Mechanisms of thermal conductivity degradation in enzyme-induced carbonate precipitation-cemented sand subjected to wetting–drying cycles

Abstract

The long-term performance of bio-cemented geomaterials under cyclic environmental conditions is crucial for energy geotechnics applications. This study investigates the degradation mechanisms of thermal conductivity in enzyme-induced carbonate precipitation (EICP)-cemented sand under wetting–drying cycles, focusing on microstructural evolution. Homogeneous specimens with controlled saturation levels were prepared using a chemical–thermodynamic equilibrium approach. Nuclear magnetic resonance was correlated with thermal conductivity measurements to quantify the co-evolution of pore structure and thermal properties. Results demonstrate a nonlinear decrease in thermal conductivity with decreasing saturation, marked by a sharp transition below 15% saturation. wetting–drying cycles progressively coarsened the pore structure, transforming small and medium pores into larger voids and inducing an exponential decay in thermal conductivity with increasing porosity. Microstructural analysis reveals that highly cemented specimens, featuring dense and crystalline CaCO₃ networks, exhibit greater structural integrity and thermal stability, whereas low-cementation specimens undergo rapid deterioration. Furthermore, heat transfer efficiency is governed by CaCO₃ deposition patterns and crystal morphology: continuous cubic crystals establish low-resistance, face-to-face thermal pathways, in contrast to the less efficient point or line contacts formed by spherical or cylindrical crystals. This study elucidates the microstructural drivers of thermal degradation, providing critical insights for designing durable bio-cemented backfills in energy geostructures.

Graphical abstract

Keywords

EICP / wetting–drying cycles / thermal conductivity / degradation mechanism / microstructure evolution

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