Nanomaterials have received increased concentration in the field of civil engineering, as their incorporation can effectively modify the mechanical and transport properties of cementitious composites. In this study, to understand the effect of graphene oxide (GO) nanoparticles on the durability and mechanical properties of cementitious composites serving underwater, mortars incorporated with GO were taken for study. To match the real circumstance, all specimens were immersed directly in a flowing river for three years, and their transport properties, mechanical properties and microstructure before, and after, river experience were studied separately. The results showed that the incorporation of GO could reduce both early-age permeation coefficient and later-age chloride migration coefficient of mortar specimens. The average porosities of mortars could be reduced by the range of 3.37–11% with GO incorporation. Moreover, through a novel dual-scan method, GO incorporation was confirmed effective in enhancing both the leaching and cracking resistance. Furthermore, the compressive strengths, flexural strengths and splitting tensile strengths could be improved by the range of 4.37–9.82%, 7.78–22.33%, 8.14–28.73%, respectively with GO incorporation, and the tested mechanical strengths for GO-incorporated mortar after three-year river experience could be retained to a higher extent. Finally, based on durability and mechanical properties, the optimum mix proportion of GO was determined to be 0.06 wt.% in this study. The work presented here is of high reference value for the designing of marine infrastructure and can help promote the application of nanomaterials in civil engineering.

To improve the environmental efficiency of the reverse filling system, three strategies aim to optimize the packing density, and the mechanical property were adopted in this study. Based on the compressive packing model (CPM), the relationship between the D50 ratio and maximum theoretical packing density for a reverse filling system with 25% and 30% superfine Portland cement was established. For comparison, silica fume and steel fiber were also added to the reverse filling system, respectively. The improvement of packing density by adjusting the D50 ratio was verified through the minimum water demand method, CPM, and modified Andreasen and Andersen (MAA) model. Compared to the reverse filling system added with 3 wt % silica fume, which possesses a comparable mechanical property with the optimized group (adjusted D50 ratio), the incorporation of steel fiber shows a more significant increase. The environmental efficiency of all the samples was quantified into five aspects through the calculation based on the mix proportion, compressive strength, and hydration degree. The comprehensive evaluation demonstrated that the optimized reverse filling system exerts a lower environmental impact and possesses a much higher cement use efficiency compared to the majority of ultra-high performance concrete (UHPC)/ ultra-high performance fiber-reinforced concrete (UHPFRC) reported in published papers.