A Semi-Mechanistic Model for Predicting the Service Life of Composite Coatings on VW63Z Magnesium Alloy

The application of Mg alloys is always accompanied by various coating technology, but a reliable model predicting the service life of coatings on Mg alloys is lacking but urgent. In this work, a semi-mechanistic model was proposed to predict the service life of plasma electrolytic oxidation (PEO) coating/electrophoretic coatings on a VW63Z Mg alloy;the model was decomposed into three parts: a first part depicting the degradation time of organic coating (L_(1)) and the diffusion time of electrolyte in the inorganic coating (L_(2)), respectively;a second part interpreting the breakdown of coatings due to the corrosion process (L_(3));a final part establishing an algorithm converting the accelerated tests into the real service environment (α);the effect of structural stress and dissimilar metal joints on the service life of coatings was also considered. Based on the ongoing accelerated experiments, the semi-mechanistic model could be able to predict the service life of both PEO coatings and composite coatings on VW63Z Mg alloy with a satisfiable precision.

Durability problems of lining structures for Xiamen Xiang'an subsea tunnel in China

Durability problem of reinforced concrete for underground structures is a hot issue in the field of structural engineering. For underground structures, the prediction of structural service life and methodology for durability design are needed to estimate structural durability. Taking the case of Xiamen Xiang＇an subsea tunnel as background, which is designed to meet the requirement of lO0-year service life, the influential factors on tunnel lining durability are analyzed. Under the criteria of crack controlling and bearing capacity of linin~ structures, the theoretical service life of Xiamen Xiang＇an subsea tunnel lining is studied. The regulations, which are needed for the diffusion capability of chloride ions in concrete by the relevant diffusion tests, are proposed. After a quick corrosion test, the bearing capacity test on eccentric short columns is implemented to investigate the variation rules in the bearing capacity of models with time. Influence of the corrosion degree of steel bars on the bearing capacity of models is also investigated. Based on the results of model tests, the acceleration ratio between the quick corrosion in laboratory test and the natural corrosion environments is established. Thus, the natural service life of subsea tunnel lining structures can be obtained by means of laboratory tests. Then, the proposed method using this modified model is employed to predict the service life of tunnel lining structures. Finally, the design and construction measures for improving the durability of lining structures of subsea tunnel are introduced. The proposed method in the present study based on a real engineering project is superior to those with only theoretical assumptions, and would be more suitable for similar projects.

Experimental Investigation on Contribution of CFRP Attachment to Durability of Reinforced Concrete Structure Subjected to Chloride Attack

The function of externally-bonded carbon fiber reinforced polymer （CFRP） in preventing chloride from entering into concrete is verified by experiment. The results show that externally-bonded CFRP can be considered as a part of corrosion prevention system of strengthened concrete structures subjected to chloride ingress, and the contribution of CFRP should be considered in evaluation of durability of reinforced concrete structures with externally-bonded CFRP. With the effective shielding function of CFRP considered, an equation for residual lifetime prediction of concrete structures with externally-bonded CFRP is derived from Fick＇s dispersion law. CFRP has two functions for coastal concrete structures, including strengthening and increasing durability as part of corrosion prevention system.