Marine structures show earlier deterioration mainly due to the corrosion of steel bars in concrete caused by the chloride ingress from seawater. Prevention of chloride ingress is a great hurdle to make long-term durable concrete structures. Based on the investigations on the short-term accelerated laboratory and natural exposure, it was understood that utilization of slag cement results in significant reduction in chloride ingress compared to the commonly used ordinary portland cement (OPC). To verify it's long-term performance, three series of specimens were exposed to the marine exposure zone of Port and Airport Research Institute, a very special and rare exposure facility in the world. Recently the age of the specimens became 10, 15, and 30 years for these series. Physical appearance, compressive strength, carbonation depth, evaporable water content, concrete resistance, water and acid soluble chloride ingress, microstructures, mineralogy, corrosion of steel bars in concrete, and interfaces of concrete were evaluated and compared with OPC. All of these results are summarized here. The results will be very useful to the concrete professionals dealing with the long-term durability of marine concrete structures.
　No harmful effect of using slag cements is found after long-term exposure. Compared to OPC, slag cement shows more long-term strength gain. The outer crust of the specimens made with slag cements becomes denser after a long-term of exposure. It screens chloride at the outer crust of the specimens.Corrosion of steel bars in concrete is very low for slag cement. Relatively denser interface and microstructure are found for concrete made with slag cements. It is clearly understood that slag cement can be used for making long-term durable concrete structures. Besides the above-mentioned results, it is also found that voids at the steel-concrete interface initiate corrosion even for a low chloride concentration. Improvement of the steel-concrete interface is necessary to ensure long-term durability of marine concrete structures.