Alkaline Activation of Volcanic Ash as Binder for Soil Improvement

Abstract

An experimental investigation on chemo-mechanical evolution of alkali-activated binders as alternative and economical solution for soil improvement has been developed. Alkaline activation of volcanic ash from Mount Etna has been analyzed. Reactivity of the volcanic ash has been investigated considering two alkaline activators with different molar concentrations (i.e. 8M and 12M NaOH solutions). Mineralogical evolution of the binders has been monitored at increasing curing times by means of X-ray Diffraction Analysis (XRD) and Scanning Electron Microscopy (SEM). The experimental evidence at microscale has been related to the results of investigations at macroscopic level. Ultrasonic wave velocities and Uniaxial Compressive Strength tests (UCS) have been performed and interpreted considering the mineralogical evolution of the system. Test results showed that the high reactivity of ash, treated with 8M NaOH solution, promotes the formation of minerals (i.e., clays and zeolites) from amorphous substance, determining an increase in compressive strength values over curing time. The use of alkaline solution with higher molar concentration (i.e., 12M NaOH solution) prevents the ongoing of alkaline activation reactions inhibiting the potential mechanical improvement of the binder.