Study On The Preparation And Corrosion Performance Of The Concrete Reinforced By Zinc Phosphate Pretreated Steel Fiber

Steel fiber reinforced concrete?SFRC?is a new kind of composite material which is mixed with random distributed steel fibers.The existence of steel fiber can effectively prevent the propagation of micro-cracks in concrete and improve the toughness and ductility of concrete matrix,so it is widely used in various load bearing structures.However,in some special areas,such as ports,wharves,offshore platforms and other environments with corrosive medium,the steel fibers in concrete are easily corroded,thus affecting the bridging ability of the fibers and reducing the service life of concrete structure.In view of the poor corrosion resistance of steel fiber reinforced concrete,the steel fiber was modified,and the interface structure and properties,and the deterioration law of the properties of steel fiber reinforced concrete under different corrosion environments?NACL solution,Na₂SO₄ solution,acetic acid solution?,the corrosion mechanism of steel fiber reinforced concrete under different corrosion environment is revealed.It aims to improve the corrosion resistance of steel fiber reinforced concrete and further the application range of steel fiber reinforced concrete is expanded.The main results are drawn as follows:?1?A phosphating solution composed of H₃PO₄,ZnO,Zn?NO₃?₂ and distilled water was developed,and the parameters of phosphating process were optimized by studying the effects of phosphating temperature and time on the microstructure and corrosion resistance of zinc phosphate coating.The phosphating film was characterized by means of phase analysis,microstructure and corrosion resistance.The results showed that the phosphating film was mainly composed of zinc phosphate phase Zn₃?PO₄?₂·H₂O The change of phosphating time and temperature has no effect on the phase composition of phosphating film,but has great effect on the microstructure and corrosion resistance of phosphating film.When the phosphating temperature is lower than 75°C and the time is less than 20 min,the nucleation number of zinc phosphate crystal is less and it can not completely cover the surface of the substrate.When the phosphating temperature is higher than 75°C or the phosphating time is longer than 20 min,the crystals dissolve.The damage and corrosion resistance of the film are decreased.When the phosphating temperature is 75°C and the phosphating time is 20 min,the phosphating film is fine and compact,and the corrosion resistance is the best.?2?The microstructure and interface characteristics of concrete reinforced by zinc phosphate pretreated steel fiber and common steel fiber concrete were studied,and the effects of different corrosion media on the interface structure and properties of steel fiber concrete were compared.The results show that the Zn₃?PO₄?₂·H₂O phase reacts with cement particles and water in the interface layer of concrete reinforced by zinc phosphate pretreated steel fiber.The thickNess of interface layer of zinc phosphate modified steel fiber concrete is 20 m lower than that of common steel fiber concrete.The interfacial strength of ZINC PHOSPHATE STEEL FIBER reinforced concrete?SFRC?did not decrease obviously after corrosion by NaCl solution,Na₂SO₄ solution and acetic acid solution.The average bond strength decreased by 1.9%,66.7%and 35.9%,respectively.?3?The effect of Zinc phosphate on the mechanical properties of steel fiber reinforced concrete?SFRC?in different corrosion environments was studied by dry-wet accelerated corrosion test.The corrosion mechanism of SFRC in different corrosion media was discussed.The results show that after 30 cycles of corrosion in NaCl solution,Na₂SO₄ solution and acetic acid solution,no obvious corrosion occurred in steel fiber reinforced concrete modified by zinc phosphate.The basic properties of untreated steel fiber reinforced concrete are significantly affected.The effect of the three corrosion solutions on the mechanical properties of steel fiber reinforced concrete is as follows:Acetate>NA₂SO₄>NACL.The corrosion of acetic acid solution causes the mortar to fall off,which is the reason for the concrete to intensify the corrosion.