Research On The Durability Of Offshore Concrete Structures

An increasing attention has been directed to develop renewable energy sources by different countries,due to the urgent fact that we are now facing serious problems of greenhouse effect and energy exhaustion.As wind energy is widely accepted as one the most mature renewable energy source,the construction of offshore wind turbine tower is now under booming development.Concrete wind turbine towers are preferred over their steel counterparts.This is mainly due to the more suitable properties that concrete structures possess,e.g.lower maintenance requirements,better dynamic performance and high versatility.The hostile marine environment may create many concerns for the durability of offshore concrete structures,in particular,the diversified corrosion-induced degradation cause by the ingress of marine particles and different exposure situations.This paper aims at examining the possible factors that may affect the durability of offshore concrete structures,and establishing quantified methods to assess the chloride content.This paper initiated with a brief introduction to the main degradation mechanisms of offshore concrete,after which the corrosion process of steel bars and four categories of exposure situation were analyzed.After a thorough investigation of the possible factors that affect the chloride diffusion coefficient,a prediction model based on Artificial Neural Network(ANN)was proposed.The developed ANN model used as many as 13 input parameters,varying from concrete constituents,mechanical property and experiment process,to achieve one output parameter,referred to as the chloride diffusion coefficient.It is easy to use and has fairly high prediction accuracy.Principal component analysis was performed to discover the most affecting factors.In addition,the present study also revealed some important features of ANN model which was rarely studied by previous researches.An empirical approach to predict chloride content in offshore concrete was also proposed by calibrating the Fick's second law,considering the exposure zone,water-cement ratio and service time as relevant factors.The proposed model was validated by two alternative methods and the results suggest that it is feasible in predicting the chloride content and penetration depth of concrete structures in a marine environment under chloride ion attack.