Dry-wet cycle and chloride ion (Cl-) penetration are the main factors affecting the durability of marine concrete. To study the influences of different environmental conditions and the addition of nano-particles on the Cl-penetration resistance of marine concrete

nano-SiO2 and nano-Fe3O4 were respectively added into ordinary concrete with different amounts

and the contrast test of Cl-penetration was carried out by dry-wet cycle and full immersion

then the Cl- content in concrete at different depths by chemical titration was measured. The test results show that dry-wet cycle accelerates the Cl-migration to the inner of concrete

which makes that the total Cl- content

free Cl- content and bound Cl- content in concrete and the Cl- binding capacity of concrete under dry-wet circle condition are all higher than those under full immersion condition at the same age

and the difference in Cl- content between the two environmental conditions becomes more and more larger with the increasing number of dry-wet cycles. Under the two environmental conditions

the total Cl- content and free Cl- content in concrete with nano-particles are all lower than those in ordinary concrete

but the bound Cl- content and the Cl- binding capacity are all higher than those in ordinary concrete. The optimum amount of two nano-particles in marine concrete is 2%

and the Cl-penetration resistance of concrete with nano-SiO2 is superior to that of concrete with the same amount of nano-Fe3O4. The surface effect and filling effect of nano-particles improve the pore structure of concrete

resulting in the Cl-migration in concrete difficult. Both nano-SiO2 and nano-Fe3O4 with different amounts can enhance the chemical binding capacity and physical adsorption capacity of hydrated products to Cl- in different extent

which can reduce the free Cl- content in concrete to improve the Cl- penetration resistance of marine concrete. This study can provide references for the durability design of marine concrete.