Environmental Zonation On Design Methodology For Durability Of Concrete Structures

Research in this paper is the deepening and development of the methodology of Durability Environmental Zonation Standard (DEZS). Focusing on the interaction between the external environments and the structures, the area of natural environments related to the durability of concrete structures are divided into different parts according to the degree of external environments’ effects on the structures, and the corresponding durability design regulations and design methods are presented and established. Research work in this paper could be introduced as:1. Based on the requirements of durability design of concrete structures, basic connotation of research on environmental zonation based durability design of concrete structure is given, and also systems of the general provisions, principles and framework are put forward. With the discussion of multi-dimensional spatial attribute of durability design, the method system of environmental zonation and durability design for zones obtained is presented. Differences in regional environment, in local environment, in structure/component, in material composition, and in expected life time are taken into consideration in the method system.2. The durability of concrete structures is closely related to its exposure environments. Effect of various environmental factors and the corresponding quantitative index on the deterioration mechanism for different durable problems is analyzed and determined. Also, their statistical values and regional characteristic distribution are achieved by analyzing the historical climatological data and data obtained from observations or durability tests of concrete structure. These works lay a foundation of the environmental durability zonation.3. The reference environment and standard specimen are fixed for general atmospheric environment. The carbonation depth prediction model is established correspondingly based on the experimental study of the influence of temperature, humidity and concrete strength on carbonation depth in concrete. Then, the limit state and the target reliability index under carbonation are determined, and the probabilistic method is applied for the prediction of concrete structural durability. Taking the environmental action coefficient as the zoning index, the environmental zonation method system of general atmospheric environment is established with zonation map of the reference environment and zonation level adjustment according to local environment. Based on the results of environmental zonation, the corresponding durability design method for each zone level is given, which contains the design regulations of specimen in each zone, correction coefficient for different strength and correction coefficient for different age.4. The reference environment condition and standard specimen are determined respectively for marine vertical environment and offshore atmospheric environment. Concept of the nominal surface chloride concentration is proposed based on the engineering practice, and its statistical relation with the measured chloride content of concrete surface is given. Relations between the nominal surface chloride concentration and altitude, between the age coefficient and altitude, between the surface chloride concentration and distance from sea are given based on tested data. Introducing into the influence of environmental temperature and chloride content, formula for calculating the apparent chloride diffusion coefficient is established by considering only data from "bulk diffusion tests"(similar to the procedure outlined in the Scandinavian standard test NT Build443) are used in the analysis. Then, the probabilistic method is applied for the prediction of durability of concrete structures based on Fick’s second law. Taking the ratio of wetting time as the zoning index of marine vertical environment and distance from sea as the zoning index of offshore atmospheric environment, the environmental zonation method system is established for marine chloride environment. Based on the results of environmental zonation, the corresponding durability design method for each zone level is given, which contains the design regulations of specimen in each zone, correction coefficient for different water binder ration, correction coefficient for different age, correction coefficient for different temperature, and correction coefficient for different chloride content.5. The reference environment condition and standard specimen are determined for freezing-thawing environment. A statistical method is put forward to get the on-site freeze-thaw cycles by using the average annual number of negative-temperature days as an index. In addition, a practical formula is obtained accordingly to predict the natural freeze-thaw cycles. Then, according to the average freezing rate in the freezing and thawing, the proportion of concrete damage between different freeze-thaw environments is obtained based on the hydrostatic pressure theory, and a method for predicting the equivalent laboratory freeze-thaw cycles from on-site freeze-thaw cycles is given. Furthermore, the durable life of concrete in natural frost environments can be predicted easily by the equivalent cycle number. Taking the equivalent laboratory freeze-thaw cycles as the zoning index of freezing-thawing environment, the environmental zonation method system of frost environment is established with zonation map of the reference environment and zonation level adjustment considering time of concrete in saturated condition. Based on the results of environmental zonation, the corresponding durability design method for each zone level is given. The equivalent laboratory freeze-thaw cycles considering the influence of the average freezing rate, the lowest freezing temperature and the proportional coefficient of water saturation time for concrete during the freezing and thawing, can be used easily in the prediction and assessment of the structural durability in natural frost environments.6. Zhejiang province, with more intensive distribution of environmental data obtained, is taken as a complete implementation of the method system of environmental zonation and durability design for concrete structures in each zone proposed in this paper. With achievements for the general atmospheric environment, the marine chloride environment and the freezing-thawing environment of Zhejiang province, a geography information query system for durability design zonation of concrete structures is developed. The implementation of Zhejiang province, on the one hand, can be a refining guidance for durability design of concrete structure in Zhejiang province; on the other hand, can be taken as sample for checking the results of the national environmental zonation with a relatively sparse data distribution.7. Based on the methodology of environmental zonation and durability design for zones established, durability design of concrete structures in differenent environments has been achieved for the chosen typical projects. The results of the design aplications show that the established methodology of durability design for concrete structures is reasonable.