| Research and Development on Durability of Concrete Structures |
In 1824, with the invention of Portland cement by Asptin, the history of human application of concrete in building began. At the same time, the durability issue of concrete structures also emerged. During this period, Portland cement was mainly used to build a large number of coastal breakwaters, docks, lighthouses, etc. These structures are subjected to strong external influences over a long period of time, including physical effects such as wave impact, erosion from mud and sand, and freezing, as well as chemical effects such as the dissolution of salt in seawater, all of which can cause rapid damage to the aforementioned structures. Therefore, the initial research on the durability of concrete was mainly aimed at understanding the corrosion of concrete in offshore structures. In the 1840s, in order to explore the reasons for the destruction of docks built during this period by seawater, the outstanding French engineer Vicat conducted research on the properties of hydraulic lime and mortar made from lime and volcanic ash, and wrote the book "Chemical Causes and Protection Methods of Corrosion of Hydraulic Components by Seawater", which is the first scientific research work on the corrosion damage of concrete made from hydraulic cementitious materials by seawater. From 1880 to 1890, when the first batch of reinforced concrete components were introduced and first applied to industrial buildings, people began to study whether reinforced concrete could be safely used under corrosive conditions of chemical active substances and its durability in the atmosphere of industrial areas.
In the early 1920s, with the relative maturity of structural calculation theory and construction technology, reinforced concrete structures began to be widely adopted, and their application fields became increasingly broad. Therefore, many new types of durability damage are gradually emerging, which directly prompts targeted research on the durability of reinforced concrete. In 1925, under the leadership of Miller, the United States began long-term experiments in soils with extremely high sulfate content, with the aim of obtaining concrete corrosion data for 25, 50, and even longer periods of time; The Federal German Association for Reinforced Concrete also conducted a long-term test on the corrosion of concrete under natural conditions, using examples of concrete structures being damaged by swamp water corrosion; In the 1930s, American scholar Stanton first discovered and defined the alkali aggregate reaction, which received attention in many countries. In 1945, Powers et al. analyzed the effect of pore water on pore walls from the submicroscopic perspective of concrete and proposed the hydrostatic pressure hypothesis! 2] Starting with the osmotic pressure hypothesis [13], research has been conducted on the freeze-thaw failure of concrete. In 1951, Soviet scholars Bekov, Moskvin, and others began researching the problem of steel corrosion in concrete. The initial goal was to solve the anti-corrosion problem of thin-walled structures with the smallest concrete protective layer and the use of high-strength steel to make reinforced concrete components. Later, they did a lot of work in this area, which was reflected in Moskvin's monographs "Corrosion of Concrete" and "Corrosion and Protection Methods of Concrete and Reinforced Concrete". Based on large-scale research work, anti-corrosion standards and specifications were developed, laying the foundation for durable concrete and reinforced concrete structures in buildings [14].
In the 1960s, the use of reinforced concrete reached its peak, and research on the durability of concrete structures also reached a climax, beginning to develop towards systematization and internationalization. This was reflected in the establishment of various international academic organizations and the convening of international academic conferences. The establishment of these academic organizations and the development of academic activities have greatly strengthened cooperation and exchanges among academic communities in various countries, achieving significant results. Some scientific research achievements have been applied to engineering practice and have become standard technical documents guiding engineering design, construction, maintenance, etc. For example, the American ACI437 Committee proposed the latest report on "Evaluation of Resistance of Existing Concrete Buildings" in 1991, which provided detailed methods and steps for testing experiments. The Concrete Committee of the Japanese Society of Civil Engineers formulated the "Guidelines for Durability Design of Concrete Structures" in 1989, and the "Guidelines for Durability Design of Concrete Structures" issued by the European Concrete Committee in 1992 reflect the current level of durability research on concrete structures in Europe. Recently, the international community has gradually focused on durability design and management based on the concept of the entire life cycle. In 2011, the Japanese government established a major international cooperation project "Prediction and Management of Full Life Performance of Concrete Structures", aiming to unite international experts in the field of durability of concrete structures to jointly solve the problems of durability prediction and full life management of concrete structures. Researchers from Germany, the UK, and other countries have successively developed durability monitoring components for concrete structures, which can monitor durability parameters such as chloride ion concentration inside the structure; These durability monitoring components are embedded in the structure during the construction period, providing important measured data for the durability performance analysis and full life management of concrete structures.
China began researching the durability of concrete structures in the 1960s, with the main focus on carbonation of concrete and corrosion of steel reinforcement. After the 1990s, durability issues received high attention from the government, and multiple major scientific research projects related to concrete structure durability were established, including the National Basic Research Major Project (Climbing Plan) "Basic Research on Safety and Durability of Major Civil and Hydraulic Engineering" organized by the National Science and Technology Commission (now the Ministry of Science and Technology, hereinafter referred to as the Ministry of Science and Technology) in 1994; In 2006, the National Natural Science Foundation of China funded two key durability projects, "Basic Theoretical Research on Durability Design and Evaluation of Concrete Structures in Chloride Corrosion Environments" and "Basic Research on Durability and Countermeasures of Concrete Structures in Atmospheric and Freeze Thaw Environments", with the aim of establishing the basic theory of durability design for concrete structures in China. In 2009, the Ministry of Science and Technology approved the 973 project "Basic Research on Environmentally Friendly Modern Concrete" and other scientific research projects, which enabled China to achieve more and more results in the field of durability of concrete structures [19-21], gradually aligning with the world.
In order to liven up the academic atmosphere and increase academic exchanges among scholars, the Chinese Society of Civil Engineering held two consecutive national durability academic conferences in 1982 and 1983, laying the foundation for the scientific revision of concrete structure specifications and promoting further research on durability. In 2001, numerous domestic experts and scholars had a lively discussion on the safety and durability issues of civil engineering at the 1st Engineering Science and Technology Forum held at Tsinghua University; The 4th Engineering Technology Forum, with the theme of durability design and evaluation methods for concrete structures, was held at Zhejiang University to discuss the issue of durability of concrete structures, which has received unprecedented attention in China. In 2008, the International Conference on Concrete Structure Durability, jointly organized by China, Japan, and the UK, was held at Zhejiang University, marking a new stage of cooperation and development in the field of concrete structure durability research in China with peers around the world.
Based on domestic and foreign research results, the Chinese Society of Civil Engineering issued the "Guidelines for Durability Design and Construction of Concrete Structures" (CCES01-2004) in 2004, and the Ministry of Housing and Urban Rural Development officially issued the "Code for Durability Design of Concrete Structures" (GB/T 50476-2008) in 2008. The newly issued "Code for Design of Concrete Structures (GB 50010-2010)" in China also includes more content on the durability of concrete structures. The promulgation of these industry norms and standards related to the durability of concrete structures indicates that China's research on the durability of concrete structures has shifted from the scientific research stage to the stage of coexistence of scientific research and application, and also reflects the importance that the Chinese civil engineering community attaches to the durability of concrete structures.
China is currently undertaking the largest infrastructure construction in history with unprecedented huge investment. Many concrete projects with investments of billions of yuan have just been completed or are currently being planned, designed, and constructed, such as the 36km Hangzhou Bay Cross Sea Bridge (Figure 1-11 (a)) completed and opened to traffic in 2008, the 36.48km Qingdao Jiaozhou Bay Cross Sea Bridge (Figure 1-11 (b)) completed and opened to traffic in 2011, and the Hong Kong Zhuhai Macao Bridge (Figure 1-12) currently under construction with an investment of over 70 billion yuan and an expected length of 49.97km. To meet the hundred year service life requirements of major concrete projects serving in these harsh environments, it is based on a profound understanding of the durability issues of concrete structures. The design and construction of these major projects provide a rare opportunity and platform for researchers in the field of durability research of concrete structures in China; The research achievements in the durability of concrete structures in China over the past few decades have been reflected and applied in these projects, and the relevant specifications for the durability of concrete structures issued by China have provided important implementation guarantees for the durability of these projects.
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