Fluidized solidified soil using construction slurry improved by fly ash and slag: Preparation, mechanical property, and microstructure

Abstract Fluidized solidified soil (FSS) is a cement-based engineering matergood working performance and mechanical properties. Based on fixed cement and desulphurisation gypsum (DG), fly 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, flexural, 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 fluidity, compressive strength, and flexural 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 fluidity of 189 mm, compressive strength of 671 kPa, and flexural strength of 221 kPa with a 28d curing time, which can meet the working requirements of FSS for filling 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 flexural strength–porosity relationships. Moreover, the investigated data agreed well with the modelling results.