Validating a numerical model for calco-carbonic reactive transport in a laboratory-scale fracture analog

Calco-carbonic reactive transport controls the dissolution of limestone by carbonic acid, a key process shaping the hydraulic and geochemical evolution of carbonate aquifers. Quantitative understanding of the coupling between flow, transport, and chemical reactions is essential for predicting karstification under variable hydraulic gradients, CO₂ CO 2 partial pressures, and pH. To support model validation, laboratory experiments were conducted in a 1 m ² 2 vertical karst-fracture analog with variable aperture, representing a simplified hydrogeologic fracture domain. Numerical simulations reproduced these experiments under controlled discharge, CO₂ CO 2 concentration, and acidity. The coupled reactive transport models capture feedbacks between forced convection, diffusion, and density variations, linking reactive interface dynamics with evolving flow fields. Simulated and measured calcium and carbonate ion concentrations showed good agreement, indicating that diffusive transport at the water–limestone interface primarily limited dissolution. Insights from the combined modeling and experimental framework refine laboratory-scale design, improve interpretation of dissolution kinetics, and strengthen the basis for upscaling to field-scale carbonate aquifers. The results enhance prediction of permeability evolution, flow-path development, and CO₂ CO 2 - H₂O H 2 O -rock interactions in karst systems.