Research On The Effect Of Non-prestressed Steel Corrosion On The Long Term Performance Of Prestressed Beams

Currently prestressed concrete structures are widely used in China,but their durability deterioration is often neglected due to the high strength and high compactness of the concrete materials used,as well as the control of cracks by prestressing.With the invasion of harmful substances in the external environment,the corrosion of reinforcement inside the prestressed concrete structure is gradually exposed to the public,which will reduce the long-term service performance of the structure.The current research on reinforcement corrosion in prestressed concrete structures mainly focuses on the corrosion of prestressing tendons,but the corrosion of non-prestressing reinforcement will also cause the deterioration of the long-term performance of the structure.On the other hand,the current research commonly uses the electric-brine dry-wet cycle to accelerate corrosion,but the introduced dry-wet cycle and brine influence are not considered.Therefore,through experimental observation and mechanical analysis,this paper studies the long-term performance development law of prestressed beams under different environments,and the test results can provide data support and mechanical analysis reference for in-depth study of the effects of wet and dry cycling,salt water and corrosion of non-prestressed reinforcement on long-term performance.In addition,the long-term performance of this paper refers to the strain of concrete and the stress of prestressed reinforcement.The main research contents and conclusions are as follows:(1)Five test environments were designed: natural environment,the drying and wetting cycles with tap water/chlorine salt solution,and the drying and wetting cycles with chlorine salt solution and longitudinal reinforcement/ stirrups.To compare the differences of concrete strains under different environments and to focus on the effects of drying and wetting cycles,chlorine salt and the corrosion of non-prestressing reinforcement on concrete strains.The results showed that drying and wetting cycles reduce concrete strain,but there is an upper limit to the degree of reduction;the use of chlorine salt reduces concrete strain,and the degree of reduction increases with the increase of the number of drying and wetting cycles;the corrosion of longitudinal reinforcement increases concrete strain,and stirrup corrosion reduces concrete strain,and the degree of effect(increase/decrease)increases with the increase of the number of drying and wetting cycles.(2)Under the same test environment,the effects of drying and wetting cycles,chloride salt and the corrosion of non-prestressing reinforcement on the stress in the prestressing tendon were concerned.The results showed that the stress growth of prestressing tendon under drying and wetting cycles was fast and then slow,and finally stabilized;the use of chlorine salts results in a positive correlation between the stress in the prestressing tendon and the number of drying and wetting cycles;the corrosion of longitudinal reinforcement decreased the stress of prestressing tendons and stirrup corrosion increased the stress of prestressing tendons,and the degree of influence(increase/decrease)increased with the increase of the number of drying and wetting cycles.(3)The corrosion of non-prestressing reinforcement affects the stress state of prestressed beams,resulting in the stress change of prestressing tendon.The effect of longitudinal reinforcement corrosion was quantified from the perspective of section damage,and the effect of stirrup corrosion was quantified from the perspective of longitudinal corrosion-induced expansion force,and the equations for the relationship between the value of change in prestressing tendon stress and the corrosion rate were derived using mechanical equilibrium and deformation coordination relationships,respectively.It should be noted that no cracks were visible on the surface of the prestressed beam affected by stirrup corrosion throughout the test.If the stirrup corrosion continues and reaches the critical corrosion rate,it may cause concrete cracking and even spalling,which may reduce the stress in the prestressing tendon.The test is still ongoing and will be followed up by our group.