Microscopic Characteristics And Experimental Study On Degradation Of Prestressed Concrete Structures Under Combined Corrosion And Freeze-thaw

Prestressed concrete is widely used in the construction industry due to its good crack resistance and durability.However,since the building structure is subjected to deterioration of concrete carbonization,freeze-thaw,rust and the like throughout the life cycle,the bearing capacity is reduced,and the safety and reliability are lowered.The reinforced concrete structure in the frozen area will be affected by the combination of steel corrosion and freeze-thaw cycles.The resulting deterioration of steel-concrete interface performance,material degradation and pre-stress loss will be different from single factor,but related research is lacking.For pretensioned prestressed concrete beams,the rusted test,freeze-thawed test,and the joint test of rusted and freeze-thaw cycles are performed.The specimens subjected to different aging tests were examined by CT scan to compare internal damage.Afterwards,the prestressed concrete beam is tested for bending resistance and its prestress loss is analyzed.The deterioration law of reinforced concrete materials under the combined action of corrosion and freeze-thaw cycles was revealed.The main results are as follows:(1)The effects of corrosion,rust and freeze-thaw cycles on the number,width and expansion of internal cracks in concrete were analyzed by CT scanning from a microscopic perspective.By comparing the changes of pore size distribution in different volume ranges under different test conditions,it is considered that the rust products have the most obvious effect on the pore filling volume of 0.1～0.5mm~3.The freeze-thaw damage effect on the pores with a volume of 0.05～1mm~3 is obvious.(2)The test results of the bending resistance of prestressed reinforced concrete beams are analyzed.The effects of corrosion,freeze-thaw cycles and the combined effects of corrosion and freeze-thaw cycles on the ultimate bearing capacity and prestress loss of prestressed flexural members were studied.The results show that the pre-corrosion effect has little effect on the bearing capacity and pre-stress of the specimen.With the increase of corrosion rate,the bearing capacity and effective pre-stress of the specimen are obviously accelerated;There is a linear relationship between the number of freeze-thaw cycles and the bearing capacity and prestress loss;Corrosion and freeze-thaw cycles have the greatest influence on the bearing capacity and prestress loss of the specimen,and the effect on the specimen is greater than the superposition of the effects of the simple corrosion test and the freeze-thaw test.(3)By comparing the cracking process of prestressed concrete beams with ordinary concrete beams,the prestressed concrete beam cracking capacity is simplified to the effective prestress in the steel bar and the ordinary concrete bearing capacity,and then the effective prestress in the prestressed concrete beam is derived.By comparing with the effective prestress in the prestressed concrete beam calculated by the formula method,it is found that the two can be well fitted.