Research On Corrosion Of Binder Composition And Reinforced Concretes To Chloride Ion

The corrosion resistance of reinforced concrete stated in marine environment were essentially characterized by two key parameters: the diffusion coefficient in concrete and the chloride threshold values for corrosion of steel. The Portland cement with different SO₃/Al₂O₃ and fly ash and slag were used as binder materials, and the influence of binder composition on corrosion resistance of reinforced concrete were investigated by means of XRD, SEM, EDS, JAF Calorimeter, Chloride penetration test, TG, MIP test, Zeta potential method, half-cell potential method, linear polarization method, and electrochemical impedance spectroscopy method, respectively. The experimental results showed that:With the same W/C, the same concrete mixing and the same cement type, the chloride profiles in concrete of South China got the highest value, and the North China got the lowest value, due to the average annual temperature and the chloride concentration in seawater of South China got the highest value and the North China got the lowest value.It can increase the chloride threshold value when the suitable S/Al (molar ratio of SO₃ to Al₂O₃) were adjusted according to the Al₂O₃ content in cement. In the range of SO₃/ Al₂O₃<1, the chloride threshold values increased first and then decreased with increasing the SO₃/ Al₂O₃ in cement. The SO₃/ Al₂O₃ decreased with increasing the Al₂O₃ content in cement, which corresponding the maximal chloride threshold values. The SO₃/ Al₂O₃ was 0.93 and 0.77 when the Al₂O₃ content was 4.43% and 5.31% respectively. The effect of SO₃/ Al₂O₃ on the chloride threshold values was essentially the influence of mortar pore structure on the chloride threshold value, and the lowest average pore size specimen got the highest chloride threshold value.The chloride threshold values increased first and then decreased with increasing the SO₃/ Al₂O₃ in cement when the specimens immersed in simulated sea water solution.when SO42- penetrated into the specimens, it reacted to hydrated calcium aluminate sulfate and then decreased the SO₃/ Al₂O₃ compared with the specimens immersed in NaCl solution, the SO₃/ Al₂O₃ decreased from 0.93 to 0.87 which cooresponding to the highest chloride threshold value. When cement used in marine environment, it's need to consider the composite impact of sulfate and chloride, and then decreased the SO₃/ Al₂O₃ in cement compared with the cement used in NaCl solution.The use of mineral admixtures led to decrease the concrete porosity and average pore size. The concrete porosity and average pore size decreased first and then increased with increasing the fly ash or slag content in binder. When the fly ash content was 30%,or the slag content was 50%, the specimen got the lowest porosity and average pore size.The corrosion resistance to chloride ion for reinforced concrete increased first and then decreased with increasing fly ash content in binder, and it researched the maximum time for depassive of film for steel when the fly ash content was 30%. The corrosion resistance to chloride ion for reinforced concrete increased first and then decreased with increasing slag content, too. It researched the maximum time for depassive of film for steel when the fly ash content was 50%. When fly ash and slag were used in concrete, it do not only made the concrete more dense and decreased the availability of oxygen at the interface of steel, but also increased the charge transfer resistance and increased the stability of passive film of steel. On the other hand, it reduced the Ca(OH)2 content in hardened paste, and the chloride threshold values decreased with decreasing the Ca(OH)2 content, but the former reason was the main factor which influenced the durability of reinforced concrete.When the composite admixture content was 50% in concrete at 28days, the chloride diffusion coefficient decreased first and then increased with increasing fly ash content in composite admixture, and the chloride diffusion coefficient got the lowest value when fly ash content was 10%. The use of mineral admixtures led to reduce the chloride diffusion coefficient in concrete due to the composite binder reduced the concrete porosity and the average pore size.The use of mineral admixtures led to change the binding capacity of hydration products due to the composite binder changed the Zeta potential of hydration products. The active silicon and aluminum phase in fly ash and slag can increase the Zeta potential of hydration products, and the chloride binding capacity increased with increasing the Zeta potential.The suitable SO₃/Al₂O₃ were adjusted according to the Al₂O₃ content in cement, which the ratio of SO₃/Al₂O₃ increased with decreasing the Al₂O₃ content, and the cement replaced by fly ash and slag at appropriate level, it do not only led to reduced the average pore size and the availability of oxygen at the interface, but also increased the chloride binding capacity, the concrete resistivity, and the stability of passive film for steel, and eventually delayed the time to failure of reinforced passive film. The use of binder appropriately led to decrease the chloride diffusion coefficient in concrete, increase the surface chloride content, and increase the chloride threshold values, and eventually improving the corrosion resistance to chloride ion for reinforced concrete.It do not only increase the corrosion resistance to chloride ions for reinforced concrete with selecting suitable SO₃/Al₂O₃ in cement and adding appropriate content of fly ash and slag in cement, but also increased the usage of fly ash and slag which was industrial by-products, and consequently improved the efficient use of resources and reduced the environmental load. It got good social and economic benefits...