Synergistic Water Absorption and Release in Water Storage Clay: Roles of Particle Size and Hierarchical Pore Structure

Water Storage Clay (WSC) is promising for soil moisture regulation, yet the pore-structure mechanisms governing its hydrodynamics remain poorly understood. We hypothesize that a hierarchical pore architecture—spanning millimeter-scale, highly connected macropores and micrometer-scale micropores—is the key structural basis for synergistically efficient water absorption and sustained slow release, and that this performance can be tuned by particle size. Verifying this hypothesis is essential for guiding the design of cost-effective, waste-derived soil amendments for water-scarce regions. This study employs integrated Micro-CT-based 3D quantitative analysis and multi-scale experiments to resolve the architecture and function of WSC granules. The material exhibits a bimodal pore network comprising a millimeter-scale backbone for rapid water conveyance and micrometer-scale micropores for interfacial retention. WSC drastically outperformed loess in both unsaturated capillary absorption and saturated water uptake. The pore network exhibited a functional synergy: millimeter-scale macropores enabled rapid water conveyance, while micrometer-scale micropores provided interfacial retention for prolonged, slow release. An intermediate particle size range optimally balanced these dual functions, maximizing both absorption capacity and sustained-release longevity. These findings establish a quantitative link between bimodal pore architecture and synergistic water absorption–release kinetics in WSC, bridging pore-scale materials design and soil hydrological function. The demonstrated structure–performance relationship provides a rational design framework for converting solid wastes into durable, cost-effective soil amendments tailored for water-scarce regions. Future validation at the field scale under diverse soil–climate conditions will be critical for translating this mechanistic understanding into widespread practice. • Hierarchical bimodal pore architecture governs WSC water regulation. • Millimeter-scale pores enable rapid water conduction and storage. • Micrometer-scale pores with narrow throats ensure sustained slow release. • Optimal particle size balances macropore flow and micropore retention. • Waste-derived WSC offers a cost-effective, durable soil amendment pathway.