Pre-mixed fluidized solidified soil (PFSS) has the advantages of pumpability, convenient construction, and a short setting time. This paper took the excavated loess in Fuzhou as the research object and used cement-fly-ash-ground granulated blast furnace slag-carbide slag as a composite geopolymer system (CFGC) to synthesize PFSS. This study investigated the fluidity and mechanical strength of PFSS under different water-solid ratios and curing agent dosages; finally, the microstructure of the composite geopolymer system-pre-mixed fluidized solidified soil (CFGC-PFSS) was characterized. The results showed that when the water-solid ratio of PFSS increased from 0.46 to 0.54, the fluidity increased by 77 mm, and the flexural strength and compressive strength at 28 d decreased to 450.8 kPa and 1236.5 kPa. When the curing agent dosage increased from 15% to 25%, the fluidity increased by 18.0 mm, and the flexural strength and compressive strength at 28 d increased by 1.7 times and 1.6 times. A large number of needle-like AFt, C-S-H gel, and C-(A)-S-H gel coagulate with soil particles to form a three-dimensional reticular structure, which is the mechanism of the strength formation of PFSS under the action of CFGC.

Fluidized solidified soil ( FSS ) is a cement-based engineering matergood working performance and mechanical properties. Based on fi xed cement and desulphurisation gypsum ( DG ) , fl y ash ( FA ) and ground granulated blast furnace slag ( GGBS ) were added as admixtures to the construction slurry to prepare three types of FSS: namely cement-GGBS-DG FSS ( CGD-FSS ) , cement-FA-GGBS-DG FSS ( CFGD-FSS ) , and cement-FA-DG FSS ( CFD-FSS ) . Considering 7 d, 14 d, and 28 d three curing times, compressive, fl exural, scanning electron microscopy ( SEM ) , and x-ray diffraction ( XRD ) analyses were conducted to explore the time-dependent mechanical properties and microscopic characterisation of FSS. The mechanical test showed that CFGD-FSS doped with FA and GGBS had better fl uidity, compressive strength, and fl exural strength than CGD-FSS doped with FA alone and CFD-FSS doped with GGBS. The CFGD-FSS specimen with a cement:FA:GGBS:DG ratio of 30: 10:40:20 in the curing agent had the best mechanical properties, i.e., the CFGD01 specimens. It has fl uidity of 189 mm, compressive strength of 671 kPa, and fl exural strength of 221 kPa with a 28d curing time, which can meet the working requirements of FSS for fi lling narrow engineering spaces. And compared with other specimens, it has the shortest setting time, which can effectively shorten the construction period. Microscopic analysis showed that a large number of hydration products, such as calcium silicate hydrate, calcium aluminate hydrate, and ettringite ( Aft ) , were well-formed in the FSS, resulting in good mechanical properties, especially for the CFGD-01 specimens. Finally, two empirical models were established to describe the compressive strength-porosity and fl exural strength-porosity relationships. Moreover, the investigated data agreed well with the modelling results.

Various problems are often encountered during the backfilling process of deep foundation pits. The development of low-cost and efficient solidified materials for the preparation of fluidized solidified soil is currently an ideal solution. This article used industrial solid waste (granulated blast furnace slag, fly ash, carbide slag, etc.) as the main raw material to study the hydration hardening properties of solidified materials and the construction feasibility of fluidized solidified soil prepared from solid waste materials. The results are as follows: Compared with cement-based materials, solid waste-based solidified materials had lower early activity. The cumulative heat release within 72 h was less than 200 J/g. Different solid wastes, such as fly ash and carbide slag, had different effects on the properties of solidified materials. Overall, they had the potential to prepare fluidized solidified soil. The prepared fluidized solidified soil had a fluidity greater than 350 mm, a 28d compressive strength greater than 3 MPa, and exhibited good workability and excellent mechanical properties. Hydration products such as CS -H and AFt were filled in the soil structure. The 28d compressive strength well above the design requirements of general engineering projects. Meanwhile, the prepared fluidized solidified soil had good adaptability to conventional water reducers (fluidity could be increased by more than 40%) and early strength agents (1d compressive strength could be increased by more than 60%).