Multi-Environmental Time Similarity (METS) Theory And Its Application In Coastal Concrete Structural Durability

The durability of reinforced concrete (RC) structures has attracted extraordinary concern in the field of civil engineering. Besides the cost of rebuilding and maintenance, it is also closely related to energy-saving, emission reduction, environmental protection and sustainable development of the society. A multi-environmental time similarity (METS) theory and its application in coastal concrete structural durability are presented in this paper. METS can be used for durability assessment and life prediction by introducing a third reference site with a certain service life and the same or similar aggressive environment to the study object to bridge the field inspections and the indoor accelerated tests. The correlation between the field inspection data and the results of indoor tests in accelerated environments is established based on METS. Furthermore, the results of indoor tests are used to predict service life of RC structures effectively. The application of METS in coastal concrete structural durability is analyzed in detail, and it makes a meaningful step towards the durability research of concrete structures in environment-level.The details are as follows:1. Based on the classical similarity theorys, a reference site with almost the same or similar aggressive environment is introduced to bridge the field inspections and the indoor accelerated tests, and the METS theory is presented. Once the correlation between the field inspection data and the results of indoor tests in accelerated environments is established, the life assessment of existing RC structures will be performed effectively. By analyzing the major influence factors of coastal concrete structural durability, the implementation process of life prediction and durability assessment for the coastal concrete structures is analyzed.2. The experimental design of METS is also included. Three tests, including field inspection test on the third reference site, the field exposure test, and the indoor test by artificial climate simulation on the concrete specimens from the third site and the investigated object are designed to lay the foundation for the application of METS.3. According to both the field inspection data and the indoor accelerated test results, it can be found that the chloride penetration varies with environmental zones. Tidal zone ranks the most serious one, followed by splash zone, and the chloride content in different depths from the concrete surface of the atmospheric zone is much lower than that of the wetting-drying cycling zone. It indicates that the indoor accelerated and the site actual environments have a certain similarity.4. The time-dependent rules of chloride diffusion coefficient and surface chloride concentration are studied. According to the indoor accelerated experimental results, the formula between the age exponent and concrete composition is established in different environmental zones, such as submerged, wetting-drying cycling and atmospheric zone. This expression is simple, easy to apply, and agreeable well with the test results. Then, the similarity of chloride diffusion coefficients between the indoor and outdoor actual environments is studied to obtain the similarity rates of diffusion coefficient in different environmental zones. By introducing Bltzmann variable, the chloride concentration at the maximum convective depth is obtained as the surface chloride concentration of pure diffusion zone by regression analysis. The accumulation rate relation of surface chloride concentration in indoor and on-site environments with time is established, and the similarity rates of surface chloride concentration in different environmental zones are established.5. Based on METS, the time similarity rates of chloride penetration between the indoor accelerated environment and field condition of different environmental zones are achieved by numerical simulation according to the indoor test results and the similarity relations of both diffusion coefficient and surface chloride concentration. chloride ingress time can be obtained where the chloride content at the depth of 60mm from the concrete surface reaches to 0.05% (by weight of concrete). The time-dependent diffusion coefficient and surface chloride concentration is taken into account in numerical analysis.6. Based on METS, the life prediction of concrete structures of Hangzhou Bay Bridge (HZBB) is carried out. The chloride ingress process of main components and life prediction are accomplished by numerical simulation based on the similarity relations of chloride diffusion results from analyzing the results of on-site inspection, indoor accelerated test and field exposure test. In order to match the actual deterioration process of concrete, and obtain reasonable, creditable and convictive prediction results, the time dependence of diffusion coefficient and surface chloride concentration is taken into account.This research was supported by the project of National Natural Science Fund "Fundamental Research on Durability Design and Assessment of Concrete Structures in Chloride Erosive Environment" (50538070), "863 program of National Hi-Tech Research Development "Durability Test Method and Assessment Technology of Important Coastal bridges" (2006AA04Z422), National Major Project Program "Concrete structural durability research on Hangzhou Bay Bridge". Their support is gratefully acknowledged.