Durability Design of Concrete Structures
Kefei Li, Professor, Civil Engineering Department, Tsinghua University, Beijing, China. Li obtained his first Ph.D in Bridge Engineering in 2000 from Tongji University (China), and the second in Material Science from Ecole des Ponts, ParisTech (France) in 2002. He began his professional life as a civil engineering consultant in OXAND S.A. (France) and transferred to Tsinghua University taking a teaching-research position in 2004. His research interests include durability mechanisms of structural concretes, durability design of concrete structures, and assessment of structural behaviors. He also participated in or led the following projects:- the design of Hong Kong-Zhuhai-Macao sea link project (design life of 120 years); the durability design and assessment of High Integrity Container for radioactive disposal (design life of 300 years, 2010-now); the Chinese design code GB/T 50476-2008 'Code for Durability Design of Concrete Structures'. He has published more than 50 journal papers and this is his first book.
Durability Design of Concrete Structures
Durability of Concrete Structures: State of the Art
Durability is a term related to both performance and time, reflecting the degree to which a structure/infrastructure meets its intended functions for a given duration of time. This description applies to all types of structure and infrastructures in civil engineering. Actually, during the service life a structure displays time-dependent behaviors by ageing of the structural materials. The ageing processes can be intrinsic to the structural materials or induced by the interactions between the service conditions and the structural materials. This picture holds for all structures and their constitutive materials. In fact, concrete structures have transient behaviors due to some well-known time-dependent properties of structural concrete, such as shrinkage and creep. Take creep, for example. Engineers had been challenged by this evolving property as early as the 1900s, the very beginning of concrete structures coming into use. During the following years the lack of consideration of creep, surely due to lack of knowledge, had caused some serious accidents in structural engineering; for example, the collapse of the Koror-Babelthuap Bridge, Palau, in 1996. The past century has witnessed considerable research efforts dedicated to this subject, and the colossal creep models and established databases. The awareness of the deterioration of concrete properties by environmental actions comes much later. In the early 1990s, field investigations from various sources showed that concrete structures, massively constructed during 1950s and 1960s, were in very poor condition. The cost of the maintenance works due to deterioration by environmental actions was reported to be reaching an alarming level and generated heavy financial burdens on the structure owners. This situation makes durability a worldwide concern for decision-makers, structural designers, and material suppliers. Accordingly, the past three decades witnessed enormous efforts dedicated to intensive research on deterioration processes of structural elements and concretes, and the durability specifications for concrete structures at the design level.
Today, the term "durability" is somewhat standardized in a technical sense. The standard ISO-13823 provided the definition as the "capability of a structure or any component to satisfy, with planned maintenance, the design performance requirements over a specified period of time under the influence of the environmental actions, or as a result of a self-ageing process"; the ACI Concrete Terminology gives the definition as the "ability of a material to resist weathering action, chemical attack, abrasion, or any other process of deterioration." Evidently, the former definition is more adapted to structural engineering, while the latter is more oriented to concrete materials. However, one can notice that both definitions exclude the most evident time-dependent properties of structural concrete: shrinkage and creep. This is doubtless due to the fact that the recent engineering concern, as well as the corresponding efforts, mainly focuses on the environmental actions, the reason why the term "environmental actions" is explicitly expressed in both definitions. In this book, this established terminology is also followed, though shrinkage and creep remain the most important transient properties of structural concretes. The awareness of structural durability leads to two important changes in structural design. First, the design changes from a "static" mode to an "evolving" mode and the evolution of certain structural and materials properties must be taken into account through appropriate approaches. The design service life, or design working life, becomes an independent design parameter and target for the design procedure. Hence, the design changes from a loading-based procedure to a service life-based one. Second, durability awareness enables the