Porous geopolymer construction materials for water-containment and treatment infrastructure: a critical review of pore engineering, durability, filtration mechanisms, and sustainability

Porous geopolymers are being developed as multifunctional components that can combine hydraulic transport, contaminant retention, chemical resistance, and construction-scale formability. This critical review evaluates their use in water-containment systems and in tertiary treatment, defined here as post-secondary polishing for removal of residual suspended matter, nutrients, dissolved metals, trace organics, and microorganisms before discharge or reuse. The synthesis links precursor chemistry and batch variability to gel assemblage, pore connectivity, tortuosity, anisotropy, surface charge, permeability, and mechanical integrity. Chemical foaming, sacrificial templating, freeze casting, pressing, retardation-induced porosity, and additive manufacturing provide different degrees of pore control, but no universal strength–porosity relationship applies across low-calcium N-A-S-H and calcium-rich C-(A)-S-H/N-A-S-H systems. Adsorption and ion exchange remain the most mature mechanisms for dissolved metals and dyes, whereas photocatalytic and antimicrobial functions require stable modifiers and explicit leaching assessment. The review further shows that total porosity and short-term removal efficiency are insufficient design criteria; construction deployment requires permeability retention, anisotropic transport characterization, resistance to hydraulic cleaning, chemical and ultraviolet stability, regeneration performance, modular manufacturability, and service-life evidence under real wastewater chemistry. A tiered reporting framework and provisional engineering screening envelope are proposed. The principal need is a chemistry-aware, performance-based route that connects pore engineering to structural reliability, treated-water quality, life-cycle impact, and scalable manufacture. Graphic abstract