Lightly Stabilized Loose Sands with Alkali-Activated Fly Ash in Deep Mixing Applications

Abstract

Deep mixing using cementitious compounds are an in-situ ground improvement method for improving the strength and compressibility of loose sands. Low-calcium class F fly ash (FA) is a sustainable low-carbon replacement for Portland cement that was utilized for stabilization of loose sand. The unconfined compression strength (UCS) of uniform fine sand and well-graded medium sands, stabilized by alkali-activated FA, were determined and the strengths of optimized blends were compared with the minimum required strength advised by guidelines for cement-treated deep mixed soils. The decementation softening behavior of lightly stabilized zone was investigated under loose and dense conditions for both types of sands with two different types of binder under k0-loading conditions. Both the stabilized sands, with 10% FA and the optimized alkali activator Na2SiO3:NaOH ratio of 70:30 satisfied the 700 kPa UCS requirement for deep mixed soil. The UCS strength has increased up to 1,400 kPa for 15% FA content. The variation of void ratio due to softening decementation of the lightly stabilized sand was in close correlation with changes in shear wave velocity. The well-graded medium sand was found to be less sensitive to decementation due to the higher coordination number of interparticular contact.