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Enzyme-induced carbonate precipitation (EICP) has emerged as an environment-friendly solution for soil improvement. As a composite material, it is challenging to determine the micromechanical properties of EICP-reinforced sand using common macromechanical tests. In this work, a systematic study was conducted to determine the micromechanical properties of EICP-reinforced sand. The development of the micromechanical properties obtained from indentations along the route of sand particle-CaCO3-sand particle was examined. The width of the interfacial transition zone (ITZ) in EICP-reinforced sand was investigated. The effect of the reaction environment on ductility (i.e., the ratio of elastic modulus over hardness) of CaCO3 was investigated. The experimental results have identified that the width of ITZ in EICP-reinforced sand ranges from 0 to 180 mu m, which is significantly influenced by the crystal crystallinity or crystal morphology of CaCO3. The presence of porous media (i.e., sand particles) leads to the decrease in impurity content in the crystal formation environment, resulting in the lower ductility of CaCO3 accordingly. The mean value of fracture toughness of CaCO3 precipitation was identified to be the lowest one among sand particles, CaCO3 precipitation, and sand particles-CaCO3 interface. The lowest fracture toughness of CaCO3 indicating the failure of biocementation is derived from the CaCO3-CaCO3 breakage.

期刊论文 2025-02-25 DOI: 10.1007/s11440-025-02576-0 ISSN: 1861-1125

Enzyme-induced carbonate precipitation (EICP) has emerged as an innovative soil stabilization technology to precipitate CaCO3 by catalyzing urea decomposition. Although extensive efforts have been made to increase the calcium carbonate content (CCC) formed in the EICP process for the better biocementation effect, the cementability and micromechanical properties of CaCO3 are rarely known. A study of the cementitious characteristics and micromechanical properties of CaCO3 precipitates with different mixing percentages of crystal morphology is essential for soil improvement. In the present study, ultrasonic oscillation tests and nanoindentation tests were performed to investigate the cementability and micromechanical properties of CaCO3 precipitate. The results show that the cementability and micromechanical properties of CaCO3 precipitate are related to the composition of the crystal morphology. A high content of calcite is beneficial to improve the adhesion of calcium carbonate precipitate. Calcite has better mechanical properties (elastic modulus, hardness and ductility) than vaterite, and the presence of vaterite can significantly affect the measured value of mechanical properties in nanoindentation tests. The ductility of CaCO3 precipitate induced by crude soybean urease (CSU) is higher than that of CaCO3 precipitate induced by commercially available pure enzyme, suggesting that commercially available pure enzyme can be replaced by CSU for cost-effective field-scale engineering applications. This work can provide insight into optimizing the properties of CaCO3 precipitate from the micro-scale. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

期刊论文 2024-12-01 DOI: 10.1016/j.jrmge.2023.08.024 ISSN: 1674-7755

In cold-region tunnel engineering, the bonding surface between concrete and surrounding rock is highly susceptible to engineering disasters such as the cracking of support structures under the influence of -freeze-thaw cycles, which severely affects the stability of tunnel engineering. This study investigates the macroscopic and microscopic mechanical properties of the sandstone-concrete interface under freeze-thaw cycles and reveals the microdamage and fracture evolutionary laws during the freeze-thaw loading process via the coupled expansion of water-ice particle phase changes via particle flow numerical simulation methods, aiming to provide theoretical support for the design and construction of rock-soil and tunnel engineering in high-altitude frozen soil areas. The results indicate that the interface strength characteristics of the sandstone-concrete specimens exhibit a stable decreasing trend with an increase in the number of -freeze-thaw cycles and a decrease in roughness. Taking the most unfavorable condition as an example, the exacerbation of freeze-thaw- deterioration resulted in shear strength reductions of 16.53%, 27.01%, and 37.17% for specimens (JRC=3.727), while an increase in roughness led to shear strength increases of 11.00% and 15.14% for specimens (NT=60 cycles). The acoustic emission characteristics during the loading process of the sandstone-concrete interface specimens reflect the microcracking evolutionary activity of the specimens quite well, and setting 1.0 as the recommended value for the precursor determination of the b-value and CV(k) index is most reasonable. Under -freeze-thaw cycles, cracks first initiate partial microcracks at the interface and on the outer side of the specimen, primarily dominated by tensile cracks and evolving with a slow-fast trend toward both sides of the interface. Under shear stress, particles at the interface first undergo slip dislocation due to their lower bonding strength, generating cracks, subsequently inducing significant displacement of particles on both sides of the interface, resulting in crack propagation toward both sides of the interface, ultimately penetrating and forming shear bands leading to macroscopic failure.

期刊论文 2024-06-21 DOI: 10.1016/j.conbuildmat.2024.136584 ISSN: 0950-0618
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