Preparation and properties of gradient fire & corrosion protection magnesium phosphate cement coatings

Fire and corrosion protection are the main problems limiting the application of steel. Gradient fire & corrosion protection coating for steel structures was prepared by magnesium phosphate cement (MPC) with high bond strength, excellent anti-corrosion, and high-temperature resistance. The interface inside the MPC coating and of the MPC coating and steel plate were observed. The bonding strength, corrosion, and fire performance of MPC coating were investigated before and after dry-wet cycles. The results showed MPC had high bond strength with itself even under dry-wet cycle conditions. Only 6 mm MPC coating can meet the fire and corrosion resistance of steel structures. When the total thickness of MPC coating was 6 mm, the rising thickness (0–1.6 mm) of MPC paste improved the bond strength to 2.5 times and anticorrosive performance but reduced the fireproof performance of MPC coating. Even though the thickness of the MPC paste was 1.6 mm, the fireproof performance of MPC coating remained abundant. After 28 dry-wet cycles, the fireproof performance of MPC coating with 0.4 mm MPC paste was comparable to that before the dry-wet cycle. The bond strength was still more than 0.3 MPa, which can still meet the requirements of the specification. •Gradient fire & corrosion protection magnesium phosphate cement (MPC) coating was designed and prepared.•The thickness of gradient MPC coating satisfying for both corrosion and fire resistance was only 6 mm.•MPC paste greatly improved the bonding strength and corrosion resistance of gradient MPC coating.•The gradient MPC coating still exhibited excellent properties after dry-wet cycle.