Effect of attachment of barnacles and oysters on concrete properties

Barnacles and oysters (B&O) can quickly adhere to marine concrete structures, but there is no consensus on their effects. The properties and microstructure of concrete specimens with and without B&O adhered on the surface (BO and NBO specimens, respectively) at different ages were examined. B&O began to adhere to specimen surfaces after 56 days of exposure. After 240 days of exposure, the maximum chassis diameters of the B&O increased by 210% and 229%, respectively. The mass changes of NBO and BO groups were 1.443% and −0.493% after 240 days of exposure. Compared with the initial state, the compressive strength of NBO and BO groups increased by about 25.9% and 30.1%, respectively. The pH of NBO decreased from 12.0 to 8.0 after 240 days of exposure (about 143% of the decrease in BO). The neutralisation depth of NBO was 7.0 mm (about 233% of that of BO). The electric flux of NBO 0–50 mm from the concrete surface reached 932.8 C; the BO electric flux was only 556.5 C. The mass changes of NBO and BO after 100 freeze–thaw cycles were small. The amount of gypsum and ettringite and loss of C-S-H gel in NBO were more significant than those in BO, making the resistance of NBO 24.3% lower than that of BO. After 240 days of exposure, the maximum pore volume of NBO was 54.6% larger than that of BO. Within 240 days of exposure, the attachment of B&O positively affected concrete performance.