Research On Ability Of Cement Based Repair Material To Protect Reinforcement Bar And Its Influencing Factors

Cement based patching material has a great potential in repairing and strengthening of reinforced concrete structure,reinforcing and repairing of engineering structure reinforced when repairing material with good reinforcement performance can ensure the repair quality,improve the service life of the repaired structure.Sulphoaluminate cement and magnesium phosphate cement with excellent performance with fast setting and hardening has been used for roads,airports and bridges were repaired,but there are few researches on the reinforcement properties of sulphoaluminate cement,and some studies have shown that magnesium phosphate cement has poor water resistance.Whether to have good reinforcement performance during the rainy season,or in splash zone is still to be explored.Reinforcement performance of three kinds of cement based on Portland cement,sulphoaluminate cement and magnesium phosphate cement tested by electrochemical testing method of paste,mortar and concrete,results showed that magnesium phosphate cement mortar has obvious advantages of structure process in repair of reinforced constructs.In order to better promote the practical application of magnesium phosphate cement mortar in the reinforcement of steel structures,the study of different water cement ratio and the steel surface state effect on magnesium phosphate cement mortar reinforcement properties were studied,and the protective mechanism of steel bar is also explored.Through the discussion,we hope to guide the selection of repair materials in different repair conditions and environments,and to a certain extent,to promote the application process of magnesium phosphate cement as repair materials.Through the experiment,relative to ordinary portland cement and sulphoaluminate cement,magnesium phosphate cement reinforcement has more excellent reinforcement performance and volume stability.The reinforcement effect of concrete with three kinds of cement is obviously lower than that of mortar system.The mortar system has lower cost than paste system,so magnesium phosphate cement mortar has a greater advantage in reinforcing the structural reinforcement of steel bars.The influence factors of magnesium phosphate cement mortar reinforcement corrosion is studied,results showed that with the increase of water cement ratio,the protective effect of magnesium phosphate cement mortar reinforced gradually decreased,the actual repair application needs to reasonably control the water cement ratio;relative stainless steel,magnesium phosphate cement mortar of reinforced protective effect of corrosion products and pitting the actual application significantly decreased,repair reinforced should be completely rust.After opening the specimen,it was found that the surface of reinforcing bar in magnesium phosphate cement had a pale yellow dense bond layer.The experiment showed that the bond protection layer had good protective effect on the reinforcement.The results of X-ray diffraction analysis of the surface bonding layer and the mixture of phosphate and iron powder showed that ferrous phosphate existed.Therefore,it was speculated that the reaction between the reinforcing steel and the phosphate in the magnesium phosphate cement produced ferrous phosphate.Further experiments found that steel with bond protection layer are less prone to corrosion than steel bars soaked in phosphate solution.It is concluded that the bond protection layer is not only the corrosion product of phosphate and steel bars,and combined with magnesium phosphate cement hydration products and unreacted Magnesium Oxide products.