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Practical observations demonstrate that the corrosion deterioration of numerous reinforced concrete structures is due to the combination of carbonation and chloride ingress. However, the comprehensive combined model developed directly based on the coupling mechanism of them is very complicated. This article presents a simplified model to describe the transport of chloride ions with carbonation by introducing the Stefan condition, which is mainly used for the mathematical modelling of boundary movement caused by phase transformation in thermodynamics. Meanwhile, the influence function of carbonation on the diffusion coefficient of chloride ion is also re-discussed. An empirical formula is fitted directly according to the mix proportions of concrete, which can greatly reduce the computational cost. Then, an intuitively expressed formula of chloride concentration distribution under the influence of carbonation can be solved. Ultimately, its prediction accuracy is verified by two experiments. [ABSTRACT FROM AUTHOR]

Presented is a series of estimating methods for the parameters in a comprehensive combined model which is developed recently. The calculation of numerous intermediate-process parameters is optimised or combined to simplify the expression. The effect of carbonation on the change of apparent diffusion coefficient of chloride is expressed by three polynomial functions. Furthermore, a new simplified analytical method is proposed for the approximate study of this combined action. With the assumption of linear diffusion, the analytical results for the carbonation depth and concentration of free chloride ions can be obtained from a function of exposure time and mix proportions of concretes; the coupling effect is included by introducing an empirical factor. Several sets of experimental data are used for the verification of our equations. [ABSTRACT FROM AUTHOR]

In situ (Al,Cr) 2 O 3 -Cr composite coating was fabricated by reactive plasma spraying Al-Cr 2 O 3 composite powder. Phase composition and microstructure of the as-sprayed coating was characterized by X-ray diffractometer, scanning electron microscope and transmission electron microscope. Indentation fracture behavior of the coating was investigated. It is found that the microstructure of the coating consists of [(Al,Cr) 2 O 3 +Cr] eutectic and Cr+[(Al,Cr) 2 O 3 +Cr] hypoeutectic. The eutectic microstructure of the coating shows the characteristic of nano structure, in which Cr particles with size less than 40 nm distribute in (Al,Cr) 2 O 3 solid solution matrix. The hypoeutectic microstructure of the coating consists of Cr particles with size larger than 1 µm and [(Al,Cr) 2 O 3 +Cr] divorced eutectic. The toughness of the (Al,Cr) 2 O 3 -Cr composite coating is significantly improved compared with that of the conventional Al 2 O 3 coating. [ABSTRACT FROM AUTHOR]