Shear wave velocities to monitor curing evolution of soils treated with alkali activated binders

The use of alkali activated binders for soil improvement has been significantly increased in the past decade indicating a significant interest in the use of alternative low carbon binders. The optimisation and preliminary characterisation of the mixtures is usually addressed with destructive tests to evaluate strength such as unconfined compression strength tests. Although important and necessary, these tests require a significant number of specimens, especially when monitoring the strength evolution with time due to curing. Seismic wave velocity measurements, in particular S wave velocities, allow a fast evaluation of the elastic shear stiffness with time avoiding specimens' failure. This is even more important in soils stabilised with alkali activated binders, since its strength and stiffness evolution with time is generally very long, keeping increasing far beyond the 28 days mark usually assumed in soils improved with Portland cement. In this paper, the evolution of the elastic stiffness with time for different soils treated with alkali activated binders is presented. The compilation of the results for different soils and mixtures, allowed a clear definition of the typical trend and range.