Study on the microscale structure and anti-seepage properties of plastic concrete for cut-off walls modified with silica fume: Experiment and modelling

Abstract

A modified plastic concrete cut-off wall was synthesized using different mass ratios of silica fume (0–21.3%) and constant cement content (8%) based on the conventional soil-bentonite cut-off wall. The slump test, hydraulic conductivity and mechanical performance were analysed to determine the optimal material ratio. The hydraulic conductivity of the optimal sample could meet theanti-seepagerequirement (~10-9 m/s). The amended plastic concrete cut-off wall could obtain the appropriate compressive strength (0.896 MPa) and a low elastic modulus (1244.5 MPa). The characterization of the clayey soil materials and modified plastic concrete cut-off walls were analysed by X-ray diffraction (XRD) methods, which demonstrated that the clayey soil mainly contained quartz and feldspar (anorthite). The pozzolanic reaction between the silica fume and calcium hydroxide and the refinementofthe porestructure could increase the compressive strength and reduce the hydraulic conductivity. Microscale three-dimensional real geometry images of the modified plastic concrete for cut-off walls were obtained from X-ray microcomputed tomography. The internal structural parameters were analysed through pore-scale modelling. The hydraulic conductivity and velocity fields were simulated using the lattice Boltzmann method. The results showed that most of the pores and throats in the modified plastic concrete for cut-off walls were micropores and microflow paths (diameter ≤ 5 μm), and the connected porosity was approximately 25.89%. The simulated hydraulic conductivity was in good agreement with the measured value, and the velocity fields indicated that the microflow paths were tortuous and complex. The silica fume-modified plastic concrete for cut-off walls enabled the realization of the requirements for good controlof the waterseepage in hydraulic engineering construction applications at a low cost.