, respectively. The results showed that alkali-activated MSWIFA and MK exhibited excellent solidification performance on DS. Stabilized DS with a higher MK- to -MSWIFA mass ratio and higher alkali content exhibited higher UCS. MMDS mixtures with a MK/MSWIFA ratio of 7:3 and 22% AA yield an UCS of 4.69 MPa after 28 days curing. The UCS of all MMDS under wetting–drying cycles initially increased and then decreased with increasing cycle numbers. Similarly, the UCS of MMDS with higher MK and MSWIFA mass ratios and AA content exhibited the same trend over the number of immersion days. Microstructural analysis confirmed the enhancement in UCS and wetting–drying cycles and water immersion caused damage to the matrix of MMDS. The heavy metal concentrations in the leachates of MMDS after durability tests met the requirements of the specified limit values of standard. Compared with traditional cement or lime solidification approaches, this developed composite alkali-activated cementitious system showed prominent advantages in the co-disposal of multiple solid wastes, low-carbon performance and heavy metal immobilization. The MMDS can be used in engineering applications such as road subgrade filling.