Key Takeaways & Executive Findings
- •• MICP grouting significantly reduces pore size and connectivity in reef limestone, transforming the pore network from a loose, connected type to a dense, isolated one. • The treatment enhances mechanical properties, with elastic modulus increasing from 3.27 GPa to 6.21 GPa and peak strength approximately doubling. • Failure mode transitions from brittle to brittle–ductile, accompanied by a shift in acoustic emission energy and frequency characteristics. • A novel constitutive model incorporating a structural densification factor effectively captures the MICP-induced strengthening behavior.
Abstract
Given the high porosity, strong connectivity, and low strength of reef limestone, microbial-induced carbonate precipitation (MICP) reinforcement tests were performed under different grouting cycles. CT-based three-dimensional reconstruction, uniaxial compression, and acoustic emission analyses were employed to elucidate the coupling mechanism between microstructural evolution and macroscopic mechanical behavior. MICP-induced calcium carbonate deposition exhibited distinct scale selectivity, initially occurring in large pores and highly coordinated nodes, which reduced the average pore diameter from 221.26 lm to 75.36 lm and transformed the pore network from a highly connected loose type to a dense isolated one. The elastic modulus increased from 3.27 GPa to 6.21 GPa, and the peak strength approximately doubled, while the failure mode evolved from brittle to brittle–ductile. Acoustic emission analysis revealed a greater proportion of post-peak high-energy events and a frequency shift from high to mid–low ranges, indicating a multi-stage energy dissipation process. A reinforcement variable was introduced to quantify the MICP-induced strengthening, and a structural densification factor was incorporated to establish a constitutive model governed by densification. The study clarifies the coupling mechanism from microscopic densification to macroscopic enhancement, providing theoretical support for the green reinforcement of highly porous rock masses.
1. Introduction
As a typical biogenic porous medium, coral reef limestone is widely distributed in tropical and subtropical marine environments worldwide. It is formed from coral and other marine skeletal debris through long-term sedimentation and cementation processes [1–3]. In recent years, with the advancement of the Belt and Road Initiative and the rapid expansion of marine infrastructure, including ports, airports, and artificial islands, the engineering demand for reef limestone strata has increased significantly. Consequently, the engineering geological characteristics of reef limestone have become a growing focus of research [4,5]. Compared with conventional terrigenous rocks, reef limestone generally exhibits high porosity, strong connectivity, and low strength [6,7], which significantly reduces its bearing capacity and structural stability in engineering applications. Therefore, developing efficient and reliable reinforcement technologies suited to its unique structural characteristics and clarifying the coupling mechanism between microstructure and macroscopic mechanical behaviour are of considerable theoretical and practical significance for infrastructure development in coral reef regions [8].
Most previous studies have employed cement-based or chemical grouting methods. Wu et al. [9] injected cement slurry into coral aggregate pores using a vacuum saturation technique, resulting in an approximately 1.5-fold increase in compressive strength; however, the high viscosity of the slurry limited microscopic permeability and homogeneity. Wei et al. [10] utilized sodium silicate for chemical consolidation, resulting in a 50.36% reduction in porosity and a 19.85% increase in compressive strength, thereby confirming the feasibility of inorganic chemical reinforcement. Nevertheless, this method still suffered from limited permeability and potential environmental concerns.
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Wenxi Zhu, Huafeng Deng, Linjian Ma, Mingyang Wang, Yao Xiao, Hongya Li, Lei Cheng (2025). Reconstruction of pore structure and transformation of failure mode in reef limestone under MICP grouting. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.12.017
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Frequently Asked Questions
What is MICP and how does it reinforce reef limestone?
MICP (Microbial-Induced Carbonate Precipitation) is a bio-mediated process where bacteria catalyze the precipitation of calcium carbonate, which fills pores and binds particles, thereby densifying the rock matrix and enhancing its mechanical properties.
How does MICP affect the pore structure of reef limestone?
MICP reduces average pore diameter from 221.26 μm to 75.36 μm and transforms the pore network from a highly connected, loose type to a dense, isolated one, due to scale-selective deposition in large pores and highly coordinated nodes.
What are the mechanical improvements after MICP treatment?
The elastic modulus increases from 3.27 GPa to 6.21 GPa, and the peak strength approximately doubles, with a failure mode transition from brittle to brittle–ductile.
What is the significance of the constitutive model proposed in the study?
The model incorporates a structural densification factor and a reinforcement variable, providing a quantitative framework to predict the mechanical behavior of MICP-treated reef limestone, which is essential for engineering design.
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