Seawater resistance mechanism of reinforcing bar–concrete composite structures restored by repair material incorporating multiple admixtures in a simulated marine splash zone

Abstract

To improve the durability of concrete structures in marine environment, a marine cementitious repair material (MCRM) incorporating silica fume (SF), water-reducing admixtures (WRA), ground granulated blast furnace slag (GBFS), and desulfurized gypsum (DG) was prepared and its properties were investigated, and the seawater resistance mechanism of reinforcing bar–concrete composite structures restored by the MCRM was revealed in the simulated marine splash zone. The results show that incorporation of the SF-WRA-GBFS-DG composite materials increased the compressive strength, decreased the free chloride diffusion coefficient, enhanced the bond strength of the mortars, and improved the seawater resistance of the restored composite structures. The increase in mechanical properties and the decrease in chloride permeabilities were attributed to the combined effect of the SF-WRA-GBFS-DG composite materials, which increased hydration products such as C–S–H gel and refined the pore structure of the samples. Further, it also reduced the drying shrinkage of the mortars, which was attributed to an increase in the ettringite content, and consumed calcium hydroxide to form additional C–S–H gel, thereby decreasing the quantity of crystals at the adhesive interface. These results have important engineering significance in the safety of deteriorated reinforcing bar–concrete composite structures used in a marine environment.