Search Results (2)

Calcareous sand is a crucial construction material for island and reef development and reinforcing it using Microbially Induced Calcite Precipitation (MICP) technology is a promising new method. This study employed 3D scanning technology to assess changes in the particle size and morphology of MICP-treated, coated calcareous sand particles. Single-particle crushing tests were conducted to analyze their crushing strength, crushing energy, crushing modes, and fragment fractal dimensions. The results indicated that MICP treatment significantly increased particle size, surface area, and volume, while reducing flatness. At a cementation solution concentration of 1 mol/L, both crushing strength and crushing energy were optimized. The coated particles exhibited three crushing modes: explosive crushing, mixed crushing, and splitting crushing. Thicker coatings led to a tendency for particles to break into larger fragments through the mixed and splitting crushing modes. Fractal analysis revealed that coating thickness directly affects the local crushing characteristics of the particles. Full article

In the construction of artificial islands in distant seas, calcareous sand has been widely used as a foundation filler due to its excellent mechanical properties and extensive availability in the marine environment. How to store more fresh water on the artificial islands by reducing its permeability is currently a great challenge. Microbial-induced carbonate precipitation (MICP) has always been considered as a great potential method to improve the cemented properties of calcareous sand, but the effect of grain gradation on the permeability of MICP-improved calcareous sand remains unclear. In this research, a self-made device was developed to conduct MICP grouting and permeability tests, where the permeability coefficient (k) under different grain gradations (curvature coefficient (C_c) and uniformity coefficient (C_u)) was measured. A CT scan was conducted to investigate the variation in the porosity (n) of sand samples before and after MICP treatment. The weighting method was adopted to measure the content of induced calcium carbonate (M). A scanning electron microscopy (SEM) technique was used to further study the micromechanism of the MICP treatment. Finally, the correlations between the k of MICP-treated sand and C_u, as well as C_c, were semiquantitively analyzed. The results show that the magnitude of M, k and n changes are closely related to C_c and C_u. The reduction amount of k and n increased with the rise in C_c and C_u, and the increased amount of M increased with the rise in C_c and C_u. The SEM results show that the particle surface became rough due to the coating effect of CaCO₃ crystals, and the pore spaces were reduced because of the partially filling effect of the crystals, which was responsible for the decrease in permeability and porosity. Furthermore, k fitted well with C_u and C_c, respectively, and the fitting curve reveals that larger C_u (C_u ≥ 6.0) and smaller C_c (2.0 > C_c > 0.5) were more suitable for MICP treatments and lead to a large reduction in permeability. The above results indicate that the grain gradation of calcareous sand had a significant influence on its permeability improved by MICP. Full article