This study quantifes the relative impacts of zeolite (10 %, 20 %) and nanoclay (1 %, 4 %, 8 %) on concrete performance under standardized conditions. Key fndings reveal that 20 % zeolite and 1 % nanoclay reduced permeability by 46.8 % and 47.0 %, respectively-demonstrating near-equivalent effcacy through distinct mechanisms: zeolite’s pozzolanic reaction generated supplementary C-S-H gels, while nanoclay physically densifed the matrix via nanoscale pore-flling. Notably, nanoclay at 4 % elevated compressive strength by 18 %, whereas zeolite required superplasticizers beyond 10 % to mitigate workability loss. Microstructural evidence identifed critical thresholds: dosages exceeding 20 % (zeolite) or 8 % (nanoclay) promoted microcracking due to agglomeration. For permeability-driven applications, 1 % nanoclay delivers optimal performance; 10–20 % zeolite offers a viable alternative where cost constraints prioritize incremental enhancements. This work establishes dosage-dependent performance trade-offs and provides mechanistic criteria for additive selection in durable concrete design
