In marine environment

chloride-ion (Cl-) penetration and alkali aggregate reaction are important factors affecting the durability of concrete. In this paper

an appropriate amount of nano-SiO2 or nano-Al2O3 was added to ordinary marine concrete to study the durability of concrete with nano-particles under the combined influence of Cl- penetration and alkali aggregate reaction. The experimental results showed that Cl- penetration and alkali aggregate reaction promoted the durability of the concrete mutually. Nano-SiO2 or nano-Al2O3 of different amounts could inhibit the Cl- penetration and alkali aggregate reaction of concrete to different degrees so that the durability of the concrete under the interaction of the two factors was improved. The optimum amount of nano-SiO2 and nano-Al2O3 in concrete was both 2.0%. When the total content of Cl- in concrete was basically stable

the total amount of Cl- in concrete with nano-SiO2 or nano-Al2O3 was decreased by 18.04% and 11.60%

respectively. In the 39th week

the expansion rate of concrete with nano-SiO2 or nano-Al2O3 was reduced by 28.75% and 16.87%

respectively. The addition of nano-particles could improve the pore structure of concrete

enhance the Cl- penetration resistance of concrete

inhibit the generation of Friedel’s salt

thereby mitigating the expansion of concrete. Additionally

nano-particles can promote secondary hydration of cement

reduce the aggregation degree of Ca(OH)2 crystal in the transition zone

and restrain the formation of CaCl2 complex compound and alkaline environment required for alkali aggregate reaction.