Mechanisms of PA-Assisted MICP Reinforcement with High Concentration Few Treatments strategy: Insights from a Microfluidic Perspective

Microbially induced calcium carbonate precipitation (MICP) is a promising sustainable ground-improvement technique, yet its application under high-concentration is constrained by low Ca²⁺ utilization and premature pore clogging. A key unresolved issue is how Ca²⁺ concentration alters bacterial transport, aggregation, and viability at the pore scale, and how these coupled processes ultimately control spatial mineralization efficiency. To address this mechanistic gap, this study investigates a polycarboxylic acid (PA)–assisted MICP strategy to regulate bacterial behavior under elevated Ca²⁺ conditions. Using a microfluidic visualization platform, the coupled effects of Ca²⁺ concentration, injection strategy, and PA dosage on pore-scale bacterial dynamics and CaCO₃ deposition were systematically examined. The results demonstrate that Ca²⁺ concentration is the primary driver of deposition patterns: increasing Ca²⁺ intensifies bacterial aggregation and inactivation, producing strongly inlet-biased precipitation and inefficient Ca²⁺ utilization. Introducing PA modifies this pathway by suppressing Ca²⁺-induced cell bridging and preserving bacterial viability, thereby restoring bacterial mobility and enabling deeper, more continuous mineralization. An optimal PA dosage of approximately 3% achieves maximal improvement in mineralization uniformity, beyond which regulatory effectiveness diminishes, indicating a clear operational window and upper limit for PA control under high Ca²⁺ conditions. By directly resolving the pore-scale transport–aggregation–viability coupling that governs mineralization, this work provides mechanistic guidance for designing high-concentration, few-treatment MICP grouting strategies with improved efficiency and spatial uniformity for field applications.