Slab Concrete Under Freeze-thaw Cycles Research On The Characteristics Of Steel Corrosion

As an important structure of the face rockfill dam,the concrete panel will directly endanger the safety of the dam,and the cold environment will cause serious damage to the concrete structure.With the influence of the freeze-thaw cycle,the pores and cracks inside the concrete increased,and chloride ions penetrated into the concrete,resulting in the corrosion of the steel bars,and the performance of the reinforced concrete was seriously reduced.Therefore,it is of great theoretical research value and practical significance to study the influence of freeze-thaw environment on the corrosion characteristics of steel bars,and to evaluate the durability and improvement of concrete structures during service.In this paper,the macro-test and micro-detection are combined,and the indoor test is compared with the numerical simulation to deeply study the effect of freeze-thaw cycles on the corrosion characteristics of steel bars.The research is mainly carried out from different freezing and thawing cycles and different degrees of corrosion,the macroscopic mechanical properties of reinforced concrete,the microscopic properties of scanning electron microscopy,and the numerical analysis of reinforced concrete pull-out tests.The main conclusions are as follows:(1)Carry out freeze-thaw cycle test and steel bar corrosion test.It was found that under the same corrosion conditions,with the increase of the number of freeze-thaw cycles,the quality of the test specimens decreased significantly,and the degree of corrosion gradually increased.As the number of freeze-thaw cycles increases from 0 to 200,the ultrasonic speed decreases.The ultrasonic speed did not change much in the early freeze-thaw period.For specimens with a large number of freeze-thaw cycles,the longer the power-on time,the greater the decrease in wave speed.The ultimate pullout force is negatively correlated with the number of freeze-thaw cycles.The higher the degree of corrosion,the lower the ultimate pullout force,and the greater the influence of the number of freeze-thaw cycles.When the theoretical corrosion rate is greater than 8%,the pull-out shape of the steel bar changes from split failure to pull-out failure,and the material structure fails.(2)Carrying out microscopic research on the sampling of test specimens,and found that for unfrozen and thawing specimens,the test results showed a flat and dense accumulation of hydration products.The freezing and thawing failure path is from the surface to the inside.When 200 times of freezing and thawing,the internal microstructure of the concrete changes significantly,the material structure is destroyed,and the bonding performance decreases.For uncorroded specimens,under the action of freeze-thaw cycles,as the number of freeze-thaw cycles increases,the porosity of each selected point increases.(3)In the numerical simulation,as the displacement increases,the Mises equivalent stress of the steel bar increases continuously.After freezing and thawing,as the displacement increases,the stress of the specimen drops rapidly,and it is only 1/6 of the untreated specimen in the same state before the detachment.Comparing untreated specimens and freeze-thaw-corrosion specimens: the time for the release of the bonding layer is greatly reduced,and the maximum Mises stress during the separation is 0.145 Mpa,which is only 10% of the untreated specimens.(4)The damage of concrete spreads out from the bonding interface of reinforced concrete.At the same node,the damage value of the specimen subjected to freeze-thaw corrosion is much larger than that of the untreated specimen,and the influence range becomes smaller...