Synergistic use of silica fume and limestone powder for durable and low-carbon marine concrete: Experimental and environmental assessment

Concrete structures in marine environments are subject to relentless chemical degradation from sulfate and chloride ions, posing a threat to their long-term durability and structural integrity. This study presents a novel strategy to enhance chemical resistance and sustainability by integrating silica fume (SF) and limestone powder (LP) into concrete formulations. A comprehensive experimental program was conducted, encompassing 1,296 cubic specimens across 36 mix designs, systematically varying water-to-cementitious ratios (W/CM = 0.25, 0.30, 0.40), SF dosages (0%, 5%, 10%, and 10% with 7% air), and LP replacement levels (0%, 15%, 30%). Specimens were exposed to four aggressive environments, i.e., tap water, magnesium sulfate, magnesium chloride, and a combined sulfate–chloride solution, to simulate real-world marine conditions. Durability was assessed via compressive strength, water absorption, mass loss, and chloride penetration depth over 3, 4.5, and 6 months. Results revealed that replacing 15% of the cement with LP reduced compressive strength by only 1–5% while significantly improving sulfate resistance. In contrast, a 30% LP replacement resulted in a 5–10% reduction in strength, highlighting a trade-off between mechanical performance and chemical durability. Environmental performance was evaluated using the IMPACT 2002+ life cycle assessment method. Mixes with lower cement content and higher SCM substitution demonstrated up to 30% reductions in climate change and resource depletion indicators. Notably, superplasticizers, despite their low dosage, had a disproportionate impact on human health and carbon emissions. This study introduces a scalable pathway for designing marine-grade concrete that is both chemically resilient and environmentally optimized. By synergistically combining LP and SF, the research advances low-carbon concrete technology tailored for coastal and offshore infrastructure, offering a meaningful contribution to sustainable construction practices.