On the use of one-part geopolymer activated by solid sodium silicate in soft clay stabilization

Abstract

The application of geopolymers in ground improvement has garnered significant attention in recent years. However, most geopolymer preparations have focused on the two-part method, which not only has negative environmental impacts but also falls short of meeting practical requirements. This study aimed to address these limitations by employing solid sodium silicate (Na2O·nSiO2, n is the molar ratio, NS) to activate binary precursors (fly ash [FA] and ground granulated blast furnace slag [GGBFS]), along with water, to synthesize a one-part geopolymer (OPG) for soft clay stabilization. The primary factors on the properties of the OPG binder were firstly identified through macro- and micro-tests. Subsequently, the optimization of the OPG mixing proportion was achieved by reducing the molar concentration of NS, and was further used for soft clay stabilization. The effects of the FA/GGBFS ratio (0, 0.1, and 0.2), curing period (7, 14, and 28 days), and binder content (0.15, 0.20, and 0.25) on the mechanical properties of the OPG-stabilized soft clay were then evaluated using unconfined compressive strength (UCS) tests. Furthermore, mercury intrusion porosimetry (MIP), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), and X-ray diffraction (XRD) techniques were employed to examine the evolution of microstructure, hydrate composition, and mineral/phase of the OPG-stabilized soft clay samples. The experimental results indicated that an appropriate OPG stabilizer proportion was achieved with an FA/GGBFS ratio of 0.1, water/precursor ratio of 0.8, molar ratio of NS of 1.0, and molar concentration of 3 mol/L. The high-early-strength feature of OPG binder contributed to the rapid strength development of the stabilized soft clay at an early age. A noticeable pozzolanic reaction was observed in the OPG-stabilized soft clay sample with an FA/GGBFS ratio of 0.1. Additionally, a binder content of 0.20 was recommended for the stabilization of soft clay due to its optimal balance between economic benefits and meeting the required UCS criteria in soil stabilization. Finally, a reliable nonlinear relationship between UCS and porosity of OPG-stabilized soft clay was established to assess the mechanical properties and stabilization effects of the OPG-stabilized soft clay for practical applications. This study greatly enhances the scientific understanding of geopolymerization in the OPG system by using a combination of the binary precursor of FA and GGBFS and the solid NS activator. It sheds light on the stabilization mechanism of OPG-stabilized soft clay. The outcomes of this study make a valuable contribution to the advancement of environmentally friendly soil stabilizers, promoting green and low-carbon practices in the field of ground improvement.