Study On The Corrosive Cracking Of Corrosion Resistant Reinforced Concrete Column

The durability of reinforced concrete structures in chloride ions is generally a serious problem.Corrosion resistant reinforcement is one of the effective measures to improve the performance and prolong the service life of concrete structure.However,there is still a lack of research on the rust-expansion and cracking of concrete protective layer and the degradation of mechanical properties caused by corrosion resistant rebar.Therefore,the rust-expanding and cracking properties of corrosion-resistant reinforced concrete columns and ordinary reinforced concrete columns under the coupling effect of loads(including axial compression loads and eccentric compression loads)and chloride ions,as well as the law of mechanical properties degradation of corrosion-resistant rebar and corroded ordinary rebar are studied.The main research work is as follows(1)The accelerated corrosion of corrosion-resistant reinforced concrete columns and ordinary reinforced concrete columns under the coupling effect of axial load and chloride ion environment is carried out by adopting the method of "dry and wet circulation-constant current".At the same time,the distribution,trend and crack width of corrosion resistant reinforced concrete columns were compared with those of ordinary reinforced concrete columns during each accelerated corrosion cycle.The results show that:under the coupling effect of axial load and chloride ion,the corrosion resistant reinforced concrete column is mainly cracked on one side along the bar.At the initial stage of corrosion.the distribution of rust expansion cracks is concentrated at the bottom of the specimen with concentration of chloride ion solution.The width of rust expansion crack increases slowly first and then rapidly with the acceleration of corrosion time,which shows a ladder upward trend.However,the rust cracks of ordinary reinforced concrete columns are mostly caused by the double-sided cracks along the bars,and the local falling off of the protective layer of concrete occurs frequently.The crack width of ordinary reinforced concrete column is slightly smaller than that of corrosion-resistant reinforced concrete column,which is mainly caused by the release of more rust expansion force caused by double-sided cracking.(2)The accelerated corrosion of corrosion-resistant reinforced concrete columns and ordinary reinforced concrete columns under the coupling effect of eccentric load and chloride ion was studied by adopting the accelerated corrosion method of "dry and wet circulation-constant current".The results show that:under the action of eccentric load and chloride ion coupling,there are differences in the law of rust expansion and cracking on different surfaces of concrete columns.The rust expansion and cracking of corrosion-resistant reinforced concrete columns are mainly distributed at the top and the side of the specimen when the corrosion begins.With the increase of corrosion time,other areas on the side and the bottom gradually appear rust expansion cracks;The rust expansion crack width has a nonlinear growth relationship with the dry and wet cycle time.The crack width of corrosion-resistant reinforced concrete column is the largest by ramen and the smallest by compression surface.The distribution of rust expansion cracks in ordinary reinforced concrete columns is relatively uniform,and the distribution of rust expansion cracks in each surface is less different.The rust crack width of ordinary reinforced concrete columns also shows a nonlinear growth trend.The crack width of corrosion-resistant reinforced concrete columns subjected to ramen is larger than that of ordinary steel columns,while the crack width of corrosion-resistant steel columns subjected to compression is smaller than that of ordinary steel columns.By comparing the rust expansion and cracking phenomenon of the members under axial compression load,it is found that the length of the rust expansion crack of the corrosion-resistant reinforced concrete column under eccentric compression load is 1.19 times that of the specimens under axial compression,and the length of the ordinary reinforced concrete column is 1.36 times that of the members under axial compression at 144 days of accelerated corrosion.The average rust crack width of corrosion-resistant reinforced concrete eccentric columns is 1.09 times that of axial columns and 1.14 times that of ordinary rebar.It shows that the rust expansion cracks on concrete surface develop faster under eccentric load.(3)Accelerated corrosion of concrete columns under eccentric load is carried out to obtain corrosion-resistant rebars and ordinary rebars under different stress states.The corrosion morphology,yield strength,ultimate strength and elongation of corrosion-resistant rebars and ordinary rebars were studied.The results show that the corrosion-resistant steel is mainly concentrated pitting corrosion,and the non-uniform corrosion is along the girth of the steel section,while the general steel is uniformly corroded.The yield strength and ultimate strength of corrosion-resistant steel bars decreased with the increase of corrosion rate after rust,and the yield strength of corrosion-resistant rebars subjected to pressure corrosion decreased slightly faster than that of rebars subjected to tension.The change of mechanical properties of ordinary reinforcement after corrosion is similar to that of corrosion-resistant reinforcement,but the ductility declines faster than that of corrosion-resistant reinforcement.