Effects of nano-silica and reactive magnesia on the microstructure and durability performance of underwater concrete

Abstract Non-dispersible underwater concrete is a kind of construction material which is seeking its growing application in the offshore structures. However, the offshore structures are exposed to aggressive environment and harmful ions. Therefore, this study is conducted to investigate the mechanical, physical, microstructural, and durability-related properties of underwater concrete containing nano-silica and MgO. Nano-SiO2 was added at dosages of 0%, 1%, and 2%, and MgO was replaced at a rate of 0%, 5%, and 10% by weight of the binder. The effects of nano-silica and MgO particles was assessed via compressive strength test, Thermogravimetric analysis, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. Chloride and carbonation resistance of the concrete specimens were also examined. The results suggest that the incorporation of nano-silica and MgO (at a dosage of 5%) improved the microstructure resulting in an elevated compressive strength and enhanced resistance to carbonation and chloride penetration. The addition of 10% MgO reduced the performance of concrete specimens, however, the incorporation of nano-silica compensated the reduction in performance.