Properties of Eco-Friendly Grade C60 High-Performance Concrete for Marine Structures in Coastal Central Vietnam

Developing and expanding infrastructure along Vietnam’s central coast—a key driver of the marine economy—requires a type of concrete that is both highly durable in seawater environments and compatible with the marine ecosystem. To address this need, this study evaluates C60-grade concrete incorporating sulfate-resistant cement, 5% silica fume, and an L-arginine additive (designated as C60 HPEAC) in terms of its mechanical properties, chloride resistance, and capacity to support marine organisms. L-arginine (A) was added at 1–7% by mass of cement. The designation C60-iA (where i = 1–7) refers to a C60 HPC sample containing i % A. Laboratory tests included compressive and flexural strength, chloride penetration, SEM, XRD and A leaching, while field exposure at Da Nang and Nha Trang bays for 1–12 months was used to assess biological colonization via chlorophyll-a. Compressive and flexural strengths were determined in accordance with ASTM C39 and ASTM C78, respectively. The chloride penetrability of the concrete was evaluated in accordance with the TCVN 9337:2012 test method. Although the 28-day compressive strength of the A mixtures decreased by 1.78–18.8% relative to the control, all mixtures still satisfied the C60 grade, while chloride penetration resistance improved by 6.4–48.78%. Flexural strength decreased by 1.1–21.8% but remained within the insurance compliance with concrete grade specifications. Microstructural analyses revealed that higher A dosages (5–7%) significantly reduced the quantity and peak intensity of portlandite, which is attributed to the suppression of its crystallization and the enhancement of pozzolanic reactions. The moderate amount of CH is finely distributed within the A-containing specimens—sufficient to maintain a pH level that protects the steel—without aggregating into coarse, weakening crystals. Chlorophyll-a on specimen surfaces was two to four times higher than that of the control at A contents of 3–7%, indicating enhanced biological colonization. Leaching experiments were conducted on concrete specimens immersed in seawater representative of the coastal environment of Central Vietnam for periods of 30, 90, 150, and 180 days under laboratory conditions. The release rate of additive A decreased progressively from 90 to 180 days, and higher additive contents resulted in higher release rates. Among the tested mixtures, C60-7A exhibited the highest release rate, reaching 0.104 × 10−3 g/cm2/day after 180 days of immersion. Based on the leaching rate measured at 180 days, the average leaching-service life of the specimens investigated in this study was estimated to be approximately 10 years. The predictive models developed in this study indicate that the release process is sufficiently slow and sustained over time. Consequently, C60 environmentally active high-performance concrete (HPEAC) appears to be a promising material for marine infrastructure requiring both high durability and ecological compatibility in the coastal regions of Central Vietnam. Nevertheless, further validation through long-term field exposure studies is still required.