Integrating microbial induced calcium carbonate precipitation (MICP) in geothermal pavements: A coupled thermo-economic numerical evaluation

As the demand for sustainable infrastructure grows, integrating microbial induced calcium carbonate precipitation (MICP) with geothermal pavements presents a promising approach to improve both energy efficiency and structural performance. This study explores the technical and economic feasibility of incorporating MICP into geothermal pavement systems. Using a validated numerical finite element (FE) model, the thermal performance of MICP-treated geothermal pavements is evaluated under a range of conditions, including different climates, subbase saturation levels, and subgrade thermal conductivities. Results show that MICP treatment significantly enhances system performance in dry conditions, particularly when subgrade thermal conductivity is low (0.3 W/(m·K)). In a representative scenario for a Mediterranean climate, applying 4.1 wt% CaCO3 increased annual thermal output from 177 to 290 kWh/m (64% increment). However, the benefit of MICP diminishes with increasing subbase saturation or high subgrade conductivity. The subbase-to-subgrade thermal conductivity ratio emerges as a key design parameter, with higher ratios generally leading to greater thermal output but diminishing gains from MICP treatment when the natural ratio is already large. Economically, under optimal dry soil conditions, MICP treatment can achieve a net present value (NPVT) exceeding 300 AUD/m, offsetting more than 60% of typical road construction costs. A tornado analysis shows that MICP material cost has the greatest impact on NPVT/m, followed by discount rate and electricity price. This research highlights the potential of MICP for enhancing shallow geothermal system efficiency. These findings emphasise the importance of balancing technical gains with economic considerations to optimise the application of MICP in geothermal pavements.