Macro/micro characteristics variation of ultra-high performance fibre reinforced concrete (UHPFRC) subjected to critical marine environments

•The durability of UHPC servicing in critical marine environments is studied.•The effect of high temperature sea water on UHPC is tested.•The effect of steel fibre network on UHPC durability is evaluated.•Detailed mechanism on irons attacking effect on UHPC is clarified.•The approach to produce an advanced UHPC with good durability is shown. This study presents the macro/micro characteristics variation of ultra-high performance fibre reinforced concrete (UHPFRC) subjected to critical marine environment. The UHPFRC matrix is designed based on the modified Andreasen & Andersen model, and the steel fibres are included by 0 vol%, 0.5 vol%, 1.0 vol%, 1.5 vol%, 2.0 vol%, 2.5 vol% and 3.0 vol%, respectively. Generally, three kind of marine environments are simulated in this study: high temperature-seawater, dry-wet cycle-seawater and normal seawater. Then, after servicing in these mentioned marine environments for 180 days, the properties of UHPFRCs are evaluated, including the sample appearance, compressive strength, electrochemical parameters, hydration products and pore structure. The obtained experimental results show that compared to the samples serviced in dry-wet cycle-seawater and normal seawater, the UHPFRC subjected to high temperature seawater can be seriously deteriorated. Additionally, though the UHPFRC can be treated as a dense composite with advanced durability, the connection of short steel fibres can easily induce electrochemical corrosion for UHPFRC, especially under the multiply effects of high ions concentration and dry-wet cycle of critical marine environment.