Research On Durability Of Reinforced Concrete Structure Based On The Correlation Between Field Exposure Test And Indoor Durability Test

At present, concrete structure durability design all of world mainly is dependent on lab durability data or basis of field exposure data. Lab and field correlation is rarely established. Thus, almost all important projects need to do lab durability test for making durability design. If economic conditions permit, some field exposure test can be done. If the theory of lab durability and field engineering durability correlation can be build, on basis of lab durability test, concrete structure durability design can be done according to lab durability and field engineering durability correlation for specific engineering data. In order to obtain the law of lab and field durability correlation This paper focus on concrete beams in harsh salt lake field environment, C30、C45FA30(adding 30% FA in C45)、C45SG50(adding 50% SG in C45)、C50、C60、、C65SF10SG45(adding 10% SF and 45%SG in C65)、C70SF10FA27(adding 10% SF and 27%FA in C70)and C80SF10 concrete in salt lake brine immersion、dry-wet cycle、immersion-load and dry-wet-load indoor durability test is systematically investigated, the same thing happens in salt lake field exposure and salt lake field exposure-load; The dynamic elastic modulus、surface scaling time 、chloride diffusion、flex bearing capacity and deflection are studied; Relation between indoor test and field environment is calculated, the time-variant of compress strength、chloride diffusion and steel bar corrosion is calculated, Concrete beam bending capacity and life predication model is modified by application of three stage life predication model, it can be use to predict service life of great bridge across railway for salt lake group, and it provide theoretical reference for concrete structure durability design in salt lake area. The main study content is list as follow:1)A new method of on basis of permanent immersion, application lad and field conversion coefficient as bridge is introduced. The system of concrete structure durability design in harsh environment is established based on lab and field correlation(CLFT). A method of data conversion of concrete structure between lab test and field test is introduced.2)The rule of concrete relative modulus and surface scaling variety is researched. The test result showed that Compared with immersion condition, both loading and dry-wet cycle speeds up reinforced concrete corrosion and surface scaling, dry-wet cycle has more significant efficient. The relative dynamic elastic modulus time-varying equation is build to predict concrete in field environment, field-load, field-dry-wet cycle, field-dry-wet cycle-load. Reinforced concrete beam surface scaling is associated with concrete compress strength grade. The more strength, the later of concrete scaling time occur in same corrosion environment.3)The rule of concrete chloride diffusion property in salt lake is study. Test result show that Concrete chloride ion binding capacity(R) is unconcerned with test condition. Concrete surface chloride content(CS) is independent of indoor test condition. Concrete surface chloride content(CS) of indoor environment is more big than field. Field structure chloride content can be predicted on basis of permanent immersion test data by introducing the indoor and field conversion function with Concrete surface chloride content(CS). Concrete apparent chloride diffusion coefficient decreased with increase of time. In the concrete mix design, the method of reduction concrete apparent chloride diffusion(D0) including: enhancing concrete strength and adding mineral admixture reduce D0, and the later is more obvious than the former. Thus, concrete design rule in salt lake area is the first choice of highly adding mineral admixture by means of single(C45FA30 �'� C45SG50) and double(C65SF10FA27 �'� C70SF10SG45) technique, is not only enhancing concrete strength grade.4)Reinforced concrete flex structural member capacity and deflection are study. Concrete structure capacity and deflection degradation model is build based on lab and field correlation(CLFT). Concrete structure time-variant of concrete strength is established. Time variant model of steel corrosion rate and tensile strength is established. Concrete structure ultimate capacity and deflection model is modified and validated by thinking of time-variant of concrete strength and reinforcement mechanical properties and concrete scaling depths, Test result is pretty close to the facts, this model can be applied.5)Combined with theory of reliability and “induction period+ deterioration period + expiration period ”three stage life predication model, Formula of bearing capacity of concrete structure is correction by application to on basis of lab and field correlation(CLFT) design. calculations show that:in salt lake environment, Induction period or deterioration period of concrete beam and pier is depend on corrosion responsible for concrete deterioration. Concrete beam and column is made of concrete with concrete strength C30~C60, the durability design only think of induction and corrosion; Concrete beam and column is made of concrete with concrete strength C65~C80, the durability design only think of induction.6)The example of predication service life of concrete structure by different concrete in Salt lake field is provided. The result show that depth of the concrete cover is 30 mm, concrete beam and column service life in salt lake air condition can meet to 100 a design demand by application with high performance concrete with strength over C65, which service life design is 50 a, is made of high performance concrete with strength C45~C60. Concrete beam and column in saline soil and salt lake brine service life can reach to 100 a design demand by means of both applying high performance concrete with strength over C65 and surface protection. Which service life design is 50 a is made of C80SF10 high performance concrete.7) Combined with theory of reliability, the problem of the actual bridge under harsh environment durability design is study based on lab and field correlation(CLFT) design and provided example. The service life and durability design of precast box beam、bent cap、bridge pier and strip-shaped base for special railway bridge of salt lake group are analyzed. Test result show that concrete strength C50、50mm concrete cover depth precast box beam service life can satisfy design demand 100 a, must be take surface protection method for precast box beam web. concrete strength C50、50mm concrete cover depth bend cap service life can meet with 100 a design demand. Bridge pier with C40 and 60 mm protection thick service life satisfy with design demand 100 a by using 30 mm steel sheet piling cofferdam protection+ 2 times fluorine carbon coating surface protection. Concrete strip-shaped base with C50 and 60 mm protection thick with 64 mm steel sheet piling cofferdam protection+ 2 times fluorine carbon coating surface protection service life can meet with 100 a design demand.8) Optimization durability design is based on reinforced concrete bridges in salt lake area and some suggestions are posed. Beam web in salt lake is made of highly mineral admixture high performance concrete with 30 mm concrete protection cover can meet with 100 a design demand. Box beam and bent cap service life can satisfy design demand 100 a with high performance concrete compress strength over C45. Bridge pier with C65~C70 high performance concrete service life satisfy with design demand 100 a by using immersion 2mm silane coupling agents. Concrete strip-shaped with compress strength over C65 high performance concrete service life satisfy with design demand 100 a by using 64 mm steel sheet piling cofferdam protection+ 1times fluorine carbon coating surface protection.