Deep soft soil improvement by alkaline activation

This research studied the use of alkaline activation of fly ash, as a silica and alumina amorphous source, to improve soft soils. A laboratory programme – including tests to study strength and deformability development, alternative curing methods, the effect of the different components of the grout, effect of raising initial temperature and comparison with a cement grout – was carried out. Laboratory tests revealed that the use of fly ash and alkaline activator resulted in a soil strength improvement up to 11·4, 16·7 and 43·4 MPa, at 28, 90 and 365 days curing, respectively. The most effective combinations obtained in the laboratory were chosen for the field application with jet grouting. The grout performed adequately to pass standard engineering specifications for soil mixing, achieving up to 26·4 MPa at 90 days curing. The main conclusion is the potential of alkaline activation for soil improvement, and therefore this research has created a basis for further studies.