Water stability of bonding properties between nano-Fe2O3-modified magnesium-phosphate-cement mortar and steel fibre

•Steel fibre pull-out test from NF-modified MPCM after water immersion was studied.•Bonding properties between fibre and MPCM after water immersion is improved by NF.•The optimal content of NF in MPCM was 2 vol%.•Formation of interfacial cracks due to water immersion is inhibited by NF. Magnesium phosphate cement (MPC) presents high early strength, fast setting and hardening, excellent bonding performance, and good corrosion and freezing resistance. The excellent performance of MPC enables it to have a wide range of potential applications. However, the brittleness and poor water stability limit its wide application. Incorporating fibres into MPC is a common toughening method, and the bonding between MPC and fibre has a significant impact on the toughening effect. In this paper, effects of the amount of nano-Fe2O3 (NF) and water immersion time on the bonding properties between steel fibre and MPC mortar (MPCM) were investigated using fibre pull-out, compressive, and splitting tensile tests and microstructure analysis. Incorporating NF significantly improved the bonding strength and pull-out energy between steel fibre and MPCM after water immersion. The optimal content of NF was 2 vol%. New hydration products (such as dense iron phosphate) and the compact structure formed with the addition of NF inhibited the interfacial cracks that result from water immersion. This research is very beneficial for construction project applications of fibre-reinforced MPCM in watery environments.