# Experimental Investigation and Mechanism of Fly Ash/Slag-Based Geopolymer-Stabilized Soft Soil+
###### Abstract  
In response to the high carbon emissions and energy consumption of traditional cement curing agents, in this paper, we propose a fly ash/slag-based geopolymer as an alternative to cement for stabilizing soft soils. In this study, the effects of the activator modulus, activator, and slag content on the geopolymer-stabilized clay were investigated by unconfined compressive strength (UCS) tests on Hangzhou soft soils, and the water stability and resistance to wet-dry cycles of the geopolymer-stabilized soils were studied. The changes in the microstructure and mineral phases were investigated using X-ray diffraction and scanning electron microscopy, respectively, and the inner evolution of the properties of the stabilized soft soil under different conditions was clarified. The test results revealed that the UCS of the geopolymer-stabilized soft soils increased and then decreased as the content and modulus of the alkali activator increased. The optimum mix proportion of geopolymer-stabilized soil required a modulus of the alkali activator of 0.6, a content of the alkali activator of 6%, and a slag-to-fly ash ratio of 1:1. Its 28-day UCS of the test specimens reached 2 MPa. When the content of the geopolymer was 25%, the water stability coefficient reached 87.53%, and the strength was still 1.6 MPa after eight wet-dry cycles. Based on the microscopic analysis, the cementing substances in the geopolymer-stabilized clay were calcium silicate hydrate (C-S-H) and sodium aluminosilicate hydrate (N-A-S-H), which made the soil's structure denser through bonding and filling effects. f 2022 2020 20 July 2022 2020 20 July 2022 2020 2022 2020  
through an activation reaction. Also known as green cement, the role of the activator is to dissolve the aluminum (Al) and silicon (Si) present in the precursor, forming an aluminosilicate gel [5]. With their high strength, low energy consumption, low cost, good volume stability, good impermeability, and chemical resistance, geopolymers are gaining wide attention and are being used in research applications worldwide [5; 6; 7]. In recent years, geopolymers have become more widely used in the concrete field and in stabilizing the pavement base, and the application of geopolymers to strengthen deep soft soils has gradually attracted the attention of scholars. The addition of a geopolymer has been found to increase the peak strength of treated soil and decrease the corresponding axial strain failure, both of which contribute to obtaining a stiff response similar to that of ordinary Portland cement (OPC)-stabilized soils [8; 9]. [PERSON] et al. [10] studied the effect of a geopolymer on the mechanical strength of cement-stabilized soil using test methods such as UCS, scanning electron microscopy (SEM), and mercury intrusion tests; they explored the mechanism by which it improved the strength of the cement-stabilized soil and verified the practicality and economy of using the geopolymer in cement soil based on field tests. [PERSON] et al. [11; 12] used water glass as the excitation agent of metakaolin in soft ground curing tests and selected the optimal combination based on the compressive strength and permeability data from the tests conducted on the use of cement and water glass excitation of metakaolin to stabilize soft soils. [PERSON] [13] used palm oil ash and fly ash-based polymers to stabilize sand and clay soils and investigated the long-term development pattern of the strength of the stabilized soils. [PERSON] et al. [14] used an alkali-excited low-calcium fly ash cementitious material to stabilize silt soil and determined the trait evolution and microscopic mechanism of the strength of the alkali-excited fly-ash-stabilized silt by analyzing the macro- and microscopic properties, including compressive strength, chemical composition, cross-sectional morphology, and pore structure. [PERSON] et al. [15] studied fly ash/slag-based geopolymer-stabilized silt clay and found that the pre-strength of the stabilized soil decreased with increasing fly ash content.