Effect of fiber reinforcement on the mechanical behavior of bio-cemented sand

Abstract

To explore the possibility of providing additional reinforcement to bio-cemented sand through fiber inclusions, a series of sand-fiber mixtures were prepared by mixing sand with three types of fibers (polypropylene fiber, basalt fiber and carbon fiber) at different fiber contents (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.8% by volume of sand). Each mixture was subjected to two cycles of controlled microbial-induced calcite precipitation (MICP) treatments. Unconfined compression tests and calcium carbonate content tests were performed to characterize their mechanical properties and calcite amounts, respectively. Stress-strain results indicate that fiber inclusions change the bio-cemented soil from brittle to ductile failure modes. Basalt fibers with the highest tensile strength were most effective to increase the unconfined compressive strength (UCS) of the mixture. Due to higher elongation at breakage, polypropylene fiber is superior to the other two fiber types for energy absorption during the softening phase, resulting in higher residual strength. Scanning electron microscopy (SEM) photographs reveal the spatial distribution of calcite precipitations at the inter-particle contacts, on sand grain surfaces, and on the fiber surfaces, which primarily contributes to the roughening of the surface texture of particles and fibers and increases the internal friction and inter-particle bonding.