Synergistic reinforcing effects of polypropylene fiber and bio-cementation on the mechanical properties of calcareous sands in the South China Sea

Abstract

The synergistic application of polypropylene fibers and microbially induced calcite precipitation (MICP) effectively bonds calcareous sand particles and fills inter-particle voids, enhancing both strength and ductility to improve the engineering properties of calcareous sands. A series of unconfined compression tests were conducted on samples of calcareous sand treated with fiber-MICP to investigate the effects of fiber content and fiber length on calcium carbonate content, stress–strain behaviors and unconfined compressive strength. The microstructural characteristics and synergistic reinforcing mechanisms of the fiber-MICP-treated samples were investigated through scanning electron microscopy (SEM) analysis. The imaging results demonstrate that the polypropylene fibers contribute to load-bearing and enhance the bacterial adsorption, promoting additional CaCO₃ formation and thereby improving the strength and ductility. The optimal fiber content and fiber length were determined to be 0.2% and 6 mm, respectively. A thorough microstructural analysis via SEM revealed three distinct CaCO₃ precipitation patterns: surface coating, contact cementing and inter-particle bridging. Subsequent analysis identified the latter two mechanisms as the primary contributors to strength enhancement. This study provides practical insights for the stabilization of coastal and carbonate-rich soils in geotechnical applications.

Graphical abstract

Keywords

calcareous sand / polypropylene fibers / MICP / synergistic reinforcing mechanism

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