Comparative Study of the Effects of Natural and Synthetic Fibers on the Mechanical Properties of Sand Treated with Enzyme-Induced Calcium Carbonate Precipitation

AbstractEnzyme-induced calcium carbonate precipitation (EICP) is an environmentally friendly and promising method for sand treatment. However, the effect of EICP treatment alone is not sufficient to satisfy the engineering requirements for sand. The addition of fibers is an advantageous approach to enhancing the mechanical strength of EICP-treated sand. Most fibers used as reinforcement are synthetic fibers; this practice is wasteful and poses a risk of environmental pollution. The novel exploration performed in this work investigated the enhancement effect of natural fibers for EICP-treated sand. In this study, the enhancement effects of sisal, a natural fiber, and polypropylene, a synthetic fiber, on EICP-treated sand were compared. Three aspects of the enhancement effects—calcium carbonate content, strength, and toughness—were evaluated. In addition, solution analysis and microscopy observations were conducted to analyze enhancement mechanisms. The results showed that the sisal fibers did in fact contribute to the effects on EICP-treated sand, and their enhancement effect was better than that of polypropylene fibers. Specifically, with the addition of sisal and polypropylene fibers to EICP-treated sand, values of unconfined compressive strength (UCS) were 322 and 213 kPa, respectively. The solution analysis results and microscopy observations indicated that the coarser surface structure of sisal fibers resulted in stronger reinforcement than the reinforcement provided by polypropylene fibers. Practical ApplicationsThe mechanical properties of sand can be improved to a certain extent when sand is treated by enzyme-induced calcium carbonate precipitation. However, the enzyme-induced calcium carbonate precipitation–treated samples shown obvious brittleness, which would lead to a sudden destruction. This is unacceptable in practical projects. The application of fibers not only delays the destruction of samples but also improves the strength of enzyme-induced calcium carbonate precipitation–treated sand to a certain extent. Synthetic fibers have been widely used in soil reinforcement and brittleness reduction. This study found that natural fibers, represented by sisal fibers, can be used as a green alternative to synthetic fibers in the future. In addition, this study provided guidance for coastal zone development, island construction, and sand slope protection projects. However, it is important to note that this study was only a preliminary confirmation of