This paper presents data collected from 25-year-old concrete specimens exposed to tides in excess of 6 m (20 ft) and an average of 100 cycles of freezing and thawing per year at the Marine Exposure Station on Treat Island, ME. Results indicate that the incorporation of fly ash, slag cement, or silica fume and decrease in water-cementitious materials ratio (w/cm) lead to a substantial increase in the resistance to chloride penetration. However, at the same time, concretes with high levels of supplementary cementitious material may also experience greater surface loss and not be suitable for exposure to a harsh marine environment with multiple cycles of freezing and thawing unless w/cm is limited to 0.40 or less.