Reinforcement of Calcareous Sands by Stimulation of Native Microorganisms Induced Mineralization

Abstract

Calcareous sand is a special soil formed by the accumulation of carbonate fragments. Its compressibility is caused by a high void ratio and breakable particles. Because of its high carbonate content and weak cementation, its load-bearing capacity is limited. In this study, the optimal stimulation solution was obtained with response surface methodology. Then, the effect of reinforcing calcareous sand was analysed with unconfined compressive strength (UCS) tests, calcium carbonate content tests, microscopy and microbial community analyses. The components and concentrations of the optimal stimulation solution were as follows: sodium acetate (38.00 mM), ammonium chloride (124.24 mM), yeast extract (0.46 g/L), urea (333 mM), and nickel chloride (0.01 mM), and the pH was 8.75. After the calcareous sand was treated with the optimal stimulation scheme, the urease activity was 6.1891 mM urea/min, the calcium carbonate production was 8.40%, and the UCS was 770 kPa, which constituted increases of 71.41%, 35.40%, and 83.33%, respectively, compared with the initial scheme. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed that calcium carbonate crystals were formed between the particles of the calcareous sand after the reaction, and the calcium carbonate crystals were mainly calcite. Urease-producing microorganisms became the dominant species in calcareous sand after treatment. This study showed that biostimulation-induced mineralization is feasible for reinforcing calcareous sand.

Research on the Effect of Natural Seawater in Domesticating Bacillus pasteurii and Reinforcing Calcareous Sand

“…Calcareous sand is mainly deposited from the remains of marine organisms, such as coral and shells, and is mainly composed of calcium carbonate. It has an irregular morphology, angular appearance, high porosity, and is easy to break; thus, it is not conducive to directly use in engineering applications [6][7][8][9][10][11]. The traditional reinforcement methods mainly include physical tamping and vibratory ramming, using chemical cement mortar, etc., which have a high energy consumption, take a long time, are high-cost, and are prone to cause ecological and environmental pollution problems [12,13].…”