Effect of waste-derived nano pozzolans on ITZ densification in high-durability and low-carbon concrete

Marine concrete infrastructure is highly vulnerable to aggressive exposures such as sulfate, acid, chloride, moisture, and CO2. To address this, a sustainable green concrete incorporating waste-derived micro- and nano-scale supplementary cementitious materials was developed within a circular economy framework. Optimal micro-level replacements (fly ash, GGBS, silica fume, rice husk ash, and sugarcane bagasse ash) were established, followed by nano-modification. The optimum nano dosages were 1% NFA, 1% NGGBS, and 3% NSF, 3% NRHA, and 3% NSCBA. The nano-engineered concrete specimens exhibited compressive strength improvements of up to 48.4% over conventional concrete. Microstructural analysis indicated that reduced Ca/Si ratios promoted additional C–S–H formation, leading to a denser matrix and a thinner interfacial transition zone, thereby enhancing strength and durability. Sustainability assessment showed that NGGBS-based concrete achieved significant reductions in cost, carbon footprint, and energy consumption, indicating its potential for durable and eco-efficient marine infrastructure.