Research On The Quality Detection Method Of The Interface Between Old And New Concrete Based On The Corrosion Form Of Steel Bar

The problem of new and old concrete interface is a widespread problem in practical engineering,including the hinge joints of bridges,construction joints in housing construction and pavement engineering,and new and old joint surfaces formed in maintenance and reinforcement projects.The failure of the new and old concrete interface will lead to the failure of the structure to reach the expected service life.The problem caused by the weak interface has long existed in the concrete structure.Therefore,it has become an important issue to study the bonding quality of new and old concrete interface.At present,the research on the quality of the new and old concrete interface is mainly to detect the quality of the new and old concrete interface through the mechanical test method of the damaged specimen.Because the mechanical test is subject to many restrictions,the new and old concrete interface obtained by the mechanical test has good short-term performance and poor long-term performance.Therefore,in order to explore a new detection method,this paper adopts the new and old concrete interface quality detection method based on the corrosion morphology of steel bars,and designs 18 groups of specimens.The effects of four interface treatment methods on the bonding quality of the new and old concrete interface are studied by experiments.According to the generation of cracks at the interface and other locations during the corrosion process,the corrosion rate of the steel bar and the corrosion morphology of the steel bar,the weakness of the new and old concrete interface after different treatment methods is judged.Due to the uneven distribution and complex shape of the rust pits on the surface of the corroded steel bars,in order to study the uneven distribution of the longitudinal corrosion of the steel bars more accurately,a three-dimensional blue light scanning technology was used to accurately scan and measure the steel bars before and after corrosion.In order to test the applicability of the new method,this paper also uses a double-sided shear test to detect the shear strength of the new and old concrete interface after treatment.Specifically,the main conclusions of this paper are as follows :(1)The interface quality of the new and old concrete is not only related to the rough treatment of the interface,but also has a great relationship with the type of interface agent,the difference between the strength grade and type of the new and old concrete,and the bonding age of the new and old concrete.(2)When the strength grade of new and old concrete is the same(both new and old concrete are C30),after the interface of new and old concrete is rough treated,the steel bar corrosion by electrification is uneven corrosion,and the corrosion rate of steel bar crosssectional area at the interface is the largest.The interface bonding quality is improved when the manual chisel and slot are used,and the cracking time of the concrete protective layer is prolonged during electrification corrosion.Corrosion rate decreases.The effect of the reserved groove is more obvious than that of the manual chiseling method,and the difference between the cross-sectional loss rate and the average cross-section corrosion rate of the interface reinforcement is reduced.Compared with the specimens with natural smooth interface,the difference is reduced from 0.66% to 0.30%.The result of the new method is the same as that of the double-sided shear test.The shear strength of the reserved groove method is 48.84% higher than that of the natural smooth interface method.(3)When the strength grade of the new and old concrete is the same(both the new and old concrete are C30),after the use of cement slurry and cement pulping interface agent on the interface of the artificial chiselled old concrete,the electric corrosion of the steel bar is uneven corrosion,the most serious position of corrosion is not at the interface of the new and old concrete,the interface bonding quality is improved,and the cracking time of the protective layer is prolonged during the electric corrosion.Corrosion rate decreases.The effect of cement pulping is better than that of cement grouting interface agent.The difference between crosssectional area corrosion rate and average cross section corrosion rate of interfacial reinforcement is reduced.Compared with the specimen without interfacial agent,the difference is reduced from 0.43% to 0.34%.The result of the new method is the same as that of the doublesided shear test.The shear strength of the test specimen with cement bentonite interfacial agent is increased by 41.20% compared with that without interfacial agent.(4)When the strength grade of the new and old concrete is the same(both the new and old concrete are C30),the new and old concrete specimens with the bonding age of 14 d,28d and60 d are adopted.The electric corrosion of the steel reinforcement is uneven corrosion.When the bonding age increases,the interface bonding quality is improved,the cracking time of the electric corrosion protection layer is prolonged,and the corrosion rate decreases.When the bonding age is 60 days,the interface bonding quality of the new and old concrete is better,and the difference between the cross-sectional loss rate and the average cross-section corrosion rate of the interface reinforcement is reduced.Compared with the specimens with the bonding age of 14 days,the difference is reduced from 0.53% to 0.40%.The result of the new method is the same as that of the double-sided shear test.The shear strength of the specimen with a bond age of 60 d is increased by 16.8% compared with that of the specimen with a bond age of 14 d.(5)When the new and old concrete interface is treated in the same way,the old concrete is C30 and the new concrete adopts C40,C50 and UHPC respectively.When the strength of the new concrete is increased or the type of the new concrete is changed,the corrosion rate of the steel bar decreases and the interface bonding quality is improved.The difference amplitude between the cross-sectional loss rate and the average cross-sectional corrosion rate of the interfacial reinforcement is reduced.When the new concrete type is UHPC,the difference amplitude is reduced from 0.43% to 0.21% compared with the specimen whose new concrete type is C30.The result of the new method is the same as that of the double-sided shear test.When the type of new concrete is UHPC,the shear strength increases by 62.98% compared with that of the new concrete is C30.(6)When the interfacial shear strength increases(compared with the shear resistance increases),the difference between the corrosion rate of interfacial steel cross-sectional area and the average corrosion rate of interfacial steel cross-sectional area decreases,indicating that the interfacial quality is improved,the compactness is improved,and the structural durability is enhanced.On the contrary,it indicates that the interface quality is reduced and the structural durability is reduced.