Research On Double-mixture Concrete Durability Under Chloride Ion Circumstance

Because of the chloride ion permeation, the service life of the harbor project, paralic construction and some roads and bridges which used with deicing agents reduces, and which also causes the huge economy loses. As to this actuality, this paper broaches a method which uses fly ash and blast- furnace slag to promote concrete durability combining with some applications and improvements of the concrete mixed with mineral admixtures abroad.Different mixture proportioning of concrete samples which mixed with different dosages of fly ash and blast-furnace slag are designed through orthogonal table, then the samples' basic mechanical properties and durability are investigated. Basic mechanical properties concluded compressive strength, tensile strength and young's modulus et al. Some durability indexes are also systematically studied, which contains frost resistance, carbonization resistance and chloride permeability resistance. Combine with the destruct characteristics of the concrete in the chloride ion environment this paper proceeds the salty frost test, carbonization test after suffering from the chloride ion corrosion, fast corrosion of bar embedded in concrete in the seawater circumstance and electrochemical corrosion accelerating test of bar. The failure mechanism of double-mixture concrete by the coactions of the chloride ion corrosion and the freezing and thawing cycle as well as the chloride ion corrosion effect of the carbonization performance is investigated.Results show that, concrete mixed with fly ash and blast-furnace slag has good mechanic properties and durability. Because of the superimposed effect, concrete compressive strength approaches plain concrete's after 28 days cure, with the age growth, the concrete long-term strength obtains a development. After 60 days cure its strength surpasses the plain concrete.After 60 ages curing, the frost resistance, carbonation resistance and penetration resistance of the double-mixture concrete surpasses the plain concrete. In the salty frozen experiment, the destruction of the double-mixture concrete is checked by the quality loss factor achieves 5%, but the RDME drops quite slowly.Because the chloride salt intensifies the concrete destruction, the frost resistance drops obviously. The carbonization resistance generally drops after corroded by chloride ion, but comparing with plain concrete, the carbonized performance of double-mixture concrete drops obviously, mainly because the conjunction of the chloride ion and the hydrated lime hindered the secondary hydration of the fly ash, which causes the C-S-H quantity in hydrated concreteto drop and affects its durability performance.In chloride ion penetration text, the electric quantity value and the initial electric current value assumes the linear relation, the empirical formula based with the initial electric current value is deduced. In the electrochemical corrosion accelerating test of bar the corrosion amount deduced by the Faraday Formula closes the approaches the true values. In the process of rust expansive force calculation, based with the galvanic corrosion density a research method which can determine the swell increment caused by rust is advanced.The durability experimental results are studied, when the dosages of fly ash and GBFS attach 20% separately, the concrete has outstanding durable performance.