Effects of Fly Ash Content on the Strength Development of Soft Clay Stabilized by One-Part Geopolymer under Curing Stress

Abstract

The objective of this study was to evaluate the effects of fly ash content on the strength development of soft clay stabilized by one-part geopolymer (OPG) under $K_0$ stress conditions. In this study, a novel curing stress system under $K_0$ conditions was developed to investigate the strength development of OPG-stabilized soil when subjected to different stresses at various depths. Several combinations of fly ash (FA) and ground granulated blast furnace slag (GGBFS) as aluminosilicate precursors triggered by solid NaOH (NH) with certain amounts of water were prepared as OPG binders. The OPG-stabilized soil samples were cured under vertical stresses of 0, 50, 100, and 200 kPa for 1, 3, 7, and 14 days. During curing, the skeleton improvement of OPG-stabilized soil was recorded by a tactile pressure sensor, and the strength development of samples under different curing stresses and curing times was evaluated by the unconfined compressive strength (UCS) and shear wave velocity ($V_S$ ). Additionally, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) and X-ray computed tomography (CT) were also used to illustrate the role and contribution of factors on the hydrate composition and microstructure, especially the role of the porosity. The results indicated that the strength of the sample increased substantially with a reduction in porosity due to the curing stress. Furthermore, the optimum content of FA ($\mathrm{FA}/\mathrm{GGBFS}=0.1$ ) could improve the workability and microstructure of OPG-stabilized soil samples, as reflected by the increase in the UCS and $V_S$ . Finally, the UCS prediction of OPG-stabilized soft clay under curing stress is proposed based on the shear wave velocity.