Effects of silica fume on the multi-scale material properties of composite Portland cement-based cutoff wall backfill

Abstract

Soil cement bentonite (SCB) is a common material for constructing vertical cutoff walls to prevent groundwater migration at contaminated industrial sites. However, site contaminants can degrade the durability of the cutoff wall. To enhance its performance, this study developed a silica fume-SCB (SSCB). The macroscopic and microscopic properties of SSCB were assessed by unconfined compressive strength test, variable head permeability test, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy. The correlation between its multi-scale properties was analyzed based on pore characteristics. The results indicate that increasing the silica fume substitution ratio improved SSCB strength, especially in the middle and late curing stages. Moreover, increasing the substitution ratio decreased SSCB permeability coefficient, with a more pronounced effect in earlier curing stages. Silica fume addition also refined SSCB pore structure and reduced its porosity. The fractal dimension was used to quantify SSCB pore structure complexity. Increasing silica fume content reduced small pore fractal dimension in SSCB. Concurrently, SSCB strength increased and SSCB permeability coefficient decreased. The findings of this research will demonstrate the great potential of SSCB backfill for practical applications.

Keywords

silica fume / SSCB cutoff wall / multi-scale material properties / engineering properties / microscopic mechanism

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Central South University