NaOH-activated SREMA for rock preconditioning: enhanced expansive pressure and a mechanistic framework

As global demand for critical minerals and low-impact subsurface energy systems grows, the need for efficient and sustainable rock preconditioning methods is more urgent than ever. Slow Releasing Energy Material Agent (SREMA) is a promising next-generation material for enhancing rock permeability, with potential applications in mineral recovery, geothermal stimulation, and underground hydrogen storage. However, its broader adoption has been limited by suboptimal expansive pressure and a lack of mechanistic understanding. This study addresses both challenges by incorporating sodium hydroxide (NaOH) as an inorganic accelerator to enhance performance and reveal the underlying expansion mechanism. Seven SREMA formulations with varying NaOH contents were evaluated using the outer pipe method, while three representative samples underwent advanced characterization via inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results show that NaOH accelerates hydration reactions and increases 24-hour expansive pressure by 15% to 52.55%, with peak performance at 0.15 wt% NaOH. NaOH addition promoted the formation of calcium hydroxide (CH), ettringite, and optimized the microporous structure of calcium silicate hydrate (CSH)—the latter playing a critical matrix role in transforming internal expansion into effective outward pressure. A novel mechanistic framework is proposed, linking mineralogical transformations to enhanced macroscopic performance. This work delivers new insights into sustainable rock preconditioning and offers a foundation for optimizing SREMA in applications where low-carbon, high-efficiency subsurface engineering is essential.