Effect of Natural Pozzolanic Additive on Strength and Durability of Concrete Immersed in Seawater

This paper presents an experimental study on the effect of natural pozzolanic additives on the strength and durability of concrete immersed in seawater. Concrete specimens using various natural pozzolan contents from 0 to 30% were cured in normal water and then immersed in seawater for 12 months. Sulfate-resisting cement was also used for concrete as reference concrete specimens. Experiments to evaluate the effect of natural pozzolan on concrete's short-term and long-term strength were performed. Besides, concrete durability properties, including sulfate resistance, chloride permeability, and water permeability, were also tested. The scanning electron microscope technique was utilized to analyze the microstructure of concrete containing natural pozzolan. The results show that at the early age of concrete, the cement replacement with natural pozzolan from 10 to 15% is optimal in terms of strength. With respect to the long-term strength of concrete immersed in seawater, the content of replacing 15% of cement with natural pozzolan provides better performance. Moreover, durability test results show that concrete containing 15% cement replacement by natural pozzolan has higher efficiency compared to the other concrete and concrete using sulfate-resisting cement at the long-term age. This study also shows the potential for natural pozzolan use as a mineral additive in concrete exposed to marine environment.